Page 6 - Open Access-June 2019

TECHNICAL PAPER

Anders (2016) conducted experiments in order to investigate the 3. EXPERIMENTAL WORK
effects of different types of cements and aggregates, increased
number of thermal cycles and different storing climates on Calculation of mix proportions for HSC (M90) and NSC (M30)
concrete mixtures. It is demonstrated that the compressive
strength starts to decrease at temperatures above 250°C. The
temperature levels were chosen as 250°C, 500°C and 900°C. After Casting and curing of specimens
the maximum temperature was reached it was kept constant
for 4 hours. The cooling down phase took about 10 hours. The
Specimens subjected to thermal cycles
number of thermal cycles varied between 1, 8 and 24 cycles. The
decrease in strength is governed by the type of aggregate used.
Thermal cycles up to 24, do not further decrease the mechanical Determination of weight loss and residual compressive
properties. The decrease in strength seems to be governed by strength for HSC (90) and NSC (M30)
the maximum temperature instead of the number of thermal
cycles. The way and duration of storing the concrete mixtures
after high temperature exposure also seems to affect the residual Comparison of results
strength. After being exposed to 250°C, the residual compressive Figure 3.1: Flow chart for experimental procedure.
strength was decreased by about 20%.
3.1 Materials used
After review of relevant literature, in this paper it is restricted
to study the behaviour of high strength and normal strength The concrete used in this experimental work is made by
concrete subjected to 1, 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50 mixing ordinary Portland cement with hard blue granite chips,
number of thermal cycles exposed to temperature up to 400°C. sand, water, mineral admixture and chemical admixture. The
One thermal cycle means heating of specimens for 8 hours and properties of the individual materials are mentioned as follows.
subsequent cooling for remaining period of day. The specimens
are heated for 8 hours in order to resemble the structural 3.1.1 Cement
performance of concrete in chimneys, nuclear reactors vessels Ordinary Portland cement of 53 grade conforming to IS
and the elements which are close to the industrial furnaces which 12269(1987) was adopted in this work. Its chemical and physical
will be in operation for a maximum period of 8 hours in a day. properties are given in Table 1.

Table 1: Chemical and physical properties of cement
sR. nO. paRtICuLaRs tEst REsuLts REquIREMEnts as pER Is:4031(1988)
CHEMICAL REQUIREMENTS
1. Insoluble material (% by mass) 0.68 28.96 Maximum
2. Magnesia (% by mass) 1.16 6.00 Maximum
3. Sulphuric anhydride (% by mass) 1.73 3.00 Maximum
4. Loss on ignition (% by mass) 1.15 5.00 Maximum
5. Total chlorides (% by mass) 0.006 0.10 Maximum

PHYSICAL REQUIREMENTS
1. Fineness is weight retained on IS 90 micron sieve 5.5% 10% Maximum
2. Standard consistency (%) 30
3. Setting time
a) Initial (minutes) 155 30 Minimum
b) Final (minutes) 225 600 Maximum
4. Soundness
a) Le-chatelier method (mm) 1.0 10.0 Maximum
b) Autoclave method (%) 0.026 0.8 Maximum
5. Compressive strength (MPa)
at 3 days 39.61 Min. 27
at 7 days 50.05 Min. 37
at 28 days 63.60 Min. 53

10 The IndIan ConCreTe Journal | June 2019