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.
- 25-
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
USA
Average
No. of Samples
90
11
Japan
29.0 – 85.6
55.3
55
Italy
82 – 100
95
400
India
20 – 32
-
37
- 26-
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
En-450
En-197-I
En-3892-I
Sio2 minimum
25
25
20
70
70
MgO, Maximum
70
LOI(1hour)max.
6
Total alkalis, max.
1.5
SO3, maximum
5
5-7
5-7
3
2
1
1
Total/reactive CaO, maximum
10
10
34
7
40
12
34
320
75
75
80
Lime reactivity, N/mm2
80
4.5
Soundness, Le-Chatelier, mm
Autoclave, Percent
3.0
10
Blaines fineness m2/kg min.
Cement activity 28 days
5
1.5
Free CaO, maximum
Fineness, 45 micron, maximum
2003- I
35
Reactive/soluble Sio2, min.
Sio2+Al2O3+Fi2O3 minimum
IS 3812
10
0.8
10
10
10
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.
- 27-
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.
- 28-
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
- 29-
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
01
02
03
04
05
06
07
08
09
10
11
B
B
B
B
B
B
SB
SB
SB
L
L
Physical Properties
Specific
Fineness (% retained on
Blaine Specific
(LeChateli
45-u sieve)
Surface, m2 /kg
er )Method
Wet Sieving
Dry Sieving
2.53
2.58
2.88
2.96
2.38
2.22
1.90
2.05
2.11
2.38
2.53
17.3
14.7
25.2
19.2
21.2
40.7
33.2
19.4
46.0
24.9
2.7
12.3
10.2
18.0
14.0
16.1
30.3
26.4
14.3
33.0
18.8
2.5
- 30-
289
312
127
198
448
303
215
326
240
286
581
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.
- 31-
Table 4.4
CHEMICAL PROPERTIES OF FLY ASH
Sr. No.
Particular
Requirement as per
Test Results in %
IS:3812 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
- 32-
Table 4.5
MINERALOGICAL COMPOSITION OF SOME SELECTED FLY ASHES[16]
Fly Ash
Type of
Phase Composition, %
source
coal
Glass
Quartz
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
Mullite Magnetite Hematite LOI(%)
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
Water
Silicate
Calcium
Calcium
Silicate
Hydroxide
Hydrate
Portland cement only
C3S
+
H
→
C-S-H
Portland Cement + Fly Ash
S
+
CH
→
C-S-H
Silica
Calcium
(Fly Ash)
Hydroxide
- 33-
+
CH
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
- 34-
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
- 35-
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.
- 36-
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.
Rate of liberation cal per gm per
hour
Heat of liberation
7
6
5
4
3
2
1
0
0
5
10
Time, Hours
15
Figure 4.4, Heat liberation from setting cement
- 37-
20
25
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.
Rate of Hydration
1
0.9
Fraction hydrated
0.8
0.7
0.6
C2S
0.5
C3S
0.4
C3A
0.3
C4AF
0.2
0.1
0
1
180
Age in days (log scale)
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.
- 38-
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]
- 39-
Strength Development of Pure Compounds
Compressive Strength Mpa
80
70
60
50
C3S
40
C2S
30
C3A
20
C3AF
10
0
0
100
200
300
400
Age-days
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.
- 40-
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]
- 41-
Strength of concrete at different ages and fineness of
cement
Compressive Strength Mpa
45
40
35
30
1 year
25
90 days
28 days
20
150
200
250
300
7 days
Specific Surface (Wagner) m2/kg
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
- 42-
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.
- 43-
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]
- 44-
Table 4.7
CLASSIFICATION OF NATURAL AGGREGATES ACCORDING TO ROCK TYPE (BS
812:PART:1:1975).
Basalt Group
Flint Group
Gabbro Group
Andesite
Chert
Basalt
Flint
Basic porphyrites
Diabase
Dolerites of all kinds including
Basic diorite
Basic gneiss
Gabbro
Hornblende-rock
Norite
theralite
and
Epidiorite
Lamprophyre
Quartz-dolerite
Spilite
Peridoite
Picrite
Serpentinite
teschenite,
Granite Group
Gritstone Group
Hornfels Group
Gneiss, Granite
Granodiorite
Arkose, Greywacke
Grit, Sandstone
Contact-altered rocks
of
all
kinds
Granulite, Pegmatite
Quartz-diorite
Syenite
Tuff
exceptmarble
Limestone Group
Porphyry Group
Quartizite Group
Dolomite
Limestone, Marble
Aplite, Dacite
Felsite, Granophyre
Keratophyre,
Microgranite, Porphry
Quartz-porphyrite
Ganister
Quartizitic
sandstones
Re-crystallized
Quartizite
Rhyolite, Trachyte
Schist Group
Phyllite
Schist, Slate
All severely sheared rocks
- 45-
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 Minimum
mass
substantial proportion (in mm)
dispatched for testing
28 or larger
50
Between 5 and 28
25
5 or smaller
13
of
sample
As shown in above table the main sample can be rather larger, particularly when largesize 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
- 46-
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
Rounded
Irregular
Flaky
Angular
Elongated
Flaky
elongated
Description
Examples
Fully water-worn or completely River
or
seashore
shaped by attrition
gravel, desert, seashore
and wind-blown sand
Naturally irregular, or partly Other gravels, land or
shaped by attrition and having dug flint
rounded edges
Materials of which the thickness Laminated rock
is small relative to other two
dimensions.
Possessing well-defined edges Crushed rocks of all
formed at the intersection of types, talus, crushed slag
roughly planar faces
Material, usually angular, in which the length is considerably
larger than the other two
dimension
and Material having the length considerably larger than the width
and the width considerably larger
than the thickness
- 47-
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
1
2
3
4
5
6
Surface
Texture
Glassy
Smooth
Characteristics
Examples
Conchoidal fracture
Water-worn, or smooth due to
fracture of laminated or finegrained rock
Granular
Fracture showing more or less
uniform rounded grains
Rough
Rough fracture of fine or
medium grained rock containing
no easily visible crystalline
constituents
Crystalline
Containing
easily
visible
crystalline constituents
Honeycombed With visible pores and cavities
- 48-
Black flint, Vitreous slag
Gravels,
Chert,
Slate,
marble, some rhyolites
Sandstone, oolite
Basalt, felsites, porphyry,
limestone
Granite, gabbro, gneiss
Brick, pumice, formed slag,
clinker, expanded clay
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.
- 49-
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
Aggregate
Abrasion
Impact
Strength
crushing
value
value
(MPa)
value
Basalt
200
12
17.6
Flint
205
17
Gabbro
195
Granite
Attrition value
Specific
gravity
Dry
Wet
16
3.3
5.5
2.85
19.2
17
3.1
2.5
2.55
-
18.7
19
2.5
3.2
2.95
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
- 50-
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.
- 51-
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
- 52-
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,
Bulking Factor of Sand
1.4
Bulking Factor
1.3
1.2
Crushed Sand
1.1
Medium sand
1
Fine Sand
0
5
10
15
20
25
Moisture Content of Sand in Percentage
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.
- 53-
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
- 54-
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.
- 55-
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
- 56-
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
- 57-
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 fireresistant 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
Area of bar
Ultimate Tensile
Elongation
Yield Stress
bar(mm)
(sq. mm)
Strength(Mpa)
(In %)
(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
- 58-
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
Content in
Max. Permissible
Potable
Sea Water
Limits(IS456-2000)
Water
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.
- 59-