- 25-

CHAPTER 4

PROPERTIES OF MATERIALS

4.1 Fly Ash

Fly ash, the fine particulate waste material produced by pulverized coal-based thermal

power station, is an environmental pollutant, it has a potential to be a resource material. It is

nowadays used in cement, concrete and other cement based applications in India.

As per IS 3812: 2003, the generic name of the waste product due to burning of coal or

lignite in the boiler of a thermal power plant is pulverized fuel ash. Pulverized fuel ash can be fly

ash, bottom ash, pond ash or mound ash. Fly ash is the pulverized fuel ash extracted from the

fuel gases by any suitable process like cyclone separation or electrostatic precipitation.

Pulverized fly ash collected from the bottom of boilers by any suitable process is termed as

Bottom Ash. The terminology Pond Ash is used when fly ash or bottom ash or both mixed in any

proportion is conveyed in the form of water slurry is deposited in pond or lagoon. When fly ash

or bottom ash or mixture of these in any proportion is conveyed or carried in dry form and

deposited dry, it is known as Mound Ash.

4.1.1 Source, Use and Quality of Fly Ash

In view of the use of coal of relative high ash content made available to thermal power

projects. The amount of fly ash generated from 69 thermal power stations in 1998 was estimated

to be of the order of 60 mt. The estimate was updated to 90 mt. from 82 thermal power stations,

having aggregate capacity of 60,000 MW in the year 2000, 125 mt. in year 2005 to generate

1,15,000 MW and it is estimated to be 150 mt. in year of 2010 to generate1,40,000 MW

electricity, which is expected to go up every year, with increase in production of electricity from

coal-base thermal plants. The coal used in India is predominantly bituminous, which gives rise to

low-lime fly ash. Sub-bituminous lignite coal, used in some power plants gives high-lime fly ash.

In view of their large scale availability, low-lime fly ashes are mainly used in India and

elsewhere.

- 26-

Quality requirements of fly ash in India, for use in cement and concrete, are governed by

provision of Specification for fly ash for use of pozzolona and admixture, IS 3812 (part I):

2003,[13]

Bureau of Indian Standard, New Delhi. The main requirement, which govern the

performance of fly ash in cement and concrete are,

Specific surface area,

Residue on 45 ц sieve,

Glass content

Moisture content,

Unburnt carbon, commonly measured as loss on ignition

Unburnt carbon, commonly measured as loss on ignition

The dependence of lime reactivity of fly ash on its glass content. The major difference in

fly ash in India and elsewhere is in the glass content. In ASTM or EN specifications, fly ash is

described as a fine powder of mainly spherical glass particles having pozzolanic properties,

which consist essentially of reactive Sio2 and Al2O3. Value of glass content in selective Indian

fly ashes, which are considered satisfactory for use and those from other countries are shown in

table 4.1.[13]

Table 4.1

GLASS CONTENT IN FLY ASH – TYPICAL VALUES

Country Glass content in fly ash, percent

Range Average No. of Samples

USA 90 11

Japan 29.0 – 85.6 55.3 55

Italy 82 – 100 95 400

India 20 – 32 - 37

- 27-

The comparison of requirements of low-lime fly ash in ASTM, EN and IS is shown in

Table 4.2[12]

Table 4.2

SPECIFICATION FOR FLY ASH IN CEMENT AND CONCRETE

Item ASTM

C-618

European Specifications IS 3812

2003- I En-450 En-197-I En-3892-I

Sio2 minimum 35

Reactive/soluble Sio2, min. 25 25 20

Sio2+Al2O3+Fi2O3 minimum 70 70

MgO, Maximum 70

LOI(1hour)max. 6 5-7 5-7 7 5

Total alkalis, max. 1.5 1.5

SO3, maximum 5 3 2 3.0

Free CaO, maximum 1 1

Total/reactive CaO, maximum 10 10 10

Fineness, 45 micron, maximum 34 40 12 34

Blaines fineness m2/kg min. 320

Cement activity 28 days 75 75 80 80

Lime reactivity, N/mm2 4.5

Soundness, Le-Chatelier, mm 10 10 10 10

Autoclave, Percent 0.8 0.8

Nowadays the use of fly ash in construction is gaining momentum in India. One instance

of the increasing concern to put fly ash to use rather than its disposal, is in the growing list of

areas of application. In India, fly ash is not only being used in construction but also in, ceramics,

metallurgy, agriculture and environmental-related areas. Common areas of use are cement,

concrete, ready-mixed concrete, cement or lime-based fly ash bricks and blocks for walling

prefabricated building elements, land reclamation, soil stabilization, road constructions,

embankments, land fills etc. Non-engineering applications are in agriculture, plant nutrients,

ceramics, neutralizing soil acidity, metal extraction etc.

- 28-

4.1.2 Classification of Fly Ash

According to IS 3812-1981, there are two grades of Fly Ash

I, Grade I fly ash, which are derived from bituminous coal having fractions

SiO2+Al2O3+Fe2O3 greater than 70 %.

II, Grade II Fly ash, which are derived from lignite coal having fractions SiO2+Al2O3+Fe2O3

greater than 50 %.

ASTM C618 specified two categories of fly ash, Class C and Class F depending on the type of

coal and the resultant chemical analysis.

Class C fly ash, normally produced from the combustion of lignite or sub bituminous

coals, contains CaO higher than 10 percent and possesses cementitious properties in addition to

pozzolanic properties. Class F fly ash, normally produced from the combustion of bituminous

or an anthracite coal contains CaO below 10 percent and possesses pozzolanic properties.

Classification, based on the boiler operations is classified with two distinct identities:

Low temperature(LT) fly ash, Generated out of combustion temperature below 900o

C : High

temperature(HT) fly ash, Generated out of combustion temperature below 1000o C

This threshold temperature demarcates the development of metakaolinite phases in the

case of LT and the same constituents form as reactive glassy phases in the case of HT fly ash. LT

fly ash hence preferred for precast building materials such as bricks/blocks. However the higher

ignition loss, of the order of 4-8 percent makes the fly ash less desirable for cement and concrete

applications. In contrast, the initial pozzolanic reaction is slow in HT fly ash, which is

accelerated with age. This property together with a relatively low ignition loss makes HT fly ash

more suitable for use in cement and concrete industries.

4.1.3 Physical Characteristic of Fly Ash

Fly ash is a fine grained material consisting mostly of spherical, glassy particles. Some

ashes also containing irregular or angular particles. Fly ash is the pulverized fuel ash extracted

from the fuel gases by any suitable process like cyclone separation or electrostatic precipitation.

- 29-

4.1.3.1 Size and Shape of Fly Ash

The size of particles varies depending on the sources. Some ashes may be finer or coarser

than Portland cement particles. Fly ash consists of silt sized particles which are generally

spherical, typically ranging in size between 10 to 100 micron. Figure no 4.1[14]

shows the

scanning electron microscope(SEM) micrographs of polished sections of sub-bituminous and

Figure no. 4.2[14]

shows a secondary electron SEM image of bituminous of fly ash particles.

Some of these particles appear to be solid, whereas other larger particles appear to be portions of

thin, hollow spheres containing many smaller particles.

Figure 4.1 SEM micrograph of a sub-bituminous ash

Figure 4.2 SEM micrograph of a bituminous ash

4.1.3.2 Color of Fly Ash

Fly ash can be tan to dark gray, depending on its chemical and mineral constituents. Tan

and light colors are typically associated with high lime content. A brownish color is typically

associated with the iron content. A dark gray to black color is typically attributed to an elevated

unburned content. Fly ash color is usually very consistent for each power plant and coal source.

Figure 4.3 Typical ash colors

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4.1.3.3 Fineness of Fly Ash

Dry and wet sieving are commonly used to measure the fineness of fly ashes. ASTM

designation C311-77 recommends determining the amount of the sample retained after it is wet

sieve done on a 45-цm sieve, in accordance with ASTM method C 430, except that a

representative sample of the fly ash or natural pozzolana is substituted for hydraulic cement in

the determination. Dry sieving on a 45-цm sieve can be performed according to a method

established at Canada Center for Mineral and Energy Technology(CANMET). High-calcium fly

ashes were finer than low-calcium fly ashes.

The specific surface of fly ash, which is the area of a unit of mass, can be measured by

various techniques. The most common technique is the Blaine specific-surface method, which

measures the resistance of compacted particles to air flow. ASTM C204 describes this method

for measurement of the surface area of Portland cement. Reactivity of fly ashes increase with

fineness, particularly the fraction passing 45 ц sieve. Fineness of different fly ashes by wet and

dry sieving are shown in table 4.3[15]

Table 4.3

FINENESS OF DIFFERENT FLY ASHES BY WET AND DRY SIEVING

Fly ash Type of

Coal

Physical Properties

Specific

(LeChateli

er )Method

Fineness (% retained on

45-u sieve)

Blaine Specific

Surface, m2

/kg

Wet Sieving Dry Sieving

01 B 2.53 17.3 12.3 289

02 B 2.58 14.7 10.2 312

03 B 2.88 25.2 18.0 127

04 B 2.96 19.2 14.0 198

05 B 2.38 21.2 16.1 448

06 B 2.22 40.7 30.3 303

07 SB 1.90 33.2 26.4 215

08 SB 2.05 19.4 14.3 326

09 SB 2.11 46.0 33.0 240

10 L 2.38 24.9 18.8 286

11 L 2.53 2.7 2.5 581

- 31-

4.1.3.4 Specific Gravity of Fly Ash

The specific gravity of different fly ashes varies over a wide range. The specific gravity

ranged from a low value of 1.90 for a sub-bituminous ash to a high value of 2.96 for an iron-rich

bituminous ash. Some sub-bituminous ash had a comparatively low specific gravity of ≈ 2.0, and

this shows that hollow particles, such as cenospheres or plerospheres, were present in significant

proportions in the ashes.

In general, the physical characteristics of fly ashes vary over a significant range,

corresponding to their source. Fineness is probably influenced more by factors such as coal

combustion and ash collection and classification than by the nature of the coal itself. Similarly,

the type of fly ash showed no apparent influence on the specific surface as measured by the

Blaine technique. Moreover, except in some cases, there was very little relationship between the

specific surface as measured by the Blaine and the fineness as determined by percentage retained

on a 45цm sieve.

4.1.4 Chemical Composition of Fly Ash

The Chemical composition of fly ash depends on the sources of coal and also on

operating parameters of boilers thus the quality various from source to source and within the

source also. With use of pulverized coal and efficient combustion system, LOI(Loss on ignition)

is a measurement of unburned carbon remaining in the ash. Variation in LOI can contribute to

fluctuations in air content and call for more careful field monitoring of entrained air in the

concrete.

The Fly Ash used in replacement of cement in concrete is brought from SIKKA

THERMAL POWER STATION near JAMNAGAR. The chemical analysis was performed and

results are as shown in table no. 4.4, from test results it can be concluded that the Fly Ash

belongs to Grade I as per IS 3812 and Class –F according to ASTM classification.

- 32-

Table 4.4

CHEMICAL PROPERTIES OF FLY ASH

Sr. No. Particular Requirement as per

IS:3812 in %

Test Results in %

01 SiO2 35.0 Min. 60.21

02 Al2O3 Not Specified 26.08

03 Fe2O3 Not Specified 4.80

04 SiO2+Al2O3+Fe2O3 70.0 Min. 91.09

05 CaO Not Specified 1.00

06 MgO 5.0 Max. 0.25

07 Total alkali as Na2O 1.5 Max. 0.86

08 SO3 3.0 Max. 0.25

09 Cl 0.05 Max. 0.005

10 LOI(Loss in Ignition) 5.0 Max. 1.71

4.1.5 Mineralogical Characteristic of Fly Ash

Type and source both influence on its mineralogical composition. Owing to the rapid

cooling of burned coal in the power plant, fly ashes consist of non-crystalline particles(≤ 90%),

or glass and a small amount of crystalline material. Depending on the system of burning, some

unburned coal may be collected with ash particles. In addition to a substantial amount of glassy

material, each fly ash may contain one or more of the four major crystalline phases: quartz,

mullite, magnetite and hematite. In sub-bituminous fly ashes, the crystalline phases may include

C3A, C4A3S, calcium sulphate and alkali sulphates. The reactivity of fly ashes is related to the

noncrystalline phase or glass. The reasons for the high reactivity of high-calcium fly ashes may

partially lie in the chemical composition of the glass. The composition of glass in low-calcium

fly ashes are different from that is in high-calcium fly ashes. Mineralogical Composition of some

selected fly ashes is shown in table 4.5

- 33-

Table 4.5

MINERALOGICAL COMPOSITION OF SOME SELECTED FLY ASHES[16]

Fly Ash

source

Type of

coal

Phase Composition, %

Glass Quartz Mullite Magnetite Hematite LOI(%)

01 B 72.1 4.0 12.6 6.2 1.6 3.5

02 B 70.2 3.2 3.3 17.2 4.7 1.5

03 B 55.6 6.2 19.8 5.6 3.1 9.7

04 B 54.2 8.3 23.5 4.4 2.1 7.5

05 SB 90.2 2.9 6.1 - - 0.8

06 SB 83.9 4.1 10.2 - 1.4 0.4

07 SB 79.8 8.7 11.5 - - 0.8

08 L 94.5 4.6 - - - 0.9

4.1.6 Mechanism of Fly Ash

To understand the mechanism of fly ash work. The first equation in the illustration shows

the chemistry of hydration of Portland cement. About 50% of Portland cement is composed of

the primary mineral tri-calcium silicate, which on hydration forms calcium silicate hydrate and

calcium hydroxide. If we have Portland cement, and the fly ash is the pozzolana, it can be

represented by silica because non-crystalline silica glass is the principal constituent of fly ash.

The silica combines with the calcium hydroxide released on hydration of Portland cement.

Calcium hydroxide in hydrated Portland cement does not do anything for strength, so therefore

we use it up with reactive silica. Slowly and gradually it forms additional calcium silicate

hydrate which is a binder, and which fills up the space, and gives us impermeability and more

and more strength. The is show the mechanism of fly ash work.

Tricalcium

Silicate

Water Calcium

Silicate

Hydrate

Calcium

Hydroxide

Portland cement only C3S + H → C-S-H + CH

Portland Cement + Fly Ash S + CH → C-S-H

Silica

(Fly Ash)

Calcium

Hydroxide

- 34-

4.2 CEMENT

4.2.1 General

The history of cementing material is as old as the history of engineering construction,

Egyptians, Romans and Indians used some kind of cementing materials in their ancient

constructions. It is believed that the early Egyptians mostly used cementing materials, obtained

by burning gypsum.

The story of the invention of Portland cement is, however attributed to Joseph Aspdin, a

builder and bricklayer, even though other inventors had adopted similar procedures. Joseph

Aspdin took the patent of Portland cement on 21st October 1824. The fancy name of Portland

given owing to the resemblance of this hardened cement to the natural stone occurring at Portlan

in England. In his process Aspdin mixed and ground hard limestone and finely divided clay in

the form of slurry and calcined it in a furnace similar to lime kiln till the CO2 was expelled. The

mixture so calcined was then grounded to a fine powder. Perhaps, Aspdin used a temperature

lower than the clinkering temperature. Later in 1845 Isaac Charles Johnson burnt a mixture of

clay and chalk till the clinkering stage to make better cement and established factories in 1851.

In the early period cement was used for making mortar only. Later the use of cement

extended for making concrete. As the use of Portland cement was increased for making concrete,

engineers called for consistently higher standard material for use in major works.

4.2.2 Manufacturing of Portland Cement

The raw materials required for manufacturing of Portland cement, are calcareous

materials such as limestone or chalk and argillaceous materials such as shale or clay. The process

of manufacture of cement consists of grinding the raw materials, mixing them intimately in

certain proportions depending upon their purity and composition and burning them in a kiln at a

temperature of about 1300 to 1500o C. ,at which temperature material sinters and partially fuses

- 35-

to form nodular shaped clinker. The clinker is cooled and ground to fine powder with addition of

about 3 to 5 % of gypsum. The product formed by using this procedure is Portland cement.

There are two process known as wet and dry processes depending upon whether the

mixing and grinding of raw materials is done in wet or dry conditions. For many years the wet

process remained popular because of the more accurate control in the mixing of raw materials.

Later dry process gained momentum with the modern development of the technique of dry

mixing of powder materials using compressed air.

4.2.3 Chemical Composition

The raw materials used for the manufacturing of cement consist mainly of lime, silica and

alumina iron oxide. These oxides inter-act with one another in the kiln at high temperature to

form more complex compounds. The relative proportions of these oxide compositions are

responsible for influencing various properties of cement, in addition to rate of cooling and

fineness of grading.

The oxides present in the raw materials when subjected to high clinkering temperature

combine with each other to form complex compounds. The identification of the compounds is

largely based on R. H. Bogues work and hence it is called Bogues Compounds.[18]

The four

compounds usually regarded as major compounds are as below.

Bogues Compounds:-

Name of Compound Formula Abbreviated

formula

Tricalcium Silicate 3Cao.SiO2 C3S

Dicalcium Silicate 2Cao.SiO2 C2S

Tricalcium Aluminate 3CaO.Al2O3 C3A

Tetracalcium Aluminoferrite 4 CaO.Al2O3.Fe2O3 C4AF

- 36-

In addition to the four major compounds, There are many minor compounds form in the

kiln, which Influence on the properties of cement. Two of the minor oxides namely K2O and

Na2O referred to as alkalis in cement are of some importance.

Tricalcium Silicate and Dicalcium Silicate are the most important compounds responsible

for strength. Together they constitute 70 to 80 percent of cement. The average C3S content in

modern cement is about 45 percent and that C2S is about 25 percent. The sum of the contents of

C3A and C4AF has decreased slightly in modern cement.

The approximate oxide composition limits of ordinary Portland cement shown in table

4.6[18]

Table 4.6

APPROXIMATE OXIDE COMPOSITION LIMITS OF ORDINARY PORTLAND CEMENT

Sr. No. Oxide Percentage, Content

01 Cao 60-70

02 SiO2 17-25

03 Al2O3 3-8

04 Fe2O3 0.5-6.0

05 MgO 0.1-4.0

06 Alkalies(K2O, Na2O) 0.4-1.3

07 SO3 1.0-3.0

4.2.4 Hydration of Cement:

The chemical reactions that take place between cement and water are referred as

hydration of cement. The chemistry of concrete is essentially the chemistry of the reaction

between cement and water. On account of hydration certain products are formed. These products

are important because they have cementing or adhesive value. The quality, quantity, continuity,

stability and the rate of formation of the hydration products are important.

- 37-

Anhydrous cement compounds when mixed with water, react with each other to form

hydrated compounds of very low solubility. The hydration of cement can be visualized in two

ways. The first is through solution mechanism. In this the cement compounds dissolve to

produce a supersaturated solution from which different hydrated products get precipitated. The

second possibility is that water attracts cement compounds in the solid state converting the

compounds into hydrated products starting from the surface and proceeding to the interior of the

compounds with time. It is probable that both through solution and solid state types of

mechanism may occur during the course of reactions between cement and water. The former

mechanism may predominate in the early stages of hydration in view of large quantities of water

being available, and the latter mechanism may operate during the later stages of hydration.

4.2.5 Heat of Hydration

The reaction of cement with water is exothermic. The reaction liberates a considerable

quantity of heat. This liberation of heat is called heat of hydration. Heat of hydration becomes

important in the construction of concrete dams and other mass constructions. It has been

observed that the temperature in the interior of large mass concrete is 500

C above the original

temperature of the concrete mass at the time of placing and this high temperature is found to

persist for a prolonged period. Figure 4.4,[18]

shows the pattern of liberation of heat from setting

cement and during early hardening period.

Figure 4.4, Heat liberation from setting cement

0

1

2

3

4

5

6

7

0 5 10 15 20 25

Rat

e o

f lib

era

tio

n c

al p

er

gm p

er

ho

ur

Time, Hours

Heat of liberation

- 38-

Different compounds hydrate at different rates and liberate different quantities of heat.[18]

Figure no. 4.5, shows the rate of hydration of pure compounds. Since retarder are added to

control the flash setting properties of C3A, actually the early heat of hydration is mainly

contributed from the hydration of C3S. Fineness of cement also influence the rate of development

of heat but not the total heat. The total quantity of heat generated in the complete hydration will

depend upon the relative quantities of the major compounds present in cement.

Figure 4.5, Rate of Hydration of Pure Compounds

The heat of hydration should be measured for low heat cement. The heat of hydration of

low heat Portland cement shall not be more than 65cal/gm. At 7 days and 75 cal/gm, at 28 days.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1 180

Frac

tio

n h

ydra

ted

Age in days (log scale)

Rate of Hydration

C2S

C3S

C3A

C4AF

- 39-

4.2.6 Calcium Silicate Hydrates

During the course of reaction of C3S and C2S with water, calcium silicate hydrate,

abbreviated C-S-H and calcium hydroxide, Ca(OH)2 are formed. Calcium silicate hydrates are

the most important products. It is the essence that determines the good properties of concrete. It

makes up 50-60 percent of the volume of solids in a completely hydrate cement paste. The fact

that term C-S-H is hyphenated signifies that C-S-H is not a well-defined compound; the

morphology of C-S-H shows a poorly crystalline fibrous mass. The following are the

approximate equations showing the reactions of C3S and C2S with water.

2C3S + 6H = C3S2H3 + 3Ca(OH)2

Similarly 2C2S + 4H = C3S2H3 + Ca(OH)2

It can be seen that C3S produces comparatively lesser quantity of calcium silicate hydrates and

more quantity of Ca(OH)2 than that formed in the hydration of C2S. Ca(OH)2 is not a desirable

product, it is soluble in water and gets leached out making the concrete porous, particularly in

hydraulic structures. Under such conditions it is useful to use cement with higher percentage of

C2S cement.

C3S readily reacts with water and produces more heat of hydration. It is responsible for

early strength of concrete. Cement with more C3S content is better for cold weather concreting.

The quality and density of calcium silicate hydrate formed out of C3Sis slightly inferior to that

formed by C2S. The early strength of concrete is due to C3S.

C2S hydrates rather slowly. It is responsible for the later strength of concrete. It produces

less heat of hydration. The calcium silicate hydrate formed is rather dense and its specific surface

is higher. In general, the quality of the product of hydration of C2S is better than that produced in

the hydration of C3S. Figure 4.6 shows the development of strength of pure compounds with

age.[18]

- 40-

Figure 4.6, Development of strength of pure compounds with age.

4.2.7 Calcium Hydroxide

The other products of hydration of C3S and C2S are calcium hydroxide. It constitutes 20

to 25 per cent of the volume of solids in the hydrated paste. The lack of durability of concrete is

on account of the presence of calcium hydroxide. The calcium hydroxide also, reacts with

sulphates present in soils or water to form calcium sulphate, which further reacts with C3A and

cause deterioration of concrete. This is known as sulphate attack. To reduce the quantity of

Ca(OH)2 in concrete and to overcome its bad effects by converting it into cementitious product

is advancement in concrete technology. The use of blending materials such as fly ash, silica fume

and such other pzzolanic materials are the steps to overcome bad effect of Ca(OH)2 in concrete.

The only advantage is that Ca(OH)2, being alkaline in nature maintains pH value around

13 in the concrete, which resists the corrosion of reinforcements.

0

10

20

30

40

50

60

70

80

0 100 200 300 400

Co

mp

ress

ive

Str

en

gth

Mp

a

Age-days

Strength Development of Pure Compounds

C3S

C2S

C3A

C3AF

- 41-

4.2.8 Calcium Aluminate Hydrates

The reaction of pure C3A with water is very fast and this may lead to flash set. To prevent

this flash set, gypsum is added at the time of grinding the cement clinker. The quantity of

gypsum added has a bearing on the quantity of C3A present.

The hydrated aluminates do not contribute anything of concrete. On the other hand, their

presence is harmful to the durability of concrete particularly where the concrete is likely to be

attacked by sulphates. As it hydrates very fast it may contribute a little to the early strength.

On hydration, C4AF is believed to form a system of hydrated calcium ferrite of the form

C3FH6 is comparatively m ore stable. This hydrated product also does not contribute anything

to the strength. The hydrates of C4AF shows a comparatively higher resistance to the attack of

sulphates than the hydrates of calcium aluminate.

Many theories have been put forward to explain what actually is formed in the hydration

of cement compounds with water. It has been said earlier that product consisting of

(CaO.SiO2H2O) and Ca(OH)2 are formed in the hydration. Ca(OH)2 is an unimportant product,

and the really significant product is (CaO.SiO2H2O) For simplicitys sake this product of

hydration is commonly referred as C-S-H gel.

4.2.9 Fineness of Cement

The rate of hydration depends on the fineness of the cement particles and, for a rapid

development of strength, high fineness is necessary, the long-term strength is not affected.

Relation between strength of concrete at different ages and fineness of cement is shown in figure

4.7.[18]

- 42-

Figure no.4.7, Relation between strength of concrete at different ages and fineness of cement.

A higher early rate of hydration means, the cost of grinding to a higher rate of early heat

evolution. On the other hand, the cost of grinding to a higher fineness is considerable, and also

the finer cement the more rapidly it deteriorates on exposure to the atmosphere. Finer cement

leads to a stronger reaction with alkali-reactive less than a coarser one. An increase in fineness

increase the amount of gypsum required for proper retardation because, in a finer cement, more

C3A is available for early hydration. The water content of a paste of standard consistency is

greater the finer the cement, but conversely an increase in fineness of cement slightly improves

the workability of a concrete mix. Hence fineness is a vital property of cement and has to be

controlled carefully.

4.2.10 Transition Zone

Concrete is generally considered as two phase material i. e. paste phase and aggregates

phase. At macro level it is seen that aggregate particles are dispersed in a matrix of cement paste.

At the microscopic level, the complexities of the concrete being to show up, particularly in the

vicinity of large aggregate particles. This area can be considered as a third phase, the transition

zone, which represents the interfacial region between the particles of coarse aggregate and

20

25

30

35

40

45

150 200 250 300

Co

mp

ress

ive

Str

en

gth

Mp

a

Specific Surface (Wagner) m2/kg

Strength of concrete at different ages and fineness of cement

1 year

90 days

28 days

7 days

- 43-

hardened cement paste. Transition zone is generally a plane of weakness and has far greater

influence on the mechanical behavior of concrete.

Although transition zone is composed of some bulk cement paste, the quality of transition

zone is of poorer quality. Firstly due to internal bleeding, water accumulates below flaky and

large pieces of aggregates. This reduces the bond between paste and aggregate in general.

4.3 AGGREGATE

Quality of aggregate is considerable important because it has three- quarters of the

volume of concrete. Quality of aggregate effects on strength of concrete, durability and structural

performance of concrete. Aggregate consider as an inert material dispersed throughout the

cement paste largely for economic reasons. In fact, aggregate is not truly inert and its physical,

thermal and chemical properties influence the performance of concrete. Aggregate is cheaper

than cement and it is, therefore, economical to put into the mix as much of the former and as

little of the latter as possible. But economy is not the only reason for using aggregate; it confers

considerable technical advantages on concrete, which has a higher volume stability and better

durability than hydrated cement paste alone.

4.3.1 Source of Aggregate

All natural aggregate materials originate from bed rocks. There are three kinds of rocks,

namely igneous, sedimentary and metamorphic. The concrete making properties of aggregate are

influenced to some extent on the strength of geological formation of the parent rocks together

with the subsequent processes of weathering and alteration.

Most igneous rocks make highly satisfactory concrete aggregates because they are

normally hard, tough and dense. The igneous rocks have massive structure, entirely crystalline or

wholly glassy or in combination in between, depending upon the rate at which they were cooled

during formation. They may be acidic or basic depending upon the percentage of silica content.

- 44-

The sedimentary rocks with the stratified structure are quarried and concrete aggregates

are derived from it. The quality of aggregates derived from sedimentary rocks will vary in

quality depending upon the cementing material and the pressure which these rocks are originally

compacted. Some siliceous sand stones and limestone have proved to be good concrete

aggregate.

Both igneous rocks and sedimentary rocks may be subjected to high temperature and

pressure which causes metamorphism which changes the structure and texture of rocks.

Metamorphic rocks shows foliated structure and hence aggregate from such foliated structure is

not desirable characteristic from parent rocks. However many metamorphic rocks particularly

quartzite and gneiss have been used for production of good concrete aggregates.

4.3.2 Classification of Aggregate

The size of aggregate actually used varies but, in any mix, particles of different sizes are

incorporated, the particle size distribution being referred to as grading. In making low-grade

concrete, aggregate from deposits containing a whole range of sizes, from the largest to the

smallest, is sometimes used; this is referred to as all-in or pit-in aggregate. The alternative,

always used in manufacture of good quality concrete, is to obtain the aggregate in at least two

size groups, the main division being between fine aggregate, often called sand, not larger than 5

mm and coarse aggregate, which comprised material at least 5 mm. All natural aggregate

particles originally formed a part of a larger parent mass. This may have been fragmented by

natural processes of weathering and abrasion or artificially by crushing. Thus, many properties of

the aggregate depend entirely on the properties of the parent rock, e. g. chemical and mineral

composition, petrological character, specific gravity, hardness, strength, physical and chemical

stability, pore structure and colour. The classification of BS812: Part 1:1975 is most convenient

and is given in table 4.7 [18]

- 45-

Table 4.7

CLASSIFICATION OF NATURAL AGGREGATES ACCORDING TO ROCK TYPE (BS

812:PART:1:1975).

Basalt Group Flint Group Gabbro Group

Andesite

Basalt

Basic porphyrites

Diabase

Dolerites of all kinds including

theralite and teschenite,

Epidiorite

Lamprophyre

Quartz-dolerite

Spilite

Chert

Flint

Basic diorite

Basic gneiss

Gabbro

Hornblende-rock

Norite

Peridoite

Picrite

Serpentinite

Granite Group Gritstone Group Hornfels Group

Gneiss, Granite

Granodiorite

Granulite, Pegmatite

Quartz-diorite

Syenite

Arkose, Greywacke

Grit, Sandstone

Tuff

Contact-altered rocks

of all kinds

exceptmarble

Limestone Group Porphyry Group Quartizite Group

Dolomite

Limestone, Marble

Aplite, Dacite

Felsite, Granophyre

Keratophyre,

Microgranite, Porphry

Quartz-porphyrite

Rhyolite, Trachyte

Ganister

Quartizitic

sandstones

Re-crystallized

Quartizite

Schist Group

Phyllite

Schist, Slate

All severely sheared rocks

- 46-

4.3.3 Sampling of Aggregate :-

Tests of various properties of aggregates are performed on samples of the material and,

the results of the tests apply to the aggregate in the sample. Aggregate is supplied in bulk so, we

should ensure that the sample is typical of the average properties of the aggregate. There is no

define procedure to collect the sample but an intelligent experimenter can obtain reliable results

if he or she bears in mind at all times that the sample taken is to be representative of the bulk of

the material considered. The main sample is made up of a number of portions drawn from

different parts of the whole. The minimum number of these portions, called increments, is ten,

and they should add up to a mass not less than that given in table 4.8 for particles of different

sizes, as prescribed by BS:812:Part:102:1989.

TABLE 4.8

MINIMUM MASS OF SAMPLES FOR TESTING AS PER BS812:PART102:1989

Maximum particle size present in

substantial proportion (in mm)

Minimum mass of sample

dispatched for testing

28 or larger 50

Between 5 and 28 25

5 or smaller 13

As shown in above table the main sample can be rather larger, particularly when large-

size aggregate is used, and so the sample has to be reduced before testing.

At all stages of reduction, it is necessary to ensure that the representative character of the

sample as the main sample and ipso facto as the bulk of the aggregate. The reducing of sample

size is done by dividing it into two similar parts by quartering and riffling by using riffler.

4.3.4 Shape and Texture of Aggregate :-

The shape of aggregate is an important characteristic since it affects the workability of

concrete. It is difficult to really measure the shape of irregular body like concrete aggregate

which are derived from various rocks. Not only the characteristic of the parent rock, but also the

- 47-

type of crusher used will influence the shape of the aggregates. The shape of the aggregate is

very much influenced by the type of crusher and the reduction ratio, i. e. the ratio of the size of

material fed into the crusher and to the size of the finished product. Many rocks contain planes of

parting or jointing which is characteristic of its formation. It also reflects the internal

petrographic structure. As a consequence of these tendencies, schists, slates, and shales

commonly produce flaky forms, where as granite, basalt and quartizite usually yield more or less

equidimensional particles. Similarly, quartize which does not possess cleavage planes produces

cubical shape aggregates. Rounded aggregates are preferable than angular aggregates for a given

water/cement ratio for economy in cement requirement. On the other hand, the additional cement

required for angular aggregate is offset to some extent by higher strength and sometimes by

greater durability as a result of the interlocking texture of the hardened concrete and higher bond

characteristic between aggregate and cement paste. Flat particles in concrete aggregates will

have particularly objectionable influence on the workability, cement requirement, strength and

durability. In general excessively flaky aggregates makes very poor concrete. A convenient

broad classification of roundness as per BS 812:Part 1:1975 is shown in table 4.9.

Table 4.9

Particle Shape Classification of as per BS 812:Part 1:1975

Classification Description Examples

Rounded Fully water-worn or completely

shaped by attrition

River or seashore

gravel, desert, seashore

and wind-blown sand

Irregular Naturally irregular, or partly

shaped by attrition and having

rounded edges

Other gravels, land or

dug flint

Flaky Materials of which the thickness

is small relative to other two

dimensions.

Laminated rock

Angular Possessing well-defined edges

formed at the intersection of

roughly planar faces

Crushed rocks of all

types, talus, crushed slag

Elongated Material, usually angular, in

which the length is considerably

larger than the other two

dimension

-

Flaky and

elongated

Material having the length

considerably larger than the width

and the width considerably larger

than the thickness

-

- 48-

As per IS:2386(Part I) 1963 the angularity is determined in form of Angularity Number.

As suggested by Shergold the angularity number having value zero to 11 are suitable to make

suitable concrete. Murdock has suggested a different method for expressing the shape of

aggregate by parameter called Angularity Index fA. [19]

Angularity Index fA = 3fH/20 + 1.0 Where fH is the angularity number.

The mass of flaky particles expressed as a percentage of the mass of the sample is called

the flakiness index. Elongation index is similarly defined. The presence of elongated particles in

excess of 10 to 15 percent of the mass of coarse aggregate is generally considered undesirable,

but no recognized limits are laid down. However, for wearing surfaces, lower values of the

flakiness index are required.

Surface texture of the aggregate affects its bond to the cement paste and also influences

the water demand of the mix, especially in the case of fine aggregate. Surface texture is the

property, the measure of which depends upon the relative degree to which particle surfaces are

polished or dull, smooth or rough. Surface texture depends on hardness, grain size, pore

structure, structure of the parent materials, and the degree to which forces acting on the particle

surface have smoothed or roughened it. Visual estimate of roughness is quite reliable but in order

to reduce misunderstanding, the classification of surface texture as per IS :383 : 1970 is given in

table 4.10.

Table 4.10

SURFACE TEXTURE OF AGGREGATE AS PER IS : 383 :1970

Group Surface

Texture

Characteristics Examples

1 Glassy Conchoidal fracture Black flint, Vitreous slag

2 Smooth Water-worn, or smooth due to

fracture of laminated or fine-

grained rock

Gravels, Chert, Slate,

marble, some rhyolites

3 Granular Fracture showing more or less

uniform rounded grains

Sandstone, oolite

4 Rough Rough fracture of fine or

medium grained rock containing

no easily visible crystalline

constituents

Basalt, felsites, porphyry,

limestone

5 Crystalline Containing easily visible

crystalline constituents

Granite, gabbro, gneiss

6 Honeycombed With visible pores and cavities Brick, pumice, formed slag,

clinker, expanded clay

- 49-

It seems that the shape and surface texture of aggregate influence considerably the

strength of concrete. The flexure strength is more affected than the compressive strength, and the

effect of shape and texture are particularly significant in case of the high strength concrete. The

full roll of shape and texture of the aggregate in the development of concrete strength is not

known, but possibly a rough texture results in a larger adhesive force between the particles and

the cement matrix. Likewise, the larger surface area of angular aggregate means that a larger

adhesive force can be developed. The shape and texture of fine aggregate have a significant

effect on the water requirement of the mix made with the given aggregate. Flakiness and the

shape of coarse aggregate in general have an appreciable effect on the workability of the

concrete.

4.3.5 Bond and Strength of Aggregate :-

Bond between aggregate and cement paste is an important factor in the strength of

concrete, especially the flexure strength, but the nature of bond is not fully understood. Bond is

due, in part, to the interlocking of the aggregate and the hydrated cement paste due to the

roughness of the former. A rougher surface, such as that of crushed particles, results in a better

bond due to mechanical interlocking, better bond is also usually obtained with softer, porous, and

mineralogically heterogeneous particles. Generally, texture characteristics which permit no

penetration of the surface of the particles are not conducive to good bond. In addition, bond is

affected by other physical and chemical properties of aggregate, related to its mineralogical and

chemical composition, and to the electrostatics condition of the particle surface. In any case, for

good development of bond, it is necessary that the aggregate surface be clean and free from

adhering clay particles. The bond strength may not be a controlling factor in the strength of

ordinary concrete. However, in high strength concrete, there is probably a tendency for the bond

strength to be lower than the tensile strength of the hydrated cement paste so that preferential

failure in bond takes place. Indeed, the interface between the aggregate and the surrounding

cement pasties of importance, if only because coarse aggregate represents a discontinuity and

introduces a wall effect.

- 50-

Strength of aggregates is not concluded from the strength of parent rock, because the

strength of the rock does not exactly represent the strength of the aggregate in the concrete. Since

concrete is an assemblage of individual pieces of aggregate bound together by cementing

material, its properties are based primarily on the quality of the cement paste. This strength is

dependant also on the bond between the cement paste and the aggregate. Hence strong

aggregates cannot make strong concrete, for making strong concrete, strong aggregates are an

essential requirement. For strength to compressive applied load crushing value test carried out

and the crushing value of aggregated is restricted to 30 % for concrete used for roads and

pavements and 45 % for other structures. When crushing value becomes 30 % or higher, 10

percent fines value is carried out. Aggregate impact value test is carried out of concrete

aggregate in case concrete is subjected to impact. Aggregate abrasion value test is carried out

when concrete surface is subjected to wear, like road constructions, ware house floors and

pavement constructions. Strength of aggregates for different test of various type of rock group is

shown in table no. 4.11[19]

Table no. 4.11

AVERAGE TEST VALUES FOR ROCKS OF DIFFERENT GROUPS

Rock Group Crushing

Strength

(MPa)

Aggregate

crushing

value

Abrasion

value

Impact

value

Attrition value

Dry Wet

Specific

gravity

Basalt 200 12 17.6 16 3.3 5.5 2.85

Flint 205 17 19.2 17 3.1 2.5 2.55

Gabbro 195 - 18.7 19 2.5 3.2 2.95

Granite 185 20 18.7 13 2.9 3.2 2.69

Gritstone 220 12 18.1 15 3.0 5.3 2.67

Hornfels 340 11 18.8 17 2.7 3.8 2.88

Limestone 165 24 16.5 9 4.3 7.8 2.69

Porphyry 230 12 19.0 20 2.6 2.6 2.66

Quartzite 330 16 18.9 16 2.5 3.0 2.62

Schist 245 - 18.7 13 3.7 4.3 2.76

- 51-

4.3.6 Mechanical properties of Aggregate :-

Several mechanical properties of aggregate are important when it is used for special

work. Toughness is an important properties, which define as the resistance of a sample of rock to

failure by impact. Although this test would disclose adverse effects of weathering of the rock, it

is not used. Hardness or resistance to wear is an important property of concrete used in

pavements and floor surfaces subjected to heavy traffic. Other mechanical properties of

aggregate are as follows.

4.3.6.1 Specific Gravity of Aggregate :-

Specific gravity of aggregate is made used of in design calculation of concrete mixes.

With specific gravity of each constituent known, its weight can be converted into solid volume

and hence a theoretical yield of concrete per unit volume can be calculated. Specific gravity of

aggregate is also required in calculating the compacting factor in connection with the workability

measurements. Similarly, specific gravity of aggregate is required to be considered when light

weight and heavy weight concrete is designed. Average specific gravity of the rocks vary from

2.6 to 2.8, as shown in table no. 4.11.

4.3.6.2 Bulk Density of Aggregate :-

The bulk density or unit weight of an aggregate gives valuable information regarding the

shape and grading of the aggregate. For a given specific gravity the angular aggregates show a

lower bulk density. The bulk density of aggregates is measured by filling a container of known

volume in a standard manner and weighting it. The bulk density depends on the particle size

distribution and shape of the particles. The sample which gives the minimum voids or one which

gives maximum bulk density is taken as the right sample of aggregate for making economical

mix. Bulk density of aggregate is of interest when we deal with light weight aggregate and heavy

weight aggregate.

- 52-

4.3.6.3 Porosity, Absorption and Moisture Content of Aggregate :-

Some of the aggregates are porous and absorptive. Porosity and absorption of aggregate

will affect the water/cement ratio and hence the workability of concrete. The porosity of

aggregate will also affect the durability of concrete when the concrete is subjected to freezing

and thawing and also when the concrete is subjected to chemically aggressive liquids.

The water absorption of aggregate is determined by measuring the increase in weight of

an oven dry sample when immersed in water for 24 hours. The ratio of the increase in weight to

the weight of the dry sample expressed as percentage is known as absorption of aggregate. In

design calculation the relative weight of the aggregates are based on the condition that the

aggregates are saturated and surface dry. But in practice, aggregates in such ideal conditions

rarely met with. It should be noted that if the aggregates are dry they absorb water from the

mixing water and there by affect the workability and, on the other hand, if the aggregates contain

surface moisture they contribute extra water to the mix and there by increase the water/cement

ratio. Both these conditions are harmful for the quality of concrete. Corrective measure should

be taken both for absorption and for free moisture so that the water/cement ratio is kept exactly

as per the design. Figure no. 3.1[19]

shows a diagrammatic representation of moisture in

aggregates.

Figure no. 4.8 Diagrammatic Representation of Moisture in Aggregates

- 53-

4.3.6.4 Bulking of Aggregate :-

The free moisture content in fine aggregate results in bulking of volume. Free moisture

forms a film around each particle. This film of moisture exerts what is known as surface tension

which keeps the neighbouring particles away from it. Similarly, the force exerted by surface

tension keeps every particle away from each other. Therefore, no point contact is possible

between the particles. This causes bulking of the volume. The extent of surface tension and

consequently how far the adjacent particles are kept away will depend upon the percentage of

moisture content and the particle size of the aggregate. The bulking of increase with the increase

in moisture content up to a certain limit and beyond that the further increase in the moisture

content results in the decrease in the volume and at a moisture content representing saturation

point, the fine aggregate shows no bulking. Fine sand bulks more and coarse sand bulks less.

Bulking of fine, medium and coarse sand with different moisture content is shown in figure

no.4.9,

Figure 4.9, Bulking factor for sands with different moisture contents.

Coarse aggregate shows only a negligible increase in volume due to the presence of free

water, as the thickness of moisture films is very small compared with the particle size.

1

1.1

1.2

1.3

1.4

0 5 10 15 20 25Bu

lkin

g Fa

cto

r

Moisture Content of Sand in Percentage

Bulking Factor of Sand

Crushed Sand

Medium sand

Fine Sand

- 54-

4.3.6.5 Soundness of Aggregate :-

Soundness refers to the ability of aggregate to resist excessive change in volume as a

result of changes in physical conditions. These physical conditions that affect the soundness of

aggregate are the freezing and thawing, variation in temperature, alternate wetting and drying

under normal conditions and wetting and drying in salt water. Aggregates which are porous,

weak and containing any undesirable extraneous matters under go excessive volume change

when subjected to the above conditions. Aggregates which undergo more than the specified

amount of volume change is said to be unsound aggregates. If concrete is liable to be exposed to

the action of frost, the coarse and fine aggregate which are going to be used should be subjected

to soundness test.

The soundness test consists of alternative immersion of carefully graded and weighed test

sample in a solution of sodium or magnesium sulphate and oven drying it under specified

conditions. The accumulation and growth of salt crystals in the pores of the particles, is thought

to produce disruptive internal forces similar to the action of freezing of water or crystallization of

salt. Loss in weight is measured for a specified number of cycles. Soundness test is specified in

IS 2386(part V). As a general guide, it can be taken that the average loss of weight after 10

cycles should not exceed 12 percent and 18 percent when tested with sodium sulphate and

magnesium sulphate respectively.

4.3.7 Alkali-Aggregate Reaction :-

For a long time aggregates have been considered as inert materials but later on,

particularly, after 1940s it was clearly brought out that the aggregates are not fully inert. Some of

the aggregates contain reactive silica, which reacts with alkalies present in cement i. e. sodium

and potassium oxide.

The type of rocks which contains reactive constituents include traps, andesites, rhyolites,

siliceous, limestones and certain types of sand stones. The reactive constituents may be in form

of opals, cherts, chalcedony, volcanic glass, zeolites etc. The reaction starts with attack on the

- 55-

reactive siliceous minerals in the aggregate by the alkaline hydroxide derived from the alkalies in

cement. As a result, the alkali silicate gels of unlimited swelling type are formed. When the

conditions are congenial, progressive manifestation by swelling takes place, which results in

disruption of concrete with spreading of pattern cracks and eventual failure of concrete

structures. The rate of deterioration may be slow or fast depending upon the conditions. There

were cases where concrete has become unserviceable in about a year s time. The factors

promoting the alkali-aggregate reaction are

(i) Reactive type of aggregate

(ii) High alkali content in cement

(iii) Availability of moisture

(iv) Optimum temperature conditions

4.3.7.1 Alkali-Silica Reaction:-

The reaction starts with the attack on the siliceous minerals in the aggregate by the

alkaline hydroxides in pore water derived from the alkalis(N2O and K2O) in the cement. As a

result, an alkali-silicate gel is formed, either in planes of weakness or pores in the aggregate

(where reactive silica is present) or on the surface of the aggregate particles. In the latter case, a

characteristic altered surface zone is formed. This may destroy the bond between the aggregate

and the surrounding hydrated cement paste. The gel is of the unlimited swelling type: it imbibes

water with a consequent tendency to increase in volume. Because the gel is confined by the

surrounding hydrated cement paste, internal pressures result and may eventually lead to

expansion, cracking and disruption of the hydrated cement paste. Thus, expansion appears to be

due to hydraulic pressure generated through osmosis, but expansion can also be caused by the

swelling pressure of the still solid products of the alkali-silica reaction. For this reason, it is

believed that it is swelling of the hard aggregate particles that is most harmful to concrete. Some

of the relatively soft gel is later leached out by water and deposited in the cracks already formed

by the swelling of the aggregate. The size of the siliceous particles affects the speed with which

reaction occurs, fine particles (20 to 30 um) leading to expansion within a month or two, larger

ones only after many years.

- 56-

The alkali-silica reaction occurs only in the presence of water. The minimum relative

humidity in the interior of the concrete for the reaction to proceed is about 85 % at 20o. At higher

temperatures, the reaction can take place at a somewhat lower relative humidity. Generally, a

higher temperature accelerates the progress of the alkali-silica reaction but does not increase the

total expansion induced by the reaction. The effect of temperature may be due to the fact that an

increase in temperature lowers the solubility of Ca(OH)2 and increases that of silica. The

accelerating effect of temperature is exploited in tests on the reactivity of aggregate.

4.3.7.2 Alkali-Carbonate Reaction:-

Another type of deleterious aggregate reaction is that between some dolomitic limestone

aggregates and the alkalis in cement. The volume of the products of this reaction is smaller than

the volume of the original materials so that the explanation for the deleterious reaction has to be

sought in phenomena different from those involved in the alkali-silica reaction. It is likely that

the gel which is formed is subjected to swelling in a manner similar to swelling of clays. Thus

under humid conditions, expansion of concrete takes place. Typically, reaction zones up to 2 mm

are formed around the active aggregate particles. Cracking develops within these rims and leads

to a network of cracks and a loss of bond between the aggregate and the cement paste.

One distinction between the silica- and carbonate-alkali reaction which should be borne

in mind is that the latter, the alkali is regenerated. It is probably for this reason that pozzolanas,

including silica fume, are not effective in controlling the alkali-carbonate expansion. However,

ground granulated blast furnace slag, which reduces the permeability of concrete is reasonably

effective. Fortunately, reactive carbonate rocks are not very widespread and can usually be

avoided.

4.3.8 Thermal properties of Aggregate :-

There are three thermal properties of aggregate that may be significant in the

performance of concrete, ; coefficient of thermal expansion, specific heat, and conductivity. The

last two are of importance in mass concrete or where insulation is required, but not in ordinary

- 57-

structural work. The coefficient of thermal expansion of aggregate influences the value of such a

coefficient of concrete containing the given aggregate: the higher the coefficient of the aggregate

content in the mix and on the mix proportions in general.

There is, however, another aspect of the problem. It has been suggested that if the

coefficient of thermal expansion of the coarse aggregate and the hydrated cement paste differ to

much, a large change in temperature may introduce differential movement and a break in the

bond between aggregate particles and surrounding paste. However, possibly because the

differential movement is affected also by other forces, such as those due to shrinkage, a large

difference between the coefficient is not necessarily detrimental when the temperature does not

vary outside the range of, say 4 to 600 C. Nevertheless, when the two coefficient differ by more

than 5.5 × 10-6

per 0C for durability of concrete subjected to freezing and thawing may be

affected.

The coefficient of thermal expansion can be determined by means of a dilatometer

devised by Verbeck and Hass for use with both fine and coarse aggregate. The linear coefficient

of thermal expansion varies with the type of parent rock, the range for the more common rocks

being about 0.9 × 10-6

to 16 × 10-6

per 0C. Linear coefficient of thermal expansion of different

rock types are shown in table 4.12[19]

Table 4.12

LINEAR COEFFICIENT OF THERMAL EXPANSION OF DIFFERENT ROCK TYPES

Sr. No. Rock Type Thermal coefficient of linear expansion

01 Granite 1.8 to 11.9 × 10-6

per 0C

02 Diorite, andesite 4.1 to 10.3 × 10-6

per 0C

03 Gabbro, basalt, diabase 3.6 to 9.7 × 10-6

per 0C

04 Sandstone 4.3 to 13.9 × 10-6

per 0C

05 Dolomite 6.7 to 8.6 × 10-6

per 0C

06 Limestone 09 to 12.2 × 10-6

per 0C

07 Chert 7.3 to 13.1 × 10-6

per 0C

08 Marble 1.1 to 16.0 × 10-6

per 0C

- 58-

For hydrated Portland cement paste, the coefficient varies between 11.0 to 16.0 × 10-6

per 0C, the coefficient also varying with the degree of saturation. Thus, a serious difference in

coefficients occurs only with the aggregates of a very low expansion; these are certain granites,

limestones and marbles. If extreme temperatures are expected, the detailed properties of any

given aggregate have to be known. For instance, quartz undergoes inversion at 5740 C and

expands suddenly by 0.85 percent. This would disrupt the concrete, and for this reason fire-

resistant concrete is never made with quartz aggregate.

4.4 Reinforced Steel :-

The reinforcements shall be used conforming to following;

(a) Mild steel and medium tensile steel bars conforming to IS 432 (Part I).

(b) High strength deformed steel bars conforming to IS 1786.

(c) Hard-drawn steel wire fabric conforming to IS 1566.

(d) Structural steel conforming to Grade A of IS 2062.

All reinforcement shall be free from loose mill scales, loose rust and coats of paints, oil

mud or any other substances which may destroy or reduce bond. Sand blasting or other treatment

is recommended to clean reinforcement. The modulus of elasticity of steel shall be taken as 200

kN/mm2. The characteristic yield strength of different steel shall be assumed as minimum yield

stress/ 0.2 percent proof stress specified in the relevant Indian Standard. Mild steel bars of

different diameters were used in preparation of specimens of different elements casted for

testing. The physical test result of reinforced bars are shown in table 4.13

Table 4.13

PHYSICAL TEST RESULTS OF REINFORCED BARS

Sr. No. Dia. Of

bar(mm)

Area of bar

(sq. mm)

Ultimate Tensile

Strength(Mpa)

Elongation

(In %)

Yield Stress

(Mpa)

01 6 28.27 536.51 24.3 268.56

02 8 50.27 626.51 17.6 445.51

03 10 78.54 620.53 16.9 437.37

04 12 113.09 606.85 16.2 430.81

05 16 201.06 600.85 15.9 427.66

06 20 314.16 597.86 14.9 422.47

- 59-

4. 5 Water :-

The concrete mix are design with water cement ratio 0.5, accordingly the water locally

available was checked to use for construction purpose as per IS 456 – 2000 clause no. 5.4, which

is clean and free from injurious amounts of oils, alkalis, salts, sugar, organic materials or other

substances that may be deleterious to concrete or steel.

Clean potable tap water was used for the preparation of cement concrete and cement

concrete partially replaced by fly ash. The curing of elements were carried out with same potable

water and sea water(to study the effect of aggressive conditions). Physico-chemical analysis of

potable and sea water were carried out as per IS3025, part 17,18,24,32. The parameters are as

shown in table 4.14.[20]

Table 4.14

PHYSICO-CHEMICAL ANALYSIS OF POTABLE AND SEA WATER

Sr. No. Types of Solids Content in

Potable

Water

Content in

Sea Water

Max. Permissible

Limits(IS456-2000)

01 Organic 130 510 200

02 Inorganic 610 39500 3000

03 Sulphate 180 1174 400

04 Chlorides 380 27000 2000

05 Total Dissolved Solids 880 40010 2000

06 pH Value 7.2 8.0 <6.0

07 Total Hardness CaCO3 - 6760 -

08 Sodium(as Na+) 430 8705 -

09 Calcium(as Ca++) 80 496 -

All parameters are expressed in mg/lit. except pH value.