unit 4 ( road construction materials and testing )

8/6/2019 Unit 4 ( ROAD CONSTRUCTION MATERIALS AND TESTING )

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ROADS CONSTRUCTIONMATERIALS & TESTING

Highway Engineering C3010 / UNIT4

ROAD CONSTRUCTION MATERIALS AND TESTING

OBJECTIVES

General Objective

To understand basic elements of road construction materials and testing

Specific Objectives

At the end of the unit you should be able to:-

identify the material used in the road construction.

describe the function of the road materials and testing.

explain the purpose of road materials and testing.

perform the testing material testing.

analyze result of the test.

UNIT 4


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4.0 INTRODUCTION

Construction materials for roads may be broadly classified into four

categories:

a. Soil

b. Aggregates

c. Bituminous materials

d. Cement

Aggregate which has been defined as inert mineral fragments and

particles forming the main structure of a mixture such as asphalt, tar-macadam or

concrete is the basic material for road construction. This material which forms the

greater part of the body of the road, bears the main stresses occurring in the

road and resists wear from surface abrasion.

The particles are bound together using bituminous materials and cement

which act as binders and develop a strong structure forming the crust of the road.As such properties of all these materials are of great importance to the highway

engineers. A knowledge of their characteristics is useful in the design of road

structure.

ROAD = SOIL + AGGREGATES + PAVEMENTMATERIALS

(BITUMENS/CEMENTS)

INPUT

ROAD CONSTRUCTION MATERIALS AND THEIRFUNCTIONS


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4.1SOILS AND ITS CHARACTERISTIC

The term soil has different meanings and connotations to different

professional groups. From an engineering stand-point the term soil refers to all

the unconsolidated mineral material lying above the bed rock with which and

upon which highways and other structures are constructed. It may contain air,

water, organic matter and other substances which may be dispersed throughout

the minerals particles. The mineral matter is formed by the disintegration or

decomposition of the rocks. The engineering properties and behavior are

generally influenced by changes in moisture content and density or compactness

of the soil. Wide variation in soil types is generally found in nature and hence a

study of their properties becomes essential.

4.1.1 CHARACTERISTICS OF SOIL PARTICLES

Certain characteristics of the soil particles are useful in predicting

the performance and behavior of soils ; namely the grain size, shape,

surface texture, and chemical position. These are briefly discussed here.

4.1.1.1 Grain size.

The size of the soil particles and the distribution of various

sizes throughout a soil mass are important factors that influence

soil properties and performance. A number of grain size

classifications have been proposed by different highway agencies

for convenience in expressing the size characteristics of various

fractions.


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The general characteristics of the various particle size groupings

are as follows:

1. Gravel.

It consists of rock fragments more or less rounded by water

action or abrasion. Quartz which is the hardest rock forming mineral

is usually the principal constituent. Well rounded pebbles and

boulders that have undergone long wear are almost entirely quartz.

Gravels which are angular and rough due to their high resistance to

wear, usually contain rocks such as granite, schist, basalt or

limestone.

2. Course Sand.

It is frequently rounded like gravel with which it may exist in

combination. It generally contains the same minerals.

3. Fine Sand.

Particles are more angular than coarse sand particles

because the film of water that usually surrounds the finer particles

serves as cushion to protect them from abrasion. Silt grains are

usually similar to fine sand and have the same mineral composition.

However, they may be produced by chemical decay rather than by

grinding. Occasionally, silts contain pumice, loess or other

materials foreign to the associated sand. The presence of silt in fine

soil may be detected in the field by the feeling of roughness that it

gives when rubbed between fingers.


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4. Clay.

Clay results almost entirely from chemical weathering and

are often plate like in shape. The structure of moist clays is

considered to be very complicated and has not been fully

understood yet, although attempts have been made by many

Chemists, Physicists, Geologists and Engineers to interpret it in the

various fields of the Lambe has given a very good account of the

structure of clays in his paper entitled The Structure of Inorganic

Soil, presented to the ASCE.

5. Colloids.

These are finer clay particles that remain suspended in

water and do not settle under the force of gravity. When observed

under microscope they are found to be in a state of disorderly

motion. For most of the highway engineering works, coarse grained

materials are preferable. Clayey soils are extremely troublesome

and require specialized treatments and methods of handlings.Brownian Movement specially silty soils present problems in the

areas susceptible to frost action.

4.1.2 SHAPE OF PARTICLES.

Strength and toughness of the material is indicated to a large extent

by the shape of the particles. For example, gravels found in the river beds

have undergone a large process of wear and are stronger than the flat and

flaky particles.

In the construction of base courses where usually granular material

is recommended, there is little percentage of the clay particles. Here the


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shape of the bigger stone particles recommended is angular as they are

better resist the tendercy to deformation. Hence many specifications for

base-course require that the mixture of different materials used must

contain a specified percentage of crushed rock particles.

The effect of the shape of particles on the performance of mass

composed mainly of clay-size fraction is not conclusively known. Here the

presence of the free and absorbed moisture, particle ionization presence

of chemicals and density are some of the more important factors.

4.1.3 SURFACE TEXTURE

The surface texture of the large size soil particles greatly influences

their performance in granular soil mixtures. For example, the friction

developed on the grains of wind-blown and beach sands and of crushed

quartz is relatively low since the particles have slicked surfaces and as a

result thereof the mixture that contains large percentage of such materials

offer small resistance to deformation.

Some authorities assert that a rough surface of a freshly crushed

rock is more important than its angularity in developing greater strength in

soil mixture. With small size particles this effect of surface texture

becomes negligible.

4.1.4 CHEMICAL COMPOSITION

Chemical composition indirectly affects the behavior of soils since

the presence of certain chemicals influences the water-film that usually

surrounds the particle and hence the bond holding any two particles

mutually together.


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Some complex reactions might develop in the soil mass as a result

of the addition of an additive as a stabilizer in the presence of an

appropriate chemical, resulting in the improvement of structural behavior

of the compacted soil mass.

4.2 EFFECT OF MOISTURE ON THE PERFORMANCE OF SOILS

All soil engineers agree that the properties of soils composed largely of

coarse grained materials are primarily controlled by the characteristics of the

particles but for soils composed largely of clays and colloids, the properties are

primarily controlled by the characteristics of the moisture film surrounding the

particles.

The effect of the change in moisture content is reflected in

three ways :

a. The effective diameter of the soil particle

changes with change in the moisture content.

The effect is more prominent in the clay

particles than in the sand particles.

b. The soil particles have the property of

clinging to each other due to the existence of

thin tensile forces in water films. These forces

are due to the surface tension. The force

exerted by surface tension decreases as the

moisture content increases.

c. The volume of the soil-mass as a whole

changes with the change in the moisture

content at the particle surface. The changes

in volume are more prominent in clays than in

sands and silts.

The effect ofincrease in moisture

content is todecrease the

strength of soil

INFOINFO


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4.3 EFFECT OF DENSITY ON THE BEHAVIOUR OF SOILS

Dry density of soil is the dry weight per unit volume of the material. The

soil mass consists of dry soil particles and air when in the dry state, and soil

particles, air and water when in the wet state. If the density of soil changes, say

increase, the quantity of soil solids in unit volume increases so that lesser voids

would be left for air and water.

This increase in density and decrease in moisture content would add to

the strength of the soil. The maximum density is achieved at optimum moisture

content which can be determined by any standard test. In addition to the increase

in strength, the rate of water movement through the soil and volume change due

to variation in moisture, subsequent to compaction, register a measurable

decrease. In order to secure these advantages, it has been accepted as a normal

practice to compact the sub grade soils so as to obtain maximum dry density.

4.4ROAD AGGREGATE

The raw material which is used as road aggregate can be further classified

as :a. Naturally occurring aggregate :

- Crush Rock Aggregate

- Gravels

- Sand.

b. Artificial Aggregate

- Blast Furnace Slag

Each of the three types mentioned under (a) above is one or the other

form of natural rock. The crushed road aggregate is prepared by quarrying

natural rock from the quarries having suitable road construction material and

crushing it to the required size. The coarse material which results from the

disintegration of natural rocks due to weathering, is carried away by water into


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the rivers and is deposited as gravel. During transit, the particles are worn out by

attrition and become more or less rounded in shape with smooth surfaces. Sand,

on the other hand, is the final residue of resistant mineral grains resulting from

rock-weathering and has often been through many cycles of deposition and

weathering.

Blast furnace slag is, perhaps, the only artificially prepared aggregate

used in road construction. It is obtained as a by-product in the manufacture of

steel.

4.4.1 Crushed Rock

Crushed rock aggregate is produced from different types of rocks.

All rocks are composed of grains or crystals of minerals held together in a

variety of ways. The properties of rocks, therefore are dependent upon the

properties of minerals forming the rocks and the nature of the bond.

Igneous, Sedimentary and Metamorphic are the three major classifications

of these rocks.

The Igneous rocks are further classified into Plutonic Hypabyssal

and Volcanic, according to their mode of formation, the properties of acid

and basic radicals and the chemical constituents of the mineral present. In

the Plutonic variety, the main types are the Granite and Syenite, though

Diorite and Gabbro are also frequently available. They are mainly coarse-

grained varieties being Porphyry, Porphyrite, Dolorite and Diabase. These

rocks very frequently posses intergrown texture and as such are among

the best of the road stones. Basalts and Andersite fall in the Volcanic

category and are fine grained varieties of ignoeus rocks. They are usually

not considered good as road stones.


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become a very good aggregate, if it is manufactured under carefully-

controlled conditions.


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WANT TO IMPROVE YOUR UNDERSTANDING? TRY THESE

ACTIVITIES AND GOOD LUCK!!!

4.1 Name four categories of road construction materials.

a.____________________________________

b.____________________________________

c.____________________________________

d.____________________________________

4.2Write down the short information of soil characteristics in the

chart below.

SoilCharacteristics

Grain Size - ___________________________________________________________________________________

Shape Of Particles - _____________________________________________________________________________

Surface Texture -________________________________________________

_______________________________

Chemical Composition - _________________________________________________________________________

ACTIVITY 4A


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4.3 There are 10 types of crushed rock aggregate given below and

hidden within the puzzle. You are required to identify the

aggregate and then write down into their categories given in the

table.

G R A N I T E O U S A Z N X A

R A H M E N S Y E N I T E S GA H B I L A B G U S A I U V R

N O R S A K M P S D G O J H I

U R E U I O U S F R E W A R L

L N Z I L L P E W R S A Y M L

I F M O H D I K A F A R I B A

T E B I N Y J C M J L D F H C

E L W E H N L M E K L D E G E

H S K O P A D O L O R I T E O

S H Y K C I P J R J U I D H U

P U C H J K T I K L R S D F SB S C H I S T H M K H V C B E

W H J O P G O L B E G J K B Q

J Q P O R P H Y R I T E L G B

IGNEOUS SEDIMENTARY METAMORPHIC

Lets Check The Answers!

GRANITE CALCAREOUS

HORNFELS SCHIST SILICEOUS

GRANULITE SYENITE AGRILLACEOUS

DOLORITE PORPHYRITE

FEEDBACK ONACTIVITY 4A


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4.1 a. Soil

b. Aggregates

c. Bituminous materials

d. Cement

4.2

4.3

G R A N I T E O U S A Z N X A

R A H M E N S Y E N I T E S G

A H B I L A B G U S A I U V R

N O R S A K M P S D G O J H I

U R E U I O U S F R E W A R L

Grain Size The size of the soil particles and the distribution of

varies sizes throughout a soil mass are important factors that

influence soil properties and performances.

Shape of Particle Strength and toughness of the material is

indicated to a large extend by shape of the particles.

Surface Texture The surface texture of the large size soil

particles greatly influences their performance in granular soil

mixtures.

Chemical Composition Chemical composition indirectly affects

the behavior of soil since the presence of certain chemicals

influences the water-film that usually surrounds the particles and

hence the bond holding any two particles mutually together


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L N Z I L L P E W R S A Y M L

I F M O H D I K A F A R I B A

T E B I N Y J C M J L D F H C

E L W E H N L M E K L D E G E

H S K O P A D O L O R I T E O

S H Y K C I P J R J U I D H UP U C H J K T I K L R S D F S

B S C H I S T H M K H V C B E

W H J O P G O L B E G J K B Q

J Q P O R P H Y R I T E L G B

The categories are as follows :

IGNEOUS SEDIMENTARY METAMORPHIC

Granite Calcareous Hornfels

Syenite Siliceous Granulite

Dolorite Agrillaceous Schist

Porphyrite

Well, hows your performance so far?

Lets continue the adventures of unit 4.

1. The effect of the change in moisture content is reflected in three ways.

Describe two from the three ways that listed.

2. Describe the following aspects: -

Question


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a. Gravel.

b. Slag.

1. The effect of the change in moisture content is reflected in three ways :

Answer


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a. The effective diameter of the soil particle changes with change

in the moisture content. The effect is more prominent in the clay

particles than in the sand particles.

b. The soil particles have the property of clinging to each other due

to the existence of thin tensile forces in water films. These

forces are due to the surface tension. The force exerted by

surface tension decreases as the moisture content increases.

c. The volume of the soil-mass as a whole changes with the

change in the moisture content at the particle surface. The

changes in volume are more prominent in clays than in sands

and silts.

2.

i. Gravels

Gravel may consist entirely of one type of hard rock such as

Flint or Quartzite (silicious sedimentary variety) or may have a

wider variety of rocks of different types and hardnesses. Gravels of

softer variety of rocks are generally not available, though at places,limestone gravels also occur and are used for the construction of

roads, where other suitable material is not available.

In general, the properties of the gravels depend upon the

properties of the rocks from which they are formed. Mixed gravels

usually contain, in addition to the hard varieties, soft particles of

chalk, clay lumps, shale or soft sandstone and, therefore, whenever

gravels have to be used in road construction, they must be tested

lest any such materials should form a high proportion and thus act

as a source of weakness.

ii. Slag


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Slag obtained as a by-product from blast furnaces is

extensively used as road aggregate. It is composed of a number of

alumino-silicates of calcium and magnesium, minerals that are

found in some basic igneous rocks. Owing to the rapid cooling of

material, slag becomes a much more variable material than natural

rock. There is tremendous difference in the grain-size and porosity

of exterior and interior of the cooling masses, the exterior cooling

rapidly so as to form an amorphous glass. Slag can become a very

good aggregate, if it is manufactured under carefully controlled

conditions.

unit 4 ( road construction materials and testing )

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