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CHAPTER I. I. INTRODUCTION The title of this project is CHARACTERISATION OF PAVEMENT

CONSTRUCTION MATERIALS IN RWANDA

In transportation engineering, characterization of pavement construction materials is very

important because it shows the properties and suitability of pavement construction

materials.

Soil engineering for highways and stone aggregates for pavement design and construction

are used pavement construction materials.

This work is divided into five chapters and each chapter contains a certain number of

sections. Chapter one, which is introduction, it justifies and gives the objectives of the

work and the methodology used to accomplish this work.

After introduction comes literature review in chapter two reviews the elements of soil

engineering, types of pavements, some fundamentals of pavement design and stone

aggregates.

The next chapter three states the different experiments done on the soil sample as raw

material and other done on the stone aggregates. This chapter shows the data collected

during the experiments and its results.

In chapter four, comes the analysis and discussion of the results obtained in chapter three.

In chapter five, there is a conclusion and recommendation.

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I.2. OBJECTIVE OF PROJECT

The project is aimed at determining the suitability of pavement construction materials

from different sources in Rwanda.

I.3. JUSTIFICATION OF THE PROJECT

The pavement construction materials used in road construction must have good properties

such as density plasticity, compressive strength, toughness, hardness.

Contractors are obliged to determine the present properties of the soil sample or

aggregates as raw materials before constructing a road pavement.

After analyzing that the soil or aggregate is poor or weak to be used as a construction

material for road pavement, it is necessary to choose the best soil or aggregates of any

other soil or aggregate having good properties, suitable for road construction.

I.4. METHODOLOGY

Reading books

Visiting websites on internet.

Some laboratory tests are carried out to determine the present properties (suitability) of

soil or aggregates as raw materials.

Those laboratory tests are: Wet sieve analysis, proctor test, atterberg limits(liquid limit

and plastic limit), California bearing ratio(CBR) for soil as raw material and Los

Angeles, specific gravity and water absorption, aggregate impact values and bulk density,

wet sieve analysis for aggregates as raw material.

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CHAPTER II. LITERATURE REVIEW ELEMENTS OF SOIL ENGINEERING

II.1 IMPORTANCE OF SOIL ENGINEERING IN ROAD CONSTRUCTION

Soil is the cheapest and the most widely used material in any highway system,

particularly in non-bituminized roads, either in its natural form (say gravel) or in a

processed form (say stabilized soil layer). Also, all road pavement structures eventually

rest on soil foundation. However, soil are highly heterogeneous and anisotrophic in

nature and occur in unlimited varieties, with widely different engineering properties

which, in turn, can be influenced considerably by the presence of water in several

varieties. Considering all these aspects, a thorough study of the engineering properties of

soils is of vital importance in working out an appropriate design of the pavement

structure which will yield an acceptable level of performance of the road over the design

life under the given traffic and climatic conditions. In any road embankment, the bulk of

the material used is soil and if properly designed, should possess stable slopes and should

not settle to any appreciable extent. Also, the embankments require a stable foundation; if

the foundation soil happens to be soft clay, unless property designed, excessive

settlement or even ultimate failure can take place. Similarly when a road is constructed in

a cutting, sound principles of soil engineering are to be employed to ensure that the

slopes are stable under the climatic conditions prevailing in the area. Finally, the

characteristics of the road pavement i.e. the hard crust placed on the soil formation are

not only dependant on the nature of traffic but also on soil properties over which the

pavement rests. Structure like culverts, bridges, retaining walls, overhead traffic signs etc

also rest on soil and their stability depend on soil strength under the given ground water

and climatic conditions. Precautions against the adverse effects of frost action, common

in high altitude areas, can also be taken, adopting sound principles of soil engineering.

(Dr. B.C PUNMIA, ASHOK KUMAR JAIN, ARUN KUMAR JAIN(1973-74) soil

mechanics and foundation 13th edition) and

(Dr. L.R. Kadyali, Dr. N.B. Lal(2003) Principles and practices of Highway Engineering

(including Expressway and airports Engineering)4th edition)

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II.2. FORMATION OF SOILS

II.2.1. DEFINITION

Soil is defined, for civil engineering purposes, as natural aggregate of mineral grains

that can be separated easily, as for example, by agitation in water. Rock, on the other

hand, is defined as a natural aggregate of mineral grains connected by strong and

permanent cohesive forces and these mineral grains cannot be separated easily as in the

case of soil.

II.2.2 RESIDUAL AND TRANSPORTED SOIL

Soil can broadly be divided on the basis of origin into two groups. In the first group are

the soils obtained as products of physical and chemical weathering of parent rock. If the

products of rock weathering are located at the place of origin, these soils are termed

Residual soils. These residual soils may extend down to hundreds of meters especially

in warm and humid environment where the time of exposure has been long.Moorums,

extensively found in India, Africa and other parts of the world constitute weathered rock,

which may be Lateritic, Granitic etc. And are examples of residual soil. If, however, the

products of rock weathering are transported from the place of origin by transportation

agents which may be water, wind or snow, the soil termed Transported soil. Water

transported soils may be Alluvial, transported by running water; Lacustrine deposited

in lakes and Marine, deposited in sea water. Aeolian soils are transported by wind e.g.

desert dune sands; Colluvial soils are deposited by gravity as in landslides and Glacial

soils are transported by melting snow during glacier movement.

II.2.3. ORGANIC SOILS

Apart from the residual and transported soils are the organic soils which can generally be

distinguished by their characteristic dark colour, strong odour and compressible nature. In

many parts of the world there are huge deposits of organic soils, notable examples being

the peaty swamps of Africa and Muskeg of Canada. Organic soils with very low strength

characteristics make poor construction materials and are not used for road construction

purposes.

(Dr. B.C PUNMIA, ASHOK KUMAR JAIN, ARUN KUMAR JAIN(1973-74) soil

mechanics and foundation 13th edition).

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II.3. PARTICLE SIZE AND SHAPE

A soil is termed Gravel or Sand or Silt or Clay according to its predominant particle size.

To determine the size of soil grains that constitute a soil sample and to determine the total

weight of soil grains in various size ranges, the particle size distribution of soil sample is

to be studied. The simplest method of determining the particle size distribution of a soil

sample is to use a standard set of sieves of different sizes as per IS460. However, sieve

analysis is carried out up to 0.075 mm size only because in sieves of sizes lower than

that, the mesh becomes too small to be effective and sedimentation or hydrometer

analysis has to be resorted to.

In granular (coarse-grained) soils, besides the particle size distribution, the particle shape

also influences the engineering properties. Grains of angular sands and gravels tend to

interlock to provide resistance to deformation.

It is due to the interlocking action that angular particles offer much greater resistance to

deformation under load than rounded particles.

The particle shape can often be inferred from the origin of soil. Wind forms uniformly

graded dune sands with over 75% of their particles falling in the size range between 0.15

and 0.4mm. Gravelly soils formed by flowing water will be rounded as high velocity

water sorts out and abrades the material; lower velocity of water would make it possible

for the material to be deposited as a river terrace material.

While for coarse grained soils, the particle size distribution and particle shape are

related to such engineering properties as permeability, compactibility, and resistance to

deformation under load, it is not so for the fine grained soils (silts and clays).

II.4. SOIL GRADING

Considering the simplicity and expediency, most road agencies carry out the particle size

distribution or soil grading tests as routine tests, using a standard set of sieves.

Conveniently, the results of such sieve analysis are graphically shown as grading curves

plotted on semi-log paper, the particle size or sieve mesh size plotted on horizontal log-

scale while on the vertical axis is the cumulative percentage passing each sieve.

A well graded plot indicates good representation of different particle sizes over a wide

range. Plot of a poorly graded soil indicates either excess or deficiency of certain sizes.

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Uniformly graded and gap-graded plots are examples of poorly graded materials. As may

only be expected, well-graded granular soils are more dense and more resistant to shear

and deformation under compressive stresses than poorly graded soils. It is, therefore, the

objective of mechanical stabilization technique to blend two or more locally available

materials with different particle-size ranges in such a manner as to get a well-graded soil

mix which, after compaction, would give a high density and high strength.

The type of gradation can effectively be gauged by the following:

(i) Effective size (D10) i.e. the diameter at which 10% of soil by weight is finer. D10 is

the approximate diameter of actual spheres that will allow water percolation at a rate

similar to that given by the graded soil for which D10 is the effective size. The coefficient

of permeabilityKis directly related to D10 power 2.

(ii) Uniformity coefficient (u) = D60/D10 where D60 is the diameter at which 60% of soil

by weight is finer and D10 is the effective size. If the ratio U has a value of 1, it implies a

uniformly graded soil or a single-sized soil e.g. a single-sized dune sand. For a well-

graded soil the value of U should be high, say more than 4.

(iii) Coefficient of curvature (Cz) = D30 square/ (D60*D10) where D30 is the diameter at

which 30% of soil by weight is finer and D60 and D10 have already been described above.

The value of Cz signifies the shape (and curvature) of grading curve, also incorporating

in between D60 and D10, an intermediate diameter D30.

For coarse-grained soils, while the particle size distribution and particle shape influence

their engineering behaviour, presence of water hardly affects their properties. In contrast,

fine-grained clay soils are very significantly affected by the presence of water, whereas

particle size distribution and particle shape have very little influence if at all, on their

engineering behaviour.

A soil particle may be either inorganic or organic. Organic soil can be easily

distinguished by their dark colour and odour and are not used as construction materials

and, therefore, need not be discussed in detail. A particle of inorganic soil may either be a

mineral or rock. A mineral may be defined as a naturally occurring chemical element or a

chemical compound having a definite chemical formula, formed as a result of some

geological process. A rock is an aggregate of one or more minerals.

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It is interesting to note that very fine fractions of a mineral show certain properties,

which are quite different from those displayed by coarser ones. To get an appreciation of

this aspect, if a mineral is crushed to different fractions and the finest fraction is shaken

in distilled water, the tiny particles in suspension will take a long time to settle down

under the force of gravity. However, if an electrolyte is added to the suspension, the

particles settle down very fast, thereby showing that there is some force of electric nature

acting on tiny particles which is stronger than the force of gravity. It is observed that finer

the particle size, stronger is this electric force and for particles of 1 micron (1/1000 mm)

size, it can be nearly 1000 times the force of gravity. The platy clay particles are known

to be negatively charged.

II. 5. CONSISTENCY AND PLASTICITY OF FINE-GRAINED SOILS

The properties of fine-grained soil are considerably influenced by its water content

(i.e.), ratio of the mass of water in the soil to the mass of solid soil particles). At

particular water content, the physical state of a fine-grained soil is termed consistency

of soil.

Depending on the water content, a soil may exist in liquid, plastic, semi-solid or solid

state. The three water contents at which the transition takes place for a given fine-grained

soil from liquid to plastic; from plastic to semi-solid and from semi-solid to solid state are

significant in reflecting the properties of the soil.

Liquid limit (LL) is the minimum water content (wl) at which the soil can flow under its

own weight (has no strength). Using casagrande apparatus, it is defined as the moisture

content at which 25 blows (taps) in the standardized liquid limit determination device,

will just close a specific groove in a sample of soil. Another common method for its

determination is the cone penetrometer test method.

Plastic limit (PL) is the minimum water content (wp) at which soil can be rolled into a

thread 3 mm in diameter, without breaking.

Shrinkage limit (SL) is the water content at which further loss of moisture does not

cause a decrease in the volume of the soil.

Plasticity index (PI or Ip) is defined as the water content range over which a soil

exhibits plastic behavior. It is the difference between the liquid and plastic limits of a

soil. PI = LL PL; Ip =wl wp

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II.6. THE NEED FOR SOIL CLASSIFICATION

While dealing with soils, it generally becomes necessary to evaluate some

engineering characteristics like compressibility, strength or permeability etc. With the

wide varieties of different soil types encountered in the actual practice of soil

engineering, it would indeed be very cumbersome and time-consuming to measure the

required soil properties for each of the different soil types one is to deal with. It,

therefore, becomes highly desirable, if not necessary; to classify soil into such groups

where in each group will represent similar engineering characteristics. The particle size

distribution for granular soils and plasticity characteristics for the fine-grained soils offer

simple yet effective parameters for such a grouping or classification of soils.

II.7. COMPACTION OF SOIL

II.7.1. Importance of soil compaction

For highway engineers, a study of the compaction properties of soil is extremely

important for the following reasons:

(i) Soils which are compacted to high density have greater strength and hence a

pavement constructed on such sub grades requires lesser thickness.

(ii) Compaction of soils reduces the possibility of settlement of embankments

during the life of the pavement and of slope failure.

(iii) Compacted sub grades are less susceptible to changes in moisture content.

This means that swelling and shrinkage of soils, accompanying moisture

changes, can be reduced.

II.7.2. Factors influencing compaction

II.7.2.1. The density to which soils can be compacted depends primarily on three

factors:

(i) Soil type

(ii) Moisture content

(iii) Compactive effort applied

II.7.2.2. The density to which soils can be compacted depends on the soil type itself.

For example, for a given compactive energy, gravels, and sands can be compacted to a

dry density of 1.7 2.3 gm per c.c. whereas clays can only be compacted to a dry density

of 1.4 1.8 gm per c.c.

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II.7.2.3. One of the most interesting factors in processing a soil for use in highway

construction is the moisture content. The study of the moisture-density relationships in

soils was pioneered R.R. Proctor in the 1930s. Since then, this subject has found

extensive application in the construction of earth dams and highway embankments.

Proctor showed that for a given soil and a compactive effort, there is one water content,

called the optimum moisture content (OMC), at which the dry density of the soil will be

maximum. At moisture contents both above and below the OMC, the dry density will be

less than the maximum.

The explanation for this phenomenon is fairly simple. At low moisture contents, the soil

is dry and stiff and it is difficult to compress the particles close together. As water is

added, the individual particles get lubricated by the water film, making it easier for the

soil particles to be packed closer together. Density thus increases by the expulsion of air

in the voids. At moisture contents above the optimum, however, the dry density decreases

since an increasing proportion of the total volume is now occupied by water. The dotted

line to the right of the moisture density 3 curves represents the theoretical zero air voids

curve when there is no air at all and the soil is in a state of full saturation; such a state,

however, cannot be attained in actual practice. At zero air voids, the maximum theoretical

dry density is given by (d) max = Gsw / 1+wGs

The general expression for dry density of a soil mass at moisture content w and an

air content A is given by equation:

d= [Gs(1- A) / 1+ wGs]*w

Putting A=0 in the above expression, the value of the maximum theoretical dry density is

obtained.

II.7.2.4. For a given soil, different dry density-moisture content curves are obtained

for different compactive efforts. The dry density-moisture content curves for the same

soil when compacted to light compaction of standard proctor test (using 2.5 kg hammer)

and when compacted to heavy compaction of modified AASHTO test (using 4.5 kg

hammer). As may be seen, a higher compactive effort gives a higher value of maximum

dry density but a lower value of optimum moisture content.

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II.7.3. Tests for compaction

Since various amounts of compactive effort produce varying degrees of

compaction, it becomes necessary to standardize the compactive effort in the laboratory.

This will facilitate comparison of the soil properties and provide a yardstick for

measuring the compaction achieved in the field. In this respect, the test developed by

proctor density.

The test consists of compacting soil in three layers in a mould 1000 cm3 volume.

The rammer used is 2.6 kg and it is dropped from a height of 31 cm on each layer. 25

blows are given to each layer. After the standard compaction, the weight of the specimen

is determined. Knowing the volume of the mould, the wet unit weight is determined. The

moisture content is also determined by drying the sample in an oven. Knowing the wet

unit weight and the moisture content, the dry unit weight is determined. If a series of

readings are obtained with varying moisture content, the moisture content-density

relationship can be determined. Thus the optimum moisture content (OMC) and the

maximum dry density of the soil can be determined.

Another test, which employs a higher compactive effort, is the modified

AASHTO compaction test. The weight of rammer is 10 Ib(4.5kg) and the height of fall is

18 inches (45.7cm). The soil is compacted in five layers, each layer being compacted

with 25 blows. This test is often used in connection with airfield construction and for

heavily trafficked roads.

In order to control the quality of compaction in the field, it becomes necessary to

determine the field density on a large scale. A common method employed is the sand

replacement method. A hole about 100mm dia. And 150mm depth is excavated with

suitable tools to the depth of the layer being tested and the weight of the soil sample

removed and its moisture contents are determined. Sand is run into the hole from a

cylinder and the weight of sand is determined before and after the filling. The different

gives the weight of sand in the hole. From the known weight and bulk density of sand,

the volume of the hole is calculated. Thus, the density of the soil in- situ is determined.

A quick method, often used in control of compaction on a large scale, is by means

of a proctor needle. The apparatus consists of a needle attached to a spring-loaded

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plunger, the stem of which is calibrated to read the density directly. The needle can be

calibrated frequently by testing against standard proctor density in proctor moulds.

A quick method of density measurement in the field is by nuclear method. A

radioactive source is kept on the surface of the soil and it emits gamma rays in all

directions. Except the gamma rays that are emitted in the direction of the soil, all other

rays are completely cut off using sufficient quantity of lead shield. The gamma rays

emitted in the direction of the soil get scattered in the medium in all directions and only

some of them reach a detector placed at a certain fixed distance from the source. The rays

reaching the detector are recorded as counts in a given time and depend on the density of

the soil.

The modern development that has taken place in measuring the compaction of

earthwork is the roller-mounted electronic compaction meter. An accelero-meter rigidly

mounted on the vibrating drum of the roller continuously registers the dynamic forces

which are generated when the roller operates on the ground surface. The signals are

treated in a special processor, which continuously calculates the compaction which can

be directly read on an instrument on the operator`s panel. Since instantaneous results are

monitored, the equipment has been found to be extremely useful.

II.8. SOIL STRENGTH

II.8.1. Importance of soil strength

For a highway engineer, knowledge of the strength of a soil (when considered

under the environmental conditions to which it will be subjected) is extremely important,

since the pavement structure and foundation of structures rest on soils. Basically, the

stability of the pavement and the structures is governed by the strength of soils on which

they rest. Difficulties arise in proper evaluation of the strength because soils are seldom

uniform in character and simulating the field conditions during strength evaluation can

often be problematic.

II.8.2. Factors affecting soil strength

Some of the factors affecting soil strength are:

1. Soil type. Granular soils have generally higher strength than fine-grained soils.

2. Particle size distribution. The size, shape and distribution of the particles

determine the internal friction and cohesion.

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3. Dry density. The degree of compaction of soil governs its strength to a great

extent.

4. Moisture content. The amount of water contained in a soil affects the density, the

cohesion and internal friction of soils.

5. Extent of confinement. Soils like sands exhibit greater strength when confined

than when unconfined.

6. Permeability. The rate of drainage of water as loading takes place affects the soil

strength. The more effective the drainage, the better is the shearing resistance.

II.8.3. Penetration Tests

II.8.3.1. California Bearing Ratio (CBR) Test. The most widely used test for

design of flexible pavements is the California Bearing Ratio test, abbreviated as the CBR

test. The test was originally developed by the California Division of highways by O.J.

Porter and a design methodology was evolved from survey of pavement conditions

carried out in California in 1929. The U.S. Corps of engineers developed the method

further during war. Now most of the countries in the world adopt this standard method.

The test is basically a penetration test, in which the load required to cause a

plunger of standard size to penetrate a specimen of soil at a standard rate is measured.

The test can either be conducted on remoulded specimens or undisturbed

specimens in the laboratory or in-situ on the sub grade soil itself.

For laboratory testing, a phosphor-bronze mould with internal dimensions 150mm

dia. * 175 mm height is used. The mould has a detachable perforated base which can be

fitted at either end. A bronze displacer disc 50 mm deep and 152 mm dia. enables a

specimen exactly 127 mm high to be obtained.

The loading is done by a machine giving a constant rate of strain. If such a machine is not

available, an ordinary hydraulic testing machine is used, provided the rate of penetration

is controlled by a stop watch.

The plunger is standardized with a dia of 50 mm and is placed at the centre of the

mould containing the soil specimen. A dial gauge records the penetration. The vertical

load from the testing machine is noted.

For the in-situ test, a loaded truck is used to provide the reaction and loading is

achieved by a screw jack.

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In other to simulate the surcharge load caused by the pavement layers above the

sub grade soil, annular surcharge weights are placed on the surface of the specimen. As a

rough guide, 10 kg weight is equal to 25 cm pavement.

The specimens have to be prepared with great care. Undisturbed specimens can be

obtained by fitting a cutting edge to the mould and pushing the same into the ground as

gently as possible. The sample is then trimmed. For preparing remoulded specimens,

static or dynamic compaction processes can be used. Static process is preferred. The

volume of the mould being 2244 c.c., the weight of the wet soil at the required moisture

content to give the intended density is calculated as following:

Volume of mould: 2244 c.c.

Weight of dry soil: 2244 d.

Weight of wet soil: [(100 + m)/100]*2244d

Where d = required dry density in gm/c.c.

m = required moisture content (per cent)

If dynamic compaction process is used, the soil is compacted in three layers by

using a standard rammer.

The selection of the density and moisture content is crucial for the test. For new

roads, the specimens should be compacted to a dry density corresponding to the

minimum state of compaction likely to be achieved in the field. Current standards require

that the sub grade should be compacted to 100 per cent proctor density, and hence this

density may be used for the test. The choice of the moisture content is not simple.

The recommended practice for new roads is to prepare the samples at the optimum

moisture content corresponding to proctor compaction and soak them for 4 days prior to

testing. For existing roads requiring strengthening, the moisture content should be the

field moisture content, preferably after rains. The density of the specimens should in such

cases be the field density. The field moisture content and density are determined at a

distance of 0.6 to 1m from the pavement edge below the pavement.

The procedure of soaking is dispensed with for:

(i) Road having a comparatively thick bituminous surfacing of

impermeable nature (other than open graded carpet, surfacing, dressing

or grouted macadam) and where simultaneously water table is too deep

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(greater than 1m in sands, 3 m in sandy clays and 6 m in heavy clays)

and good drainage exists.

(ii) Roads in arid zones having rainfall less than 50 cm annually. Some

authorities now propose that the CBR test should be conducted on

samples compacted at Equilibrium Moisture Content (EMC). The EMC

is determined from considerations such as the depth of water table,

pore water pressure, applied stress due to pavement and soil suction.

The loading is done at a rate of 1.25mm/ minute. The loads at 2.5 mm and 5 mm

penetration are recorded. A load-penetration curve is drawn. A correction is needed for

curves curving concave upwards. The loads for penetration of 2.5mm and 5 mm are

noted. For standard crushed stones, loads of 6.895 MN/m2 and 10.343 MN/m2 cause the

above penetrations respectively (see fig. below). The CBR value is expressed as a

percentage of the actual load causing the penetrations of 2.5 mm or 5 mm to the standard

above mentioned loads, respectively.

Thus:

CBR= [Load carried by specimen/Load carried by standard crushed stone specimen]*100

Two values of CBR will thus be obtained. If the value at 2.5 mm is greater than that at

5 mm penetration, the former is adopted. If not, the test is repeated and if the new value

of load at 5 mm penetration is still greater, this value is used for the calculation of the

CBR.

II.9. TYPES OF PAVEMENTS II.9.1. Functions and desirable characteristics of pavements

A highway pavement is designed to support the wheel loads imposed on it from

traffic moving over it. Additional stresses are also imposed by changes in the

environment. It should be strong enough to resist the stresses imposed on it and it should

be thick enough to distribute the external loads on the earthen sub grade, so that the sub

grade itself can safely bear it.

For satisfactorily performing the above functions, the pavement should have many

desirable characteristics.

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These are:

1. It should be structurally sound enough to withstand the stresses imposed on it.

2. It should be sufficiently thick to distribute the loads and stresses to a safe value

on the sub grade soil.

3. It should provide a reasonably hard wearing surface, so that the abrading action

of wheels (pneumatic and iron-tyred) does not damage the surface.

4. It should be dust-proof so that traffic safety is not impaired.

5. Its riding quality should be good. It should be smooth enough to provide

comfort to the road users at the high speeds at which modern vehicles are

driven.

6. The surface of the pavement should develop as low a friction with the tyres as

possible. This will enable the energy consumption of the vehicles to low.

7. The surface of the pavement should have a texture and adequate roughness to

prevent skidding of vehicles.

8. The surface should not produce excessive levels of sound from moving

vehicles.

9. The surface should be impervious so that water does not get into the lower

layers of the pavement and the sub grade and cause deterioration.

10. The pavement should have long life and the cost of maintaining it annually

should be low.

Some of the requirements enumerated above are conflicting. A good pavement

should be a compromise among such conflicting needs.

II.9.2. Pavement courses

A pavement consists of one or more layers. The topmost layer is the surfacing,

the purpose of which is to provide a smooth, abrasion resistant, dust free,

reasonably water proof and strong layer. The base, which comes immediately

next below, is the medium through which the stresses imposed are distributed

evenly. Additional help in distributing the loads is provided by the sub-base

layer. The sub grade is the compacted natural earth immediately below the

pavement layers. The top of the sub grade is also known as the formation level.

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In a concrete road, the concrete slab itself acts as the wearing surface and

distributes the load. The slab may be directly placed on the sub grade, or, in

case of weak soils, a base and sub-base may be interposed between the slab and

the sub grade.

In American practice, the top course in a flexible pavement is itself composed

of the surface course and a binder course beneath it. In U.K. practice, the

surfacing is similarly composed of the wearing course at top and a base course

beneath it.

The functions of the sub-base layer are:

(i) To provide additional help to the base and surface courses in

distributing loads.

(ii) To prevent intrusion of fine-grained road-bed soils into base courses.

(iii) To minimize the damaging effects of frost action.

(iv) To facilitate drainage of free water that might get accumulated below

the pavement.

The functions of the base course are:

(i) To act as the structural portion of the pavement and thus distribute the

loads.

(ii) If constructed directly over the sub grade, to prevent in intrusion of sub

grade soils into the pavement.

The functions of the surface course are:

(i) To perform as a structural portion of the pavement.

(ii) To resist the abrasive forces of traffic.

(iii) To reduce the amount of surface water penetrating the pavement.

(iv) To provide a skid-resistant surface.

(v) To provide a smooth and uniform riding surface.

II.9.3. Pavement types

III.3.1. From the point of view of structural performance, pavements can be

classified as:

(i) Flexible (ii) Rigid

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(iii) Semi-rigid (iv) Composite.

A flexible pavement is essentially a layered system which has low flexural strength.

Thus, the external load is largely transmitted to the sub grade by the lateral distribution

with increasing depth. Because of the low flexural strength, the pavement deflects

momentarily under load but rebounds to its original level on removal of load. The

pavement thickness is so designed that the stresses on the sub grade soil are kept within

its bearing power and the sub grade is prevented from excessive deformations. This

implies that in a flexible pavement, the sub grade plays an important role as it carries the

vehicle loads transmitted to it through the pavement. The strength and smoothness of the

pavement surface depends to a great extent on the permanent deformation suffered by the

sub grade and its resistance to such deformation. If the pavement itself is very strong, but

it is constructed on loose and poor sub grade, it can fail.

As a contrast, a rigid pavement derives its capacity to withstand loads from flexural

strength or beam strength (modulus of elasticity), permitting the slab to bridge over minor

irregularities in the sub grade, sub-base or base upon which it rests. This implies that the

inherent strength of the slab itself is called upon to play a major role in resisting the

wheel load. Minor imperfection or localized weak spots in the material below the slab

can be taken care of the slab itself. This is not to under-rate the role of the sub grade soil.

In fact, a good, stable and uniform support is necessary for a rigid pavement as well. But

as long as a certain minimum requirement is met with in this regard, the performance of

the rigid pavement is more governed by the strength of the slab itself than by the sub

grade support.

A third category of pavements has become popular during recent times. Known as

semi-rigid pavement, it represents an intermediate state between the flexible and the rigid

pavement. It has much lower flexural strength compared to concrete slabs, but it also

derives support by the lateral distribution of loads through the pavement depth as in a

flexible pavement. Typical examples of a semi-rigid pavement are the clean-concrete

base, soil-cement and lime-puzzalona concrete construction.

A composite pavement is one which comprises of multiple, structurally significant

brick-sandwiched concrete pavement, which has been tried in India. It consists of top and

18

bottom layers of cement concrete which sandwich a brick layer in the neutral axis zone.

The design of composite pavements lies outside the well-established fields of flexible or

rigid pavement design and is still in its infancy.

III.3.2. A very frequent term in highway engineering practice in developing countries is

low-cost pavements. These pavements represent specifications involving the use of

locally available materials, often with stabilization techniques.

III.3.3. Another distinction in pavement description is between paved and unpaved

and surfaced and unsurfaced. The exact definition of these terms is lacking. One

often uses the terms paved roads to mean a road which has at least a stone-aggregate

course laid over the sub grade. The stone-aggregate course may be left bare without any

bituminous surfacing in which case the road, though paved, is unsurfaced. An

unpaved road is one which has only gravel or earthen surface. A surfaced road is one

which has a bituminous or concrete surface. In contrast,unsurfaced roads are those

which have no bituminous or concrete surfaces.

II.10. STONE AGGREGATES II.10.1. Aggregates

II.10.1.1. Aggregate is the major component of materials used in road making. It used in

granular bases and sub-bases, bituminous courses and in cement concrete pavements. A

study of the types of aggregates, their properties and tests is of great-importance to a

highway engineer.

II.10.2. Types of aggregates

Natural aggregate for road-making are obtained from rock. The road-making aggregates

fall into the following geological groups:

1. Igneous rocks, which are formed by the cooling of molten material.

2. Sedimentary rocks, which are formed by deposition of granular

material.

3. Metamorphic rocks, which are igneous or sedimentary rocks that

have undergone transformations due to heat and pressure.

(Dr. L.R. Kadyali, Dr. N.B. Lal(2003) Principles and practices of Highway Engineering

(including Expressway and airports Engineering)4th edition).

19

II.10.3. Testing of aggregates

The tests required to be conducted on representative samples of aggregates depend on the

specific use in a road pavement, so as to ensure that they meet the specified requirements

laid down for that specific use. First and foremost, it needs to be emphasized that the

repeatibility and reproducibility of test results depend primarily on the sampling. A

laboratory sample is obtained from a bulk sample collected, either in a number of

increments or in one go, from a batch or a stockpile. Samples are normally collected

using a samples which is in the form of metallic tube or a scoop whose opening is 3 times

the maximum aggregate size. Sampling of aggregates is sometimes done at various

production sources in order to avoid the segregates is sometimes done at various

production sources in order to avoid the segregation which occurs in stockpiles. Some of

the sampling procedures followed are:

1. Sampling from stationary conveyor belt.

2. Sampling at belt and chute discharge points.

3. Sampling from stockpiles

4. Sampling from railway wagons, transporting dumpers/trucks etc.

A sample collected for testing purposes has to be reduced in size to prepare laboratory

samples. The aggregates are quartered either manually or by using riffle boxes.

Some common laboratory tests are:

- Water absorption and bulk specific gravity

- Particle size distribution

- Aggregates Impact value

- Los Angeles Abrasion value and Bulk density.

II.10.3.1. Particle size distribution or gradation of aggregates.

Maximum size of aggregate is the mesh size of the smallest sieve through which 100%

of material will pass. Nominal maximum size is the largest specified sieve size upon

which any of the aggregate material is retained.

Gradation analysis of both coarse and fine aggregates is carried out by

sieving, using standard set of sieves.

20

Dry sieve analysis is generally suitable for the testing of graded coarse

aggregates. However, when the aggregate contains fine dust or clay sticking to the

coarser aggregate particles, a wet/washed sieve analysis should be carried out.

Maximum size and grading of aggregates are invariably controlled by the

specifications, which describe the distribution of particle sizes to be used for a particular

work.

II.10.3.2. Water absorption and bulk specific gravity tests.

These two tests are conducted together. The specific gravity of aggregates is an

indirect measure of its strength. The higher the specific gravity, the denser the rock is and

stronger is the aggregate. Similarly, water absorption depends on the pores and voidage

in the rock. The more the water absorption, the higher the voidage. Some rocks are

adversely affected in their strength when water enters the material and softens it. Laterite

is a good example.

The test is performed by immersing in distilled water a sample (2-3 kg) of

aggregates enclosed in a wire-mesh container for 24 hours. The container with the

aggregates is weighed when immersed in water, thus giving its buoyant weigh (W1). The

material is then surface dried and weighed in air, giving the saturated weight (W2).

Thereafter the material is oven dried at a temperature 100-110 C and the dry weight

determined (W3).

The percentage of water absorption = 100* [(W2-W3)/W3]

Bulk specific gravity of aggregates= Dry weight of aggregates/Volume of

aggregates. = W3/Volume of displaced water. = W3/ (W2-W1), since Sp. Gravity of water

= 1

It is seen that bulk specific gravity of aggregates varies from 1.9 to 3.0. Those with

values above 2.5 are generally good. Aggregates having water absorption above 1.0 per

cent are unsatisfactory, for use in wearing courses while those having water absorption

over 2.0 per cent are considered unsatisfactory for use in base courses.

II.10.3.3. Aggregate Impact Test.

This is a test designed to evaluate the resistance of an aggregate to sudden impact. Since

vehicle loads cause impact, this test gives an indication of the performance of aggregates

to resist crushing under impact.

21

The test consists of subjecting a specimen of aggregates (passing 12.5 mm sieve

and retained on 10 mm sieve) filled into a cylindrical mould 10.2 cm internal dia and 5

cm height. The impact is provided by dropping a hammer of weight 13.5-14.0 kg through

a height of 380 mm. Aggregate passing fully through 12.5 mm sieve and retained on 10

mm sieve are filled in the cylindrical measure in three layers, each layer being given 25

strokes with a rod. The sample is then transferred to the cup of the aggregate impact

testing machine and tapped 25 times with the rod.

After subjecting the specimen to 15 blows through the hummer, the crushed

aggregate is sieved on 2.36 mm sieve. The weight of materials passing through this sieve

expressed as a percentage of the total weight of the sample gives the aggregate impact

value.

The test is conducted in dry state as well as in wet state. For low-grade aggregates,

a maximum of 50 per cent wet aggregate impact value is allowed when used in sub-base.

When used as base course, the limit is 40 per cent. For surfacing courses, the limit is 30

per cent.

II.10.3.4. Los Angeles Abrasion Test.

This is a very popular test for measuring the abrasion resistance of aggregates. The top

layers of a pavement get abraded due to the movement of tyres. A material which is

highly abrasion resistant has a long life.

The machine consists of a circular drum of internal diameter 700 mm and length

500 mm mounted on a horizontal axis enabling it to be rotated. An abrasive charge

consisting of cast iron spherical balls of 48 mm dia. and weight 390-445 gm is placed in

the cylinder along with the aggregates. The weight and number of the abrasive spheres

varies according to the grading of the sample. The quantity of aggregates to be used

depends upon the gradation and is 5-10 kg. The cylinder is rotated at a speed of 30-33

revolutions per minute; for 500-1000 revolutions (depending upon the material). After the

specified revolutions, the material passing through 1.7 mm size sieve is separated. The

weight of this material (fines) expressed as a percentage of the total weight of the sample

is known as the Los Angeles Abrasion Value. For WBM base course, a maximum value

of 40 per cent is allowed. For bituminous courses, a maximum of 30 to 35 per cent is

specified.

22

CHAPTER III. METHOLOGY and EXPERMENTS DONE SOIL MECHANICS LABORATORY

III. 1. STANDARD COMPACTION TEST (Proctor test method)

In soil mechanics laboratory, I carried out experiments on two different samples: Laterite

of Karongi mountain and volcanic ash of Nkamira that deal with the properties of soil

and their behavior under stress. Some experiments are: Standard compaction test

(Proctor), Atterbarg Limits, Sieve Analysis, and California Bearing Ratio.

III. 1. 0. Definition:

Compaction proctor is the method of compaction where compactive amount of

mechanical energy is applied to the soil mass. We applied the tamping method using

standard hummer developed by R.R Proctor in 1933 hence the origin of name the

Proctor test.

III. 1. 1. Brief description

In laboratory, we determined the following data:

M2 (weight of mould + base + compacted soil in grams) M1 (weight of mould + base in grams)

III. 1. 2. Objective

This test is done to determine the quantity of water to be added in the sample for field

compaction of sub grade soil and resulting density expected. (Optimum moisture content

and maximum dry density)

Also here the standard proctor compaction method was used, and is commonly applied

where low density is required the more especially in laboratories.

III. 1. 3. Apparatus

Mould Standard hammer Straight tape Scoop Electronic balance Measuring cylinder for water Plate for mixing Sieves

23

Shaker machine Specimen. Soil (4000g) and water (2% of the soil sample)

III. 1.4. Procedures

1. We measured 4000g of dry soil and poured it in a mixing plate.

2. We determined the weight of the soil sample as well as the weight of the

compaction mould with its base and the collar by the use of electronic balance and

masses were recorded.

3. We computed the initial water (2 % of soil) to be added in the sample.

4. We measured out the water, then, added it in the soil and then mixed it thoroughly

into soil by hands until soil got a uniform color.

5. We assembled the compaction mould and the color plate as well to the base; we

placed the wet soil into the mould in three layers and compacted with 25 blows

each layer. The blows were applied at a uniform rate not exceeding 1.5 seconds

per blow.

6. The soil was completely filled into the cylinder and the last compacted layer had

to exceed up to the collar at least 6mm if not, the sample was not sufficiently

compacted and had to be repeated.

7. After compaction, we removed the collar plate and trimmed off the soil using the

straight edge until the top of the mould and leveled accurately. Where necessary,

the gaps left were filled with some soil.

8. We weighed the compacted sample while it was still in the mould with the base,

then we recorded the mass. We also determined the weight of the wet sample by

subtracting the weight of the mould and base.

9. We removed the soil from the mould and took the sample for moisture content,

that is, from both top and the bottom of the sample. We put them in different

moisture cans and put them in the oven for 24 hours.

10. We placed soil specimen in large tray and broke up the soil until it appeared

visually as if it would pass through 4 sieve (75mm), we added 2% more water of

the original mass of sample, and remixed as in steps 4, repeated the steps 5 up to

9. Based on the wet mass a peak value was reached followed by lesser compacted

soil masses.

24

III.1.5. Data analysis

i. We calculated the moisture content of each compacted soil specimen by

computing the average of the five moisture contents.

ii. We computed the wet density in grams per cubic cm of the compacted soil

sample by dividing the wet mass by the volume of the mould used.

iii. We computed the dry density using the wet density and the water content

determined in step 1, using the following formula : d= p/1+w

Where wet density in grams per cubic cm

W moisture content in percent divided by 100.

iv. We plotted the dry density values on Y- axis and the moistures on X- axis.

Then using excel, we draw a smooth curve connecting the plotted points as the

graph shows.

v. We identified and reported the optimum moisture content and the maximum

dry density on the data sheet, by the use of standard proctor test method.

25

Data and results

For Laterite of Karongi mountain

Test number 2 % 4% 6% 8% 10%

Wt of mould + base +

compacted soil (m2)

5726 5785.3 5806.5 5754.2 5712.7

Wt of mould + base (m1) g 3604 3604 3604 3604 3604

Wt of compacted soil (m2-m1) 2122 2181.3 2202.5 2150.2 2108.7

Bulk density = (m2-m1)/1000

Mg/m3

2.122 2.1813 2.2025 2.1502 2.1087

Moisture content container no 71 78 48 73 40

Wt of wet soil + container (m4)

g

94.4 97.9 115.2 116.7 116.2

Wt of dry soil + container (m5)

g

94.1 95.7 110.8 111.6 110.1

Wt of container (m3) g 69.6 68.4 70.2 67.4 70.2

Wt of moisture (m4-m5) g 0.3 2.2 4.4 5.1 6.1

Wt of dry soil (m5-m3) g 24.5 27.3 40.6 44.2 39.9

Moisture content

W= [(m4-m5)/ (m5-m3)]*100

7.65 8.06 10.84 11.54 15.3

Dry density pd = 100p/100+w

Mg/m3

1971 2019 1987 1928 1829

Table III.1 : Proctor data of Karongi mountain (laterite)

26

Moisture

Dry

density

content(%) Kg/m3

5.2

1931

8.1 2019

10.8 1987

12.5 1928

15.3 1829

Maximum Dry Density(MDD)=2020 Kg/m3

Optimum Moisture

Content(OMC)8.8%

Fig.III.1. Proctor curve of Karongi mountain soil(laterite)

27

For volcanic ash of Nkamira

Test number 2% 4% 6% 8% 10% 12% 14% 16% Wt of mould + base + compacted soil (m2) g

5007.2 5034.6 5069.2 5106.7 5189.9 5245.8 5323.2 5364.9

Wt of mould + base (m1) g

3604 3604 3604 3604 3604 3604 3604 3604

Wt of compacted soil (m2-m1) g

1403.2 1430.6 1465.2 1502.7 1585.9 1641.8 1719.2 1760.9

Bulk density = (m2-m1)/1000 Mg/m3

1.4032 1.4306 1.4652 1.5027 1.5859 1.6418 1.7192 1.7609

Moisture content container no.

36 42 47 45 51 57 74 28

Wt of wet soil + container(m4) g

92.9 88.5 92.1 97.8 92.2 95 103.9 127.1

Wt of dry soil + container (m5) g

91.4 86.9 89.7 94.6 89.0 91.2 98.0 116.6

Wt of container (m3) g

71.3 69.3 69.1 70.7 68.9 69.9 69.4 69.9

Wt of moisture (m4-m5) g

1.5 1.6 2.4 3.2 3.2 3.8 5.9 10.5

Wt of dry soil (m5-m3) g

20.1 17.6 20.6 23.9 20.1 21.3 28.6 46.7

Moisture content w= (m4-m5)/ (m5-m3)*100 %

7.5 9.1 11.65 13.4 16 18 20.63 22.5

Dry density pd= 100p/100+w Mg/m3

1305 1311 1312 1325 1367 1391 1425 1437.5

Table.III. 2 : Proctor data of Nkamira (Volcanic ash)

28

Moisture

Dry

density

content (%) Kg/m3

16

1367

20.6 1425

22.5 1437

26.5 1391

Maximum Dry Density(MDD)=1438 Kg/m3

Optimum Moisture Content(OMC)22.0% Fig.III.2. proctor curve of Nkamira volcanic ash

III. 2. ATTERBERG LIMITS

III.2.0. Aim of the experiment

This experiment is performed to determine the plastic and liquid limits of a fine grained

soil.

III.2.1 Brief description

In engineering practice, the liquid and plastic limits are commonly used:

- The atterberg limits are based on the moisture of soil

- The plastic limits is the moisture content that defines where the soil changes from

a plastic to viscous fluid states.

- Atterberg limits are also used to classify a fine grained soil according to the

unified soil classification syste.

29

III.2.2. LIQUID LIMIT

III.2.2.0. Definition

The liquid limit is defined as the water content, in percent at which a paste of soil in a

standard cup by a groove of standard dimensions will flow together at the box of the

groove for a distance of 13mm, when subject to 25 blows from the cup being dropped

10mm in standard liquid limit apparatus operated at a rate of two flows per second.

III.2.2.1. Objective

To determine the liquid limit of a soil sample.

III.2.2.2. Equipments

- Casagrande apparatus

- Groove tool

- Spatula

- Drying oven (electrical oven)

- Balance

- Glass plate

- Wash bottle + distilled water - 425m sieve (I.S sieve)

- Mixing dishes

III.2.2.3. Procedures

- The sample of air dried soil from thoroughly mixed portion of material passing 425m I.S sieve is to be obtained.

- Distilled water is mixed to the soil thus obtained in a mixing disc to form uniform

paste. The paste shall have a consistency that would require 30 to 35 drops of cup

to cause closer of standard groove for sufficient length.

- A portion of the paste is placed in the cup of liquid limit device (casagrande

apparatus) and spread into portion with few strokes of spatula.

- Trim it to a depth of 1cm at the point of maximum thickness and return excess of

soil to the dish.

- The soil in the cup shall be divided by the firm strokes of the grooving tool along

the diameter through the center line of the can follower so that clean sharp groove

of proper dimensions is formed.

30

- Lift and drop the cup by turning crank at the rate of 2 revolutions per second until

the two halves of soil cone in contact each other for a length of about 10mm by

flow only.

- The number of blows required to cause the groove chose for about 10mm shall be

recorded.

- A representative portion of soil is taken from the cup water content determination.

- The test was repeated with different moisture content at least three more times for

blows between 10 and 40.

III.2.2.4. Data analysis

Liquid limit test No 1 2 3

No. of blows 41 29 19

No. of container (g) 48 45 36

Wt. of wet soil + container (g) 99 93.9 96.6

Wt. of dry soil + container (g) 94.1 89.7 91.7

Wt. of container (g) 70.2 70.7 70.9

Wt. of moisture (g) 4.9 4.2 4.9

Wt. of dry soil (g) 23.9 19 20.8

Moisture content % 20.5% 22.1% 23.56% Table.III. 3 : Liquid limit of Karongi mountain (laterite)

31

Blows Liquid

limit

41 20.5

29 22.1

19 23.6

LL=22.8%

PL=13.9%

PI = 8.9% Fig.III.3. Liquid limit graph of Karongi mountrain soil(laterite)

III.2.3. PLASTIC LIMIT TEST

III.2.3.0. Definition:

The plastic limit of soil is defined as the water content at which the soil begins to crumble

when rolled into a thread 3mm in diameter.

III.2.3.1. Objective

The plastic limit test is used to determine the lowest moisture content at which the soil

behaves plastically it is carried out only on the soil fraction passing sieve number 40 i.e

(425m) and is usually performed in the conjunction with the liquid limit test.

III.2.3.2. Equipments

- Surface for rolling the thread such as a glass or plastic plate or smooth lineleneum

table top

- Short metal rod of 3mm diameter

- Spatula with a blade about 10cm long and about 2cm wide

- Specimen container (moisture can) for determination of water content.

- Balance sensitive to 0.01g

32

- Hair dryer and drying oven.

III.2.3.3. Procedures - Take sample thoroughly mixed portion of the material passing through 425m I.S

sieve obtained in accordance with I.S 2720

- Mix it thoroughly with distilled water in the evaporating dish (glass plate) until

the soil mass becomes plastic enough to be easily moulded with fingers.

- Allow it to season for sufficient time (24hrs) to allow water to penetrate

throughout the soil mass.

- Take small sample of this plastic soil mass and roll it between fingers and glass

plate with just sufficient pressure to roll the mass into a thread of uniform

diameter throughout its length. The rate of rolling shall be between 60 and 90

strokes per minutes.

- Continue rolling until you get a thread of 3mm diameter

- Kneel the soil together to a uniform mass and re-roll.

- Continue the pieces of the crumbled thread in air tight container for moisture

content determination.

- Repeat the test to at least 3 times.

- Take the average of the results calculated to the nearest whole number.

III.2.3.4. Data presentations

PLASTIC LIMIT (PL)

Container No 39

Mass of wet soil + container (m2) 86.8

Mass of container (m1) 77.8

Mass of dry soil + container (m3) 85.7

Mass of dry soil (m3-m1) 7.9

Mass of moisture (m2-m3) 1.1

Moisture content W= [(m2-m3)/ (m3-m1)] * 100 13.9 % Table .III.4 : Plastic limit data of Karongi mountain (laterite)

33

III.2.3.5. Computation

The plastic limit (PL) is reported as the above of two similar values. If it is not

possible to obtain a plastic limit in the plastic limit test, the soil is reported as non-

plastic. This also applies if PLLL. Errors in computing the liquid limit or plastic

limit can be detected by plotting the point (LL, PL) on the plasticity chart. This

should fall under the U-line.

Plasticity index of the sample = Liquid Plastic limit

Plasticity index = 22.80-13.9 = 8.9%

III.3. SIEVE ANALYSIS III.3.0. Introduction

The desired sand for a particular work should be selected by Engineering charge of

work site considering three main aspects: quality, availability and cost; because of a

good sand quality consumes less cement and makes the structure strong and durable

keeping maintenance cost low.

Sieve analysis should be made and the fineness modulus of sand should be found out.

It is to be seen whether the sand contains grains of different grades to make a good

mortar. It is also a great important to find whether the sand can be improved by

screening out or by adding the fine or coarse particles of sand.

III.3.1. Objective

The objective of this experiment is to determine the sand size and to know in which

category the sand can be classified.

III.3.2. Apparatus

In sieve analysis of sand we can use different apparatus such as:

1. Sieves: for taking different sizes of sand according to the size of the sieve.

2. Plat form balance: for measuring the sample of the sand.

3. Tray: for taking the sample from the scoop.

4. Shake Machine: for shaking the sand which is in the sieve in order to pass through

them.

5. Scoop: for carrying the sample which is going to be tested.

6. Timer/watch: for regulating the required time to be used (10 minutes)

34

III.3.3. Setting of sieves

In setting of sieves; you can use upward or downward method:

Upward Downward

Pan 20.0mm

75m 14.0mm

150m 10.0mm

300m 4.75mm

425m 2.36mm

600m 1.18mm

1.18mm 600m

2.36mm 425m

4.75mm 300m

10.0mm 150m

14.0mm 75m

220.0mm Pan

III.3.4. Procedures

1. Preparation of the sample by putting it in the oven leaves it for 24 hours at 105oC

to 110oC.

2. Setting the sieves.

3. Fitting the sieve set to the shaken machine.

4. Weighing a certain quantity of sand sample.

5. Purring the sample at the top sieve and fix the top cover.

6. Starting the shaker machine (5 minutes for electrical machine and 10 minutes for

hand operated machine).

7. Weighing each quantity of the sand retained on each sieve.

35

III.3.5. Results

By taking 100g of the sample before testing; the results are reported in the common

table as following:

Sample of laterite (of Karongi mountain)

Test Sieve Mass retained Percentage

retained

Percentage passing

20.0mm - - -

14.0mm - - -

10.0mm - - 100

4.75mm 6.8g 6.8g 93.2g

2.36mm 8.5g 8.5g 84.7g

1.18mm 4.9g 4.9g 79.8g

600m 4.0g 4.0g 75.8g

425m 3.3g 3.3g 72.5g

300m 6.1g 6.1g 66.4g

150m 18.1g 18.1g 48.3g

75m 10.6g 10.6g 37.7g Table.III. 5 : Sieve analysis data of Karongi mountain (laterite)

36

Sieve

size %Passing

Mm

14 100

10 100

4.75 93.2

2.36 84.7

1.18 79.8

0.6 75.8

0.425 72.5

0.3 66.4

0.15 48.3

0.075 37.7

Fig.III.4. Sieve graph of Karongi mountain soil(laterite)

Sample of volcanic ash of Nkamira

Test Sieve Mass retained Percentage

retained

Percentage passing

20.0mm - - -

14.0mm - - -

10.0mm - - 100 g

4.75mm 1.3 g 1.3 g 98.7 g

2.36mm 4.4 g 4.4 g 94.3 g

1.18mm 3.7 g 3.7 g 90.6 g

600m 3.4 g 3.4 g 87.2 g

425m 2.6 g 2.6 g 84.6 g

300m 7.3 g 7.3 g 77.3 g

150m 25.1 g 25.1 g 52.2 g

75m 21.4 g 21.4 g 30.8 g Table.III. 6 : Sieve analysis data of Nkamira (volcanic ash)

37

Sieve

size %Passing

Mm

14 100

10 100

4.75 98.7

2.36 94.3

1.18 90.6

0.6 87.2

0.425 84.6

0.3 77.3

0.15 52.2

0.075 30.8

Fig.III.5.Sieve graph of Nkamira volcanic ash

III.4. THE CALIFORNIA BEARING RATIO (CBR)

III.4.0. Definition:

It is the ratio of the force per unit area required to penetrate a soil mass with standard

circular piston at the rate of 25mm/min. to that required for corresponding penetration

of a standard material.

CBR= [Test load/Standard load]*100.

III.4.1. Scope

The California Bearing Ratio test is penetration test meant for the evaluation of sub grade

strength for roads and pavements. The results obtained by these tests are used with the

empirical curves or charts to determine the thickness of pavement and of its component

layers. This is the most widely used method for the design of flexible pavement.

38

III.4.2. Apparatus

- Moulds

- Extension collar

- Perforated base plate

- Spacer disk

- Rammer

- Swell plate

- Tripod support

- Two dial indicators

- Surcharge weight

- Penetration piston

- Loading device

- Soaking tank

- Drying oven

- Mixing pans

- Spoons

- Straightedge

- Filter paper

- Balance

III.4.3. Sample

Prepare a sample in accordance with AASHTO 99.Material passing the 50mm sieve and

retained on the 19mm sieve shall be replaced with material passing 19mm and on the

4.75mm. Select a representative portion weighing approximately (4 kg) for moisture

density test and divide the remainder of the sample to obtain 3 representative portions.

III.4.4. Procedures

1. Normally 3 specimens must be compacted so that their compacted densities range.

2. Clamp the mould to the base plate, attach the extension collar and weigh to the

nearest 5 gr. Insert the spacer disk into the mould and place a coarse filter paper

on top of the disk.

3. Mix each of the three (4kg) portions prepared with sufficient water to obtain the

optimum moisture content determined.

39

4. Compact one of the portions of soil-water mixture into the mould in three equal

layers to give a total compacted depth of about (127mm) compacting each layer

with the lowest selected number of blows in order to give a compacted density of

95 percent or less of the maximum density.

5. Determine the moisture content of the material being compacted at the beginning

and end of the compaction procedure. Each moisture sample shall weigh at least

100g for fine grained soils and 500g for coarse grained soils.

6. Remove the extension collar, and using a straightedge, trim the compacted soil

even with the off the mould. Surface irregularities should be patched with small

sized material. Removed the spacer disk, place a coarse filter paper on the

perforated base plate, invert the mould and compacted soil and place on the filter

paper so the compacted soil is in contact with the filter paper. Clamp the

perforated base plate to the mould and attach the collar. Weigh the mould and

specimen to the nearest 5gr.

7. Compact the other two (4kg) portions in accordance with the procedure in the step

4 through steps 6 except that an intermediate number of blows per layer should be

used to compact the second specimen and the highest number of blows per layer

shall be used to compact the third specimen.

III.4.5. Soaking

Place the swell plate with adjustable stem on the soil sample in the mould and apply

sufficient annular weights to procedure an intensity of loading equal to the mass of

the sub base and base courses and surfacing above the tested material.

Place the tripod with dial indicator on top of the mould and make an initial dial

reading. Immerse the mould in water to allow free access of water to top and bottom

of the specimen.

During soaking, maintain the water level in the mould and the soaking tank

approximately (25.4mm) above the top of the specimen. Soak the specimen 96 hrs

(4days).

At the end of the 96hrs make a final dial reading on the soaked specimen and

calculate the swell as a percentage of the initial sample length:

Percent swell = {change in length in during soaking/4.584in}*100.

40

Remove the specimens from the soaking tank, pour the water off the top and to drain

down ward for 15min. Care shall be taken not to disturb the surface of the specimens

during removal of the water. After draining, remove the surcharge weights and

perforated plate.

III.4.6. Penetration test

Application of surcharge: Place a surcharge of annual and slotted weights on the

specimens equal to the used during soaking. To prevent displacement of soft

materials into the hole of the surcharge weights, seat the penetration piston after one

surcharge weight has been placed on the specimen. After seating the penetration

piston the remainder of the surcharge weights shall then be place around the piston.

DETERMINATION OF PRESENT MOISTURE CONTENT OF SOIL FOR

CBR OF KARONGI MOUNTAIN (laterite)

Container number 52

Weight of container m1(g) 69.3

Weight of wet soil + container m2 (g) 152.5

Weight of dry soil + container m3 (g) 148.6

Weight of dry soil= m3-m1 (g) 79.3

Weight of moisture= m2-m3 (g) 3.9

Moisture content (%) w= [(m2-m3)/(m3-m1)]*100 4.9 Table.III. 7 : Determination of moisture content presents in Karongi mountain

41

Take Optimum moisture content determined by proctor test is 8..8%. Present moisture

content of soil is 4.9%.

The quantity of water to be added is calculated as follow: 8.8%-4.9%= 3.9% of soil for

CBR test.

Take 4kg of soil and weight of water to be added= 3.9%*4000g= 156 ml. This is for

Karongi mountain soil (laterite).

For Nkamira soil (volcanic ash), take Optimum moisture content determined by proctor

test is 22%. Present moisture content of soil is 4.5%.

The quantity of water to be added is calculated as follow: 22%-4.5%= 17.5% of 4kg of

soil for CBR test.

Take 4kg of soil and weight of water to be added= 17.5%*4000g= 700 ml.

RESULTS AND DATA

For laterite of Karongi:

Weight of mould + base plate= 5032.7gr

Weight of mould + base plate + wet soil= 7737.3gr

Expension= 0.05mm

Dry density= 2020kg/m3

Optimum moisture content= 8.8%

For volcanic ash:

Weight of mould + base plate= 5022.5g

Weight of mould + base plate + soil= 7115.7g

Expension= 0.045 mm

Dry density= 1438kg/m3

Optimum moisture content= 22%

42

Curing (laterite) of Karongi mountain soil

Penetration of plunger (mm) Division*0.01 0.25 0.03 0.50 0.03 0.75 0.05 1.00 0.07 1.25 0.09 1.50 0.11 1.75 0.14 2.00 0.16 2.25 0.18 2.50 0.21 2.75 0.23 3.00 0.25 3.25 0.27 3.50 0.29 3.75 0.31 4.00 0.33 4.25 0.34 4.50 0.36 4.75 0.38 5.00 0.40 5.25 0.41 5.50 0.43 5.75 0.44 6.00 0.45 6.25 0.48 6.50 0.49 6.75 0.51 7.00 0.52 7.25 0.54 7.50 0.55 Table.III. 8 : Curing of CBR penetration vs division for Karongi mountain soil (laterite)

43

Penetration of plunger (mm) Force on plunger (Top) KNmm 0.25 0.71 0.50 0.71 0.75 1.19 1.00 1.67 1.25 2.14 1.50 2.62 1.75 3.33 2.00 3.81 2.25 4.29 2.50 5.00 2.75 5.48 3.00 5.95 3.25 6.43 3.50 6.90 3.75 7.38 4.00 7.86 4.25 8.10 4.50 8.57 4.75 9.05 5.00 9.52 5.25 9.76 5.50 10.23 5.75 10.47 6.00 10.70 6.25 11.40 6.50 11.63 6.75 12.09 7.00 12.33 7.25 12.79 7.50 13.02 Table 9 : Curing of CBR loads for Karongi mountain soil (laterite)

44

Penetration Force(KN)

(mm)

0.00 0

0.25 0.71

0.50 0.71

0.75 1.19

1.00 1.67

1.25 2.14

1.50 2.62

1.75 3.33

2.00 3.81

2.25 4.29

2.50 5

2.75 5.48

3.00 5.95

3.25 6.43

3.50 6.9

3.75 7.38

4.00 7.86

4.25 8.1

4.50 8.57

4.75 9.05

5.00 9.52

5.25 9.76

5.50 10.23

5.75 10.47

6.00 10.7

6.25 11.4

6.50 11.63

6.75 12.09

7.00 12.33

7.25 12.79

7.50 13.02

Fig.III.6. Curing CBR value for Karongi mountain soil(laterite)

45

Soaking(laterite) of Karongi mountain soil

Penetration of plunger (mm) Division*0.01 0.25 0.03 0.50 0.05 0.75 0.08 1.00 0.10 1.25 0.13 1.50 0.15 1.75 0.18 2.00 0.20 2.25 0.22 2.50 0.25 2.75 0.27 3.00 0.29 3.25 0.30 3.50 0.32 3.75 0.34 4.00 0.36 4.25 0.37 4.50 0.39 4.75 0.40 5.00 0.42 5.25 0.43 5.50 0.45 5.75 0.46 6.00 0.47 6.25 0.49 6.50 0.50 6.75 0.52 7.00 0.53 7.25 0.54 7.50 0.55

Table.III. 10 : Soaking of CBR penetration vs division for karongi mountain soil

46

Penetration of plunger (mm) Force on plunger (Top) KNmm 0.25 0.71 0.50 1.19 0.75 1.90 1.00 2.38 1.25 3.10 1.50 3.57 1.75 4.29 2.00 4.76 2.25 5.24 2.50 5.95 2.75 6.43 3.00 6.90 3.25 7.14 3.50 7.62 3.75 8.10 4.00 8.57 4.25 8.81 4.50 9.29 4.75 9.52 5.00 10.00 5.25 10.23 5.50 10.70 5.75 10.93 6.00 11.16 6.25 11.63 6.50 11.86 6.75 12.33 7.00 12.56 7.25 12.79 7.50 13.02

Table.III. 11 : Soaking of CBR loads for Karongi mountain soil (laterite)

47

Penetration Force(KN)

(mm)

0.00 0

0.25 0.71

0.50 1.19

0.75 1.9

1.00 2.38

1.25 3.1

1.50 3.57

1.75 4.29

2.00 4.76

2.25 5.24

2.50 5.95

2.75 6.43

3.00 6.9

3.25 7.12

3.50 7.62

3.75 8.1

4.00 8.57

4.25 8.81

4.50 9.29

4.75 9.52

5.00 10

5.25 10.23

5.50 10.7

5.75 10.93

6.00 11.16

6.25 11.63

6.50 11.86

6.75 12.33

7.00 12.56

7.25 12.79

7.50 13.02

Fig.III.7. Soaking CBR value for Karongi mountain soil(laterite)

48

CURING (for volcanic ash) of Nkamira

Penetration of plunger (mm) Division*0.01 0.25 0.01 0.50 0.02 0.75 0.04 1.00 0.06 1.25 0.08 1.50 0.12 1.75 0.15 2.00 0.19 2.25 0.22 2.50 0.27 2.75 0.29 3.00 0.34 3.25 0.37 3.50 0.41 3.75 0.45 4.00 0.48 4.25 0.51 4.50 0.54 4.75 0.57 5.00 0.60 5.25 0.63 5.50 0.66 5.75 0.68 6.00 0.71 6.25 0.74 6.50 0.76 6.75 0.78 7.00 0.81 7.25 0.83 7.50 0.86

Table.III. 12 : curing of CBR penetration vs division for Nkamira volcanic ash

49

Penetration of plunger (mm) Force on plunger (Top) KNmm 0.25 0.24 0.50 0.48 0.75 0.95 1.00 1.43 1.25 1.90 1.50 2.86 1.75 3.57 2.00 4.52 2.25 5.24 2.50 6.43 2.75 6.90 3.00 8.10 3.25 8.81 3.50 9.76 3.75 10.70 4.00 11.40 4.25 12.09 4.50 12.79 4.75 13.49 5.00 14.19 5.25 14.88 5.50 15.58 5.75 16.05 6.00 16.74 6.25 17.44 6.50 17.91 6.75 18.37 7.00 19.07 7.25 19.53 7.50 20.24

Table.III. 13 : Curing of CBR loads for Nkamira volcanic ash

50

Penetration Force (kN)

(mm)

0.00 0

0.25 0.24

0.50 0.48

0.75 0.95

1.00 1.43

1.25 1.9

1.50 2.86

1.75 3.57

2.00 4.52

2.25 5.24

2.50 6.43

2.75 6.9

3.00 8.1

3.25 8.81

3.50 9.76

3.75 10.7

4.00 11.4

4.25 12.09

4.50 12.79

4.75 13.49

5.00 14.19

5.25 14.88

5.50 15.58

5.75 16.05

6.00 16.74

6.25 17.44

6.50 17.91

6.75 18.37

7.00 19.07

7.25 19.53

7.50 20.24

Fig.III.8. Curing CBR value of Nkamira volcanic ash

51

Soaking (volcanic ash) of Nkamira

Penetration of plunger (mm) Division*0.01 0.25 0.02 0.50 0.04 0.75 0.07 1.00 0.09 1.25 0.12 1.50 0.16 1.75 0.19 2.00 0.23 2.25 0.27 2.50 0.31 2.75 0.34 3.00 0.38 3.25 0.41 3.50 0.45 3.75 0.48 4.00 0.51 4.25 0.54 4.50 0.57 4.75 0.60 5.00 0.63 5.25 0.65 5.50 0.68 5.75 0.70 6.00 0.73 6.25 0.75 6.50 0.77 6.75 0.79 7.00 0.81 7.25 0.83 7.50 0.86 Table.III. 14 : Soaking of CBR penetration vs division for Nkamira volcanic ash

52

Penetration of plunger (mm) Force on plunger (Top) KNmm 0.25 0.48 0.50 0.95 0.75 1.67 1.00 2.14 1.25 2.86 1.50 3.81 1.75 4.52 2.00 5.48 2.25 6.43 2.50 7.38 2.75 8.10 3.00 9.05 3.25 9.76 3.50 10.70 3.75 11.40 4.00 12.09 4.25 12.79 4.50 13.49 4.75 14.19 5.00 14.88 5.25 15.35 5.50 16.05 5.75 16.51 6.00 17.21 6.25 17.67 6.50 18.14 6.75 18.60 7.00 19.07 7.25 19.53 7.50 20.24 Table.III. 15 : Soaking of CBR loads for Nkamira volcanic ash

53

Penetration Force(KN)

(mm)

0.00 0

0.25 0.48

0.50 0.95

0.75 1.67

1.00 2.14

1.25 2.86

1.50 3.81

1.75 4.52

2.00 5.48

2.25 6.43

2.50 7.38

2.75 8.1

3.00 9.05

3.25 9.76

3.50 10.7

3.75 11.4

4.00 12.09

4.25 12.79

4.50 13.49

4.75 14.19

5.00 14.88

5.25 15.35

5.50 16.05

5.75 16.51

6.00 17.21

6.25 17.67

6.50 18.14

6.75 18.6

7.00 19.07

7.25 19.53

7.50 20.24 Fig.III.9.Soaking CBR value of Nkamira volcanic ash

54

III.5. HIGHWAY AND TRANSPORTATION ENGINEERING LABORATORY In the highway and transportation Laboratory, I carried out experiments on pavement

construction materials from different sources in Rwanda (Gahara, Bugesera, Giti

cy`inyoni, Karongi, Mukungwa, Gatumba and Musanze) that deal with

Transportation Engineering. Some of these experiments are:

- Los Angeles Abrasion Test

- Aggregate Impact Test

- Specific Gravity and Water Absorption

- Bulk Density

III.5.1. Los Angeles Abrasion Test

III.5.1.0. Objective

Resistance to abrasion of small size coarse aggregate by use of the Los Angeles

machine or Hardness to resist the abrasion effect of traffic over a long period of time.

III.5.1.1. Scope

This method covers a procedure for testing sizes of aggregate smaller than 37.5mm for

resistance to abrasion.

III.5.1.2. Definition

Resistance to abrasion is the measure of hardness of aggregate under action of traffic

resistance to relative movement and rubbing of aggregate with each other.

III.5.1.3. Apparatus

- Los Angeles Abrasion machine equipped with a counter, hallow steel cylinder close at both ends with inside diameter of 7115mm and inside length of

5085mm.

- Sieve conforming to the specifications for wire cloth sieve for testing purposes.

- Abrasion charges (Sphere)

- Balance or scale accurate within 0.1 percent of test load over a range required for

this test.

- Oven capable of maintaining a uniform temperature of 1105oC

55

III.5.1.4. Abrasion Charges

These consist of steel sphere averaging approximately 46.8mm in diameter and each

weighing between 390 and 450g. The abrasion charge, depending upon the grading of the

test sample as described, shall be as follows:

GRADING No OF SPHERE MASS OF CHARGE

A 12 500025

B 11 458425

C 8 333020

D 6 250015

III.5.1.5 Test sample

Test sample shall consist of clean aggregate representative of material to be tested. If the

aggregate representative of material is dirty or coated, shall be washed until clean, then

dried to constant mass, separated to individual size fraction and recombined to the

grading of the above table most nearly corresponding to the range of size in the

aggregates as furnishes for work.

The mass of sample prior to the test shall be recorded to the nearest 5g.

III.5.1.6. Grading of test samples

SIEVE SIZE MASS OF INDICATED SIZE GRADING (g) PASSING (mm)

RETAINED (mm)

A B C D

37.5 25.0 125025 25.0 19.0 125025 19.O 12.5 125025 250010 12.5 9.5 125025 250010 9.5 6.3 250010 6.3 4.75 250010 4.75 2.36 500010TOTAL 500010 500010 500010 500010

56

III.5.1.7. Procedure

- Test the sample and abrasive charge shall be placed in Los Angeles abrasive

testing machine rotated at speed of 30 to 33 rev. per min. for 500 revolutions.

- After the prescribed number of revolutions the material shall be discharged from

the machine and preliminary separation of the sample made on a 4.75mm B.S.

Sieve.

- The finer portion shall be sieved on a 1.7mm sieve then the material coarser than

a 1.7mm sieve shall be washed, dried to a constant mass and weighed to the

nearest 5g

III.5.1.8. Calculation

The Los Angeles Value (L.A.A.V) = (Mo-MR1.7mm)/Mo* 100

Where: Mo is the original mass

MR1.7mm is the final mass retained on the sieve of 1.7mm

So, as I carried out Los Angeles Test on different pavement construction materials from

different source like: GAHARA (quartzite); BUGESERA (quartzite); GITI CY`INYONI

(quartzite); KARONGI (dolerite); MUKUNGWA (basalt); GATUMBA (dolerite);

MUSANZE (amphibolites). I got different Los Angeles Value.

L.A.A.V of GAHARA

Mo= 5000g

MR1.7mm= 4154.3g

Then, L.A.A.V= [(5000-4154.3)/5000]*100= 16.9%

The Los Angeles Value is 16.9%

L.A.A.V of BUGESERA

Mo= 5000g

MR1.7mm = 3789.1g

Then, L.A.A.V= [(5000-3789.1)/5000]*100= 24.2%

The Los Angeles Value is 24.2%

57

L.A.A.V of GITI CY`INYONI

Mo= 5000g

MR1.7mm = 3494.2g

Then, L.A.A.V= [(5000-3494.2)/5000]*100= 30%

The Los Angeles Value is 30%

L.A.A.V of KARONGI

Mo= 5000g

MR1.7mm = 4104.2g

Then, L.A.A.V= [(5000-4104.2)/5000]*100= 17.9%

The Los Angeles Value is 17.9%

L.A.A.V of MUKUNGWA

Mo= 5000g

MR1.7mm = 3722.1g

Then, L.A.A.V= [(5000-3722.1)/5000]*100= 25.5%

The Los Angeles Value is 25.5%

L.A.A.V of GATUMBA

Mo= 5000g

MR1.7mm = 4087.4g

Then, L.A.A.V= [(5000-4087.4)/5000]*100= 18.25%

The Los Angeles Value is 18.25%

L.A.A.V of MUSANZE

Mo= 5000g

MR1.7mm = 3399.4g

Then, L.A.A.V= [(5000-3399.4)/5000]*100= 32%

The Los Angeles Value is 32%

58

III.5.2. Aggregate Impact Test

III.5.2.0. Objective

Toughness of an aggregate which is its resistance to failure by impact and is as curtained

in the laboratory by the aggregate impact test.

III.5.2.1. Scope

This method covers a procedure for testing sizes of aggregate smaller than 12.5mm for

resistance of an aggregate to failure by impact.

III.5.2.2. Definition

Resistance of an aggregate to failure by impact defined as the percentage fines produced

an application of standard impact load; the aggregate impact value gives a relative

measure of the resistance to impact.

III.5.2.3. Apparatus

- Impact test machine

- Sieves conforming to the specifications for wire cloth sieves for testing purposes

- Balance or scale accurate within 0.1 percent of test load over a range required for

this test. - Oven capable of maintaining a uniform temperature of 1105oC

- Stroke of a 10mm diameter metal rod 23cm long rounded at one end

- Steel cup at the base of the impact testing machine.

III.5.2.4. Preparation of test sample

- The material for the standard test shall consist of aggregate passing 14.0mm and

retained on 10.0mm BS test sieve.

- For smaller sizes the aggregate shall be prepared in the manner using the

appropriate sieves.

- The aggregate shall be tested in a surface-dry condition. If dried by heating the

period of drying shall not exceed 4hours the temperature shall not exceed 110oC

and the sample shall be cooled to room temperature before testing.

- The quality of aggregate sieved out shall be sufficient for two tests.

- The measure shall be filled about 1/3 with aggregate with means of scoop;

discharged from a height not exceeding 50mm above the top of container.

59

- The aggregate shall then be tamped with 25 blows of rounded end of tamping rod;

discharged from a height of about 50mm above the tasting sample and blows

being distributed evenly over the sample

- A further similar quantity of aggregate shall be added on the same manner and

further tamping of 25 blows given.

- They shall finally be filled to over flowing tamped 25 blows and surplus

aggregate removed by rolling the tamped, the tamping rod across and in contact

with the top of container, any aggregate which impedes its progress being

removed by hand aggregate being added to fill any obvious depressions.

III.5.2.5. Procedures

- Rest the impact machine, without wedging or packing, upon the level plate block

or floor so that it is rigid and hammer guide columns are vertical.

- Fix the cup firmly in the position on the base of the machine and place the sample

in it and compact it with single tamping of 25 strokes of the tamping rod as above.

- Adju