Tests of Soil and Bitumen

8/2/2019 Tests of Soil and Bitumen

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MATERIAL TESTING AND THEIR SIGNIFICANCE


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Soil1.Grain Size Analysis2.Atterbergs Limit3.Compaction Test4.Free Swell Index5.Direct Shear6.

California Bearing Ratio

7.Tri-Axial Compression Test


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Grain Size Analysis(IS 2720: part 4)

PURPOSE

The commonly used properties for classification of soil are the grain

size distribution and atterbergs limits which are also used to determine

the suitability of soil as a sub-grade material and other purposes.

The soils are generally divided into four groups based on their particle

size Gravel: coarser particles of rock and sand between 80mm and

4.75mm

Sand: smaller fraction of particles between 4.75mm and 75micron Silt: soil fractions smaller than 75 micron are called fines which

consist of silt and clay.75 micron to 2 micron is silt

Sand: microscopic and sub-microscopic particles lower than 2micron is clayey particles.

Dry sieve analysis is generally carried out on coarse aggregates or sandy

soil either retained or passing through 4.75 mm sieve if they are

cohesion less and without lumps. Otherwise wet sieve analysis is

conducted.

Wet sieve analysis is carried if the sample contains cohesive lumps and

it is not possible to break them into their respective grain size by any

pulverizing methods. Soils with fractions which are likely to causeflocculation are added with 2 gm of sodiumhexameta-phoshate or 1 gm

of sodium hydroxide / sodium carbonate as a dispersing agent and left

for soaking.


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Uniformity coefficient U, is expressed as (D60 /D10 ), where D60 and D10

are particle size corresponding to 60 % and 10% fines in the grain size

distribution curve. A high value of uniformity coefficient such as U

greater than 4 or 5 indicates the presence of wide range of particle sizeor soil is well graded. A low U of the order of lower than 2 indicates

uniformly graded soil

Soil classification

Ordinarily sieve analysis (dry/wet) will be quite sufficient along with the

tests for consistency limits for identifying and classifying soil.

Proportioning soils for mixed designThe principle of mechanical soil stabilization is to mix two or more

number of selected soils and gravels or aggregates in a suitable

proportion that a desired grain size distribution is obtained for the

combined materials as per mix design


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ATTERBERG`S LIMIT(IS 2720 PART 5 & 6)

PURPOSE

The physical properties of fine grained soils, especially of clayey soils

differ considerably at different water contents present in soil. The tests

for determination of consistency limits are all empirical.

Liquid Limit: It is defined as the minimum water content at which the

soil will flow under the application of a very small shearing force.

Plastic Limit: It is defined as the minimum water content at which soil

remains in a plastic state and posses moulding characteristics.

Shrinkage Limit: it is defined as the maximum water content at which

further reduction in water content does not cause reduction in volume.

LIQUID LIMIT TEST (By cone penetration one point method)

In the case of soils whose liquid limit exceeds by 120% in case of one

point method mechanical method should be used.

PRINCIPLE

Since the depth of penetration is in an indirect reflection of shear

strength at different water contents, it has been found, within the

framework of a scientific base that W/WL against logD or D is unique

and is independent of soil type. The resulting linear relation enables to

determine liquid limit water content at specified penetration of 20 mm

depth.


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CALCULATION

The water content is determined for any accepted trial and the liquid

limit water content is calculated by any one of the following

relationships.

WL = WN / 0.77 LogD

WL = WN / (0.65 + 0.0175 D)

The liquid limit of the sample shall be reported to first decimal place

and history of the sample that is natural state, oven dried, or any

pretreatment done should be mentioned.

Shrinkage Limit of remoulded sample, Ws = w (v- vo/wo)100

where

Ws = shrinkage limit in percent,

w = moisture content of wet soil pat

V = volume of wet soil pat in ml,

Vo = volume of dry soil pat in ml, and

Wo - weight of oven-dry soil pat in g.

Application of consistency limits

Identification and classification of soils

Compressibility

Plasticity index

Application of data in the construction of highway material

Group index method of classifying sub grade soil


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COMPACTION TEST

PURPOSE

Compaction of a soil is a mechanical process by which the soil particles

are constrained to be packed more closely together by reducing air

voids. Soil compaction decreases air voids and consequently increases

dry density. This may result in increase in shear strength. The possibility

of future settlement or compressibility decreases and also the tendency

for subsequent changes in moisture content decreases.

Light compaction is done filling the mould in three equal layers and

compacted by 2.6 kg hammer with 25 blows in small mould and 55

blows in large mould of 150 mm diameter

Heavy compaction is done by filling the mould in 5 layers and

compacting by 4.9 kg hammer with 25 blows each in small mould of

100 mm diameter and 55 blows in large mould of 150 mm diameter.

RESULT

Moisture- dry density graph is plotted with moisture content on the X

axis and dry density on Y axis and a smooth curve is drawn connectingthe points, which is called compaction curve.

From this curve, the maximum density is noted and the corresponding

value of moisture content is taken as optimum moisture content OMC

DISCUSSION

The objective of the compaction test is to determine the relationship

between compacting moisture content and dry density achieved for the

soil keeping the compacting energy per unit volume constant.

Therefore to increase the accuracy of results the volume to be struck

off from the collar should not be very different in each case and it

should be like 6 mm of soil should be there after removing the collar to

be struck off to get good reproducibility.


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APPLICATION OF COMPACTION TEST

In field compaction the compacting effort is first controlled at OMC and

the adequacy of compaction is checked by checking the dry density

achieved

The results are used for quality control in the construction of

pavements as IRC and MORTH recommends achieving 97% of the dry

density achieved in heavy compaction in sub-grade layer and 95% in

compacted embankments.

Suitability of the soil to be used in highway work is based on the

specified minimum value of dry density achieved in compaction test. As

per MORTH for deciding suitability of soil to be used as sub-grade, themaximum dry density should not be less than 1.75 g/cc

The maximum dry density indicates the strength property of the soil,

lower the dry density it indicates weaker is the soil although it is just

qualitative idea quantification is done by conducting strength tests.


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SHEAR TESTS ON SOILS(IS 2720 part 11, 12, 13)

PURPOSE

The strength parameters namely the cohesion and the angle of internalfriction or shearing resistance of soils are usually found from the shear

tests. Two commonly used methods are direct shear test and triaxial

compression test

DIRECT SHEAR TEST

In this test the soil specimen is placed in the shear box between two

halves and a normal load is applied. Then a longitudinal displacementor the shear force is applied and its magnitude is increased until the

specimen fails along the predetermined horizontal plane between the

two halves of shear box

By repeating the direct shear test at different magnitudes of normal

load, a graph is plotted with normal stress values on the X-axis and the

shear stress values on Y-axis. The value of cohesion C, and the

magnitude of angle of internal friction are obtained from the graph

DISCUSSION

The main advantage of direct shear test is its simplicity and less time

consuming in comparison to tri axial. But it is also associated with some

disadvantages as follows

The failure is forced to take place along pre determined horizontalplane not the weakest plane

The area of cross section of specimen progressively decreases during

the test.


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There is no uniform shear stress distribution within the failure plane

and drainage conditions are not controlled

TRI-AXIAL COMPRESSION TEST

In triaxial test the load applied is mostly transient and it is carried out

on the soil having more cohesive properties

APPLICATIONS

The shear strength parameters C and internal friction can be found and

thus shearing resistance can be found out

Elastic modulus values or modulus of deformation values of sub grade

and other pavement layer materials are determined from tri axial test.

The unconfined compression test is considered to be the special case in

which lateral confining pressure is zero.

FREE SWELL INDEX

PURPOSE

Free swell index is conducted on soils which have the potential to swell.

It is desirable to carry out further detailed investigations on soils with

high free swell index.

DISCUSSION

The volume of the soil sample in the jar is noted as Vk and water as Vw

than FSI = 100* (Vw - Vk )/Vk


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CALIFORNIA BEARING RATIO

PURPOSE

The CBR test denotes a measure of resistance to penetration of a soil orflexible pavement material of standard plunger under controlled test

conditions. It is a method for evaluating the strength of sub grade soil

and other pavement materials for the design and construction of

flexible pavements.

DISCUSSION ON RESULTS

The CBR values at 2.5 and 5.0 mm penetration levels are calculated foreach specimen from the corresponding graphs. Generally the CBR value

at 2.5 mm penetration is higher but if the value is higher at 5.0 mm

than test is repeated and If still it is higher than higher value is adopted.

The initial concavity of the load penetration curve calling for the

correction may be due to one or more of the following reasons:

The top layer of soaked soil specimen is too soft or slushy after soakingin water.

The top surface of the specimen is not even.

The penetration plunger of the loading machine is not vertical result in

bottom surface of plunger not being horizontal and fully in contact with

the top surface of specimen.

APPLICATIONS

Based on CBR data collected, empirical design charts were developed

by the California state highway department, correlating the CBR value

and pavement thickness requirement.


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AGGREGATES1.Aggregate Impact test2.Los Angeles Abrasion test

3.Specific gravity and water absorption test

4.Shape test

5.Soundness test

6.Stripping value test


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Aggregate Impact test(IS 2386 Part 4)

PURPOSE

Toughness is the property of the material to resist impact. During the

construction process of pavement layers, particularly compaction by

heavy rollers and also due to movement of heavy wheel loads of traffic,

the road aggregates are subjected to impact therefore stone aggregates

should therefore be sufficiently tough to resist fracture under impact

loads.

DISCUSSION

Aggregate impact value test of a sample not only depends on

toughness and strength parameters it also depends on the shape

factors such as flakiness and elongation of the aggregates

APPLICATION

The aggregate impact test is considered to be an important test to

assses the suitability of the aggregated as regards the toughness for usein various constructional purpose mainly highway.

RESULTS

It is expressed as percentage of finer material passing 2.36 mm IS sieve

after test to original weight.

Aggregate impact value Toughness property

Less than 10 Exceptionally strong/tough

10 to 20 Very tough

20 to 30 Good for pavement construction

Above 35 Weak for pavement construction


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LOS ANGELES ABRASION TEST(IS 2386 part 4)

PURPOSE

Due to movement of traffic, the road stones are used in the surfacingcourse of pavements are subjected to wearing action at the top surface.

Resistance to wear or hardness is hence a essential property for road

aggregates especially when used in wearing course. Thus road stones

should be hard enough to resist the wearing under heavy traffic loads.

RESULT

The result is expressed as a percentage wear and the average value of

the two test. Percentage wear is the amount of fines to the originalweight passing through 1.70 mm IS sieve

DISCUSSION

Los angeles test is very commonly used to evaluate the quality of

aggregates for use in pavement construction, especially to decide

hardness of aggregate M

Maximum allowable los angeles abrasion value of aggregates given by

MORTH for different layers is given in the tableTypes of pavement layer Los angeles abrasion value,

maximum

WBM sub-base, WBM, WMM and

CRM base course

40Bituminous macadam and binder

course

Dense graded bituminous

macadam binder

Dense graded bituminous

macadam binder course 35

Cement concrete pavement


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SPECIFIC GRAVITY AND WATER ABSORPTION(IS 2386 PART 4)

PURPOSE

The specific gravity of an aggregate is considered to be measure ofstrength or quality of the material. Stone having low specific gravity are

generally weaker than those with higher specific gravity values. The

specific gravity is made to use in weight-volume conversions.

CALCULATION

Specific gravity, apparent specific gravity and water

Absorption shall be calculated as follows:

Specific gravity= (dry weight of aggregate)/(weight of equal volume of

water)

Water absorption (percent of dry weight) = % by weight of water

absorbed in terms of oven dried weight of aggregates

DISCUSSION AND APPLICATION

The water absorption test does not always gives reproducible results inaggregates with high porosity.

The specific gravity of coarse aggregates used in road construction

ranges from 2.5 to 3.2 with an avg value of 2.70.

Water absorption is accepted as measure of its porosity. Sometimes

this value is even considered as a measure of its resistance to frost

action though not has been confirmed by adequate research.

Water absorption of about 0.1 to 2.0 percent for coarse aggregates

normally used in road construction.


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SHAPE TEST(IS 2386 part 1)

PURPOSE

The shape of aggregate particle is determined by the percentage of

flaky and elongated particles contained in it. Presence of flaky particles

in the construction is undesirable as they may cause weakness with

possibilities of breaking down under loads.

APPLICATION

In the road construction work MORTH has specified the limits of

flakiness index and elongation index. Though elongated shape of

aggregates also gets broken down under heavy rollers duringcompaction and also during compaction under heavy traffic load.

MORTH has specified the maximum permissible value of combined

flakiness and elongation index of coarse aggregates as 30% for WMM

base course and other

SOUNDNESS TEST

(IS 2386 PART 5)PURPOSE

Soundness test is intended to study the resistance of course and fine

aggregates to weathering action. In the absence of adequate

information the laboratory test simulation accelerated weathering

condition is carried out to judge the durability or the soundness of the

course aggregates.

DISCUSSIONIf the sample contains less than 5% of any of the sizes specified under

procedure that size should not be tested, but for the purpose of testing

it shall be considered to have the loss in sodium sulphate or magnesium

sulphate treatment as the avg of next smaller or next greater size


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APPLICATION

The soundness test is useful to asses the resistance of the aggregates to

weathering. For cement concrete likely to be exposed to the action of

frost, coarse, and fine aggregates should pass an accelerated soundness

test. As a general rule, it may be taken that the avg loss of weight after

10 cycles should not exceed 12% with sodium sulphate and 18% with

magnesium sulphate

Indian road congress has specified maximum permissible loss in weight

in soundness test after 5 cycles as 12% with sodium sulphate and 18%

with magnesium sulphate for the aggregates to be used in bituminous

binder course and surfacing of road pavements.

STRIPPING VALUE(IS 6241)

PURPOSE

Stripping of coated binder or detachment of a portion of bitumen

coating from the aggregate due to the presence of water. So to

measure and deal with this problem test is conducted to calculate

stripping value. The stripping is due to the fact that those aggregateshave higher affinity towards water than bituminous binders and this

displacement of bituminous coating from the aggregates depends on

the physio-chemical forces acting on the system. Most road aggregates

are electrically charged for example silica, a common constituent of

igneous rock posses a weak negative charge and hence have a higher

affinity for polar compounds like water

DISCUSSIONThe stripping value is the ratio of uncovered area observed visually to

the total area of aggregates in each test, expressed as percentage.


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BITUMEN1.Penetration Test

2.Ductility Test

3.Viscosity Test

4.Softening Point Test

5.Flash and Fire Point Test


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PENETRATION TEST(IS 1203)

PURPOSE

Determination of absolute viscosity is not so simple therefore theconsistency of these materials are determined by indirect methods.

Penetration test is indirect method to determine consistency by

measuring the depth to which a standard needle will penetrate

vertically under its own weight. Thus the basic principle of the

penetration test is the measurement of the penetration.

DISCUSSION

It may be noted that the penetration value is influenced by anyaccuracy as regards of following factors

Pouring temperature, size of needle, weight placed on needle, test

temperature, duration of releasing the penetration needle, period of

cooling etc.

APPLICATION

It is most commonly adopted test to determine the grade of the

material in terms of its hardness.Penetration test is empirical test and there is no direct relation to the

fundamental properties of binder.

DUCTILITY TEST(IS 1208)

PURPOSE

It is desirable that the bitumen binders used in the bituminous mixes

form ductile thin films around the aggregates. The binder material

which posses sufficient ductility would crack and thus provide pervious

pavement surface


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DISCUSSION

The ductility value gets seriously affected if any of the following factors

are varied

1.Test temperature2.Pouring temperature3.Diameter of briquette, particularly the cross section at the

minimum width should be 10x10 mm

4. Improper level of briquette placement or the stretched thread ofspecimen touching the top or bottom surface of water bath

5.Rate of pulling6.Period of cooling

APPLICATIONS

A certain minimum ductility is considered essential because of the temp

change in the bitumen mix and the repeated deformations that occur. If

the bitumen is low in ductility pavement may crack and lead to failure.

VISCOSITY TEST(IS 1206 PART I, II, III)

Viscosity of a liquid is the property that retards its flow due to internal

friction and it is a measure of resistance to flow of the liquid. The

viscosity is of two types as

ABSOLUTE VISCOSITY: the ratio between the applied shear stress and

the rate of shear is called the absolute viscosity measured in poise.

KINEMATIC VISCOSITY: it is the ratio of the absolute viscosity to the

density of the liquid, both at the same temperature measured instokes.


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APPLICATIONS OF ABSOLUTE AND KINEMATIC VISCOSITIES

Previously grading of bitumen is done as per the penetration test but

now more rational methods are available to categorize bitumen

material known as VISCOSITY GRADING (VS)

SOFTENING POINT TEST(IS 1205)

PURPOSE

Bitumen does not suddenly change from solid to liquid state, but as the

temperature increases it becomes softer until it flows readily.the

softening point is the temperature at which the substance attains

particular degree of softening under specified condition of test. And asall bitumen mixes are required to be soft and flowable so as to make

possible their mixing with aggregates

DISCUSSION

To ensure the credibility of the test the following conditions should be

taken care of:

1.Quality and type pf liquid in the bath2.Weight of balls3.Distance between bottom ring and bottom base plate4.Rate of heating

APPLICATIONS

Softening point thus gives an idea of the temperature at which the

bituminous material attains a certain viscosity. Bitumen with higher

softening point may be preferred in warmer places.it is also used to

sometimes specify hard bitumens and pitches


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FLASH AND FIRE POINT TEST(IS 1209)

PURPOSE

Flash point test gives an indication of the critical temperature at andabove which suitable precautions should be taken while heating the

bitumen.

FLASH POINT: it is the minimum temperature at which bituminous

binder starts emitting the volatile vapours and these volatile vapours

can momentarily catch fire though the binder does not burn itself.

FIRE POINT: on further heating it is the lowest temperature at which

application of test flame causes the binder material to ignite and burn

atleast for 5 seconds under specified conditions.

Documents

Tests of Soil and Bitumen