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O R I G I N A L A R T I C L E

Cement stabilised rammed earth. Part A: compaction

characteristics and physical properties of compacted cementstabilised soils

B. V. Venkatarama Reddy P. Prasanna Kumar

Received: 13 October 2009 / Accepted: 16 August 2010 / Published online: 31 August 2010

RILEM 2010

Abstract Rammed earth is used for load bearing

walls of buildings and there is growing interest in this

low carbon building material. This paper is focused

on understanding the compaction characteristics and

physical properties of compacted cement stabilised

soil mixtures and cement stabilised rammed earth

(CSRE). This experimental study addresses (a) influ-

ence of soil composition, cement content, time lag on

compaction characteristics of stabilised soils and

CSRE and (b) effect of moulding water content and

density on compressive strength and water absorptionof compacted cement stabilised soil mixes. Salient

conclusions of the study are (a) compaction charac-

teristics of soils are not affected by the addition of

cement, (b) there is 50% fall in strength of CSRE for

10 h time lag, (c) compressive strength of compacted

cement stabilised soil increases with increase in

density irrespective of moulding moisture content and

cement content, and (d) compressive strength

increases with the increase in moulding water content

and compaction of CSRE on the wet side of OMC is

beneficial in terms of strength.

Keywords Soil cement Soil Compaction

Compressive strength Rammed earth

Stabilised earth

1 Introduction

Rammed earth wall is a monolithic construction

formed by compacting processed soil in progressive

layers in a formwork. Use of rammed earth walls for

both load bearing and non-load bearing applicationscan be seen across the world. Rammed earth

constructions can be grouped into two broad catego-

ries: stabilised rammed earth and un-stabilised

rammed earth. Soil, sand and gravel constitute the

materials used for unstabilised rammed earth. In

addition to soil, sand and gravel, stabilisers (cement,

lime, etc.) are added for stabilised rammed earth.

Loss of strength on saturation and erosion due to rain

impact are the two major drawbacks of unstabilised

rammed earth walls. Use of inorganic additives like

cement for rammed earth walls has been in practicesince the last 56 decades. Successful use of cement

stabilised rammed earth for walls can be seen in

several countries across the world [16]. Seamless

wall surface, scope for adjusting the surface texture

and colour, flexibility in wall thickness and plan

form, etc. represent some of the major advantages of

rammed earth construction. There is a growing

interest to use cement stabilised rammed earth for

structural applications including buildings.

B. V. Venkatarama Reddy (&)

Department of Civil Engineering, Indian Institute

of Science, Bangalore 560 012, India

e-mail: [email protected]

P. Prasanna Kumar

Department of Civil Engineering, BMS College

of Engineering, Bangalore 560 019, India

e-mail: [email protected]

Materials and Structures (2011) 44:681693

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Cement stabilised rammed earth (CSRE) wall

construction involves (a) processing of materials

(soil, sand, cement, etc.), (b) mixing the dry mate-

rials with water, (c) compacting the processed

materials into a dense mass, and (d) curing. Thus

the strength and performance of cement stabilised

rammed earth walls are influenced by (a) soil gradingand soil composition (particularly clay type and

percentage), (b) dry density, (c) cement content and

(d) elapsed time since mixing water and commence-

ment of CSRE wall compaction process (termed as

time lag). Compaction characteristics of cement

stabilised soils, influence of moulding water content

on compressive strength of compacted cement stabi-

lised soils, and effect of time lag on compaction

characteristics and strength of CSRE form the main

parameters of the investigations in Part A. Part B of

the investigations is focused on compressive strengthand elastic properties of CSRE considering the

influence of moisture content, soil composition,

cement content and density.

2 Earlier studies

Stabilised soils find applications in the construction of

base courses for roads and pavements, ground improve-

ment and for the construction of superstructure of

buildings (mainly walls). Accordingly the propertiesexpected from the stabilised soils vary depending upon

the specific engineering application. Compressive/

shear strength, CBR value, permeability, etc. are some

of the characteristics examined for stabilised soils

finding applications in the construction of roads and

pavements, and ground improvement. For superstruc-

ture applications in buildings attention is paid to the

properties like compressive strength (in saturated

condition), dimensional stability and durability. In

majority of the applications stabilised soils are densi-

fied through a suitable compaction process.There are many investigations on soil stabilisation

as applicable to the construction of roads/pavements,

embankments, ground improvement, etc. Similarly

there are another class of investigations focused on

the technology of compacted stabilized soil blocks

used for masonry construction. The third category of

investigations on CSRE for structural walls is

emerging since the last 23 decades. The basic soil

stabilization principles remain the same, but the

limits on certain strength and performance character-

istics vary depending upon the type of application.

Reviews of some papers on cement stabilized soils

and CSRE construction have been highlighted below.

Compressive strength of rammed earth is the most

important physical property needed for assessing the

load carrying capacity of such walls subjected togravity loads. Focused studies on strength of CSRE

are limited. Verma and Mehra [1] specified that sand

content of the soil should not be less than 35%, liquid

limit should not be greater than 25% and plasticity

index in the range of 8.510.5. Eastons [2] mono-

graph is a compilation of his experiences of rammed

earth construction in the USA. He states that (a) soil

with 30% clay and 70% sand is ideal for rammed

earth, (b) strength of rammed earth wall can be

increased by as much as 500% with the addition of

cement (7%) and (c) stabilised rammed earth is muchless susceptible to damage from rain, snow, or runoff

than a wall built of plain rammed earth.

King [7] conducted strength tests on cement

stabilised (11% cement) cylindrical rammed earth

specimens and reports compressive strength between

9.8 and 26.85 MPa for curing duration varying from

14 to 215 days with a large scatter (150%) in the

strength values. Walker [8] examined the behaviour

of reinforced composite CSRE panels under flexure.

He reports a cylinder compressive strength (air dry)

varying between 3.9 and 7.9 MPa. Hall et al. [9] andHall [10] discuss some issues on stability of CSRE

walls and the relevant building regulations in UK.

They mention tests on durability for CSRE exposed

to pressure driven rainfall in the climatic chamber.

The results show that CSRE specimens with 6%

cement are highly resistant towards moisture pene-

tration and no significant erosion is noticed when

subjected to pressure driven rainfall.

Walker et al. [6] compiled design and construction

guidelines for rammed earth, and they mention dry

compressive strength of[10 N/mm2 for stabilisedrammed earth. They suggest that soil for rammed

earth should be well graded containing 4580% sand

and gravel, 1030% silt, 520% clay, liquid limit

\45% and plasticity index 230. Structural proper-

ties of cement stabilised rammed earth using three

types of Sri Lankan laterite soils with three cement

contents (6%, 8% and 10%) has been examined by

Jayasinghe and Kamaladasa [11]. They observed that

(a) strength increases with increase in cement content

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and wet compressive strength of CSRE panels was

about 0.450.6 times the dry compressive strength

and (b) saturated strength is a function of cement

content and fines content of the soil and sandier

laterite soils resulted in higher compressive strength.

Houben and Guillaud [5] report [2 MPa wet

compressive strength for 8% cement with excel-lent durability characteristics. Prasanna Kumar and

Venkatarama Reddy [12] established relationships

between density, moisture content and compressive

strength of CSRE and concluded that compressive

strength of CSRE is sensitive to the dry density and

moisture content of specimen at the time of testing.

Bui et al. [13] attempted to measure the compressive

strength and modulus of rammed earth stabilized with

5% lime exposed for 20 years under natural weath-

ering conditions and reported dry strength of about

1.0 MPa with a modulus of 100 MPa. Burroughs [14]attempted to define the criteria for selecting soils

applicable for stabilised rammed earth. A comparison

of strength and elastic properties of CSRE and stabi-

lised rammed earth brick masonry has been examined

by Venkatarama Reddy and Prasanna Kumar [15].

This study shows that compressive strength of CSRE

is 2030% more than that of rammed earth brick

masonry. Also, the study indicates that the wet com-

pressive strength of CSRE and rammed earth brick

masonry is about half of their respective dry strengths.

CSRE in dry condition shows ductile behaviourhaving strains at failure of the order of 2%. The

investigations of this study pertain to only one type of

soil with 8% cement content.

There are some codes of practice on earth con-

struction also dealing with some aspects of rammed

earth constructions. Bulletin 5 [16] specifies the

requirements for the rammed earth and other earth-

wall constructions. IS: 2110 [17] code recommends

that CSRE shall be used only for single storeyed

buildings with a minimum wall thickness of 300 mm

for load bearing walls. Soil for rammed earth shouldcontain minimum 35% sand having a maximum liquid

limit of 27% and plasticity index in the range of

8.510.5. Cement content shall not be less than 3.5%

and dry density should be above 1800 kg/m3. Com-

pressive strength of the soilcement (cylindrical

specimen) shall not be less than 1.4 and 0.70 MPa

in dry state and saturated condition respectively. NZS:

4297 [18], NZS: 4298 [19] and NZS: 4299 [20] codes

from New Zealand provide specifications for the

construction of rammed earth apart from other earth

building methods. Lehmbau Regeln [21] is used as

earth construction standard or guide in Germany.

Rammed earth specifications by this guide include dry

density in the range of 17002200 kg/m3, dry com-

pressive strength of 23 and 35 MPa for unstabilised

and stabilised rammed earth respectively.The literature on stabilised rammed earth indicates

wide range of values for soil grading, density, thick-

ness and strength. Literature recommends use of sandy

soils with cement content in the range of 512%. There

is a need for more comprehensive studies to under-

stand the structural behaviour of CSRE. Hence, the

present investigations are focused towards under-

standing various aspects of CSRE through extensive

experimentation. The results of the investigations are

presented in Part Adealing with compaction char-

acteristics and physical properties of compactedcement stabilised soil mixes and Part Bdealing with

strength and elastic properties of CSRE.

3 Objectives and scope of the investigation

Understanding the influence of various parameters on

the compaction characteristics and physical proper-

ties of cement stabilised soils and CSRE is the main

objective of the investigation. Therefore the param-

eters considered in this investigation (Part A) include:

(a) Influence of moulding water content on com-

pressive strength of compacted cement stabi-

lised soils.

(b) Compaction characteristics of cement stabilised soil

as the soil grading and cement content are varied.

(c) Influence of time lag on OMC and MDD for

various combinations using four different soil

gradations and three cement contents.

(d) Strength loss in cement stabilised rammed earth

versus time lag.

4 Methodology

Type and quantity of clay fraction in the soil

influences the characteristics of the compacted CSRE

or compacted stabilised soil bricks/blocks. Therefore,

a natural soil with high clay fraction was reconstituted

by adding river sand and thus generating different soil

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grading curves keeping the same clay mineral but

varying its quantity in the soil mixes. Reconstituted

soil mixes were used in various experiments on

compacted soil mixes and CSRE.

Compaction characteristics of soils are generally

evaluated with reference to two important parame-

ters: optimum moisture content (OMC) and maxi-mum dry density (MDD). OMC and MDD were

determined by conducting Standard Proctor tests.

Standard Proctor test (as per IS: 2720 [22] guidelines)

was conducted on reconstituted soils including the

natural soil and the soilcement mixes. Generally, the

cement percentages used for CSRE vary in the range

of 512% and hence three cement contents (5%, 8%

and 12% by weight) were considered.

Time lag was varied between 0 and 10 h. The main

objective of the experiment was to throw some light on

influence of time lag on compaction characteristics ofcement stabilised rammed earth and the resulting

consequences on strength. Influence of time lag on

compressive strength of CSRE was examined by testing

rammed earth prisms (of size 150 9 150 9 300 mm).

Rammed earth wall construction can be carried out

to achieve any desired dry density using water content

equivalent of Proctor OMC of the mix. It is possible to

achieve higher dry density ([MDD) during rammed

earth construction by supplying more compaction

energy as compared to Standard Proctor test energy.

In such situations the question arises regarding opti-mum moulding water content to be used in order to

achieve best possible strength for the cement stabilised

rammed earth. In order to throw more light on strength

and moulding water content relationships an explor-

atory experimental study was planned to establish

relationships between dry density, moulding water

content and compressive strength. Tests were per-

formed on compacted soil samples considering three

moulding water contents (dry of OMC, near OMC and

wet of OMC) and three cement contents (5%, 8% and

12%).

5 Characteristics of materials used

in the investigations

5.1 Soil and river sand

Locally available soil, river sand and ordinary Portland

cement were used in the experimental investigations.

Grain size distribution curves for the natural soil (S1)

and river sand are displayed in Fig.1. The soil S1

contains 31.6% clay size fraction. This soil wasreconstituted by mixing with various proportions of

river sand and thus generating five soil compositions

having different grain size distributions. Mix propor-

tions of reconstituted soils are given in Table1. The

table gives details of mix ratios, percentage of sand

silt and clay fractions, and designation of each mix.

The clay fraction of the soil and reconstituted soil

mixtures vary between 9.0 and 31.6%. The grain size

distribution curves for these five different soil mix-

tures are shown in Fig.1. Natural soil and the

reconstituted soils are well graded. Table2 givesvarious properties of the sand, natural soil and the

reconstituted soils. Details of textural composition,

Atterberg limits, pH, organic matter, predominant

clay minerals and compaction characteristics of the

five different soil compositions have been presented in

the table.

Natural river sand has small percentage of silt size

fraction (5%). Natural soil (S1) possesses sand, silt

and clay fractions of 50.3%, 18.1% and 31.6%

0

10

2030

40

50

60

70

80

90

100

0.001 0.01 0.1 1 10

Particle size (mm)

%Finer

S1

River sand

S2

S3

S4

S5

Fig. 1 Grain size distribution curves for sand, soil and

reconstituted soils

Table 1 Mix proportions of reconstituted soilsand mixtures

Proportion (by weight) Mix composition (%) Designation

Soil Sand Sand Silt Clay

1 0.0 50.3 18.1 31.6 S1

1 0.5 65.1 13.9 21.0 S2

1 1.0 72.6 11.6 15.8 S3

1 1.5 77.0 10.4 12.6 S4

1 2.5 82.1 8.9 9.0 S5


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respectively. S1 soil has 40% liquid limit and

plasticity index of 21, and the clay mineral is

Kaolinite. Reconstituted soilsand mixes have clay

fraction ranging between 9 and 21%, whereas the

sand fraction is in the range of 65.1 to 82.1%. Soils

S1, S2, S3 and S4 belong to class SC and soil S5

belongs to the class SPSC in USC system. Atterberg

limits and compaction characteristics vary as the soilcomposition changes. The pH of sand, natural soil

and reconstituted soils is in the range of 7.739.05.

Organic matter for the soils is low, in the range of

0.270.94%.

5.2 Portland cement

Ordinary Portland cement (OPC) conforming to IS:

8112 [23] was used in the experiments. IS: 4031 [24]

specifies procedure for testing the cement sample

using Vicat apparatus for Initial and final setting timesdetermination, and tests on cube specimens for

strength. 7 and 28 day compressive strengths of the

OPC tested following the guidelines of IS: 4031, was

38.5 and 57.5 MPa respectively as against 30 and

43 MPa specified in IS: 8112 code. The initial

and final setting times for the cement were 183 min

and 312 min respectively. The initial setting time

specified in IS: 8112 for OPC is 30 min, whereas the

OPC used in the present study has a higher initial

setting time. The manufacturer of the OPC used in the

present study quotes an initial setting time of 180 min.

6 Casting specimens and testing procedures

Rammed earth prisms and cylindrical specimens wereused in the investigations. Details of casting/prepa-

ration of these specimens are discussed below.

6.1 Casting CSRE prisms

Prisms of size 150 mm 9 150 mm square cross-

section and 300 mm height were used for determining

compressive strength of CSRE. Procedure adopted to

prepare the rammed earth prisms is as follows.

(a) Manually powdered oven dried soil (at 60C)

sieved through a 4.75 mm mesh was used. Thedried soil was mixed with required quantity of

cement and then with water (OMC) manually. It

was ensured to distribute the cement and water

uniformly in the mix.

(b) The wetted mix was stored in a sealed plastic

bag till the end of designated time lag. Then the

mix was poured into a metal mould and

compacted in three layers of 100 mm each.

The mass of the material in each layer was

Table 2 Properties of sand, natural soil and reconstituted soils

Properties Type of soil

Sand S1 S2 S3 S4 S5

1. Textural composition (mass%)

Sand (4.750.075 mm) 94.8 50.3 65.1 72.6 77.0 82.1

Silt (0.0750.002 mm) 5.2 18.1 13.8 11.6 10.4 8.9

Clay (\0.002 mm) 31.6 21.1 15.8 12.6 9.0

2. Atterbergs limits

Liquid limit (%) NP 40 32.0 26.9 25.6 24.9

Plasticity index 21 19.7 17.5 NP NP

3. Unified soil classification (USC) SC SC SC SC SPSC

4. Predominant clay mineral Kaolinite Kaolinite Kaolinite Kaolinite Kaolinite

5. Chemical properties

pH 9.05 7.73 7.81 8.0 8.13 8.32

Organic matter (%) 0.0 0.94 0.63 0.47 0.38 0.27

6. Compaction characteristicsMaximum dry density (kg/m

3) 1814 1910 1992 1980 1958

Optimum moisture content (%) 15.52 11.30 10.28 9.38 9.26


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controlled such that the final designated dry

density of the prism was achieved.

(c) The prism specimen was removed from the

metal mould after 24 h of casting and kept for

curing under wet burlap. After 28 days, curing

was discontinued and the prisms were allowed

to dry in air inside the laboratory for 2 weeks

and then tested for strength. Figure 2shows theCSRE prism.

6.2 Casting cylindrical specimens for unconfined

compressive strength

Establishing relationships between dry density,

moulding water content (dry of OMC, near OMC

and wet of OMC) and compressive strength for three

cement contents (5%, 8% and 12%) involves testing

large numbers of samples. Hence, use of prisms (ofsize: 150 9 150 9 300 mm) for such a parametric

study requires handling of huge quantity of soil and

cement. Therefore, smaller cylindrical specimens of

size 76 mm height and 38 mm diameter (Fig. 3) were

prepared for determining unconfined compressive

strength. Procedure followed for casting of the

cylindrical specimens is as follows.

(a) Oven dried soil (at 60C) containing small

lumps was powdered and then blended with

requisite quantity of Portland cement. The

powdering and cement blending was carried

out in a small ball mill for 8 min to ensure

uniform mixing of cement.

(b) Requisite quantity of potable water was mixed

(manually) with soilcement blend. A small

sprayer was used for spraying water during

mixing and it was ensured that the moisture was

uniformly distributed in the entire mix.

(c) Wetted soilcement mixture was fed (knownweight) into an open-ended cylindrical mould.

The mould was then mounted horizontally and

compaction carried out from both the ends using

a mechanical screw-jack arrangement as shown

in Fig.4.

(d) The specimen was extruded from the mould

immediately after the compaction. Compacted

specimens were kept for curing under wet

burlap after 24 h of casting.

Fig. 2 CSRE prism

Fig. 3 Cylindrical specimens used for unconfined compres-

sive strength tests

Fig. 4 Screw-jack set-up for casting the cylindrical specimens


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6.3 Testing CSRE prisms and cylindrical

specimens

After 28 day curing, the specimens were air dried

inside the laboratory for 2 weeks. Air dried speci-

mens were soaked in water for 48 h. Then the

specimens were removed from water, the dimensionsand mass were measured. The saturated cylindrical

specimens were tested in a loading frame at constant

piston displacement of 1.25 mm/min, whereas prism

specimens were tested in a displacement controlled

universal testing machine. Failed specimen was

immediately transferred to a beaker and its moisture

content was assessed by drying at 110C in an oven

for 24 h. Based on the test data, wet compressive

strength, dry density and saturated moisture content

of the specimens were calculated.

7 Results and discussion

7.1 Influence of soil composition and cement

content on compaction characteristics

Standard Proctor compaction tests were carried out

on four soil compositions (S1, S2, S3 and S5) with

three cement contents (5%, 8% and 12% by weight).

In case of cementsoil mixes compaction tests werecarried out immediately after mixing with the water.

Density and moisture content relationships were

plotted and the respective OMC and MDD values

were determined. Figures5 and 6show the plots of

OMC versus cement content and MDD versus cement

content respectively. Figures7 and 8 show the

variation of OMC and MDD with clay fraction of

the mix for the cement contents of 0%, 5%, 8% and

12%. The following observations can be made from

the results shown in Figs. 5,6,7, and8.

(a) There is a marginal variation (23%) in OMCand MDD values as the cement content

increases. Thus OMC and MDD are not sensi-

tive to the variation in cement content of the mix

irrespective of clay fraction of the mix.

(b) OMC increases as the clay content of the mix

increases. There is a steep increase in OMC

value as the clay content of the mix is increased.

The increase in OMC is about 5070%, as the

clay content increases from 9 to 31.6%.

(c) There is hardly any variation in MDD for the

clay content in the range of 915.8%. For

15.831.6% clay content range there is 810%

decrease in MDD irrespective of cement content

of the mix.

Variation in OMC and MDD values as clay

content of the soil increases is on the expected lines

as found in the literature for stabilised soils [25]. But

9

11

13

15

17

5 6 7 8 9 10 11 12

Cement content (%)

OMC(%

)

S1, 0 min lag S2, 0 min lag

S3, 0 min lag S5, 0 min lag

Fig. 5 Standard Proctor OMC versus cement content

1700

1800

1900

2000

2100

5 6 7 8 9 10 11 12

Cement content (%)

MDD

(kg/m3)

S1, 0 minutes time lagS2, 0 minutes time lagS3, 0 minutes time lagS5, 0 minutes time lag

Fig. 6 Standard Proctor MDD versus cement content


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the results clearly show that addition of cement to

soils did not affect the OMC and MDD values much.

This may be attributed to the fact that the compaction

tests were performed immediately after mixing the

water where the scope for cement setting was

avoided. Influence of cement setting on compaction

characteristics is discussed in the following section.

7.2 Effect of delayed compaction (time lag)

on compaction characteristics

Compaction characteristics of the different soil mixes

were examined with three cement percentages (5%,

8% and 12%) and by varying the time lag between 0

and 10 h. Time lag versus MDD and OMC values forthe three cement contents (5%, 8% and 12%) were

plotted and examined. OMCtime lag and MDD

time lag relationships appear similar for all the four

soil mixtures and three cement contents attempted.

Figure9shows a typical plot of OMC versus time lag

and MDD versus time lag. The following points

emerge from these results.

OMC steadily increases with increase in time lag

irrespective of soil type and cement content. The

percentage increase in OMC varies between 25 and

40% for the time lag between 0 and 10 h. For 1 htime lag, the increase in OMC is about 510% for all

the four soil mixtures and three cement percentages

attempted. Aggregation of cement mixed soil parti-

cles with increase in time lag was noticed and may be

due to hydration and setting of cement. Figure10

illustrates the aggregated cementsoil particles with

time lag. The size of the aggregated lumps of

particles increases as the time lag increases. Energy

supplied in Standard Proctor compaction test is fixed

and hence, some of this energy will be utilised to

break the already established bonds due to aggrega-tion of particles, the remaining energy may not be

sufficient to properly compact these aggregated

particles and thus leading to creation of more porous

9

10

11

12

13

14

15

16

8 12 16 20 24 28 32

Clay content (%)

OMC(%)

0% cement

5% cement

8% cement

12% cement

Fig. 7 Standard Proctor OMC versus clay content of soil

1700

1800

1900

2000

2100

8 12 16 20 24 28 32

Clay contet (%)

MDD(kg/m3)

0% cement

5% cement

8% cement

12% cement

Fig. 8 MDD versus clay content of soil

1100

1300

1500

1700

1900

2100

0 2 4 6 8 10

Time lag (Hours)

MDD(K

g/m3)

10

11

12

13

14

15

OMC

(%)

5 % Cement8% Cement12% Cement

OMC

MDD

Fig. 9 MDD/OMCtime lag relationships for S5 soil


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structure. This could be the reason for higher OMC

values with increase in time lag.

In contrast to the increase in OMC with time lag,

the MDD steadily decreases with an increase in time

lag for all the four soil mixtures with three cement

contents attempted. The decrease in MDD is in the

range of 1016% for the time lag between 0 and 10 h.For 1 h time lag there is hardly any variation (13%)

in MDD for all the four soils and three cement

percentages attempted. Decrease in MDD could be

attributed to increase in porosity due to improper

compaction of aggregated soil particles. There is

marginal variation in OMC and MDD values as the

cement content is changed from 5 to 12% throughout

the time lag period (from 0 to 10 h).

West [26] studied the influence of elapsed time on

density of medium clay stabilised with 10% cement.

He reports *15% reduction in dry density for a timelag of 7 h. The present study clearly indicates the

influence of delayed compaction on OMC and MDD

of cement stabilised soils. The results indicate a fall

in density with time lag. Fall in density could affect

the strength and absorption characteristics of cement

stabilised rammed earth. Hence, it is preferable to

complete the compaction process of cement stabilised

rammed earth walls within an hour of mixing with the

water.

7.3 Variation in strength of cement stabilised

rammed earth with time lag

Influence of time lag on compressive strength of

CSRE was examined by testing rammed earth prisms.

Rammed earth prisms of size 150 9 150 9 300 mm

were prepared using S3 soil (clay content = 15.8%)with 8% Portland cement by weight. The dry density

of the prisms was controlled and maintained at

1800 kg/m3, thus avoiding the interference of density

on strength. Three prisms were tested in each category

and the mean values were obtained. Figure 11shows a

plot of wet compressive strength versus time lag. For

the time lag beyond 10 h it becomes difficult to cast

the prisms at the designated dry density of 1800 kg/m3

due to the larger sized aggregated cementsoil

particles and hence, the strengths were obtained only

up to 10 h of time lag. It is clear from the plot inFig.11 that the wet compressive strength steadily

decreases with increase in time lag. The strength falls

from 3.3 to 1.66 MPa (50% decrease) for a time lag of

10 h. This decrease in strength can be attributed to the

fact that the compaction of cement stabilised soil has

been carried out after the setting time of cement and

aggregation of particles, wherein already established

cementitious bonds were broken during compaction.

Fig. 10 Aggregation of wetted cementsoil mixture particles

with time lag

1

2

3

4

0 2 4 6 8 10

Time lag ( hours)

Wetc

ompressivestrength(MPa)

Fig. 11 Compressive strength versus time lag for rammed

earth prisms (clay content of the soil mix = 15.8%, cement

content = 8%, dry density = 1800 kg/m3

, Moulding water

content = OMC)


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West [26] reports 37% reduction in compressive

strength for a time lag of 7 h, for a medium clay

stabilised with 10% cement. These results indicate

that the wetted cementsoil mixture should be

rammed into a wall within an hour after mixing with

water. Beyond an hour of time lag the strength

decreases rapidly.

7.4 Influence of moulding water content, cement

content and density on strength

S3 soil was used in casting specimens for these

experiments. OMC for S3 soil with 512% cement is

in the range of 10.7511.5%. Compressive strength of

cement stabilised compacted soil specimens using S3

soil and with three cement contents (5%, 8% and

12%) was evaluated by considering three different

moulding moisture contents of 8.5% (dry of OMC),12% (near OMC) and 14.5% (wet of OMC). From the

results of density and strength relationships shown in

Fig.12 it is clear that the curves corresponding to

moulding water content of 14.5% (wet of OMC) lie

above the curves corresponding to moulding water

content of 12% (near OMC) and 8.5% (dry of OMC)

in that order, irrespective of density and cement

content. Figure13 shows the variation in strength

with the moulding water content for the dry densities

of 1700 and 1900 kg/m3. It is clear from this figurethat the compressive strength increases with the

increase in moulding water content. For 5 and 8%

cement contents the strength increase is in the range

of 2050% as the moulding water content changes

from 8 to 14.5%, whereas for 12% cement the

strength increase is in the range of 4070%.

Dry soilcement mixture contains cement and clay

particles both having affinity for water. When the

water is added to the dry soilcement mixture, the

water is shared by both cement and clay particles.

When the samples are compacted using small quan-tity of moulding water (say 8%) there could be

insufficient supply of water for proper hydration of

cement to take place. As the moulding water content

is increased (say 14.5%) more water is available for

cement hydration. This could be the reason for

increased strength when higher percentage of mould-

ing water was used.

Figure13illustrates that the compressive strength

increases with increase in cement content. For the dry

0

1

2

3

4

5

6

7

8

1500 1600 1700 1800 1900 2000 2100

Dry density (kg/m3)

Wetcom

pressivestrength(MPa)

5% cement, dry of OMC5% cement, close to OMC

5% cement, wet of OMC

8% cement, dry of OMC

8% cement, close to OMC





Fig. 12 Compressive strength versus density for various

moulding moisture contents

0

1

2

3

4

5

6

7

8 10 12 14 16

Moulding moisture content (%)

Compressivestrength(MPa)

5% cement, 1700 kg/m3






Fig. 13 Compressive strength versus moulding moisture

content (for densities of 1700 and 1900 kg/m3

)


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density range of 17001900 kg/m3, the wet compres-

sive strength increases by 200250% as the cement

content changes from 5 to 12%. Venkatarama Reddy

and Gupta [27] report 250% increase in compressive

strength for compacted soilcement blocks for a

change in cement content from 6 to 12%.

Compressive strength of compacted cement stabi-lised soil mixes increases with increase in density

irrespective of cement content and moulding mois-

ture content. The relationship between density and

strength is nearly linear. The strength increases by

46 times for a change in dry density from 1600 to

2000 kg/m3, for the three cement contents and three

moulding moisture contents considered. There is a

considerable increase in strength for small changes in

dry density. For example 10% increase in density

from 1600 kg/m3 results in about 300% increase in

compressive strength for 5% cement irrespective ofthe moulding moisture content. Similarly for 8 and

12% cement contents the compressive strength

increases by 200% for a 10% increase in dry density

from 1700 kg/m3. This trend is in tune with results

reported by Venkatarama Reddy [28] for compacted

stabilised mud blocks. He reports linear relationship

between density and strength, and sharp increase in

strength for small increase in dry density. Increase in

strength due to increase in (closer contact among

particles) dry density can be attributed to reduction in

the porosity of the compacted specimen resulting inbetter bonding due to cement hydration products.

7.5 Density versus water absorption (saturated

water content)

Variation in the percentage of saturated water content

with the dry density of the cement stabilised com-

pacted soil specimens with different cement contents

as well as different moulding water contents is

displayed in Fig.14. Figure reveals that the saturated

water content of the specimens decreases with theincrease in dry density of the specimen for differ-

ent combinations attempted. Figure shows a linear

relationship between density and water absorption

and is of the form: Water absorption (%) = 57.92 -

0.0242cd, where cdis in kg/m3 and water absorption is

in (%). The saturated water content doubles (from

*10%) as the dry density changes from 1600 to

2000 kg/m3. The saturated water content is in the

range of 1020% (and lie in the same band) for all the

three cement contents (5%, 8% and 12%) attempted

and for the dry density range of 16002000 kg/m3. It

is obvious that lower density will have higher porosity

and hence can accommodate more water at saturated

condition. The porosity of the specimens is 0.26 and

0.42 for the dry densities of 2000 and 1600 kg/m3

respectively.

8 Summary and conclusions

Results of experimental investigations in understand-

ing various physical characteristics of compacted

cement stabilised soil mixes and CSRE were dis-

cussed. The major conclusions emerging out of the

experimental work are as follows.

OMC and MDD values of soil with a wide range

of clay contents are not affected by the addition of

ordinary Portland cement. But MDD and OMC

values of cement mixed soils vary as the soil

composition changes. Generally, MDD decreasesand OMC increases as the clay fraction of the cement

mixed soil increases. OMC increases and MDD

decreases as the time lag increases, irrespective of

soil type and cement content. There is 2540%

increase in OMC for the time lag between 0 and 10 h.

The decrease in MDD is in the range of 1016% for

the time lag between 0 and 10 h.

The wet compressive strength of CSRE steadily

decreases with increase in time lag. There is a 50%

1500

1600

1700

1800

1900

2000

9 11 13 15 17 19 21

Water absorption (%)

Drydensity(kg

/m3)










Fig. 14 Densitywater absorption relationships (for 5%, 8%,and 12% cement)


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fall in strength for a time lag of 10 h. This decrease in

strength can be attributed to the compaction of

cement stabilised soil being carried out after the

commencement of setting of cement, wherein already

established cementitious bonds are broken during

compaction. These results indicate that the wetted

cementsoil mixture should be rammed into a wallwithin an hour after mixing with water.

Compressive strength of compacted cement stabi-

lised soil is sensitive to density and increases with

increase in density irrespective of cement content and

moulding moisture content. For small increase in

density there is a considerable increase in strength.

Compressive strength increases with the increase in

moulding water content. For a 2% increase in water

content beyond OMC the strength increase is of the

order of 2070%. It is preferable to carry out the

compaction of CSRE on the wet side of OMC. Waterabsorption of the compacted cement stabilised soil

mixes decreases with the increase in dry density of

the specimen. There is linear relationship between the

water absorption and dry density (cd) and is of the

type: Water absorption (%) = 57.92 - 0.0242cd,

where cd is in kg/m3 and water absorption in (%).

Some important findings of these investigations

which directly affect the quality of cement stabilised

rammed earth construction are:

(1) Compressive strength is sensitive to dry density.Strength increases with increase in density

irrespective of moulding water content. Achieve

higher dry densities for CSRE by using mould-

ing moisture contents wet of Standard Proctor

OMC.

(2) Cementsoil mixture should be rammed into a

wall within an hour after mixing with the water.

Time lag results in lower strength and difficulty

in achieving higher density.

References

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