Page 7 - Open Access-June 2019

TECHNICAL PAPER

3.1.2 Fine aggregate out trial mixes and finally mix proportion were adopted for
M 30 and M 90 grades of concrete according to IS:10262 (2009)
Locally available river sand was used. Fineness modulus and
specific gravity of the sand are 2.85 and 2.66 respectively. The and ACI 211.4R-08 respectively. The quantities of ingredient
sand used conforms to grading Zone II of IS: 383(1970). materials used in these mixes and workability results are shown
in Table 2.
3.1.3 Coarse aggregate
Table 2: Mix proportions of M30 and M90
In the present study the coarse aggregate was used after
sR. InGREdIEnt
nORMaL
soaking in water for 24 hours and then completely air dried. nO. stREnGtH HIGH stREnGtH
COnCREtE M 90
The fraction of coarse aggregate passing through 20 mm COnCREtE M 30
and retained on 10 mm is taken as 2/3 of total aggregate. 3 3
The remaining 1/3 fraction is aggregate passing from 10 mm 1 Cement (OPC 53 370 kg/m 594 kg/m
and retained on 4.75 mm. For M 30 grade of concrete, both grade)
sizes of aggregates were used but for M90 grade of concrete 2 Micro silica (10% Nil 66 kg/m 3
aggregate passing through 10 mm was used in mix. The higher of cementitious
the targeted compressive strength, the smaller the maximum material)
size of the coarse aggregate should be. The fineness modulus 3 Fine aggregate 740 kg/m 3 650 kg/m 3
and specific gravity of coarse aggregate are 6.30 and 2.78 4 Coarse aggregate 1214 kg/m 3 1105 kg/m 3
respectively.
5 Water 165 l/m 3 145 l/m 3
3.1.4 Water 6 Superplastcizer Nil 0.8% by weight
Master Glenium of cementitious
Water is the most important ingredient of concrete and a part ACE 30 material
of mixing water is utilized in hydration of cement to form the
binding matrix and the remaining water acts as a lubricant to 7 Workability 45 mm slump 0.85 (compaction
make the concrete readily in pouring state. Locally available factor)
potable water having pH value of 7 conforming to IS: 3025 (1986)
is used in this work. Usually mixing is done in two different stages for HSC. Dry
mixing is done before the addition of water and wet mixing is
done after addition of water. After dry mixing of the ingredients
3.1.5 Superplasticizer
for one minute, 60% of water is added to the ingredients and
Master Glenium ACE 30 (JP) is a chemical admixture of a new mixed uniformly. The remaining 40% of water is mixed with
generation based on second-generation poly carboxylic ether superplasticizer, Master Glenium ACE 30 and is introduced into
polymer with high early strength gains. Master Glenium ACE 30 the mixer and ingredients are mixed for 3 minutes until the mix
(JP) is free of chloride and low alkali. It has specific gravity of 1.09 is uniform. The total mixing time is 4 minutes. After mixing,
and solids content not less than 34% by weight. the concrete is poured on the pre wetted platform then filled
into moulds. The cube moulds of 100 mm x 100 mm x 100 mm
3.1.6 Mineral admixture size are used to prepare specimens. All moulds are retained
The specific gravity of micro silica is 2.2. Specific surface area for a period of 24 hours in a moist air. Then the specimens
of micro silica was 19,000 m /kg (from manufacturer’s data). are demoulded, marked and cured in a curing tank with fresh
2
The high surface area of micro silica would increase the water water. They are cured for a period of 28 days. The specimen is
demand. The use of micro silica can reduce bleeding and heated in oven without preload at a prescribed rate to a target
improve cohesion of the mix. The cohesiveness of concrete temperature, which is maintained until a thermal steady state
containing micro silica is good for pumping and for underwater is reached within the specimen. The temperature of oven is
concrete. controlled by using thermostat. Their double walled insulation
maintains the heat in oven and conserves energy. The rate
of heating of specimens in oven follows time– temperature
3.2 Casting, curing and testing of specimens
heating curve of ISO 834 (1975) as shown in Fig. 3.2. The
The sequence of feeding ingredients in the pan mixer depends specimen is allowed to cool to room temperature. The load is
on the properties of mix and those of mixer. In this work, a applied without shock and increased continuously at rate of
small amount of water is fed first, followed by coarse aggregate approximately 140 kg/sq.cm/min as specified in IS: 516 (1959)
in saturated surface dry condition and fine aggregate. These until the resistance of the specimen to the increasing load
materials are mixed uniformly and cementitious material fed breaks down and no greater load can be sustained. The results
into the mixer. After attaining uniform mixture of all ingredients, of this test are more suitable for assessing the post fire (residual)
water is added. The mix proportions were arrived after carrying properties of concrete.

The IndIan ConCreTe Journal | June 2019 11