CEMENT-BOUND ROAD BASE MATERIALS

Report 7-11-218-1

Prepared by

Pengpeng Wu, MSc

Delft University of Technology

Supervised by

Prof.dr.ir. A.A.A. Molenaar and Ir. L.J.M. Houben

Delft University of Technology

In cooperation with

PowerCem Technologies, Netherlands

July 2011

I

TERM DEFINATION

In this literature study the technical terms are defined as listed below.

Additive A chemical or material applied atop or mixed into a

material to alter or improve the general quality or to

counteract undesirable properties.

Atterberg limits Soil properties that help to identify a given soil in

terms of its water retentively and plasticity and these

consistency limits are Liquid Limit, Plastic Limit and

Plasticity Index.

Bitumen

Black, viscous liquid to solid obtained as residue from

petroleum coke by preparation or naturally derived.

Bitumen is a binder for asphalt mixtures.

California Bearing Ratio A penetration test for evaluation of the load-carrying

capacity (mechanical strength) of soils, expressed as a

percentage of a standard.

Characterisation In materials science, it refers to the use of external

techniques to probe into the internal structure and

properties of a material in form of actual materials

testing, or analysis, for instance in some form of

microscope.

Clay A general term for colloid sized (<0.002 mm in

equivalent diameter) fine particles of inorganic

(mineral) origin in soil that has a high Plasticity Index

in relation to the Liquid Limit.

Crystalline Having a definite form, that is the atoms in a solid

matter are arranged in a regular pattern, and there is as

smallest volume element that by repetition in three

dimensions describes the crystal.

Capillary

Ability of a material to water-sucking and holding it

above the phreatic surface.

II

Illite It is a non-expanding, clay-sized, micaceous mineral.

A hydrous alluminosilicate clay mineral with

structurally mixed mica and smectite or vermiculite,

similar to montmorillonite but containing potassium

between the crystal layers. Also referred to as hydrous

mica or mica. It has a cation exchange capacity (20-40

me/100 g).

Kaolinite It is a layered clay with silicate mineral, with one

tetrahedral sheet inked through oxygen atoms to one

octahedral sheet of alumina octahedral. It has a low

shrink-swell capacity and a low cation exchange

capacity (1-15 me/100 g). Rocks that are rich in

kaolinite are known as china clay or kaolin.

Maximum dry density The highest dry density obtainable when using a

specified amount of compaction effort (Standard or

Modified Proctor) on a soil with various moisture

contents.

Moisture content That portion of the total dry mass of material that

exists as water, expressed in percentage.

Montmorillonite It is a very soft phyllosilicate mineral that typically

forms in microscopic crystals, forming clay. A member

of the smectite family that is a 2:1 clay, meaning that it

has 2 tetrahedral sheets sandwiching a central

octahedral sheet. Its water content is variable and it

increases greatly in volume when it absorbs water. It

has a high cation exchange capacity (60-100 me/100

g).

Modulus of elasticity

Relationship between a load and the resulting elastic

deformation of the material.

Optimum moisture content The percentage of water (by mass) in material that

allows it to be compacted to the greatest density.

Permeability (Soil) Measure of the ability of a soil to transmit water and

air from upper to lower soil layers.

Petroleum An oily flammable bituminous liquid that may vary

from almost colorless to black, and that is a complex

III

mixture of hydrocarbons with small amounts of other

substances.

Porosity The volume of all the open spaces (pores) between the

solid grains of a soil/material.

Proctor test Standard Proctor compaction effort using a 2,49 kg

hammer, falling through 305 mm with 3 layers each

compacted by 55 blows yielding a total energy of 0,15

kWh/m3.

Soil Naturally occurring material that is used for

construction of pavement layers

Soil stabilizer A chemical or material mixed into a material to

permanently increase or improve density, compaction,

shear strength, and/or changes in plasticity

characteristics. In addition, a chemical or mechanical

treatment designed to increase or maintain the stability

of a mass of soil/material or to otherwise improve its

engineering properties.

Strength (Soil) The capacity of a soil to withstand forces without

experiencing failure, whether by rupture,

fragmentation, or shear.

Unconfined compressive test In this test, a soil sample is compressed to measure its

strength. It is a measure of the shearing resistance of

cohesive soils, which may be undisturbed or

remoulded samples, using strain-controlled application

of the axial load. It is also a measure of the

compressive strength of soils, stabilized with bitumen,

lime or cement or a combination.

IV

V

LIST OF SYMBOLS

cf Unconfined compressive strength

tf Flexural tensile strength

itf Indirect tensile strength

sE Static modulus of elasticity

dE Dynamic modulus of elasticity

V

Pulse velocity

N

Number of load repetitions

ε

Applied strain level

tε Flexural strain at break

σ Applied stress

tσ Ultimate flexural stress (flexural strength)

SN Ratio of applied stress and ultimate stress

η Porosity of specimen

uC Coefficient of uniformity of grain size distribution curve

cC Curvature index of soil distribution curve

Ac Activity of clay

fE Stiffness modulus in flexure

eqN Number of equivalent load repetitions

VI

VII

LIST OF ACRONYMS

OMC Optimum Moisture Content

PI Plasticity Index

PL Plasticity Limit

LL Liquid Limit

SL Shrinkage Limit

UCS Unconfined Compressive Strength

USCS Unified Soil Classification System

AASHTO American Association of State Highway and Transportation Officials

ASTM American Society for Testing and Materials

CBR California Bearing Ratio

NEN European Norms

PCT PowerCem Technologies

MPD Maximum Proctor Density

VIII

IX

LIST OF FIGURES

Fig. 2.1 Liquid limit for stabilized marl samples at different curing time .............. 8

Fig. 2.2 Dry and wet CBR values for natural and stabilized marl soil ................... 9

Fig. 2.3 Initial strength development of a lime and cement stabilization ............... 9

Fig. 2.4 UCS of cement stabilized soil as a function of lime and cement content . 9

Fig. 2.5 The compressive strength of cement stabilized and lime stabilized soil . 10

Fig. 2.6 UCS at optimum water content for cement stabilized fly ash ................. 11

Fig. 2.7 Uniaxial compressive strength of fly ash stabilized clay ........................ 11

Fig. 2.8 The compressive strength of soil stabilized with multiple soils .............. 12

Fig. 3.1 Typical soil particle size distribution curves ........................................... 16

Fig. 3.2 Particle size distribution curves for various soils .................................... 17

Fig. 3.3 Particle size gradation coefficient ............................................................ 17

Fig. 3.4 Relationship between clay content and plasticity index .......................... 19

Fig. 3.5 Volume change of a soil specimen during drying .................................... 20

Fig. 3.6 Phases of soil and Atterberg limits .......................................................... 20

Fig. 3.7 AASHTO plasticity chart ......................................................................... 22

Fig. 3. 8 USCS classification chart ....................................................................... 22

Fig. 3.9 USCS plasticity chart ............................................................................... 23

Fig. 3.10 Effect of addition of cement on the swell .............................................. 25

Fig. 3.11 Reduction of silt-clay content due to cement modification ................... 25

Fig. 3.12 Comparison of CBR with RoadCem ..................................................... 30

Fig. 4.1 Particle size analysis of coarse grained soils using sieves ....................... 34

Fig. 4.2 Wet sieving for particle size distribution of fine grained materials ......... 34

Fig. 4.3 Cone equipment ....................................................................................... 35

Fig. 4.4 Example of relationship between water content and cone penetration ... 35

Fig. 4.5 Soil pat after groove closed ..................................................................... 36

Fig. 4.6 Test for Plastic Limit ............................................................................... 36

Fig. 4.7 Moisture-density curves of a cohesive soil for different compaction...... 39

Fig. 4.8 Effect of compaction methods on the density.......................................... 39

Fig. 4.9 Effect of compaction methods on the compressive strength ................. 40

Fig.4.10 Dry density-moisture curves for sandy clay soil .................................... 40

Fig. 4.11 Dry Density-Moisture curves for a sand stabilized ............................... 40

Fig. 4.12 Dry density-moisture curves for a range of soil types ........................... 41

Fig. 4.13 Effect of a time lapse on the dry density and UCS ................................ 42

Fig. 4.14 Soil gradings for cement-bound mixture ............................................... 43

Fig. 4.15 Coded test conditions for the central composite rotatable design ......... 44

Fig. 4.16 Variation of strength at 1, 7 and 28 curing days of samples .................. 46

Fig. 4.17 Relationship between UCS and curing temperature .............................. 46

Fig. 5.1 SEM photos of cement stabilized sand specimens after testing .............. 50

Fig. 5.2 Relationship between UCS and curing period ......................................... 51

Fig. 5.3 Relationship between moisture content and UCS ................................... 52

X

Fig. 5.4 Relationship between water to cement ratio and UCS ............................ 52

Fig. 5.5 28-day strength of cement treated clay .................................................... 53

Fig. 5.6 Effect of curing age on the unconfined compressive strength ................. 54

Fig. 5.7 Compressive strength for dry and wet specimens at 28 days .................. 54

Fig. 5. 8 28-day strength variation with number of wetting ................................. 55

Fig. 5.9 Compressive strength of samples at different dry density ....................... 55

Fig. 5. 10 Variation in the 1, 7 and 28 curing days strength of samples ............... 56

Fig. 5.11 Effect of curing age on compressive strength ........................................ 56

Fig. 5.12 SEM images of RoadCem and Cement treated soil/material ................ 57

Fig. 5.13 Indirect tensile test ................................................................................. 58

Fig. 5. 14 Effect of cement content on the indirect tensile strength at 28 days .... 58

Fig. 5.15 Variation of the indirect tensile strength of cement ............................... 58

Fig. 5.16 Variations of the indirect tensile strength with cement content ............. 59

Fig. 5.17 Relationship between UCS and indirect tensile strength ....................... 59

Fig. 5.18 Flexural tensile strength plotted against compressive strength ............. 60

Fig. 5.19 Typical stress-strain curve for cement stabilized materials ................... 61

Fig. 5.20 Typical unconfined compressive stress-strain relationships .................. 61

Fig. 5.21 Stress-strain curve for samples under compression ............................... 62

Fig. 5.22 Influence of clay content on the modulus of elasticity .......................... 62

Fig. 5.23 Cement-bound granular mixtures of tensile strength ............................ 63

Fig. 5.24 Dynamic modulus and pulse velocity .................................................... 64

Fig. 5.25 28-day compressive strength and dynamic modulus of elasticity ......... 64

Fig. 5.26 Relationship between dynamic modulus and flexural strength ............. 64

Fig. 5. 27 Dynamic modulus and modulus of rupture .......................................... 65

Fig. 5.28 Measurement of dynamic modulus of elasticity .................................... 65

Fig. 5.29 Comparison of damped harmonic vibration with RoadCem ................. 66

Fig. 5.30 Dynamic flexure tests for 28-day curing time ....................................... 66

Fig. 5.31 Stress ratios versus number of cycles to failure..................................... 67

Fig. 5.32 General fatigue curves for cement-treated bases ................................... 68

Fig. 5.33 Effect of loading frequency on stress/life relationship for concrete ...... 68

Fig. 5.34 Fatigue behavior of cement bound materials ......................................... 69

Fig. 5.35 Weight loss in wet-dry testing of soil stabilized cement and lime ....... 70

Fig. 5.36 Change in weight loss with exposure period in the samples tested for . 71

Fig. 5.37 Effect of cement content on the water permeability .............................. 71

Fig. 5.38 Water absorption versus binder quality for specimens at 28 days ......... 72

Fig. 5.39 Capillary rise with time for 28-days cured specimens .......................... 72

Fig. 6.1 Reflection cracks ..................................................................................... 75

Fig. 6.2 Cracking as a result of t shrinkage stress, strength and time ................... 76

Fig. 6.3 Effect of cement content on shrinkage .................................................... 77

Fig. 6.4 Effect of sand and cement content on the shrinkage ............................... 78

Fig. 6.5 Development of shrinkage during first 28 days ....................................... 78

Fig. 6.6 Variation of final shrinkage at 28 days with mixing water content ......... 79

Fig. 6.7 Effect of density and moisture on shrinkage ........................................... 79

Fig. 6.8 7-day UCS vs. beam shrinkage ................................................................ 80

XI

Fig. 6.9 Addition of fly ash to reduce drying shrinkage ....................................... 81

Fig. 6.10 Stabilization with RoadCem showing no cracks after 4 years ............ 82

Fig. 6.11 Picture from an electron microscope of the crystalline structure .......... 82

Fig. 7.1 Comparison of calculation for traditional and RoadCem constructions .. 85

Fig. 7.2 Strains of the bounded layer over the width of the road .......................... 87

Fig. 7.3 Strains in the bounded layers in the length (X) of the road with ............. 87

Fig. 7.4 Stresses in the bottom of the bounded layers in the width of the road .... 88

Fig. 7.5 Stresses in the bottom of the bounded layers in the length of the road ... 88

Fig. 7.6 Deflections in the traditional structure .................................................... 90

Fig. 7.7 Deflections in the RoadCem structure ..................................................... 90

XII

XIII

LIST OF TABLES

Table 2.1 Application of traditional stabilization methods ..................................... 6

Table 2.2 Stabilization methods most suitable for specific applications ................ 6

Table 3.1 Particle size ranges in different countries ............................................. 16

Table 3.2 Indication of uC and cC ...................................................................... 18

Table 3.3 Three physical states of the soil-aggregate mixtures ............................ 18

Table 3.4 Plasticity and dry strength related to Plasticity Index PI ...................... 19

Table 3.5 Soil classification according to AASHTO ............................................ 21

Table 3.6 Symbols used in USCS ......................................................................... 22

Table 3.7 Examples of the effect of cement-modification .................................... 23

Table 3.8 Cement requirement for different soil types ......................................... 24

Table 3. 9 Relationship between shrinkage limit, PI and swell potential ............. 25

Table 3.10 Average change in properties for clay soils ......................................... 27

Table 3.11 Cement requirement of different soils ................................................. 28

Table 3.12 DCP-CBR strength for stabilized panels with different stabilizers .. 30

Table 4.1 Cone penetration requirement ............................................................... 35

Table 4.2 Summary of sample preparation methods ............................................. 38

Table 4.3 Dimensions of the new cylindrical test mould ...................................... 38

Table 4.4 Summary of the Proctor test and modified Proctor test ........................ 38

Table 4.5 Maximum dry density and moisture contents of soil-cement ............... 41

Table 4.6 Cement content requirement for soils ................................................... 43

Table 4.7 Minimum cement content according to the grain sizes ......................... 44

Table 4.8 Variables for central composite design.................................................. 44

Table 6. 1 Effect of fines content on soil-cement crack pattern ............................ 80

Table 7.1 Stresses and strains at the bottom of the bounded layers ...................... 87

Table 7.2 The results of lifetime for traditional and RoadCem construction ........ 89

XIV

XV

TABLE OF CONTENTS

1 INTRODUCTION ...................................................................................................... 1

1.1 BACKGROUND .............................................................................................. 1

1.2 PROBLEMS ..................................................................................................... 2

1.3 OBJECTIVES ................................................................................................... 2

1.4 CONTENT OF LITERATURE REVIEW ........................................................ 2

2 STABILIZATION AGENT ......................................................................................... 5

2.1 BITUMEN ........................................................................................................ 7

2.2 LIME ................................................................................................................. 7

2.3 FLY ASH ......................................................................................................... 10

2.4 CEMENT ........................................................................................................ 12

2.5 CONCLUSIONS ............................................................................................. 12

3 MATERIALS FOR CEMENT STABILIZATION ................................................... 15

3.1 SOIL ................................................................................................................ 15

3.1.1 Particle size and soil structure ............................................................... 15

3.1.2 Atterberg limits ..................................................................................... 19

3.1.3 Soil classification .................................................................................. 21

3.1.4 Shrinkage and swell .............................................................................. 24

3.1.5 Organic content ..................................................................................... 26

3.2 CEMENT ........................................................................................................ 27

3.3 WATER ........................................................................................................... 28

3.4 ADDITIVE ...................................................................................................... 29

3.4.1 Traditional additives .............................................................................. 29

3.4.2 RoadCem ............................................................................................... 30

3.5 CONCLUSIONS .......................................................................................................... 31

4 PRELIMINARY INVESTIGATIONS ...................................................................... 33

4.1 SOIL TESTS ................................................................................................... 33

4.1.1 Particle size distribution ........................................................................ 33

4.1.2 Liquid Limit and Plastic Limit .............................................................. 34

4.1.3 Chemical analysis ................................................................................. 36

4.2 COMPACTION OF MIXTURE ..................................................................... 37

4.2.1 Compaction test .................................................................................... 37

4.2.2 Factors influencing compaction ............................................................ 39

4.3 MIX COMPOSITION .................................................................................... 42

4.3.1 Requirements for materials ................................................................... 42

4.3.2 Mix design method ............................................................................... 44

4.4 CURING CONDITIONS ................................................................................ 45

4.5 CONCLUSIONS ............................................................................................. 46

5 MAIN MECHANICAL PROPERTIES .................................................................... 49

5.1. COMPRESSIVE STRENGTH ...................................................................... 49

5.2 TENSILE STRENGTH................................................................................... 57

5.2.1 Indirect tensile strength ......................................................................... 57

5.2.2 Flexural tensile strength ........................................................................ 60

XVI

5.3 ELASTIC MODULUS ................................................................................... 61

5.3.1 Static modulus ....................................................................................... 61

5.3.2 Dynamic modulus ................................................................................. 63

5.4 FATIGUE PROPERTIY .................................................................................. 66

5.5 DURABILITY ................................................................................................ 69

5.6 WATER PERMEABILITY AND ABSORPTION .......................................... 71

5.7 CONCLUSIONS ............................................................................................. 73

6 CRACKING BEHAVIOR......................................................................................... 75

6.1 SHRINKAGE ................................................................................................. 76

6.2 FACTORES INFLUNCING SHRINKAGE ................................................... 77

6.3 METHODS OF CONTROLLING .................................................................. 81

6.4 CONCLUSIONS ............................................................................................. 82

7 EFFECTS OF A FLEXURAL STABILIZATION .................................................... 83

7.1 INTRODUCTION .......................................................................................... 83

7.2 ASSUMPTIONS ............................................................................................. 83

7.3 DESIGNS ........................................................................................................ 84

7.4 CALCULATION METHOD .......................................................................... 85

7.5 DEFLECTIONS .............................................................................................. 89

7.6 CONCLUSIONS ............................................................................................ 90

8 CONCULSIONS AND RECOMMENDATIONS .................................................... 93

8.1 CONCLUSIONS ............................................................................................. 93

8.2 RECOMMENDATIONS ................................................................................ 94

REFERENCES ............................................................................................................ 95

Appendix A ................................................................................................................ 101

Appendix B ................................................................................................................ 102

Appendix C ................................................................................................................ 107

1

CHAPTER 1

INTRODUCTION

1.1 BACKGROUND

High quality road infrastructure is of utmost importance for economic development

and growth of any country in the world. As a consequence of economic growth, road

traffic is increasing in vehicle numbers and in truck axle loads. This requires

extension of the road network. Especially for the main road network availability for

traffic should be as high as possible (Molenaar, 2010). Both asphalt and concrete

pavement structures can be designed and constructed. However, both types of

pavement require a base with good structural performance and a long service life

below the asphalt or concrete. Also for the demand of less construction time and

resistance to natural disasters, new road materials with environmental friendly

technology are increasingly required.

For road bases, there is a variety of soils or granular materials available for

construction, but they may exhibit insufficient properties (e.g. low bearing capacity,

susceptibility for frost action), which then results in substantial pavement distress and

reduction of the pavement life. However, the properties of soil can be improved by

addition of a stabilizing agent such as cement, bitumen and lime. Among these

different stabilized materials, cement-bound materials develop a quite high stiffness

and strength, and exhibit good performance for pavement serviceability and high

durability.

The soil or granular materials to be stabilized can be almost any combination of sand,

silt, clay, gravel, or crushed stone. When there are not many suitable soils available

for construction, the stabilization of less suitable soil with cement becomes a

beneficial option. Also there exists a large amount of waste materials and recycled

aggregates which could be widely available near the work sites, which can not only

lower the construction and transportation cost but also save natural resources and

2

offer much environmental benefit.

1.2 PROBLEMS

In practice, when the granular material is stabilized, the stabilization of soil improves

the soil gradation, reduces the plasticity index or swelling potential of soil, and

increases the stiffness, strength and durability, which consequently reduces the

required thickness of the pavement structure. However, the hardening cement-bound

materials exhibit shrinkage cracks and susceptibility to overloading. Cracks due to the

shrinkage or overloading result in stress concentration and even base failure and

reflective cracking through the overlying layer, which definitely increases

maintenance and repair costs. Also not all types of soil can be bounded well with

cement, like high organic soils and some type of clayey soils. Additives are available

that can be added to a normal type of cement to reduce or eliminate the disadvantages

of a cement-bound road base (shrinkage, cracks, brittle behavior) (Molenaar, 2010).

1.3 OBJECTIVES

The objectives of this research are to evaluate the properties of cement-bound

materials in order to design appropriate cement stabilized materials for structural

design of pavements. An innovative product RoadCem together with cement has been

proven to be well in all types of granular materials. In this research, the mechanical

properties to be investigated are not only the stiffness and the strength (compressive

strength and/or indirect tensile strength and/or (fatigue) flexural tensile strength) but

also the thermal cracking, frost thaw behavior and erosion.

RoadCem from PowerCem Technologies is used as additive to improve the

performance of the cement stabilized materials. In this literature review information

was used from PowerCem Technologies for related soils. However it has to be kept

in mind that small differences in soils and test conditions can have a big influence on

the mechanical properties of the stabilized material. The comparison of the test results

for soils stabilized with cement and RoadCem and (nearly) the same soil stabilized

with only cement or another stabilizer therefore is indicative rather than absolute.

1.4 CONTENT OF LITERATURE REVIEW

In this literature review, the properties of cement-bound materials from a number of

research studies are summarized. In Chapter 2, various stabilization methods are

reviewed, as well as the comparison of the applications of different stabilizing agents.

The materials for cement stabilization are described in Chapter 3, including soil,

cement, water and additives. The soil properties play a significant role in stabilization.

3

Preliminary tests to indicate the soil properties and mix composition are illustrated in

Chapter 4. Compaction and curing methods in the laboratory, which significantly

contribute to the strength of samples are also described. Chapter 5 focuses on the

mechanical properties of cement bound materials, which are summarized from

previous research results. The cracking behavior, mainly due to the hydraulic reaction,

is addressed in Chapter 6. In Chapter 7 the effects of a more flexural stabilization is

presented. Finally in Chapter 8 the conclusions and recommendations are presented

based on this literature study.

In this review, the units that are used are SI units. During the literature study, some

results were originally mentioned in the British/American units. To prevent the errors

in the interpretation of the results due to the differences in SI and British/American

units, everything is converted into the SI system. Due to this conversion the numbers

can vary a bit of the original figures. The conversion tables are included in Appendix

B. Appendix C gives the translation of general terms mentioned in this review.

4

5

CHAPTER 2

STABILIZATION AGENT

Stabilization of soil is an effective method to improve the soil properties and enhance

the pavement performance. The aims of stabilization are to

(a) Increase stiffness and strength and thus stability and bearing capacity

(b) Increase volume stability to control the swell-shrink characteristics caused by

moisture changes

(c) Increase durability, resistance to erosion and frost attack

(d) Reduce permeability and avoid the intrusion of water

Basically there are five types of traditional stabilization, which are

1) Mechanical stabilization

2) Bitumen stabilization

3) Lime stabilization

4) Fly ash stabilization

5) Cement stabilization

Mechanical stabilization means improvement of the grain size distribution by mixing

the soil or gravel with another type of soil, and optimum compaction of materials.

The choice between these types of stabilization is dependent on the nature of the basic

material to be stabilized and the desired function of the stabilized layer in the

pavement structure (e.g. construction platform or structural layer). The overall costs

should also be taken into account.

There may be more than one candidate stabilizer applicable for one type of soil, which

is indicated in table 2.1. Cement is particularly effective in stabilizing coarse granular

material like sands and is not suited to treat fine-grained soil like clay owing to the

high cement content required. Lime is more efficient to stabilize clay. Table 2.2 lists

stabilization methods which are most suitable for specific applications of a particular

soil.

6

Table 2.1 Application of traditional stabilization methods (Ingles, 1972)

Designation Fine

clay

Coarse

clay

Fine

silt

Coarse

silt

Fine

sand

Course

sand Aggregate

Particle size

(mm) <0.006 0.006-0.02 0.02-0.01 0.01-0.06 0.06-0.4 0.2-2 >2.0

Volume

stability

Very

poor Fair Fair Good Very good

Lime

Cement

Bitumen

Range of maximum efficiency Effective, difficult quality control

Table 2.2 Stabilization methods most suitable for specific applications (FM 5-410)

Purpose Soil Type Methods

Sub-grade Stabilization

Improves load-carrying and

stress-distribution

characteristics

Fine-grained SA, SC, MB, C

Coarse-grained SA, SC, MB, C

Clays of low PI C, SC, CMS, LMS, SL

Clays of high PI SL, LMS

Reduces frost susceptibility Fine grained CMS, SA, SC, LF

Clays of low PI CMS, SC, SL, LMS

Improves waterproofing and

runoff Clays of low PI CMS, SA, LMS, SL

Control shrinkage and swell Clays of low PI CMS, SC, C, LMS, SL

Clays of high PI SL

Reduces resiliency Clays of high PI SL, LMS

Elastic silts or clays SC, CMS

Base-course Stabilization

Improves substandard materials

Fine-grained SC, SA, LF, MB

Clays of low PI SC, SL

Improves load-carrying and

stress-distribution

characteristics

Coarse-grained SA, SC, MB, LF

Fine-grained SC, SA, LF, MB

Reduces pumping Fine-grained SC, SA, LF, MB

7

The methods of treatment are

C = Compaction MB = Mechanical Blending

LMS = Lime-Modified soil SA = Soil-Cement

LF = Lime-Fly ash SL = Soil-Lime

CMS = Cement-Modified Soil

2.1 BITUMEN

Bitumen is obtained through distillation of crude oil in an oil refinery. It is sensitive to

temperature changes. At high temperature it is liquid and deformations (especially

rutting) can occur. When it becomes hard when temperature lowers, cracks may occur.

A bitumen-bound material is a mixture of mineral aggregates (sand, gravel or crushed

stone) glued together by the bitumen to form a stable base or wearing course. Bitumen

increases the cohesion and load-bearing capacity of the soil and renders it resistant to

the action of water. There are three types of bituminous stabilized soil:

• Sand bitumen. Sand particles are cemented by bitumen to provide a material with

increased stability.

• Gravel or crushed aggregate bitumen. A mixture of bitumen and a well-graded

gravel or crushed aggregate that, after compaction, provides a highly stable

waterproof mass of sub-base or base course quality.

• Bitumen lime. A mixture of soil, lime and bitumen that, after compaction, may

exhibit the characteristics of any of the bitumen-treated materials indicated above.

The stabilization of soils with bitumen differs greatly from cement and lime

stabilization. Unlike cement and lime which act chemically with the material being

stabilized, bitumen acts as a binding agent and simply sticks the particles together and

prevents the ingress of water (Sherwood, 1993). Freeze-thaw and wet-dry durability

tests are not applicable for bitumen stabilized mixtures.

2.2 LIME

Lime is most effective in stabilizing soil with a sufficient amount of clay. Lime reacts

with medium, moderately fine and fine-grained soil to result in decreased plasticity,

improved workability, reduced volume change characteristics and higher resistance to

the damaging effects of moisture. The most substantial improvements in these

properties are seen in moderately to highly plastic soils, such as heavy clays. The

most commonly used lime products are hydrated lime and quick lime. Dry hydrated

lime is effective in drying out soils, but produces a dust problem that makes it

undesirable for use in urban areas, and the fast drying action of lime requires an

excess amount of water during hot, dry weather. The quicklime is more economical

8

than hydrated lime as it contains approximately 25 percent more available lime, but it

requires more water for stabilization (Sherwood, 1993). The physical properties and

chemical composition of quick lime and hydrated lime for soil stabilization shall

conform to ASTM C977-89.

The treatment of pavement subgrades with lime can significantly improve the

engineering properties of a wide rang of soils. There are many recommendations for

soils to be treated with lime. For example, soils that should be considered for lime

treatment include soils with a Plasticity Index (PI) that exceeds 10 and have more than

25 percent particles passing the #200 sieve (0.075 mm) (Little, 1995). Lime is used in

case the material to be stabilized has a high PI, i.e. above 10 (UFC, 2004).

In stabilizing the clay, lime performs two basic functions: flocculation and

cementation. Flocculation reduces the PI of soil, thereby improving the workability

and reducing the swell potential of the soil. The cementation process is a slow

reaction after compaction, which increases the strength and durability of the soil.

Cementation also creates a working platform during construction. Lime has also been

used as an admixture to highly plastic materials to facilitate pulverization and mixing,

and to increase the compressive strength (Kersten, 1961).

Lime increases the soil strength by pozzolanic action, which results in the formation

of cementitious silicates and aluminates. Fly ash is generally high in silicate and

alumina, so fly ash can be added to lime stabilized soil to accelerate the pozzolanic

action (Molenaar, 1998). So the lime and fly ash are often used in combination in

stabilizing cohesive materials successfully. However the material is brittle and has not

much flexibility especially in clay soils.

Factors influencing the strength of lime-treated soils are similar to those affecting the

strength of cement-treated soils, i.e. the soil type, the amount of lime and the

compacted density (TRH 14, 1985). Yong and Ouhadi (2007) investigated the effect

of lime on the properties of marl soil (see Appendix A), which is indicated in Fig. 2.1

and Fig. 2.2. I

Fig. 2.1 Liquid limit for stabilized marl samples at different curing time

9

Fig. 2.2 Dry and wet CBR values for natural and stabilized marl for lime

Compared with the cement hydration process, the initial stage of lime reaction seems

quite rapid. Fig. 2.3 shows the rapid initial strength development of lime stabilization.

lime has a beneficial effect in the form of early hardening of the mixture. Due to this

advantage, lime can be used for cement stabilized soil to improve the strength

development.

Fig. 2.3 Initial strength development of a lime stabilization

and cement stabilization (Ingles, 1972)

British studies (Maclean, 1952) have shown that the addition of 2 percent of lime to

cement treated soil increased the compressive strength and limited the reduction in

strength due to immersion in water. The relationships between lime content and the

compressive strength for cement treated soil with 30% and 15% cement content are

shown in Fig. 2.4.

Fig. 2.4 Compressive strength of lime stabilized soil with different cement content

10

As can be seen above, the addition of 2 percent of lime can effectively increase the

strength of cement stabilized materials. Based on a study of PowerCem Technologies,

the 7-day compressive strength with a mixture of clay1 with 15% cement and 0,15%

of RoadCem was 6.4 MPa.

Bnattacharja and Bhatry (2003) investigated the compressive strength of some lime

or cement stabilized clay as a function of time, as shown in Fig. 2.5.

(a) Cal soil (sandy clay: A-7-6)

(b)

(c) Texas 1 soil (clay: A-7-6)

Fig. 2.5 The compressive strength of cement stabilized and lime stabilized soil

As it can be seen in figure 2.5, the strength at all ages of the cement-stabilized soil is

generally higher than lime-stabilized soil of the same age. Lime-stabilized soil starts

weaker but gains strength with time in comparison with this type of soil. So the

increase in strength of lime-stabilized soil is more dependent on the time rather than

on the lime content.

2.3 FLY ASH

Fly ash is the by-product produced by coal-burning electricity generating power plants

that contains silica, alumina, and calcium-based minerals. Depending upon the source

and makeup of the coal being burned, the components of fly ash vary considerably,

but all fly ash includes substantial amounts of SiO2 and CaO. Research (Kalinski and

1 Clay type of soil was tested in the project RC. 20110607. NL. 0495. PowerCem Technologies,

Moerdijk

11

Hippley, 2005) evaluated the cement stabilized fly ash. The results show that the

compressive strength of fly ash can be significantly increased by compaction and

addition of cement, as shown in Fig. 2.6.

Fig. 2.6 Unconfined compressive strength at optimum water content

for cement stabilized fly ash

For stabilization, fly ash helps to reduce the Plasticity Index and swell and to give the

soil additional strength. Since fly ash begins to hydrate immediately after the addition

of water, and the rate of hydration for fly ash is much higher than for Portland cement,

the soil strength and density are dependent on the mixing and compaction time.

Delays in compaction will decrease the strength and density of the soil dramatically

(Ferguson, 1993).

Studies (Kolias, Kasselouri-Rigopoulou et al. 2005) give the effect of addition of fly

ash on the compressive strength of clay soil (A-6), which indicates that clay combined

with 20% fly ash produces a high strength, as shown in Fig. 2.7.

Fig. 2.7 Uniaxial compressive strength of fly ash stabilized clay

The properties of fly ash differ significantly due to the production methods. Two major

classes of fly ash are specified in ASTM C 618 on the basis of their chemical

composition resulting from the type of coal burned; these are designated Class F and

Class C. Class F is fly ash normally produced from burning anthracite or bituminous

coal, and Class C is normally produced from the burning of subbituminous coal and

lignite (Halstead, 1986). Class C fly ash usually has cementitious properties in addition

to pozzolanic properties due to free lime, whereas Class F is rarely cementitious when

mixed with water alone. In their studies (Kalinski and Hippley, 2005) state that Class

C fly ash contains sufficient quicklime to be self-cementing, and doesn’t require the

12

addition of a cementing agent such as Portland cement to achieve significant strength.

However, addition of cement can increase the strength and accelerate strength gain,

because cement hydrates faster than fly ash.

2.4 CEMENT

Cement stabilization has become a popular option to enhance pavement performance.

The stabilized base material is stronger, more uniform and more water resistant than

the un-stabilized base material. Loads are distributed over a larger area and stresses in

the subgrade are reduced (Yoon and Abu-Farsakh, 2009). For stabilizations several

types of cement can be used several types of cement. In the world there are different

names of cement that are used. In the European Union a CEM II Portland fly ash

cement (6-35% fly ash and Portland Cement) is often used in stabilizations. CEM III

Blast furnace cement (36-65% blast furnace slag and 35-64% Portland Clinker) and

CEM I (100% Portland Cement) are less frequently used.

Parsons and Milburn (2003) investigated the properties of soil with the addition of

different stabilizers. The improved compressive strength results are indicated in Fig.

2.8. The results showed that lime and cement stabilized soils exhibited the most

improvement in soil performance for multiple soils.

Fig. 2.8 UCS of soil stabilized with multiple soils

In this literature study, the review focuses on the cement stabilization, which is

described in the following chapters in detail.

2.5 CONCLUSIONS

In this chapter, various stabilizing agents are briefly described. The addition of a

stabilizing agent can help to improve the properties of the basic soil (e.g. reduction of

plasticity, increase in bearing capacity) or secondary or primary granular materials

and to obtain a more durable material.

The choice between these types of stabilization is dependent on the nature of the basic

material to be stabilized and the desired function of the stabilized layer in the

13

pavement structure. Lime is effective in stabilizing cohesive materials such as clay

and silt, while cement is more effective in stabilizing granular materials such as

gravel and sand.

14

15

CHAPTER 3

MATERIALS FOR CEMENT STABILIZATION

Cement-bound materials are defined as mixtures of in-situ and/or secondary soil,

cement and water that binds and hardens after compaction and curing to form a strong

durable paving material.

Soils treated with a relatively small proportion of cement (less than that required for

the hardened soil-cement) are commonly classified as cement-modified soil, which

aims to improve the properties of the in-situ soil such as susceptibility for moisture

conditions. Soil and/or granular material (crushed aggregates, asphalt…), cement and

water are the three basic materials needed to produce cement stabilized materials.

3.1 SOIL

3.1.1 Particle size and soil structure

Soil used in stabilization contains a wide range of grain sizes, like gravel, sand, silt

and clay. The chemical composition of the soil has an important influence on the

properties of the stabilizations. Especially highly organic soils (peat) have a negative

influence on the properties of cement stabilizations. With RoadCem also an organic

soil was successfully stabilized2. However, the scope of this study is on inorganic soils.

The type of soil is generally specified in terms of the particle size. Soils can be

generally classified into two categories according to the grain size.

a) fine grained soil (mainly clay and silt)

2 Trail on Piako Road, reference number, RC.20100211.NZ.0292, PowerCem Technologies, 2010,

Moerdijk

16

b) coarse grained soil (sand and gravel predominantly)

or in shear strength terms

a) cohesive (e.g. clays, clay silt mixture, organic)

b) non-cohesive(e.g. sands and gravels)

The soil types shall be classified according to the detailed particle size and the

classification is different for various countries, which is indicated in Table 3.1.

Table 3.1 Particle size ranges in different countries

Range (mm)

Netherlands United kingdom USA

Clay <0.002 <0.002 <0.005

Silt 0.002-0.063 0.002-0.060 0.005-0.075

Sand 0.063-2 0.060-2 0.075-4.75

Gravel 2-63 2-60 4.75-76.2

Cobbles >63 60-200 >76.2

Boulders − >200 −

In order to specify the type of soil, the particle size distribution curve is to identify the

range of particle sizes. The particle size distribution is usually described in terms of

the cumulative percentage (by mass) of particles passing each sieve used in the

analysis and may be plotted in the form of a graph. Examples of particle size

distribution curves are indicated in Fig. 3.1.

Fig. 3.1 Typical soil particle size distribution curves (K.H, 1980)

A−uniformly-graded curve (poorly-graded curve)

B−well-graded curve

C−gap-graded curve

There are three typical types of distributions in Fig.3.1. A well-graded soil is

characterized by a smooth curve of a wide range of particle sizes. For a gap-graded

soil, the soil particles are deficient in a certain range of sizes. A uniformly-graded soil

consists of a small range of particle sizes. If the grain size distribution approaches the

Fuller curve, this means that the densest packing is approached.

Examples of particle size distribution curves of some typical soils are given in Fig.

17

3.2.

Fig. 3.2 Particle size distribution curves for sands and gravels (K.H, 1980)

There are also some specified coefficients to characterize the grading of a soil. The

coefficient of uniformity ( uC ) and the curvature index ( cC ) are used to determine

whether the soil is well graded or poorly graded and they are defined as follows:

60u

10

dC

d= (3-1)

2

30C

60 10

dC

d d=

×

(3-2)

d10 − sieve size through which 10% of material passes

d30 − sieve size through which 30% of material passes

d60 − sieve size through which 60% of material passes

d10, d30, and d60 are shown in Fig. 3.3.

Fig. 3.3 Particle size gradation coefficient

Table 3.2 gives the indication of the coefficients, uC and cC for gravel and sand.

18

Table 3.2 Indication of uC and cC

Index Gravel Sand

uC ≥4 ≥6

cC 1-3 1-3

Rating Well graded Well graded

In addition to the particle grain size, the particle arrangements also play an important

role with respect to the soil properties. Soil consists of particles, voids and moisture.

Three typical examples are indicated in table 3.3.

Table 3.3 Three physical states of the soil-aggregate mixtures (Molenaar, 2005)

(a) Aggregate with no

fines

(b) Aggregate with

sufficient fines

(c)Aggregate with great

amount of fines

Grain-to-grain contact Grain-to-grain contact

with increased resistance

against deformation

Grain-to-grain contact

destroyed, aggregate

‘floating’ in the soil

Variable density Increased density Decreased density

Non-frost susceptible Frost-susceptible Frost-susceptible

High stability if confined,

low if unconfined

High stability in confined

and unconfined conditions

Low stability

Not affected by adverse

water condition

Not affected by adverse

water condition

Greatly affected by adverse

water condition

Very difficult to compact Moderately difficult to

compact

Not difficult to compact

It should be noted that the fine particles can cause problems when they interact with

the moisture. An excessive amount of fine particles can lead to loss of stability,

susceptibility to frost action, and even mud pumping under traffic loads in practice.

Especially, when the fine particles are clay, the soil structure will become strong when

it is dry, and then will lose strength when it becomes wet. So in practice, the fines

content in the soil should be limited as required in the specifications.

19

3.1.2 Atterberg limits

In the presence of different amounts of water, cohesive soil can exist in four states:

solid, semi-solid, plastic and liquid. The Atterberg Limits are moisture contents which

are used to give empirical information on the soil’s reaction to water. The Atterberg

limits comprise the Liquid Limit, Plastic Limit and Shrinkage Limit:

The Liquid Limit (LL) is the water content at which a soil changes from a liquid to a

plastic state. The Plastic Limit (PL) is the relatively low water content at which soil

changes from a plastic to a solid state. The range of moisture content between PL and

LL is defined as Plasticity Index: PI=LL-PL.

The Plasticity Index (PI) is a measure of the soil’s cohesive properties and is

indicative for the amount and nature of the clay minerals in the soil. High PI soils

have the potential for detrimental volume changes during wetting and drying which

subsequently can lead to pavement roughness. The higher the PI, the more plastic the

soil will be (PCA, 2003).

Depending on the PI value, the soil can be qualified as being more or less plastic,

indicated in Table 3.4.

Table 3.4 Plasticity and dry strength related to Plasticity Index PI (Molenaar, 2005)

Plasticity Index PI Rate of plasticity Dry strength

0-5 Non-plastic Very low, can be crumbed

between thumb and finger

6-15 Medium plastic Moderate to low, can be broken

with the hands

16-35 Plastic Moderate to low, can hardly be

broken with hands

>35 Very plastic Very high, can’t be broken under

the palm of the hand

Clay with a high Plasticity Index (PI) also indicates a high clay content. Fig.3.4 shows

the values of clay content of a wide range of soils, together with the Plasticity Index.

Fig. 3.4 Relationship between clay content and Plasticity Index (Croney, 1977)

20

A high clay content can lead to severe volume changes as the moisture content

changes. A high clay content also requires more cement for stabilization, which

definitely results in shrinkage. So it is suggested to first treat clay soil with lime and

then stabilize the clay with less cement to reduce the adverse effects.

The shrinkage limit (SL) indicates a certain moisture content below which the volume

of the soil doesn’t change anymore when it is dried, as indicated in Fig. 3.5.

Fig. 3.5 Volume change of a soil specimen during drying

The shrinkage limit should be higher than the optimum moisture content, which is

determined in a Proctor density test (see Paragraph 4.2).

Fig. 3.6 gives an overview of the Atterberg limits of soil with the variation of water

content.

Fig. 3.6 Phases of soil and Atterberg limits (Molenaar, 2005)

Soil with a moisture content greater than the liquid limit has no bearing capacity. And

soil with a moisture content lower than the plastic limit is difficult to compact. And

soils with a high PI and LL can experience a large amount of moisture loss and

absorption, which can result in excessive shrinkage or swelling. These volume

changes can result in lower bearing capacity and cause significant damage to the

pavement structure. So it is preferred to stabilize a cohesive soil with a low PI-value

21

to decrease the moisture-susceptibility (Molenaar, 2005).

3.1.3 Soil classification

Soil classification systems have been developed based on the particle size distribution

and their Atterberg limits. The best known classification systems are the AASHO and

USCS classification systems.

1. AASHTO Soil Classification System

The AASHTO system is developed by the Association of American State Highway

and Transportation Officials. The system contains seven classes to identify soils and

granular materials. Materials belonging to the groups A-1 to A-3 are coarse grained

materials while materials belonging to the groups A-4 to A-7 are fine grained

materials. The A-1 and A-2 groups have a sub-rating. Table 3.5 is an overview of this

system (Molenaar, 1998).

Table 3.5 Soil classification according to AASHTO

Main type Group Symbols Requirement

Coarse-grained

(<35% passing 0.075 mm)

A-1

A-1-a

<15% passes 0.075 mm,<30% passes

0.425 mm.<50% passes 2 mm and PI

<6

A-1-b <25% passes 0.075 mm, <50% passes

0.425 mm and PI <6

A-2 <35% passes 0.075 mm, except A-1

and A-3

A-2-4 to A-2-7 Depending on the plasticity limits ,

refer to plasticity chart in Fig. 3.7

A-3 <10% passes 0.075 mm, >50%passes

0.425 mm, no plastic

For fined-grained (<35%

passing 0.075 mm) A-4

>35% passes 0.075 mm, PI<10 and

LL<40

A-5 >35% passes 0.075 mm, PI<10 and

LL>40

A-6 >35% passes 0.075 mm, PI>10 and

LL<40

A-7 >35% passes 0.075 mm, PI>10 and

LL>40

22

Fig. 3.7 AASHTO plasticity chart

2. Unified Soil Classification System (USCS)

The USCS classification system identifies three major soil divisions: coarse-grained

soils, fine-grained soils, and highly organic soils. These three divisions are further

divided into a total of 15 basic groups. Table 3.6 presents the symbols used in USCS.

Table 3.6 Symbols used in USCS

Primary letter Secondary letter

Coarse-grained soils G=Gravel

S=Sand

W=Well-graded

P=Poorly graded

Fine-grained soils F=Fines

M=Silt

C=Clay L=Low plasticity

H=High plasticity Organic soils

PT=Peat

O=Organic

The USCS classification system is shown in Fig. 3.8 and the fine grained materials are

classified according to the plasticity chart as shown in Fig. 3.9 (ASTM D2487-85).

Fig. 3.8 USCS classification chart

23

Fig. 3.9 USCS plasticity chart

The differences between both systems are distinct. The particle size boundary in the

AASHTO system used to decide whether a material is coarse or fine grained is rather

larger than in the USCS system. The AASHTO system can’t indicate whether or not

the material is well graded, while the USCS system doesn’t allow to identify highly

plastic soils (Molenaar, 1998).

Clay can be made to exhibit plasticity within a range of water contents and exhibits

considerable strength when air dry. For classification, clay is fine-grained, or the

fine-grained portion of a soil, with a plasticity index equal to or greater than 4 (ASTM

D2487).

Clay soils present problems of shrinkage and swell under different moisture

conditions. The amount and type of clay determine its expansive characteristics. There

are three main groups of clays: kaolinite, montmorillonite and illite. Soils with more

than 50% clay in the fine fraction are called heavy clay. Clay is the finest of the soil

particles and can actually bond other particles together if sufficient clay and moisture

is present (Croney, 1977).

In spite of the high clay content, cement and lime can be used to stabilize clay to

reduce its high Plasticity Index and increase the strength. Some typical results are

shown in Table 3.7.

Table 3.7 Examples of the effect of cement-modification

on clay soils (PCA, 2003)

Soil No. Cement content (%) Plasticity Index Shrinkage Limit (%)

1 None 30 13

3 13 24

5 12 30

2 None 36 13

3 21 26

5 17 32

It is clear that the addition of cement substantially reduces PI and increases the

24

shrinkage limit, which indicates the improvement in the volume change characteristics

and stability.

The term “Activity” (Ac) has been developed to evaluate the activity of clay by

considering PI and the amount of fine particles.

c

PIA

C= (3-3)

Where

PI − Plastic Index

C − Percentage of particles < 2 µm

cA < 0.75 inactive clay

0.75 < cA < 1.25 normal clay

1.25 < cA < 2 active clay

cA > 2 highly active clay (Molenaar, 1998)

An increasing PI due to a greater activity of the clay leads to a decrease of the

cohesion. A very great activity makes the soil unsuitable for application in pavement

structures.

For stabilization, some typical cement contents for sandy clays and non-expansive

clays with low plasticity are shown in Table 3.8 (Lay, 1998).

Table 3.8 Cement requirement for different soil types

Clay types Cement requirement by mass of dry soil (%)

Well graded sandy clay 2-5

Sandy clay 4-6

Silty clay 6-8

Heavy clay 8-12

Very heavy clay 12-15

In this research, the soil to be used for stabilization is mainly sand and clay. Sands in

the Netherlands are usually uniformly graded. The average grain size d50 is mostly

between 146 and 269 µm and the coefficient of uniformity Cu = d60/d10 is between

1.55 and 2.45. The CBR value varies between 10 and 15% (Molenaar, 2001).

3.1.4 Shrinkage and swell

Most soils contain a fraction of clay as a part of their overall composition. Shrinkage

and swell of soils containing a relatively large clay fraction (particles < 2 µm) can

lead to severe damage on road pavements. Unequal swell can result in serious

25

cracking and unevenness of the pavements (Molenaar, 1998). However, cement

modification can decrease the plasticity and volume change characteristics, increase

the bearing capacity and provide a stable platform for the construction equipment.

(PCA, 2003).

The swell potential is dependent on the amount and type of clay in the soil. The

Plasticity Index is a rough measure for the swell potential as PI is determined by the

fine fraction of the soil (Donaldl, 1994). Table 3.9 gives the relationship between PI

and swell potential (Molenaar, 1998).

Table 3.9 Relationship between shrinkage limit, PI and swell potential

Shrinkage limit Plasticity Index Swell potential

>18 <15 Small

12-18 15-24 Moderate

8-12 25-46 Great

<8 >46 Great

Fig. 3.10 shows that the swell of a natural clay soil strongly reduces through

stabilization with addition of cement.

Fig. 3.10 Effect of addition of cement on the swell (PCA, 2003)

The tests were performed to evaluate the effect of the addition of cement to a

moderately expansive AASHTO Class A-7-6 (16) clay soil. The results showed that

three percent cement reduced the expansion, as measured in a CBR test, from 3.9% to

0.15%.

Fig. 3.11 gives an example of the effect of cement addition on the reduction of the

silt-clay content.

Fig. 3.11 Reduction of silt-clay content due to cement modification (PCA, 1949)

26

As seen above, the silt-clay content of 93% in the untreated soil was reduced to 53%

by the addition of 6% cement. A cement content of about 3% or 4% by weight would

reduce the PI sufficiently to meet the specifications. The cement hydration products

bind some of the particles together to form larger grains in the size ranges of fine sand

particles. The result is that the treated soil contains less silt and clay and more sand,

and in addition, the remaining clay has been altered chemically to become a less

expansive material (PCA, 2003).

3.1.5 Organic content

Organic materials are mostly present in soils like peat and mud and soils with a low

bearing capacity. They can interfere with the hydration of the cement, which will

cause a reduction in strength and durability. Sulfate may influence the long-term

durability of the cement-stabilized layer and thus pavement structure.

Soils that do not react with cement may owe to the presence of organic matter which

causes delayed reaction or to the presence of sulfates that cause swelling or reduction

in strength in the presence of water (Kersten, 1961). Kersten investigated the effect

of sulfate concentration. Results showed that a sulfate concentration in excess of 0.5

to 1.0 percent greatly reduced the strength of the immersed specimens. Research at

RRL has shown that for non-cohesive materials the total sulfate content should not

exceed 1% (as SO3). For cohesive materials the limit is 0.25%. In order to avoid the

adverse effect of organic content and sulfate, a chemical analysis should be done prior

to the mixing to determine the content of organic material.

In highly organic soils, the cement reaction will be adversely affected by the presence

of destructive acids, resulting in lower strength gain in mud and peat. Therefore, this

research concentrates on inorganic soil rather than organic soil. However, PowerCem

Technologies is contributing to the application of the stabilization of all types of soil

(even clay and high organic soils) and contaminated soils3.

Another issue that should be considered in the stabilization of soils is chromium,

which is an unavoidable trace element in many raw materials used in industry and

mining as well as the manufacturing of Portland cement clinker. Chromium VI

compounds are classified as extremely toxic because of their high oxidation potential

and their ability to penetrate the human skin and many are carcinogenic. For normal

strength concrete the content of Cr VI would be 140 ppb (part per billion), where the

acceptable risk limit in South Africa is 200 ppb. For high strength concrete or

variation in the manufacturing of cement, it may lead to an environmental risk when

considering the Cr VI. However, tests in PowerCem Technologies have shown that the

Cr VI content was reduced from 200 000 ppb to 140 ppb using industrial waste from a

3 Trail on Piako Road, reference number, RC.20100211.NZ.0292, PowerCem Technologies, 2010,

Moerdijk

27

chrome melter in a concrete matrix with the addition of PowerCem additive (Kurt,

2006).

3.2 CEMENT

Cement can be used as an effective stabilizer for a wide range of materials, and it is

particularly effective in stabilizing medium to low plasticity materials. The types of

cement are mainly are Portland, mixed with fly-ash and with high blast furnace slags.

Hydraulic cement refers to any cement that sets and hardens after it is combined with

water. Portland cement is hydraulic cement composed primarily of hydraulic calcium

silicates and is the most common used, ranging from TypeⅠto Type Ⅴ. TypeⅠis for

general purpose use and TypeⅡis used where precaution against moderate sulfate

attack is required. Type Ⅲ cements are chemically and physically similar to TypeⅠ

except they are ground finer to provide the early strength. Blended cement is also

hydraulic cement and is made by mixing two or more types of cement. Usually the

primary materials used in blended cement are Portland cement and slag cement. There

are two main types of blended cement: Portland blast furnace slag cement and

Portland-pozzolan cement.

Soil can be modified by cement to improve its quality or stabilized with a relatively

larger amount of cement to increase the strength and durability. Because when cement

is mixed with water, hydration is initiated rapidly. Cement hydration produces

cementitious material (e.g. C-S-H). Cement develops a high bond strength between

the hydrating cement and the soil particles. It also improves the gradation of the

stabilized clay soil by forming larger aggregate particles from fined-grained particles.

Although it is possible to treat almost any soil with cement to improve its properties,

in practice it is difficult to treat fine, clayey materials with cement owing to the high

cement content required and the difficulty in pulverizing the soil and mixing the

cement (TRH 14, 1985). In general, the soil should have a PI less than 30.

For the plastic materials, the addition of cement reduces their plasticity in terms of

Plasticity Index and increases the shrinkage limit as well as the UCS of the hardened

cement-bound mixture, which is shown in Table 3.10.

Table 3.10 Average change in properties for clay soils

% Stabilizer Plasticity Index Shrinkage Limit 7-day UCS 28-day UCS

3% Cement -52% 122% 468% 605%

3% Lime -55% 123% 183% 348%

5% Cement -64% 158% 775% 993%

5% Lime -64% 151% 266% 481%

As indicated in table 3.10, cement and lime accomplish a similar reduction in PI and

increase in shrinkage limit at similar content levels. Cement generally produces a

much higher strength than lime at all ages (Kersten, 1961).

28

The cement content plays a significant role in the properties of cement-bound

materials The selection of the cement content to be used is dependent on the soil

classification and the desired degree of improvement in soil quality. Generally small

amounts of cement are required when it is simply desired to modify the soil properties

such as gradation, workability and plasticity. When it is desired to improve the

strength and durability significantly, larger quantities are required (Donaldl, 1994).

Table 3.11 shows examples of required cement contents for the different soils.

Table 3.11 Cement requirement of different soils (Molenaar, 1998)

Soil type Amount of cement (%)

By weight By Volume

A-1-a 3-5 5-7

A-1-b 5-8 7-9

A-2 5-9 7-10

A-3 7-11 8-11

A-4 7-12 8-13

A-5 8-13 8-13

A-6 9-15 10-14

A-7 10-16 10-14

As indicated in the research (Kersten, 1961; Donaldl, 1994; Molenaar, 1998), a

good quality mix is obtained with a cement content generally in the range of 8% to

14% (depending on the soil type). The compressive strength increases as the cement

content increases. However, the higher the percentage of cement, not only the higher

the costs but also the more severe the shrinkage cracking.

For the field condition, it is generally accepted that the full-scale field-mixing process

is less efficient than the closely controlled laboratory mixing process, and hence it is

common practice to increase the lab-determined cement content by a multiplication

factor of about 1.5 to give a cement content appropriate in the field (Guthrie and

Rogers, 2010).

3.3 WATER

Water serves two purposes for stabilization: it helps to obtain the maximum dry

density during compaction and it is essential for cement hydration. The water content

for maximum compaction should be at optimum moisture content, for less or more

water will reduce the dry density. For cement hydration, sufficient water contributes to

the complete hydration and to achieve a high strength.

The Optimum Moisture Content (OMC) is the moisture content at which the material

reaches the maximum dry density, which can be obtained by the Proctor test

(described in paragraph 4.3). Prior to the mixing, the Proctor test should be performed

29

to get the Optimum Moisture Content, which is an important parameter for the

stabilization. After the mixing and compaction, the mixture should be covered to

avoid moisture loss. The specimen should be cured in a moist environment to ensure

hydration.

3.4 ADDITIVE

Many additives are currently available to improve the performance of the stabilized

material. In this research the effect of additive on the performance of the cement

stabilized soil will be investigated. The additive technology for stabilization is

summarized in this review.

3.4.1 Traditional additives

(1) Limestone based additives

When the soil contains a large amount of clay, the soil particles have a large surface

area and subsequently adsorb much water. The adsorbed water is strongly bonded to

the clay particles and difficult to remove unless by particular chemicals. Limestone

can be used to remove the bonded water, by ion exchange, which results in a lower

bonded water content.

Based on this, some products were introduced for clay stabilization, which have

advantages of improving workability, compaction and increase the soil’s shear

strength and bearing capacity, etc. They also can be applied as a stabilizer for sands

and silty soils.

(2) Polymer additives

Orts, Sojka et al. (1999) present a polymer that can be applied for reduction of the

soil erosion. Polymers are brought in the stabilization in a liquid form in order to

obtain a more homogeneous mixture (Egyed, 2010).

The product based on polymer technology has been applied as an environmentally

safe stabilizer at various soil conditions. It is reported that it can reduce or eliminate

the following problems: base failure of paved and unpaved roads, dust pollution, soil

permeability and soil erosion. However the lifetime of the polymers in soil

stabilization is short.

(3) Enzymes additives

A liquid enzyme stabilizer has been used for soil stabilization, which contributes to

increase in bearing capacity and reduction in soil permeability. Compared with

conventional additives, the use of an enzyme additive is more cost effective, and this

provides a beneficial alternative for road construction. Some additives of enzymes

have been proven to strengthen the road structure and significantly reduce the

30

construction cost.

3.4.2 RoadCem

The RoadCem additive is based on Nano technology and produced by PowerCem

Technologies. It has been used world widely as an additive and specifically designed

for applications in road construction and stabilization. It enhances and increases the

strength and flexibility of stabilized road layers and improves the overall performance

of cement-bound materials used in road construction. This study is intended to

evaluate the effect of RoadCem on the performance of cement-bound materials.

The marl soil (see Appendix A) was stabilized with RoadCem–cement to investigate

the effect of the additive. The results in terms of CBR values are shown in Fig. 3.12.

Fig. 3.12 Comparison of CBR values for lime stabilized marl soil

In Fig. 3.12 the CBR values are much higher with RoadCem than only with cement4.

Moloisane (2009) evaluated the strength behavior of unpaved roads stabilized with

non-traditional stabilizers. Table 3.12 presents the DCP-CBR strength of the stabilized

experimental panels after 8 months. DCP indicates Dynamic Cone Penetrometer.

Table 3.12 DCP-CBR strength for stabilized panels with different stabilizers

(Moloisane, 2009)

Panel

Number Stabilizer used

In-situ DCP-CBR Soaked DCP-CBR

Maximum CBR in

first 5 months

Maximum CBR in

first 5 months

1 Cement 222 179

2 Perma-Zyme 11X 152 49

3 RoadCem and cement 336 246

4 Dustex and Bitumen Emulsion 207 75

5 Dustex 154 121

6 Ecobond ((UF) resin) 190 150

7 Bitumen Emulsion 222 157

In this research, seven different commercial stabilizer products from five generic

4 Trail on Piako Road, reference number, RC.20100211.NZ.0292, PowerCem Technologies, 2010,

Moerdijk

31

group types were applied: one from the electro-chemicals generic group type

(Perma-Zyme 11X), and others were from the organic non-petroleum group (Dustex),

organic petroleum group (Bitumen Emulsion), polymer group

(Ecobond/urea-formaldehyde (UF) resin) and cement catalyst group (RoadCem). It

can be seen that the soaked CBR strength decreased for every type of stabilizer, but

the RoadCem and Cement treated experimental panel showed the highest strength. In

comparison with the panel with only cement, the panel treated with cement plus

RoadCem significantly outperformed in both in-situ and soaked conditions.

Also by environmental investigations and testing on the end-product, RoadCem has

been proven to be an environmentally friendly fine-powder substance5 . 6 . 7

(PowerCem Technologies, 2008).

3.5 CONCLUSIONS

In this chapter, the soil properties (e.g. particle size, classification and swell) are

discussed. Clay has a relative large particle surface area which will results in more

cement consumption for stabilization. Sand and gravel are the most suitable for

cement stabilization. Clay soil due to the high clay content is reported to be

susceptible to volume change. A chemical analysis should be done to determine the

content of organic material.

The cement content is a significant factor for the properties of stabilized materials.

The cement content should be determined to meet the requirement in accordance to

the strength and durability specifications. The water content must be determined by

the Proctor test to obtain the Optimum Moisture Content, which is essential for the

compaction and cement hydration. Compared with traditional additives, RoadCem is

reported to be effective in improving the properties of the cement stabilization.

5 Analyses of drilling Invert Cuttings versus PowerCem/OPC modifications and reference

mixtures, ref number: 60769/06, UEG, May 2006, Wetzlar (D) 6 Material Safety Data Sheet RoadCem,ref. number: 15-9722, Chemwatch , July 2008, Moerdijk

7 Immobilization of Cr VI in cement materials using PowerCem, reg.No: 1956/01084/06,

Bateman, April 2006, Pretoria (RSA)

32

33

CHAPTER 4

PRELIMINARY INVESTIGATIONS

The properties of cement-bound materials are dependent on several factors:

(a) The nature of the materials whether it is clay, silt, sand or coarse aggregate

(b) The proportions of the mix (soil, cement and water)

(c) Degree of compaction and curing conditions (temperature and age)

(d) Environmental factors.

In this chapter, the review is mainly about the soil tests and compaction of the

soil-cement mixture.

4.1 SOIL TESTS

Prior to mixing with cement, the following soil tests should be conducted to classify

the soil type and evaluate the soil properties:

• Particle size distribution

• Atterberg limits (Plastic Limit, Liquid Limit and Shrinkage Limit)

• Maximum Dry Density

• Chemical analysis

4.1.1 Particle size distribution

The particle size distribution of soil is investigated by sieving. The soil sample is

distributed through various sieves of decreasing sieve size. The percentage passing

through every sieve against the sieve size is plotted to get the particle size distribution

(see Fig. 3.1). This test is performed based on the standard NEN-EN 933-1. The

equipment for the analysis is shown in Fig. 4.1.

34

Fig. 4.1 Particle size analysis of coarse grained soils using sieves

The smallest sieve size opening generally used is 0.063 mm, and below this the

distribution of silt and clay particles is determined using sedimentation techniques.

Wet sieving of the soil particles is the process to separate the fine grained soil from

the coarse grained soil, which is shown in Fig. 4.2.

Fig. 4.2 Wet sieving for particle size distribution of fine grained materials

4.1.2 Liquid Limit and Plastic Limit

The determination of the Plastic Limit is normally made in conjunction with the

determination of the Liquid Limit. Standard testing methods for Liquid Limit (LL)

and Plastic Limit (PL) are described in ISO/TS 17892-12 and ASTM D4318 -84. Both

LL and PL are determined on particles smaller than 0.425 mm.

1. Liquid Limit (LL)

In standards of ISO/TS 17892-12, the cone equipment (shown in Fig. 4.3) is used to

determine the Liquid Limit. The soil sample at its original state is mixed with a

certain amount of distilled water and then placed in the cup. The cone is allowed to

penetrate and the penetration is recorded, after this the water content is determined.

The procedure is repeated at least three times with different water content. For the

calculation of LL, the water content (%) and the cone penetration are plotted on a

35

linear scale (as shown in Fig. 4.4).

1. adjustable stand arm

2. plexiglass with graded scale

3. cone

4. specimen

5. mixing cup

6. index line

Fig. 4.3 Cone equipment

020406080100

10 12 14 16 18 20 22 24 26 28cone penetration/mmwater content/%

Fig. 4.4 Example of relationship between water content and cone penetration

The Liquid Limit is the water content determined from the specified penetration,

which is dependent on the cone (shown in Table 4.1).

Table 4.1 Cone penetration requirement

Cone penetration requirements 80g/30º (cone) 60g/60º (cone)

Initial penetration about 15 mm about 7 mm

Penetration range 15 to 25 mm 7 to 15 mm

wL determined from the penetration 20 mm 10 mm

In ASTM 4318-84 the liquid limit is determined by shaking the soil sample. The soil

sample is placed in a metal cup and a 2 mm wide groove is made in the center. The

soil is shocked by dropping the cup at a rate of 2 drops per second and the number of

drops when the two parts of the soil are drawn together along a distance of 13 mm

(shown in Fig. 4.5) is recorded. This procedure is repeated at different water content.

Plot a graph of number of drops and water content. The water content at 25 drops is

36

the liquid limit.

Fig. 4.5 Soil pat after groove closed

2. Plastic Limit (PL)

For determination of the plastic limit, the methods described in the standards ISO/TS

17892-12 and ASTM 4318-84 are similar. In ASTM 4318-84 the Plastic Limit is

determined by alternately pressing together and rolling into a 3.2 mm diameter thread

(shown in Fig. 4.6) a small portion of plastic soil until its water content is reduced to a

point at which the thread crumbles and is no longer able to be pressed together and

rerolled. The water content of the soil at this stage is reported as the Plastic Limit.

Fig. 4.6 Test for Plastic Limit

3. Plasticity Index

The Plasticity Index is calculated as the difference between the Liquid Limit (LL) and

Plastic Limit (PL). PI=LL-PL.

4.1.3 Chemical analysis

Soil with a high organic content corresponds to increased water absorption and in

most of the cases a low PH value, both have a big negative influence on the cement

reaction. It is essential to detect the presence and content of organic matter.

Organic material contains high amounts of carbon compounds, which when heated to

high temperatures are converted to carbon dioxide and water. In chemical analysis, a

dry solid sample is heated to a high temperature. The organic matter in the soil is

37

given off as gases. This results in a change in weight which allows for calculation of

the organic content of the sample.

First dry the granular materials to 100ºC ± 5ºC, so the water evaporates. This must be

done until constant weight to determine the presence of soil and organic material.

To determine the exact amount of organic matter, dry the soil sample for four hours to

600ºC and calculate the weight change. Because the organic material starts burning at

temperatures > 500ºC.

4.2 COMPACTION OF MIXTURE

Compaction is the process of packing the particles more closely together and reducing

the porosity which can increase the bonding strength and enhance durability. With

good compaction the materials can also obtain a better resistance to water and an

increased life span. This procedure can be performed according to standard NEN-EN

13286-2.

The dry density of the compacted soil is one of the main factors that influence the

strength of the sample. And the optimum moisture content is essential to achieve the

maximum dry density and to aid in cement hydration (Yoon and Abu-Farsakh, 2009).

There is an optimum moisture content for compaction, above or below which reduced

dry densities are obtained (J.Kennedy, 1983). The compaction curves are developed

to identify the maximum dry density and the optimum moisture content.

4.2.1 Compaction test

There are two approaches for compacting cement stabilized materials as described in

NEN-EN 13286-2, i.e. the standard and modified Proctor compaction test respectively.

The tests consist of compacting materials inside moulds with different dimensions

(shown in Table 4.2 and 4.3) according to the soil particle sizes, using a hammer

weight dropped from a fixed height at a prescribed number of drops. The procedure is

repeated for a sufficient number of water contents. The dry density is then plotted

against water content and the compaction curve is obtained.

38

Table 4.2 Summary of sample preparation methods

Percentage passing test sieves Mass of sample ( Kg) Proctor

mould 16 mm 31.5 mm 63 mm

100 ─ ─ 15 A

40 B

75 to 100 100 ─ 40 B

<75 75 to 100 100 40 B

─ <75 75 to 100 200 C

Table 4.3 Dimensions of the cylindrical test mould

Proctor mould Diameter (mm) Height (mm)

Thickness

Wall (mm)

Base

plate (mm)

A 100.0±1.0 120.0±1.0 7.5±0.5 11.0±0.5

B 150.0±1.0 120.0±1.0 9.0±0.5 14.0±0.5

C 250.0±1.0 200.0±1.0 14.0±0.5 20.0±0.5

Table 4.4 illustrates the summary of the Proctor test and modified Proctor test.

Table 4.4 Summary of the Proctor test and modified Proctor test

Types of test Characteristic Dimension

Proctor mould

A B C

Proctor test Mass of rammer kg 2.5 2.5 15.0

Diameter of rammer mm 50 50 125.0

Height of fall mm 305 305 600

Number of layers - 3 3 3

Number of blows per layer - 25 56 22

Modified

Proctor test

Mass of rammer kg 4.5 4.5 15.0

Diameter of rammer mm 50 50 125.0

Height of fall mm 457 457 600

Number of layers - 5 5 3

Number of blows per layer - 25 56 98

As indicated above, the modified Proctor test corresponds to a larger compaction

effort. Fig. 4.7 gives a comparison of the results of the two compaction methods.

39

155015701590161016301650167016900 2 4 6 8 10Moisture content (%)Dry density (kg

/m3) Modified Proctor Standard Proctor

Fig. 4.7 Moisture-density curves of a cohesive soil for

different compaction (Molenaar, 1998)

It can be noted that Modified Proctor compaction results in a higher dry density due to

the larger compaction effort. For practical use, whether standard or modified, the

required field density for base and sub-base layers is between 95% and 101% of the

maximum Proctor density determined in the laboratory.

4.2.2 Factors influencing compaction

1. Compaction methods

Soil is usually compacted by different compaction methods. Bahar, Benazzoug et al.

(2004) investigated the effect of different compaction methods on the strength of soil

stabilized with cement (5% percent by weight). Compaction was achieved by means

of static, vibratory and dynamic compaction. Static compaction was obtained by

applying a static pressure using a universal compression testing machine. The soil is

classified as moderately plastic clay type A-6 according to the AASHTO system. The

results are shown in Fig. 4.8 and Fig. 4.9.

Fig. 4.8 presents the compaction curves obtained by different compaction methods. It

can be observed that the three different methods of compaction used didn’t affect

significantly the dry density of the soil. The highest density was obtained with the

dynamic method when the water content is on the dry side of the curve and with the

vibro-compaction method when the water content is on the wetter side.

Fig. 4.8 Effect of compaction methods on the density

40

Fig. 4.9 Effect of compaction methods on the compressive strength

In Fig. 4.9 it can be found that, for dry specimens, dynamic compaction yields the

highest compressive strength for every cement content of the stabilized soil (Bahar,

Benazzoug et al. 2004).

Compaction with different energy should result in different dry density-moisture

curves, which is indicated in Fig. 4.10.

Fig. 4.10 Density-moisture curves for sandy clay soil with different compaction effort

It is clearly that the maximum dry density increases and the optimum moisture content

decreases with increasing compaction effort (Croney, 1977).

2. Cement content

Compared with the compaction of the raw materials, the compaction of the mixture of

soil-cement may be a little different. Fig. 4.11 gives examples of the compaction

curves obtained for an un-stabilized and cement stabilized sands (A-2, according to

AASHTO system) with different cement contents.

Fig. 4.11 Dry Density-Moisture curves for a sand stabilized with

different cement contents (Yoon and Abu-Farsakh, 2009)

41

The dry density increases with an increase in cement content. The optimum moisture

content of the cement stabilized sands (OMC = 10% to 11% ) is slightly lower value

than that of the un-stabilized sand (OMC = 11.5%).

The optimum moisture content and maximum dry density of compacted soil-cement

are approximately the same as those of the raw materials. Some soils do, however,

exhibit marked differences in optimum moisture content and maximum dry density,

but they are limited in the range of 1 to 3 pcf (pounds per cubic foot) (Kersten, 1961).

Table 4.5 gives typical ranges of increases and decreases for different soils stabilized

with cement.

Table 4.5 Maximum dry density and moisture contents of soil-cement compared to the

corresponding values for the raw soils (Kersten, 1961)

Soil group and type Change in Maximum

Density (in pcf)

Change in Optimum

Moisture Content (in

percentage units)

A-2 sandy loams 0 to +3 -1 to +1

A-3 sands 0 to +6 0 to -1

A-4 silts and loams 0 to -6 0 to +3

A-5 silts -3 to +1 0 to -3

A-6 medium clays 0 to +1 0 to -2

A-6 heavy clays -1 to +2 0 to -4

3 Soil type

Clay is very difficult to compact when dry or wet. The compaction of clay very much

depends on the water content. To achieve good results, the water content should stay

within ±2% of the optimum moisture content (Molenaar, 2005). Fig. 4.12 presents

examples of compaction curves of typical raw soils.

G = gravel S = sand

M = silt C = clay

W = well graded L = low plasticity H = high plasticity

Fig. 4.12 Dry density-moisture curves for a range of soil types

As shown above, with a decrease in soil particle size, the optimum moisture content

for a given compaction method is increasing. Clay particles have a relatively large

42

surface, so they need a larger amount of water for compaction.

4. Delayed compaction

In many studies it is found that delayed compaction has a detrimental effect on the

compressive strength and maximum dry density. Because cement begins hydrating as

soon as it comes into contact with water, compaction should be performed as soon as

possible after mixing in order to minimize the adverse effect of cement hydration on

the stabilized materials to be compacted.

Fig. 4.13 gives examples of delayed compaction influencing the dry density and

strength (TRH 14, 1985). Fig. 4.13 shows the loss in density and strength with

increase in time between mixing and compaction. So it is essential to perform the

compaction as soon as possible after mixing.

Fig. 4.13 The effect of a time lapse between mixing and compaction on the dry

density and unconfined compressive strength

4.3 MIX COMPOSITION

The proportions of cement, water and soil in the mixture significantly affect the

properties of the stabilized material. Therefore, the mix composition design is an

important process for stabilization.

4.3.1 Requirements for materials

In many studies, there are different requirements for soils suitable for cement

stabilization. In a research study (Molenaar, 1998) it is presented that the soil is

suited for cement-stabilization if:

% < 0.075 mm (#200 sieve): <35%

% > 0.075 mm: > 55%

Maximum grain-size: <75 mm

LL: < 50

PL: < 25

The specification for soil-cement requires:

43

1. The material should be well-graded with a coefficient of uniformity of not less

than 5.

2. The material passing the 425 µm sieve should have a Liquid Limit not greater

than 45 percent and a Plastic Limit not greater than 20 percent (Croney, 1977).

According to NEN-EN 14227-1, the aggregates grading for cement-bound granular

mixture is indicated in Fig. 4.14.

Y−Percentage passing by mass

X−Sieve size, in millimeter (mm)

1−Envelope A

2−Envelope B

Fig. 4.14 Soil gradings for cement-bound mixture

Fig. 4.14 covers all gradings with which practical experience in cement bound

granular mixtures exists. Gradings characterized by envelope A include sands.

Gradings characterized by envelope B include well-graded coarse aggregates with

limited contents of fines < 0.063 mm.

For a given soil that reacts normally with cement, the cement content determines the

nature of the cement-stabilized soil. The proportion of cement alters the plasticity,

volume change, susceptibility to frost heave, elastic properties, resistance to wet-dry

and freeze-thaw cycles (Kersten, 1961).

For stabilization, the quantity of cement required to give the specified strength for

soil-cement varies with the grading of the soil. Table 4.6 gives the ranges of cement

contents likely to be required for different type of soils.

Table 4.6 Cement content requirement for soils (Croney, 1977)

Soil Cement content (% by weight)

silt-clays 9-12

sandy-clays 8-10

well-graded sands 5-7

sandy gravels 3-5

Standard (NEN-EN 14227-1) gives the minimum cement content required for

stabilization (Table 4.7).

44

Table 4.7 Minimum cement content according to the maximum grain size

Maximum nominal aggregate size (mm) Minimum cement content (% by weight)

> 8.0 to 31.5 3

2.0 to 8.0 4

< 2.0 5

For stabilizing soil, the water content of the mixture should be the Optimum Moisture

Content obtained by the Proctor test. Water to be used should be clean and free from

deleterious materials and other organic substances without using RoadCem. Water

suitable for drinking is generally accepted for use.

4.3.2 Mix design method

In this research, the central composite design method is employed for mix

composition. The two independent variables are the cement content (C) and the

additive content (A). In a PhD thesis (Medani, 2000) the central composite design

method is described, see Table 4.8 and Fig. 4.15.

Table 4.8 Variables for central composite design

Trial Ccoded Acoaded

1

2

3

4

-1

+1

-1

+1

-1

-1

+1

+1

5

6

7

8

-ψ

+ψ

0

0

0

0

-ψ

+ψ

9-13 0 0

Fig. 4.15 Coded test conditions for the central composite rotatable design

As indicated in Table 4.8 and Fig. 4.15, trials 1-4 combine the corner values with the

distance from the center point ±1. Trials 5-8 are called star points, and the distance

45

from the center is ψ, which depends on certain properties desired for the design and

on the number of factors involved. If the value of ψ is set at 2 , the design is called

rotatable. This means that the variance of the predicted response at any point x

depends only on the distance of x from the design center point.

To scale the coded terms of Table 4.7 into values within the range of interest, ψ= 2

is set equal to half the ranges of the variables and the scaling factors for the tests

follow from (Medani, 2000):

scaling max min

12 ( )

2C C C= − (4-1)

scaling max min

12 ( )

2A A A= − (4-2)

In which

scalingA − scaling factor for additive content

scalingC − scaling factor for cement content

maxA − maximum additive content (kg/m3)

minA − minimum additive content (kg/m3)

maxC − maximum cement content (kg/m3)

minC − minimum cement content (kg/m3)

Finally the experimental values of the cement content and additive content follow from:

max min

1( )

2coded scaling

C C C C C= × + + (4-3)

max min

1( )

2coded scaling

A A A A A= × + + (4-4)

4.4 CURING CONDITIONS

The curing condition plays an important role in the properties of cement stabilized

materials on the short and long term. Proper curing methods significantly contribute to

the development of the strength of specimens. Appropriate temperature, moisture

conditions and time are required for curing.

Fig. 4.16 gives an example of the strength development of samples with different

cement content during the first 28 days. The soil is classified as ML/A-4 according to

USCS/AASHTO.

46

Fig. 4.16 Variation of unconfined compressive strength at 1, 7 and 28 curing days of

samples with different cement contents (Altun, Sezer et al. 2009)

The compressive strength increases rapidly during the first 7 days and after that the

rate of increase rate is relatively low. After 28 days, the compressive strength almost

remains the same.

The strength is also related to the curing temperature, which is essential for the

cement hydration. During curing, moisture may be lost by evaporation, which will

affect the cement hydration and reduce the final strength, so the specimen should be

cured properly to avoid moisture loss. An example of the effect of the curing

temperature on the 7 days compressive strength of cement-stabilized sand (cement

content 6%) is shown in Fig. 4.17.

Fig. 4.17 Relationship between unconfined compressive strength and curing

temperature for cement stabilized sand (TRH 14, 1985)

As shown in Fig. 4.17, the 7-day strength increases as the temperature increases and

this effect has been used to develop accelerated test methods, i.e. curing at high

temperature, to give an early indication of the long-term strength.

4.5 CONCLUSIONS

For stabilization laboratory soil tests should be performed first to indicate the soil

properties. The tests consist of grain size distribution, Liquid Limit and Plastic Limit,

and chemical analyses, which can be performed according to the specified standards.

Proctor test is usually used for laboratory compaction. Also the Proctor compaction is

essential to obtain the Optimum Moisture Content for stabilization and the maximum

dry density as a reference for field density. Compaction of the soil-cement mixture is

essential for stabilization, which can increase the strength and durability of cement

47

stabilized materials. Different soil types result in different compaction curves. The

moisture content for mix design is consequently determined from the optimum

moisture content of the curve. The curing condition should also be taken into account

for the strength development.

The selection of the materials for stabilization should refer to the specifications, and

the quantities of the components are determined according to the guidelines and

practical experiences. In this research, the central composite design method is

employed for the mix composition.

48

49

CHAPTER 5

MAIN MECHANICAL PROPERTIES

Four major variables control the degree of stabilization with cement:

1. The nature of the soil

2. The cement content

3. The moisture content during compaction

4. The dry density attained in the compaction.

If the moisture content and the dry density are controlled according to the standard

methods, and normal mixing and curing procedures are applied, the nature of soil and

the cement content used determine the degree of stabilization (Kersten, 1961).

5.1. COMPRESSIVE STRENGTH

The compressive strength is the most commonly used mechanical property for

evaluating cement treated materials, and is extensively used for the mix design and

quality control (TRH 14, 1985). The compressive strength is dependent on the soil

type, the amount and type of cement and the degree of compaction. The moisture

content and curing conditions also affect the compressive strength. These influencing

factors are described hereafter.

1. Cement content

The cement content has a significant effect on the strength of cement stabilized

materials. The strength increases as the cement content increases, because the

hydration products fill the pores of the matrix and enhance the bond strength between

the particles.

50

Park (2010) has published 12 SEM (Scanning Electron Microscopy) photos of

specimens after failure, which clearly show the microstructure of the cement

stabilized material specimens with different cement content, as presented in Fig. 5.1.

Fig. 5.1 SEM photos of cement stabilized sand specimens after testing

(a) 4% cement; (b) 8% cement; (c) 12% cement; (d) 16% cement (Park, 2010)

As shown in the pictures, for the specimens with a cement content of 4 and 8% the

sand particles protrude from the mixture, and some voids between these particles can

be observed. However, when the cement ratio was relatively high, such as 12 and 16%,

the sand particles are buried into cement and don’t appear.

Examples of the effect of the cement content on the compressive strength are

presented in Fig. 5.2. In this research (TRH 14, 1985) the compressive strength of

different soils stabilized with various cement contents was investigated. Similar

research results from PowerCem Technologies are also included in Fig. 5.2 to get an

indication of the trends. It should be realized that the soils stabilized with cement plus

RoadCem are not exactly the same as the soils stabilized with only cement in the

eighties.

Furthermore, the test conditions (specimen size, loading rate, etc.) might be different.

The strength increases more or less linearly with the cement content but at different

rates for different soils. The larger the particle sizes of the soil, the higher the

compressive strength of the stabilized material. A well-graded particle size

distribution also results in a better strength. As for the addition of RoadCem, the

compressive curves are all above the curves for the same cement content but without

additive, which indicates that Roadcem can improve the compressive strength, when

the right doses of RoadCem is used, for all types of raw materials.

51

(1) Silty clay

(2) Uniformly graded sand

(3) Well graded sand

(4) Gravel

Fig. 5.2 Relationship between unconfined compressive strength and curing period for

different soils stabilized with various cement content

2. Moisture content

The water content is also an important factor to determine the compressive strength

because the moisture content is essential to achieve the Maximum Dry Density and to

52

hydrate with the cement to gain strength. Yoon and Abu-Farsakh (2009)

investigated the effect of the moisture content and the water/cement ratio on the

compressive strength at 7 days, shown in Fig. 5.3 and Fig. 5.4. The soil is classified as

silty sand (SM) and A-2 according to the UCCS and AASHTO system, respectively.

Fig. 5.3 Relationship between moisture content and UCS

Fig. 5.4 Relationship between water to cement ratio and UCS

As shown above, the unconfined compressive strength has a positive correlation with

the moisture content at the dry side of the Optimum Moisture Content. The optimum

water to cement ratios that correspond to the highest strength are about 0.75, 1.05 and

1.25 for the silty sand sample mixed with 12, 10, and 8% cement, respectively.

Yoon also proposed a correlation model to estimate the unconfined compressive

strength of cement stabilized sand:

0.62( / )

wc a

ini

Cf p

e w c= × (5-1)

Where

cf −unconfined compressive strength (kPa)

ap − reference pressure (atmospheric pressure) (kPa)

ini

e − initial void ratio unit (%)

wC − cement content (%)

The moisture is not only needed for compaction, but must also be sufficient to ensure

the cement hydration. The effect of ratio of water and cement on the compressive

strength was investigated by Yoon, which is shown in Fig. 5.5.

53

0123456789

0 2 4 6 8 10Water/Cement RatioUnconfined Compressive strength (MPa) soil/cement ratio=0.47soil/cement ratio=1.0soil/cement ratio=1.54soil/cement ratio=4

Fig. 5.5 28-day strength of cement treated clay

Fig. 5.5 shows the data plotted separately according to the soil-cement ratio. As can be

seen, for a given water-cement ratio. This relationship can be expressed in the

following equation

( / )

0( / )

m s c

c n

ef f

w c= (5-2)

Where

0f , m and n are experimentally assigned values. For the cemented slurry clay

samples, m =0.62, n =3 and 0f = 4,000 kPa for the 7-days strength and 6,000 kPa

for the 28-days strength (Yoon and Abu-Farsakh, 2009).

The experimental work in (Kersten, 1961) showed that the compressive strength

increases to a maximum at a moisture content slightly less than the optimum moisture

content for the sandy soil and the silty soil, and at a greater moisture content than the

optimum moisture content for clay soil.

The influence of the moisture content is more related to its ability to improve

workability and facilitate compaction to obtain a coherent mass than that it is to the

water requirement for hydration, because adequate water for compaction ensures

adequate water for hydration provided it is not lost during curing (Kersten, 1961).

3. Curing conditions

Appropriate curing conditions significantly help develop the compressive strength.

The curing age is an important factor affecting the strength development. In research

(TRH 14, 1985) the effect of the curing age on the compressive strength was

investigated for soil stabilized with two types of cement. Based on this result, the

effect of adding Roadcem is included in Fig. 5.6. The curve with RoadCem is

obtained from Powercem Technologies. It can be seen that by use of RoadCem, the

compressive strength at 28 days is 20% to 30% higher than the strength only with

cement. However, it has to be realized that the soil type and test conditions will have

been different.

54

00.511.522.533.544.553 4 5 6 7 8 9 10 11 12 13 14Cement content (%)Compressive strengt

h (MPa) 112days56days28days14days7days4days2days1day112 days withRoadCem

(a) Ordinary Portland Cement

(b) Portland Blast Furnace Cement

Fig. 5.6 Effect of curing age on the unconfined compressive strength

Fig.5.6 shows the increase in strength with age. It has been found that the 28-days

strength is between 1.4 and 1.7 times the 7-days strength. For estimation purposes a

factor of 1.5 may be used.

Bahar, Benazzoug et al. (2004) investigated the strength of immersed specimens

stabilized with cement (5% percent by weight). The soil is classified as moderately

plastic clay type A-6 according to the AASHTO system. The compressive strength of

specimen at dry state and after 48 hours immersion at an age of 28 days are given in

Fig.5.7.

Fig. 5.7 Compressive strength for dry and wet specimens at 28 days

After immersion in water for 48 hours, the strength of the specimens decreased

significantly compared to the dry specimens, because soaking reduces the bonding

strength of the particles. Experiments by Kersten (1961) show that the compressive

strength after 28 days immersion was in all cases lower than after 7 days immersion.

55

In practice the field strength may differ from the laboratory results due to the

environmental conditions. In order to predict the variations of strength due to

environmental changes, (Davis, Warr et al. 2007) evaluated the effect of wetting on

the strength of cement-stabilized sand (SP, according to the USCS system) by soaking

(1 day) the specimens up to 5 times and measuring the strengths after 28 days curing,

as presented in Fig. 5.8.

Fig. 5. 8 28-day strength variation with number of wetting

At low cement ratio (4%) the compressive strength varied a little. But at relatively

high cement ratios of 8%, 12% and 16% the strength increased gradually up to three

cycles of wetting and drying, and after that it stayed constant or decreased a little.

4 Dry density

The strength and durability of cement stabilized soil are strongly influenced by the dry

density. The cement stabilized soil samples must be compacted to the maximum dry

density in order to reduce the porosity and enhance the bond strength.

Croney (1977) determined the unconfined compressive strength of cylinders of a

cohesive soil sample compacted to different dry density. The results in Fig. 5.9 show

that a higher dry density yields a higher compressive strength.

Fig. 5.9 Compressive strength of samples at different dry density (Croney, 1977)

For design purposes, the minimum compressive strength should be specified. In UK,

the minimum strength of 2.76 MPa at 7 days is required for moist-cured cylindrical

specimens having a height/diameter ratio of 2:1 (Guthrie and Rogers, 2010).

5. With RoadCem

Based on the research (Altun, Sezer et al., 2009) and (Bnattacharja and Bhatry,

2003), similar compressive test results from PowerCem Technologies are added in Fig.

56

5.10 and Fig. 5.11. Again it has to be realized that the soil type, the methods of

manufacturing specimens and the testing conditions might be different.

Fig. 5.10 Variation in the 1, 7 and 28 curing days strength of samples

Fig. 5.11 Effect of curing age on compressive strength

The main observation in Fig. 5.10 and Fig. 5.11 is that due to the addition of

RoadCem the strength keeps on developing during a longer period of time, compared

to cement stabilization only. In this latter case, the gain in strength after 7 days is very

limited.

Fig. 5.12 illustrates the SEM images A–D of the experimental panel treated (stabilized)

with RoadCem and Cement, at 5 000 (images A and D), 2 500 (image C), and 1 500

(image B) times magnification. Fig. 5.12 (A) and (C) are the images of one month and

five months after construction and show the dense crystalline microstructure

(indicated by arrows). It is worth noting that an extended and more profound

crystalline microstructure formation is visible in image (C). The image in Fig. 5.12 (B)

is the image three months after construction and it does not show the microstructure

clearly (lowest magnification), hence, it was disregarded for the analysis.

Fig. 5.12 (D) is the image of eight months after construction and it shows a

dense-cemented matrix in the form of interlocked clusters (indicated by circles), and it

is an increase in linking between particles. That contributed to bond strength and

strength gain. The cementitious growths have fully developed between the particles

forming bonds; hence, there is no evidence of shrinkage cracking. This efficiency to

fill up the voids improves strength.

The typical needle-like crystals seen in the experimental panel are not visible when

the soil is stabilized with only cement. Therefore, it looks as if the RoadCem stabilizer

affects conventional cement stabilization. The SEM images show different

57

characteristics because of the different magnifications sizes.

Fig. 5.12 SEM images of RoadCem and Cement treated soil/material

(PowerCem Technologies, 2008)

5.2 TENSILE STRENGTH

Sub-bases and bases in pavements structures are subjected to tensile stresses and

strains under applied traffic loads. Therefore the tensile strength of the cement-bound

base material is required for most design methods.

The direct tensile test, the indirect tensile test and the flexural tensile test are three

tests that can be used to determine the tensile strength of cement stabilized materials.

The indirect tensile test is easy to perform, therefore it is to be preferred to the direct

tensile test, which is more difficult (TRH 14, 1985). According to NEN-EN 14227-1,

the tensile strength tf can be derived from the indirect tensile strength itf using the

relationship t it0.8f f= . In practice the indirect tensile test and the flexural tensile test

are the two primary types of test utilized to obtain the tensile strength.

5.2.1 Indirect tensile strength

The indirect tensile strength is defined as the stress at failure of a cylindrical specimen

subjected to a compression force applied on two opposite directions, shown in Fig.

5.13. It can be performed according to the standard NEN-EN 13286-42.

58

1 − specimen

2 − packing strips

F − load

Fig. 5.13 Indirect tensile test

Kolias, Kasselouri-Rigopoulou et al. (2005) have presented test results on the effects

of the cement content on the indirect tensile strength of cement stabilized clay (soil

type: A-6, according to the AASHTO system), see Fig. 5.14.

Fig. 5. 14 Effect of cement content on the indirect tensile strength at 28 days

The indirect tensile strength increases significantly with the cement content up to

about 10% and beyond that the rate of increase is slower.

Consoli, da Fonseca et al. (2011) have evaluated the effect of the cement content and

porosity on the indirect tensile strength. The soil is classified as well graded silty sand

(SM). The results of 7-day strength by use of cement (CEM Ⅲ) are presented in Fig.

5.15.

Fig. 5.15 Variation of the indirect tensile strength of cement

59

As shown in Fig. 5.15, the addition of cement promoted an increase in the indirect

tensile strength, and a reduction of the porosity also results in increased indirect

tensile strength. Reduction of the porosity results in much more contact between the

particles which enhances the bonding strength.

In this research (Consoli, da Fonseca et al., 2011), the relationship between the

voids/cement ratio and the 7-day indirect tensile strength is also given, as shown in

Fig. 5.16.

Fig. 5.16 Variations of the indirect tensile strength with cement content and porosity η

It is shown that the voids/cement ratio ( ivη / C ) is an appropriate index parameter to

evaluate the indirect tensile strength.

The relationship between indirect tensile strength and compressive strength has been

evaluated, as shown in Fig. 5.17. It can be seen that a high compressive strength

corresponds to a high indirect tensile strength.

Fig. 5.17 Relationship between compressive strength and indirect tensile strength

(Shacklock, 1974)

In research (Babi, 1987) two linear mathematical models were utilized to define the

correlation between the compressive strength and the indirect tensile strength.

i t cf af b= + (5-3)

it c'f a f= (5-4)

Where

itf is the indirect tensile strength

60

cf is the compressive strength

a , b and 'a are the coefficients

The gradation of the granular materials has practically no influence on the relationship

between itf andc

f . The compaction of the mix influences the relationship. With a

degree of compaction of 98%, 95% and 90% (Modified Proctor) the indirect tensile

strength was 11.5%, 13.0% and 15.0% of the compressive strength, respectively.

5.2.2 Flexural tensile strength

The flexural tensile strength is often referred as the modulus of rupture. The flexural

test simulates the field condition of the cemented layer in a pavement structure when

subjected to a wheel loading, and it is easy and quick to perform, so it is preferred to

be used. The flexural test assumes the applicability of the beam-bending theory and

that the material has the same elastic modulus in compression and tension (Otte,

1978)

The flexural tensile strength of cemented materials is about one-third of the

compressive strength for low-strength materials and about one-fifth of the

compressive strength for high-strength materials (TRH 14, 1985). Research (Ronald

et al. 1979) gives an almost linear relationship between the flexural tensile strength

and the compressive strength, indicated in Fig. 5.18.

Fig. 5.18 Flexural tensile strength plotted against compressive strength

In another research (Kersten, 1961) comparable data on unconfined compressive

strength and flexural strength of hardened cement-treated soils shows a nearly linear

relationship at all cement contents and at all ages. The flexural strength was

approximately 20 percent of the compressive strength.

The strain at break is defined as the strain beyond which the material fails in response

to the applied load. It is a determining factor for calculating the structural thickness

for static loading or roads with high axle loads. The higher the strain at break, the

61

thinner the required pavement structure.

The strain at break can be obtained based on the flexural strength and the deflection.

Traditional cement-bound materials like concrete and cement stabilized sand have a

strain at break of 150 to 200 µm/m and about 125 µm/m, respectively. Through the

addition of Roadcem the strain at break increases very substantially. So it is possible

to create more flexible cement-bound materials by the addition of RoadCem

(PowerCem Technologies, 2008).

5.3 ELASTIC MODULUS

5.3.1 Static modulus

A typical stress-strain curve for an unconfined compression test on a cemented

material is shown in Fig. 5.19.

Fig. 5.19 Typical stress-strain curve for cement stabilized materials

The slope of the initial straight line represents the elastic modulus of the cemented

material. When concrete and other cemented materials are subjected to tensile stress

the stress-strain relationship becomes non-linear when the applied stress exceeds

40-70 percent of the failure stress (Maclean, D.J., Robinson et al. 1952).

The stress-strain relationship can be affected by many factors. Fig. 5.20 gives the

curves for basaltic crushed rock stabilized with different cementitious binders with

3% additive content.

Fig. 5.20 Typical unconfined compressive stress-strain relationships for 7-days cured

specimens with different binders (Chakrabarti and Kodikara, 2003)

Fig. 5.21 presents the effect of addition of cement on the elastic modulus of samples

62

at the age of 28 days (Bahar, Benazzoug et al. 2004). The soil is classified as

moderately plastic clay type A-6 according to the AASHTO system. In can be seen

that the cement stabilization increases the slope of the curve.

Fig. 5.21 Stress-strain curve for samples under compression

Kersten (1961) investigated the variation of the static modulus of elasticity of cement

treated sand-clay mixtures with the clay content ranging from 0 to 100 percent. The

results show that the static modulus decreased with increasing clay content, which is

shown in Fig. 5.22.

Fig. 5.22 Influence of clay content on the modulus of elasticity (Kersten, 1961)

In order to estimate the elastic modulus of cement stabilized materials, it is usually

related to the strength. TRH 14 (1985) reports the following relations:

Cement-treated crushed stone tE 8 3500f= + (5-5)

Cement-treated natural gravel tE 10 1000f= + (5-6)

Cement-treated crushed stone 0.88

cE 4.16( ) 3484f= + (5-7)

Cement-treated natural gravel 0.88

cE 5.13( ) 1098f= + (5-8)

Where:

E − static modulus of elasticity (kPa)

cf − unconfined compressive strength (kPa)

tf − flexural tensile strength (kPa)

63

Molenaar (2005) reported that the flexural strength and flexural stiffness for cement

treated fine grained, cohesive soils can be estimated using the following equations.

t c0.0042 0.1427f f= − + (5-9)

0.885

f cE 1435 f= (5-10)

Where:

cf − compressive strength (MPa)

tf − flexural tensile strength (MPa)

fE − stiffness modulus in flexure (MPa)

According to the standard NEN-EN 14227-1, cement bound granular mixtures shall

be classified by the tensile strength and the elastic modulus, shown in Fig. 5.23.

Fig. 5.23 Characterization of cement-bound granular mixtures by the

tensile strength (MPa) and modulus of elasticity (MPa)at 28 days

The tensile strength ( tf ) shall be derived from the indirect tensile strength using the

relationship t it0.8f f= . The elastic modulus shall be measured in indirect tension.

5.3.2 Dynamic modulus

The dynamic modulus of elasticity is a material property that indicates how the load is

distributed when the material is dynamically loaded. A model (5-11) was given to

indicate the relationship between the pulse velocity and the dynamic modulus (Babic,

1987).

d

bE aV= (5-11)

Where:

V is the pulse velocity (km/s)

a and b are coefficients.

64

An example of relation (5-11) is given in Fig. 5.24.

Fig. 5.24 Dynamic modulus and pulse velocity

For estimation of the dynamic modulus, Fig. 5.25 gives examples of an experimental

relationship between the dynamic modulus and compressive strength (Babic, 1987).

Fig. 5.25 28-day compressive strength–dynamic modulus of elasticity correlations

As indicated in Fig. 5.25, the relationship between the compressive strength and the

dynamic modulus of elasticity is mostly non-linear. The results can be described by a

mathematical model of the following form:

d cln( )E a bf c= + (5-12)

The relationship between the compressive strength and the dynamic modulus is based

on experimental results with variable cement content, soil gradation and dry density.

No single correlation for all stabilized mixes could be established.

A relationship between the dynamic modulus and the flexural tensile strength is given

in research (Croney, 1977), which is shown in Fig. 5.26.

Fig. 5.26 Relationship between dynamic modulus and flexural tensile strength at 28

days for cemented granular materials

At a given flexural tensile strength, the dynamic modulus decreases with increasing

fines content in the soil. Clays, sands and gravels show different elastic deformation

behavior under repetitive loading, so when stabilizing with cement the mixtures will

65

behave quite differently.

Kersten (1961) presents that the static modulus of elasticity in compression is on

averages slightly more than 60 percent of the static modulus in flexure. In the study

there is presented a linear relationship between the dynamic modulus and the flexural

tensile strength, except for the lower strengths of the silty and clayey soils (Fig. 5.27).

The relationship trend also fits for that with compressive strength. This relationship

can be compared with that in Fig. 5.27, which is not linear.

00.511.522.533.50 5 10 15 20 25 30Dynamic modulus of elasticity (103 MPa)Flexural strength

(MPa) Sand-gravelSandy loamClayey Sa.GravelSilt loam

Fig. 5.27 Dynamic modulus and modulus of rupture (flexural tensile strength)

Croney (1977) presents a relationship between the dynamic and static Young’s

modulus for cemented granular materials. The equation is:

d sE =1000+0.88E (5-13)

Where dE and sE are the dynamic and static modulus (MPa), respectively.

In PowerCem Technologies, the dynamic modulus is determined by ultra-waves

(nondestructive, Fig. 5.28).

Fig. 5.28 Measurement of dynamic modulus of elasticity

Fig. 5.29 shows the damped harmonic vibration with RoadCem and without

RoadCem. It can be seen that with the use of RoadCem a higher damping is achieved,

which means better harmonic absorption of vibration when there are earthquakes.

This means that through the addition of RoadCem the cement-stabilized layer has a

better chance to survive earthquakes without structural damage.

66

Fig. 5.29 Comparison of damped harmonic vibration with RoadCem

and without RoadCem

5.4 FATIGUE PROPERTIY

Fatigue testing is conducted to determine the lifespan of a material subjected to

repeated dynamic loads. Fig. 5.30 shows the variation of the modulus of rupture MOR

(also known as flexural tensile strength) with the number of cycles of failure for silty

clay stabilized with cement.

Fig. 5.30 Dynamic flexure tests for 28-day curing time

It can be seen that the flexural tensile strength decreases by about 44%, when around

100,000 load cycles are applied. So it was demonstrated that as much as 44%

reduction in strength can occur when soil-cement beams are subjected to dynamic

flexure (Bhogal, Coupe et al. 1995).

Fatigue damage usually occurs when the applied stress amounts about 35 percent or

more of the strength. The failure starts with micro-cracking and a loss of bond at the

interface between the aggregate and the matrix of fine material. It can be concluded

that the material is able to withstand an unlimited number of load repetitions when the

stress ratio remains below 0.35, for the applied stress is then too low to start the

micro-cracking. (Otte, 1978)

The stress ratios are plotted against the number of cycles to failure to obtain the

so-called S-N curves. Typical S-N relationships for cement stabilized recycled

aggregate (SRA) compared with other materials (Sobhan and Das, 2007) are shown

67

in Fig. 5.31.

Fig. 5.31 Stress ratios versus number of cycles to failure

As indicated in Fig. 5.30, the performance of SRA is quite similar to these traditional

materials.

Generally, the fatigue failure criterion of cement stabilized soil is expressed by the

SN-N equation:

log NSN a b= − (5-14)

Where

t

σ

σSN = − Ratio of applied tensile stress and ultimate tensile stress

tσ − ultimate tensile stress

σ− applied tensile stress

In Netherlands, based on laboratory testing, a strain related fatigue curve was

determined for a particular sand cement:

log N 10 0.08ε= − (5-15)

Where

ε − Flexural tensile strain at the bottom of the sand cement layer (µm/m)

Compared with the laboratory determined fatigue relation, the field fatigue relation

can be written as

log N 8.5 0.034ε= − (5-16)

Where:

N − allowable number of 100 kN equivalent single axles,

ε − flexural tensile strain at the bottom of the cement treated base (µm/m)

Furthermore it appeared that the chance on fatigue failure is very small if the flexural

tensile strain level is 60 µm/m or less.

68

In South Africa, the following relationship for cement treated granular materials is

used,

tlog N 9(1- ε / ε )= (5-17)

ε − applied strain level (µm/m)

tε − flexural strain at break (µm/m)

For fresh crushed rock materials the strain at break varies between 100 and 250 µm/m.

The mean value was reported to be 160 µm/m (Molenaar, 2005).

In research (Otte, 1978) it is suggested to use strain as the criterion for controlling

fracture. Otte proposed 2 relationships between the strain ratio and the number of load

repetitions expressed as equations (5-18) and (5-19), shown in Fig. 5.32, namely:

fε / 1- 0.11log Nb

ε = (5-18)

0.079

b fε / ε N−

= (5-19)

Fig. 5.32 General fatigue curves for cement-treated bases

Croney (1977) performed fatigue tests at various frequencies of loading on two

concrete grades. The two concrete grades used were 25 MPa and 32 MPa unconfined

compressive strength at 28 days of curing. The results are shown in Fig. 5.33. CPM

indicates cycles per minute.

Fig. 5.33 Effect of loading frequency on stress/life relationship for concrete

The mean relationship shown in Fig. 5.33 can be used for the structural evaluation of

69

concrete pavements.

Although there seems to exist a large variation in fatigue relations, the relation

between applied stress or strain and allowable number of load repetitions always

exhibits very high values for the slope, indicating a rather brittle behavior. Compared

to the traditional materials, it has been proven that the addition of a specific

PowerCem product (RoadCem) can improve the fatigue property, which is shown in

Fig. 5.34.

(a) (b)

Ed—dynamic modulus

E0—initial dynamic modulus

Fig. 5.34 Fatigue behavior of cement bound materials

From Fig. 5.34, with RoadCem it is clear that at the end of the lifetime the material is

not suddenly breaking. This is due to the higher flexibility of the material with

RoadCem. In practice no cracks and no deformation are occuring when execution and

design is according to the instructions. And the fatigue curves with RoadCem are

between the asphalt and sand cement. (Birgisson, Egyed et.al. 2008)

5.5 DURABILITY

Durability can be defined as the ability of a material to retain stability and integrity

when exposed to the environmental conditions for many years. This is an important

property especially if the material is subjected to severe environmental conditions.

70

Durability of the base contributes greatly to the satisfactory performance of

pavements. Two tests are available to evaluate the durability of cement stabilized

samples, namely, by wetting and drying and by freezing and thawing (NEN-EN

12390-9). The freeze/thaw test procedure consists of freezing the cured specimens at

-25ºC in a freezer for 24 hours, and then thawing for another 24 hours at a

temperature of +22ºC and a relative humidity of approximately 98%.

Both test results are expressed by the loss in weight of a specimen after 12 cycles of

freeze/thaw cycles or wet/dry cycles. The suggested allowable material loss values are

given in Table 5.1.

Table 5.1 Durability requirements for cemented soils (Molenaar, 1998)

Soil Allowable loss in weight

A-1, A-2-4, A-2-5, A-3 < 14%

A-2-6, A-2-7, A-5 < 10%

A-6, A-7 < 7%

The durability of stabilized soil on repeated wetting and drying primarily depends on

the pore structure and the tensile strength of the material. Research (Bnattacharja

and Bhatry, 2003) gives an example of wet/dry test results for cement and lime

stabilized soil.

Fig. 5.35 Weight loss in wet-dry durability testing of soil stabilized with

6 and 9% cement and lime

It clearly indicates that cement stabilized soil exhibits superior performance to that

stabilized with hydrated lime.

Shihata and Baghdadi (2001) investigated the effect of the time of exposure to water

on the durability of the specimen (cement content 7%). The soil is A-2-4 according to

the AASHTO classification. Samples were tested after 12 cycles and then exposed to

saline water during different periods of time, which is indicated in Fig. 5.36.

71

Fig. 5.36 Change in weight loss with exposure period in the samples tested for

(a) Freeze-Thaw and (b) Wet-Dry tests

The results show that both trends of mass loss generally increase sharply up to 90

days of exposure after which the rate of increase drops to almost zero. The soil with a

larger amount of fines exhibited a larger mass loss in the wet-dry test, which is

opposite in the freeze-thaw test.

5.6 WATER PERMEABILITY AND ABSORPTION

Permeability is an important property when materials are exposed to water. For

practical use, impermeable material may be required to protect the underlying

material to prevent the water intrusion and avoid the strength loss.

Most soils can be made practically impermeable by addition of cement. The reduction

in permeability can be attributed to the hydration products filling the voids between

the particles. Bahar, Benazzoug et al. (2004) examined the variation of permeability

of a clay soil (A-6, according to the AASHTO system) by addition of cement and the

result is shown in Fig. 5.37.

Fig. 5.37 Effect of cement content on the water permeability

As shown above, the permeability of soil is closely related to the cement content. The

72

addition of cement can reduce the permeability. The stabilization of soil with cement

can lead to a larger mechanical strength and lower permeability and hence better

durability.

Research (Moloisane, 2009) evaluated the permeability of seven different commercial

stabilizer products from the five generic group types, two stabilizers from the

electro-chemicals generic group type (Perma-Zyme 11X and Con-Aid), and others

were from the organic non-petroleum (Dustex), organic petroleum (Bitumen

Emulsion), polymer (Ecobond/urea-formaldehyde (UF) resin), cement catalyst

(RoadCem). The results show that cement stabilization with RoadCem obtained the

lowest permeability.

In-situ soils are sensitive to moisture changes, but by stabilizing them with a binder

the stability can be maintained. Chakrabarti and Kodikara (2003) tested the degree

of water absorption at basaltic crushed rock stabilized with various binder contents.

Fig. 5.38 presents the effect of addition of a binder on the water absorption.

GB − general blended cement;

GP − general purpose cement;

AAS − alkali activated slag.

Fig. 5.38 Water absorption versus binder quality for specimens cured for 28 days

The results clearly show that the water absorption decreases as the binder quantity

increases, particularly for binder quantities > 3%.

Another issue is the potential for capillary rise of water within stabilized materials.

Higher water content in pavement material can give rise to excessive water pressures

and associated distress conditions.

Fig. 5.39 Capillary rise with time for 28-days cured specimens

73

(Chakrabarti and Kodikara, 2003)

Fig. 5.39 presents the moisture capillary rise as a function of time for basaltic crushed

rock stabilized with various contents of general purpose (GP) cement. The results

show that the rate of capillary rise decreases with the increase in cement content.

5.7 CONCLUSIONS

Compressive strength is an important property used to characterize cement bound

materials. Factors influencing the compressive strength are cement content, soil type,

curing conditions, and compaction effort, which have been reported in many previous

research results.

The indirect tensile test and flexural test are commonly used to obtain the tensile

strength. The relationship between compressive strength and tensile strength is nearly

linear and mathematical models have been created to indicate the correlation, but due

to the different compositions and soil type, there is no unique relationship.

For the modulus of elasticity, many relationships have been established to indicate the

modulus from the compressive strength or flexural tensile strength. The fatigue failure

criterion of cement stabilized soil is usually expressed by an SN-N equation, which

has a large variation.

Addition of cement can help reduce the permeability and increase the durability of

in-situ soils. Freeze/thaw and wet/dry tests are used to indicate the durability, which is

mainly affected by the cement content.

Addition of RoadCem has been proven to increase compressive strength, bearing

capacity and especially higher breaking strain and fatigue relation and this also with

clay soils and soil with organic material.

74

75

CHAPTER 6

CRACKING BEHAVIOR

Failure of a pavement system is sometimes associated with cracking in the bound base

course (Little, 1987). Cracks may occur in the base course and reflect through the top

layer under loading, resulting in visible surface cracks (as shown in Fig. 6.1), which

are referred as reflection cracks. Reflection cracks may not be a problem. If the cracks

are narrow (< 1/8 in. or 3 mm), sufficient load transfer normally exists through

aggregate interlock to keep the pavement structure functioning. However, if wide

cracks (> ¼ in. or 6 mm) occur at the surface, they will result in poor load transfer and

pumping of the subgrade materials due to water intrusion (Halsted, 2007). The severe

cracking will cause unevenness and structural failure of the pavement and increased

maintenance and repair costs.

(a) Narrow reflection crack (b) Wide reflection crack

Fig. 6.1 Reflection cracks (Adaska and Luhr, 2004)

When a cemented material is loaded beyond a certain limit microcracking first

develops at the interface between coarse particles and the matrix. The extent of the

microcraking increases upon subsequent loadings, and eventually the microcracks join

up into a macro-crack. Laboratory flexural and compressive tests indicated that

76

microcraking occurs at stress levels of about 35 percent and more of the ultimate

strength and strain levels or about 25 percent of more of the strain at break (TRH 14,

1985).

6.1 SHRINKAGE

There are generally two types of crack: shrinkage cracks and traffic induced cracks.

Drying shrinkage is the main cause of the shrinkage cracks. The final crack widths are

mainly dependent on the ultimate shrinkage strain and crack spacing (Halsted, 2007).

The degree of shrinkage is affected by various factors, the type of soil, degree of

compaction, curing, cement content, temperature changes and friction with

surrounding pavement layers.

The other type of cracking is traffic induced cracking. Traffic induced cracking will

not occur in cement treated bases when the strain level remains below 60 / 1.46

(environmental factor) = 41 µm/m in cases where the load transfer across transverse

cracks is poor. When a good load transfer can be guaranteed, this strain level is 50

µm/m. These values are proposed to be used as endurance limits for the material

investigated (Molenaar, 2001). Cracking due to environmental changes should be

distinguished from subsequent cracking caused by traffic.

When the hydrating cement treated material shrinks, friction develops between the

treated layer and the underlying layer and by consequence internal tensile stresses are

induced. The internal stresses may exceed the tensile strength and cracking occurs. In

research (TRH 14, 1985) it is described that the spacing and widths of the cracks are

determined by the rate of the tensile strength development relative to the shrinkage

tensile stress development.

Fig. 6.2 Cracking as a result of the interrelationship between shrinkage stress, strength

and time (TRH 14, 1985)

If the shrinkage stresses exceed the tensile strength at a relatively low strength then

the cracks will be more numerous, narrower and more closely spaced (shown as

77

Material A in Fig. 6.2). Such cracks will vary in width from fine hair cracks to 1 mm,

and they are usually up to 2 m apart. If the material develops a greater tensile strength

before the shrinkage stress exceeds the tensile strength, there will be fewer cracks, and

they may be 2 to 3 mm wide and 4 to 6 m apart (shown as Material B and C in Fig.

6.2).

6.2 FACTORES INFLUNCING SHRINKAGE

The degree of shrinkage is dependent on soil type, cement content, moisture content.

1. Cement content

Stabilization of soil with cement can reduce the shrinkage because the cement matrix

tends to restrain the soil movement, but the addition of cement doesn’t completely

prevent the shrinkage due to the moisture loss during the hydration. Fig. 6.3 illustrates

the effect of the cement content on the shrinkage of some granular material (A-2-4

and A-3, according to the AASHTO system).

Fig. 6.3 Effect of cement content on shrinkage (George, 1968)

As seen above, shrinkage is initially reduced with the addition of a small amount of

cement, but increases steadily as the cement content increases.

The combined effect of cement content and sand percentage was evaluated in research

(Kenai, Bahar et al. 2006). Fig. 6.4 shows the effect of the addition of cement, sand

and a mixture of cement and sand on the final shrinkage of samples. It can be

concluded that the shrinkage of cement stabilized soil compared to that of

un-stabilized soil was reduced by about 20% and 44% for 6% and 10% of cement

content, respectively. The addition of sand also reduced the shrinkage about 29% and

64% for 10% and 15% of sand content, respectively.

78

Fig. 6.4 Effect of sand and cement content on the shrinkage at the age of 28 days

2. Curing time

Shrinkage cracks may increase with time. Bahar, Benazzoug et al. (2004)

investigated the effect of the curing age on the shrinkage, as shown in Fig. 6.5. The

soil, classified as moderately plastic clay type A-6 according to the AASHTO system,

is stabilized with different cement contents.

Fig. 6.5 Development of shrinkage during first 28 days

It can be clearly seen that shrinkage increases rapidly during the first 4 days, and then

the rate of increase rate is slow. Hence, curing for the first 4 days will be beneficial in

reducing drying shrinkage and cracks.

Rapid moisture loss may also cause much shrinkage and is detrimental to the final

strength, because when materials dry quickly the volume will change rapidly, which

inevitably results in more shrinkage. Also there will not remain enough moisture to

continue hydration of the cement which will reduce the final strength. So it is essential

to control the curing environment and avoid rapid moisture loss.

However, due to the unavoidable variations of the environmental conditions, cracking

in a cement stabilized layer due to temperature and/or moisture content variation can’t

be avoided and must be accepted.

3. Moisture content

The shrinkage of stabilized materials mainly results from moisture loss. And moisture

loss is mainly caused by the cement hydration and evaporation. Therefore the

moisture content is a significant factor for controlling the degree of shrinkage. Fig. 6.6

presents the final shrinkage of sand stabilized with cement at variable moisture

content.

79

Fig. 6.6 Variation of final shrinkage at 28 days with mixing water content

(Kenai, Bahar et al. 2006)

This figure shows that as the water content increases the shrinkage increases rapidly,

due to the loss of excess of water which is not needed for cement hydration. So it is

essential to control the water content of the mixture, which is referred as the Optimum

Moisture Content obtained by the Proctor test.

Molenaar (1998) reported that the specimens that were compacted at the dry side of

the optimum moisture content showed lest shrinkage. For practice this means that if

one wants to limit problems due to shrinkage, compaction at a water content

somewhat lower than the optimum moisture content is recommended.

4. Compaction

A tight matrix of a well-compacted soil reduces the shrinkage potential, because the

soil/aggregate particles are packed densely together, resulting in a reduced voids

content. Good compaction also leads to better aggregate interlock and structural

support if a crack does develop (Adaska and Luhr, 2004).

Bhandari (1973) reported that compacting cement-stabilized soil at modified Proctor

compaction reduced the shrinkage by more than 50% compared to stabilized soil

compacted to standard Proctor density. In addition, the optimum moisture content at

Modified Proctor compaction is typically less than that at standard Proctor

compaction, which also helps to reduce shrinkage.

Fig. 6.7 Effect of dry density and moisture content on shrinkage (George, 1973)

Fig. 6.7 shows that increased dry density and reduced moisture content result in less

shrinkage of a cement-stabilized A-2-4 granular material.

80

The least amount of shrinkage is obtained for the stabilized material at highest density

and lowest moisture content. Many project specifications accept minimum densities of

95% of standard Proctor compaction.

5. Soil type

Studies (George, 1968; Nakayama, 1965) show that cement-stabilized fine-grained

soils (e.g. clays) exhibit more shrinkage than cement-stabilized granular soils. The

reason is that fine-grained soils have larger particle surface areas than granular

materials and typically require a higher moisture content for compaction and need a

higher cement content to achieve an adequate durability and strength. Both factors

contribute to a high moisture content and consequently a higher drying shrinkage

(Adaska and Luhr, 2004).

Research (George, 2002) presents an example of the effect of cement stabilized soils

on the crack pattern, as shown in Table 6.1. Clay particles have a large surface area

relative to their weight, so they hold a large amount of water, and have a high

optimum moisture content, so the potential for shrinkage cracking is greater.

Table 6.1 Effect of fines content on soil-cement crack pattern

Type of soil

Crack width

when last crack

occurred, mm

Crack spacing, when

last crack occurred

and later, m

Crack width

@ 7days,

mm

Terminal crack

width, mm

#1 (A-3/SM) 1.5 @ 1.6 days 13.0 3.40 6.0 @ 20.0 days

#2 (A-2-6/SC) 2.9 @ 1.2 days 6.0 6.00 10.8 @ 22.0 days

It is clearly that the crack width is substantially affected by the fine content of the soil:

the finer the soil, the larger the crack width.

6. Other factors

The factors contributing to the shrinkage are complicated, dependent on the inherent

properties as well as the environmental conditions. Fig. 6.8 presents the shrinkage

plotted against UCS for many materials.

Fig. 6.8 7-day UCS vs. beam shrinkage.

It shows that there exists an optimum strength that will produce the minimum

81

shrinkage and the optimum strength varies depending on the soil type.

6.3 METHODS OF CONTROLLING

Shrinkage is a natural characteristic of all cement-bound materials that should be

accepted. However, proper construction techniques and mix design methods can

minimize the adverse effects. With respect to the construction process, following the

proper construction techniques and providing good quality control during the field

operation can minimize cracking (PCA , 2003).

A number of research studies (PCA, 2003; Cho, Lee et al. 2006; FM 5-410) present

various methods to minimize shrinkage cracking, which include altering the mix

design, proper construction process and techniques, the use of “pre-cracking”, and

adding additives. In research (FM 5-410) it is reported that the drying shrinkage of

cement-treated soil can be significantly reduced by replacing a part of the cement with

fly ash. Not only the maximum dry shrinkage is reduced, but also the rate of shrinkage

is affected by the addition of fly ash. Fig. 6.9 gives an example that the addition of fly

ash reduces the drying shrinkage (Cho, Lee et al. 2006).

Fig. 6.9 Addition of fly ash to reduce drying shrinkage

PCA (2003) reports that “pre-cracking” is used by applying loading into the

soil-cement layer to obtain a network of closely spaced narrow cracks which acts to

relieve the shrinkage stresses and provides a crack pattern to minimize the

development of wide cracks. Research (PCA, 2001) shows that the microcracking

process substantially reduces the amount of pavement surface cracking, but not

significantly affects the base stiffness.

In addition to this, the use of RoadCem from PowerCem Technolygies company in

cement stabilization may result in no cracks and no deformations. Even when soils are

involved with a high organic content the cement reaction will get a boost with the

addition of RoadCem. Fig. 6.10 shows a cement stabilization with RoadCem in high

organic soil conditions in a Delta area without cracks after 4 years.

82

Fig. 6. 10 Cement stabilization with RoadCem showing no cracks after 4 years

(Birgisson, Egyed et al., 2008)

Due to the PowerCem additives a complex chemical reaction with cement, fly-ash,

water and granular material is initiated which leads to another mineral structure of the

cement bound material and a new type of crystalline structure is formed, which is

shown in Fig. 6.11.

Fig. 6.11 Picture from an electron microscope of the crystalline structure

(Birgisson, Egyed et al. 2008)

This new crystalline structure formed with addition of RoadCem results in a strong

flexural bound material, which efficiently prevents the cracking.

6.4 CONCLUSIONS

Reflection cracks at the surface of pavements are mainly caused by the cracks

occurring in cement-bound bases due to drying shrinkage. Shrinkage is a natural

characteristic of cement bound materials, which should be accepted. Cement content,

compaction and soil type influence the amount of shrinkage. Many measures can be

used to minimize the cracking due to shrinkage, including altering the mix

composition and following proper construction methods. Use of specific additive is an

efficient method. Additive from PowerCem Technologies has been proven to prevent

cracks.

83

CHAPTER 7

EFFECTS OF A FLEXURAL STABILIZATION

7.1 INTRODUCTION

Based on the specific information of the current stabilization a construction design

was made with RoadCem and without RoadCem.

For this calculation example a traditional asphalt pavement structure is compared with

a RoadCem structure. Both structures are assumed to have a similar theoretical

lifetime in terms of allowable number of standard axle load repetitions. In this

example the differences in failure mechanisms and the spreading of the loads to the

substructure are given in the following paragraphs:

1. Assumptions

2. Designs

3. Calculations

4. Deflections

5. Conclusions

7.2 ASSUMPTIONS

The calculation is based on the following assumptions, divided in the following parts:

• Traffic

• Soil

Traffic

The standard axle load is: 100 kN

84

The axle configuration is 2 times dual tires

Soil

Assumptions of the soil:

• Type of soil: clay

• Dynamic modulus of elasticity: 25 MPa

7.3 DESIGNS

Fig. 7.1 gives the detailed calculation for the traditional and the RoadCem asphalt

pavement structures.

½ x SAL = 50 kN

Front view

Y- axle

Side view

½ x SAL = 50 kN

X- axle

25 kN 25 kN

85

Asphalt 40mm Asphalt wearing course

Stiffness:Edy n: 6000 Mpa 180 mm

RoadCem

Stiffness:

Edy n = 3500 MPa

Concrete granulateStiffness: 250 mm

Edy n = 600 MPa

300 mm

Total thickness structure: 290 mm

Sand sub-baseStiffness:

Edy n = 100 MPa

700 mm

Total thickness structure: 1180 mm

Subsoil: Clay

Stiffness:

Edy n: 25 MPa

Traditional structure RoadCem structure

Fig. 7.1 Comparison of traditional and RoadCem asphalt pavement structures

7.4 CALCULATION METHOD

Step 1:

Determine the stresses, strains and deflections in the critical points of the pavement

structures by the linear elastic multilayer program BISAR.

Step 2:

Check the fatigue relationships of the normative asphalt pavement structures:

86

1. Traditional structure

Normative failure mechanisms of the traditional structure are given below.

Fatigue relation of the asphalt:

Neq8= EXP

(0.33796*LN(Edyn asphalt)^2-7.3642*LN(Edyn) +77.142-5.2438*LN(Strain) (7-1)

OR

Fatigue relation of the top of the unbound base course, which leads to pavement

deformations in the base (which reflects as rutting at the pavement surface):

Neq9 = 10^(-6.211-0.482*0.674-4*LOG(Deflection*0.000001)) (7-2)

The lowest value for Neq will be normative for the lifetime of the traditional structure.

2. RoadCem structure

Fatigue relation of the RoadCem layer:

Neq10

= 7*108*e

(-0.027*strain)*0.2 (7-3)

Due to the plastic behavior and the relatively low elastic modulus of the asphalt,

deformation could occur in the sub soil and could reflect at the pavement surface as

rutting. However, the plastic behavior of the Soil-RoadCem-cement material is low

and the dynamic modulus is relatively high. Due to this behavior the deformation in

the sub soil will NOT lead to deformations at the pavement surface. Just the fatigue

relation of the RoadCem layer will be normative for the lifetime of the RoadCem

structure.

The calculation of the two pavement structures is divided into 2 steps:

• Step 1: Calculation of the stresses and strains in the normative layers.

• Step 2: Calculation of the lifetime of the structures in terms of allowable

number of 100 kN in standard axle loads (Neq)

Step 1: Calculation of the occurring stresses and strains in the construction.

The strains and stresses occurring due to a passing vehicle are given in the table

below:

8 F78 asphalt fatigue relation

9 Fatigue relation for deformations in the top of unbounded materials, source CROW, publicatie

157 10

RoadCem fatigue relation, source Project: RC.20100718.CZ.0403 – Brusnice (internal PCT)

87

Table 7.1 Stresses and strains at the bottom of the bound layers

Construction Place Maximum

strain

Maximum

stress

U-deflection

Traditional

structure

Bottom Asphalt

layer

93 µm/m 0.65

N/mm2

518 µm

RoadCem

structure

Bottom RoadCem

layer

145 µm/m 0.63

N/mm2

NA

In the following figures are the strains and stresses (X-axle) and width (Y-axle) of the

road. With herein: Y = 0 is the center of the dual tires. These values are determined by

the calculation in the BISAR program.

Fig. 7.2 Horizontal strains in transverse direction at the bottom of the bound layer

over the width of the road due to a 50 kN dual tire load

Fig. 7.3 Horizontal strains in the longitudinal direction at the bottom of bound layers

over the length (X) of the road due to a 50 kN dual tire load

In Fig. 7.2 and 7.3 a clear difference is visible between the traditional and the

RoadCem pavement structure. The wheel loads in the RoadCem structure will be

more equal spread over the sub-layers. The reason that the strains are higher in

RoadCem structure because the material has a lower dynamic elastic modulus than the

asphalt of the traditional structure.

88

Fig. 7.4 Horizontal stresses in the transverse direction at the bottom of the

bound layers over the width of the road due to a 50 kN dual tire load

Fig. 7.5 Horizontal stresses in the longitudinal direction at the bottom of the

bound layers over the length of the road due to a 50 kN dual tire load

The differences in stresses at the bottom of the bound layers are shown in Fig. 7.4 and

Fig. 7.5. The stresses in the RoadCem structure are spread over a bigger area than the

traditional structure, what leads to a lower peak stress.

89

Step 2: Calculation of the lifetime of the structure:

The results of the lifetime of the structure are given in Table 7.2.

Table 7.2 Lifetime of traditional and RoadCem asphalt pavement structure

Traditional structure RoadCem structure

Normative failure mechanism of the

traditional structure:

Fatigue relation of the asphalt:

Neq = 2.92 x 106

OR

Fatigue relation of the top of the

unbounded base course, which leads to

rutting’s in the asphalt:

Neq = 4.04 x 106

The lowest value for Neq is normative

for the lifetime of the structure.

Normative failure mechanism of the

RoadCem structure:

Fatique relation of the RoadCem layer:

Neq = 2.79 x 106

Both structures have indeed about the same theoretical lifetime. It should be realized

that traffic wander and healing have not been taken into account in the calculation of

the pavement lifetimes.

7.5 DEFLECTIONS

In the following figures (Fig. 7.6 and Fig. 7.7) the deflections at the top of the

unbounded layer (concrete granulate base is the traditional structure and subsoil in the

RoadCem structure) are shown in a 3D graphic over the length and the width of the

road:

90

Fig. 7.6 Deflections at the top of the concrete granulate base in the traditional

structure over the length and the width of the road

Fig. 7.7 Deflections at the top of the subsoil in the RoadCem structure over the

length and the width of the road

The impact area of a passing vehicle on the top of the unbounded layer is in the

RoadCem structure much higher than in the traditional structure. This is because the

bending stiffness of the total bound layers is much higher in the RoadCem structure.

7.6 CONCLUSIONS

Despite the higher occurring stresses in the RoadCem layer, this structure has a

comparable lifespan in terms of allowable number of 100 kN standard axle repetitions

with the traditional asphalt pavement structure.

The main benefit of the use of RoadCem is the limited thickness of the structure

which saves materials, and labor in the execution. Besides the amount of materials

which have to be discharged and supplied is limited what makes this type of structure

a environmentally friendly technology.

91

The influence of the structure on the subsoil settlements are not included in this

example, but the limited weight of the pavement structures will definitely lead to less

settlements in the RoadCem structure in comparison with a traditional structure.

92

93

•

Chapter 8

CONCULSIONS AND RECOMMENDATIONS

8.1 CONCLUSIONS

This literature review is undertaken to summarize the properties of cement bound

materials. Based on the literature study, the following conclusions can be given:

1) There is more than one stabilizing agent for every type of soil. The choice is

dependent on the nature of the soil and the desired function of the stabilized

layers as well as the overall cost. In general, lime is more effective to stabilize

cohesive soils like silt and clay, while cement is more suitable to stabilize

granular materials like sand and gravel.

2) Prior to soil stabilization, soil tests (Liquid Limit, Plastic Limit, sieve analysis,

chemical composition, Proctor test) should be done to obtain the soil

properties. Based on the soil information, the appropriate mix composition can

be determined. The cement content is a significant factor influencing the

strength and the durability.

3) The mechanical properties of cement bound materials are influenced by

cement content, soil type, compaction, curing conditions and other

environmental factors. It is found that cement content and in-situ material type

are the main factors to control the strength of cement bound materials.

4) Shrinkage cracks in cement bound materials due to drying and moisture

changes can’t be avoided. Many appropriate methods can be used to reduce

these cracks and the risk for reflective cracking, like optimum mix

composition and proper construction technology.

5) For fatigue property, based on stress or strain controlled flexural tests, most of

the relationships are described by SN-N curves, which exhibit a large

variation.

6) RoadCem has been proven to be a very effective additive for soil stabilization.

94

• Improvement in compressive strength, flexural tensile strength, strain at

break and fatigue life.

• High resistance against earthquakes and vibrations.

• High resistance against erosion and natural disasters.

7) To evaluate the properties and the effect of using RoadCem as additive, a

comparison needs to be made for different soil types and mixture.

8.2 RECOMMENDATIONS

Soils stabilized with traditional materials like cement, bitumen and lime, often exhibit

insufficient performance (shrinkage cracks, brittle behavior, etc), which limits the

applications. However, non-traditional stabilizers have been introduced to improve the

properties of soil stabilization.

The product RoadCem, which is based on Nano technology, from PowerCem

Technologies has been widely used in many countries for cement stabilization, and the

laboratory tests and field results show excellent performance (no cracks, high strength,

high strain at break, etc). In this review, the comparison of the properties with other

traditional additives has been presented. For the future application, more research in

laboratory and field validation should be undertaken to systematically evaluate the

improvement of Roadcem in the soil stabilization. Based on this, the research will

focus on the effect of RoadCem on the mechanical properties of cement-bound

materials.

95

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FM 5-410. Soil Stabilization for Roads and Airfields.

99

PCA (2001). "Suggested Specifications for Soil-Cement Base Course Construction ".

Portland Cement Association, Skokie, USA

PowerCem Technologies (2008). RoadCem Laboratory guide.

“Soil Stabilization with Portland Cement”, Highway Research Board 292, Washington,

D.C., 1961.

Galloway, J.W. and H.M.Harding (1976). Elastic modulus of a lean and a pavement

quality concrete under uniaxial tension and compression. RILEM. Materials and

Strucutre,13-18.

Vertical Drainage (Dutch) Publication CROW (1993) 77, Ede, the Netherlands.

C.R.O.W. 1994. Publication 81. Gefundeerd op weg.

100

101

Appendix A

Fig. 1 Indication of marl soil in classification

102

Appendix B

CONVERSION TABLES (C.R.O.W. 1994)

Chart B.2.1 Conversion table length.

Chart B.2.2 Conversion table surfaces.0

103

Chart B.2.3 Conversion table volume.

Chart B.2.4 Conversion table mass.

104

Chart B.2.5 Conversion table density.

Chart B.2.6 Conversion table power and weight.

105

Chart B.2.7 Conversion table power and elasticity.

Chart B.2.8 Conversion table permeability

Chart B.2.9 Units

106

107

Appendix C

TRANSLATION OF TECHNICAL TERMS (C.R.O.W. 1994)

EnglishEnglishEnglishEnglish FrancaisFrancaisFrancaisFrancais DeutschDeutschDeutschDeutsch

AAAA aggregate granulat Zuschlagstoff, Gesteinsmaterial

aggressiveness agressivité Aggressivität

aligator cracking faïençage Netzrisse, Elefantenhaut

analysis analyse Untersuchung

analytical model modèle analytique analytisches (Rechen)Modell

articulated lorry camion articulé LKW - Zug

asphalt asphalte Asphalt

asphalt (2nd sense, US)

asphalt binder (US)

asphalt cement (US)

bitume Bitumen

asphalt concrete béton bitumineux Asphaltbeton

asphalt mixture enrobé asphaltique,

materiau bitumineux

Asphaltmischgut

asphalt pavement revêtement bitumineux Asphaltdecke, bituminöser

Oberbau

assessment of pavement

condition

évaluation de l'état du

revêtement (d’une chaussée)

Oberbau-Zustandserfassung

axle essieu Achse

axle load charge par essieu Achslast

axle spacing distance entre essieux Achsabstand

BBBB base course (US) couche de base obere Tragschicht

bearing capacity portance Tragfähigkeit

bedrock bedrock Felsuntergrund

bend courbe, virage Kurve

berm(e) berme Berme

binder liant Bindemittel

bindercontent teneur en liant Bindemittelgehalt

binder course couche de liaison Binderschicht

bitumen bitume Bitumen

bituminous binder liant bitumineux Bitumen, bituminöses

Bindemittel

bituminous layer couche bitumineuse bituminöse Schicht

bottleneck goulot d'étranglement Engstelle, Engpass

108

CCCC calibration factor

capping layer

coefficient de calage

couche de forme

Anpassungsfaktor

verbesserter Unterbau

carriageway chaussée Fahrbahn

canalisation (of traffic) canalisation (des véhicules) Kanalisierung (des Verkehrs)

cement ciment Zement

cement-bound material matériau traité au liant

hydraulique

hydraulisch gebundenes

Material

central reserve terre-plein central Mittelstreifen

clay argile Ton

cohesion cohésion Kohäsion

coarse aggregate granulat grossier Grobkorn

commercial vehicle véhicule commerciale Nutzfahrzeug

compaction compactage Verdichtung

concrete béton Beton

concrete pavement chaussée en béton Betondecke

construction traffic trafic de chantier Baustellenverkehr

core carotte Bohrkern

course couche Schicht

crack

longitudinal crack

reflection crack

transverse crack

fissure

fissure longitudinale

remontée de fissure

fissure transversale

Riß

Längsriß

Reflektionsriß

Querriß

cracking fissuration Rißbildung

structural cracking fissuration structurelle tragfähigkeitsbedingte

surface cracking fissuration superficielle oberflächliche

crazing faïençage feine Netzrisse

cross roads carrefour Kreuzung

cross section, cross profile profil en travers Querschnitt, Querprofil

crossfall pente transversale/dévers Querneigung

crown of a carriageway plateforme Straßenkrone

curb bordure (de trottoir) Bordstein

cycle path (track) piste cyclable Radweg

DDDD debonding décollement d’interface Verlust der Schichthaftung

deflection déflexion Einsenkung

deformation

elastic

plastic

viscous

déformation

elastique

plastique

visqueux

Verformung

elastische

plastische

viskose

delamination délamination Abplatzen, Ablösen einer

109

Schicht

density masse volumique Dichte

design conception,

dimensionnement

Entwurf, Bemessung

design criterie critère de dimensionnement Bemessungskriterien

design life durée de vie Bemessungslebensdauer,

Nutzungsdauer

design mix mélange théorique,

formule d’ enrobage

Eignungsprüfungsrezeptur

design period période de dimensionnement Bemessungsperiode

design traffic trafic escompté, trafic de

dimensionnement

Bemessungsverkehr

deterioration dégradation Schädigung,

Schadensentwicklung

distress

pavement distress

dégradation

dégradation de chaussée

Schaden

Oberbauschaden

ditch fossé Graben

ditch at top of slope cunette de crête de talus oberer Abfanggraben

ditch at foot of slope fossé de pied de talus unterer Abfanggraben

drainage drainage, évacuation des

eaux

Entwässerung

dual carriageway route à double voie zweistreifige Straße

durability durabilité Dauerhaftigkeit

dynamic load charge dynamique dynamische Belastung

EEEE elastic stiffness rigidité élastique elastische Steifigkeit

embankment remblai Damm

empirical model modèle empirique empirisches Verfahren

equivalent standard axle

load

essieu standard équivalent äquivalente Standardachslast

eveness uni Ebenheit

FFFF fatigue fatigue Ermüdung

filler filler (fines) Füller

flexible pavement chaussée souple flexibler Oberbau

(ungebundene und

Asphaltschichten)

footway trottoir, chemin piétonnier Fussweg, Gehweg

forecasting

short term

long term

prévision

à court term

à long term

Vorhersage

Kurzzeit-

Langzeit-

formation (level) plate-forme Unterbauplanum

110

foundation fondation Gründung

freight transport transport de marchandises Güterverkehr

friction course couche de roulement,

couche d’usure

Rauhbelag, Deckschicht

frost-susceptibility gélivité Frostempfindlichkeit

full depth asphalt

construction

structure bitumineuse

épaisse

Vollasphaltoberbau

GGGG global index

granular layer

indice global

couche granulaire

globaler (Zustands)wert

ungebundene Schicht

granular material granulat Gesteinsmaterial

gross vehicle mass masse totale du véhicule Fahrzeuggesamtmasse

gross vehicle weight poids total du véhicule Fahrzeuggesamtgewicht

gussasphalt asphalt coulé Gußasphalt

HHHH hard shoulder for emergency

stop

bande d'arrêt d'urgence Standstreifen, befestigter

Seitenstreifen

heavy vehicle poids lourd Schwerfahrzeug,

Lastkraftwagen

highway route Straße, Fernstraße

IIII improvement of soil sol traité, sol amélioré Bodenverbesserung

improved subgrade fondation traitée,

fondation améliorée

verbesserter Untergrund

interface

rough interface

smoth interface

interface

interface collée

interface glissante

Grenzfläche

rauhe Grenzfläche

glatte Grenzfläche

intersection carrefour routier, intersection Kreuzung

JJJJ junction carrefour Knotenpunkt

joint joint Fuge

KKKK kerb bordure Bordstein

LLLL layer couche Lage

levelling course couche de reprofilage Ausgleichsschicht

long-term performance comportement à long terme Langzeit-Gebrauchsverhalten

lorry (UK), truck (US) camion, poids lourd Lastkraftwagen, LKW

lorry with trailer camion avec remorque LKW mit Anhänger

lorry with semi-trailer camion avec semi-remorque LKW mit Sattelanhänger,

Sattelzug

load charge Last, Beladung

longitudinal profile profil longitudinal,

profil en long

Längsprofil

MMMM macrotexture macrotexture Makrotextur, Grobrauheit

maintenance entretien Erhaltung

111

mastic asphalt mastic, mastic d’ asphalte Asphaltmastix

mechanistic model modèle mechanique mechanistisches

(Rechen)Modell

median (US) terre-plein central Mittelstreifen

microtexture microtexture Mikrotextur, Feinrauheit

mix mélange Gemisch

mix design formulation Eignungsprüfung,

Rezeptentwurf

mix-in-place

mix-in-plant

mélange en place

mélange en centrale

Baumischverfahren

Zentralmischverfahren

modulus module Modul

modulus of elasticity

resilient modulus

module d’elasticité

module reversible

Elastizitätsmodul

Verformungsmodul

(Untergrundmodul)

moisture humidité Feuchtigkeit

moisture content teneur en eau Wassergehalt

motorway autoroute Autobahn

OOOO overlay recouvrement,

couche de renforcement

Hocheinbau,

Verstärkungs-schicht

PPPP particle size distribution granularité, distribution

granules, distribution

granulometrique

Korngrößenverteilung

passenger car véhicule léger, V.L. Personenkraftwagen, PKW

pave recouvrir, revêtir befestigen

pavement chaussée Fahrbahn

pavement

flexible pavement

flexible composite

pavement

rigid pavement

pavement deterioration

revétement

chaussée souple

chaussée semi-rigide,

chaussée mixte

chaussée rigide

revêtement rigide

dégradation de chaussée,

du revêtement

Oberbau

flexibler (bituminöser)

Oberbau

bit. Oberbau mit

zementstab. Tragschicht

starrer Oberbau

Verschlechterung des

Oberbau-zustandes,

Oberbauschädigung

pavement design dimensionnement de

chaussée

(Straßen-) Oberbaubemessung

pavement failure rupture de chaussée,

dégât de chaussée

Oberbauschaden

pedestrian piéton Fussgänger

112

performance comportement, tenue Gebrauchsverhalten

performance factor facteur de comportement Verhaltenskenngröße

(Schadensart)

performance model modèle de comportement Verhaltensmodell

plant-mixed mélange en centrale Zentralmischverfahren

porous asphalt enrobé drainant, enrobé

poreux

Drainasphalt, offenporiger

Asphalt

pot hole nid de poule Schlagloch

precracking pré-fissuration gezielte Rißbildung

QQQQ quality qualité Qualität

quarry carrière Steinbruch

RRRR raveling arrachement Kornverlust, Kornausbruch

reconstruction reconstruction Erneuerung

regulating course couche de reprofilage Ausgleichsschicht

rehabilitation rehabilitation Instandsetzung

response model modèle de comportement Beanspruchungsmodell

resurfacing rechargement,

renouvellement du surface,

resurfaçage

Deckschichterneuerung

rigid layer couche rigide starre Schicht

rigid pavement chaussée rigide starrer Oberbau (Beton),

Betonstraße

road

trunk road

toll road

road base (UK)

road construction

route

route à grand circulation

route à péage

couche de base

construction routière

Straße

Hauptverkehrsstraße

Mautstraße

obere Tragschicht

Straßenbau

road surface surface de chaussée Straßenoberfläche, Fahrbahn

roller rouleau, cylindre Walze

rut orniére Spurrinne

rutting orniérage Spurrinnenbildung

roughness rugosité Rauhheit, rauhe Stelle

roughness uni Ebenheit

SSSS safety fence (guardrail) glissière de sécurité Schutzplanke

(A: Leitschiene, CH:Leitschranke)

screed régle (de finisseur) Bohle, Einbaubohle (Fertiger)

semi-rigid pavement chaussée semi-rigide halbstarrer Oberbau

(zement-stabilisierte und

Asphaltschichten)

serviceability viabilité Befahrbarkeit

113

shoulder accotement Bankett

shoulder bas-côté Randstreifen

single axle essieu simple Einzelachse

skid resistance adhérence Griffigkeit

slab dalle Platte

slope talus, pente Böschung

soil

non-cohesive soil

stabilized soil

soil cement

sol

sol non cohésif

sol stabilisé

sol ciment,

sol stabilisé au ciment

Boden

nichtbindiger Boden

verfestigter Boden

mit Bindemittel (Zement)

verfestigter Boden

soil mechanics mécanique des sols Bodenmechanik

specification specification Vorschrift, technische

Beschreibung

standard axle essieu standard Standardachse

stiffness rigidité Steifigkeit

stiffness modulus module de rigidité Steifigkeitsmodul

strain allongement, déformation

relative

Dehnung

strength résistance Festigkeit

strengthening,

reinforcement

renforcement Verstärkung

stress contrainte Spannung

stripping désenrobage Ablösen(ung)

studded tyres pneus à clous Spikesreifen

subbase couche de fondation untere Tragschicht,

Frostschutzschicht

subgrade sol de fondation, sol support Untergrund, Unterbau

surface dressing enduit superficiel bituminöse

Oberflächen-behandlung

surfacing couche de surface Decke

TTTT tack coat couche d'accrochage bituminöser Haftanstrich,

Vorspritzung

tandem axle essieu tandem Tandem- (Doppel)achse

tensile test essai de traction Zugprüfung

test essai Prüfung, Versuch

total land requirement emprise Straßengrund

traffic flow flux de trafic Verkehrsfluß

traffic lane voie de circulation Fahrstreifen

114

traffic volume volume de trafic Verkehrsstärke

transverse distribution distribution transversale Querverteilung (des Verkehrs)

transverse profile profil en travers Querprofil

tridem axle essieu tridem Dreifachachse

truck (US) camion, poids lourd Lastkraftwagen, LKW

tyre, tire pneu Reifen

single tire roue simple Einzelreifen

twin tire roues jumelées Zwillingsreifen

UUUU unbound material matériau non traité,

matériau non lié

ungebundenes Material

unevenness défaut d'uni Unebenheit

transverse transversal Quer-

longitudinal longitudinal Längs-

VVVV voids content teneur en vides Hohlraumgehalt

WWWW wear usure Abnützung, Abrieb

wearing course couche de roulement Deckschichte

weight poids, charge Gewicht

weigh-in-motion (W.I.M) pesage en marche Wiegen während der Fahrt

wheel roue Rad

wheel assembly roue jumelée Zwillingsrad

wheel base écartement des roues Radstand

wheel load charge par roue Radlast

wheel path frayée, bande de roulement Radspur

widening elargissement Verbreiterung

ParParParParts of the road ts of the road ts of the road ts of the road

total land requirement emprise Straßengrund

crown of a carriageway plate-forme Straßenkrone

pavement chaussée Fahrbahn

traffic lane voie de circulation Fahrstreifen

hard shoulder for emergency

stop

bande d'arrêt urgence befestigter Seitenstreifen

Standstreifen

shoulder accotement Bankett

ditch fossé Graben

berm(e) berme Berme

central reserve

median (US)

terre-plein central (TPC) Mittelstreifen

slope talus, pente Böschung

115

cycle path (track) piste cyclable Radweg

ditch at top of cunette de Oberer

slope crête de talus Abfanggraben

ditch at foot of fossé de pied Unterer

slope de talus Abfanggraben

safety fence glissière de sécurité Schutzplanke

Structure of the pavementructure of the pavementructure of the pavementructure of the pavement t t t

pavement revêtement (2e sens)

Oberbau

road foundation corps de la chaussée Tragschichten (Oberbau ohne

Decke)

subgrade sol de fondation Unterbau

road surface surface de la chaussée

couche de surface

Fahrbahnoberfläche

Decke

surface layer,

wearing course

couche de roulement Deckschichte

binder course couche de liaison Binderschicht

road base (UK)

base course (US)

couche de base (obere) Tragschicht

subbase couche de fondation untere Tragschicht,

Frostschutzschicht

capping layer couche de forme verbesserter Unterbau

natural ground terrain naturel Untergrund

formation(level) forme Planum (Unterbau-)