Page 5 - Open Access-June 2019

TECHNICAL PAPER

concrete of age 28 days and exposed to temperatures from 100 reduction after 90 thermal cycles could be due to the initiation
to 400°C for 8 hours duration and subsequent air cooling for the of micro-cracks between the paste and hard phases. The
remaining period of a day. Therefore, one thermal cycle means mechanical properties of the UHP are improved even after
8 hours heating and 16 hours cooling. The results obtained 90 thermal cycles. This could be attributed to the continued
can be useful as guidelines for fire resistant design of the hydration of unhydrated cement and to the presence of micro
structures subjected to heating and cooling cycles at elevated silica that activates the secondary reaction. The presence of
temperatures. fibres seems to counteract any possible deterioration due to
micro-cracking. NSC and HSC can be successfully repaired with
2. LITERATURE REVIEW the UHP using the technique of adhesive bonding.

Thermal cycling causes progressive degradation of concrete. Chandramouli et al. (2012) studied on the compressive strength
The loss of strength in the concrete with temperature is of ordinary grade of concrete such as M 20, M 30, M 40 and M
influenced by number of factors. The method of testing, that 50 subjected to thermal cycles at a temperature of 50ºC. The
is, the rate of heating, the duration of heating, size and shape concrete specimens of size 100 mm x 100 mm x 100 mm cubes
of the test specimen, cooling regimes, number of thermal were cast for testing compressive strength. The test specimens
cycles and the loaded condition (loaded or unloaded during were demolded after 24 hours of air cooling and kept for water
testing) have a significant effect on the change of strength with curing for 28 days. The decrease in compressive strength of
temperature.
ordinary concrete mixes in comparison with zero thermal cycles
Srinivasa Rao et al. (2006) conducted investigations on M 20, for 50°C were observed to be varied from 14 to 23 % for 28, 56,
M 30, M 40 and M 50 grades of concrete containing OPC, 90 and 180 thermal cycles.
replacement of cement with fly ash and addition of fly ash Khan (2014) investigated on flexural strength of M 80 grade
by exposing them for various thermal cycles at different concrete subjected to thermal cyclic loads. The tests were
temperatures i.e 50 and 100°C. The compressive strength of carried out on normal weight concrete specimens of size 100
concrete at various thermal cycles i.e. 7, 28, 45 and 90 were mm × 100 mm × 500 mm. The concrete was subjected to a
evaluated and compared. The results revealed that concrete constant temperature of 200°C for 7, 14, 21 and 28 heating
containing fly ash addition was more effective in resisting the cycles. One heating cycle corresponds to eight hours heating
effect of thermal cycles than ordinary and fly ash replace cement
concrete. and subsequent cooling in twenty four hours. After the desired
number of thermal cycles, the specimens were tested for flexural
Garg and Singh (2006) produced cementitious binders by strength of concrete. Thermal cycling causes loss of strength in
blending 60-70% fly ash with calcined phosphogypsum, concrete.
hydrated lime sludge, Portland and chemical activator in
different proportions. The durability of cementitious binder has Sjostrom (2014) studied the effect of heating and cooling
been studied by heating and cooling cycles at temperatures cycles on compressive strength of cubes tested at the end of
from 27 to 50°C. The results indicate that the strength of the 20, 40 and 80 heating – cooling cycles of 60°C and 90°C. The
binder decreased with increasing cyclic studies at different specimens were kept immersed in water. Compressive strength
temperatures. of concrete cubes subjected to thermal cycles is expected to rise
due to continued hydration of cement.
Kanellopoulos (2009) investigated the effect of thermal cycles
on the fracture properties of the cement-based bi-materials. Srinivasa Rao and Seshadri Sekhar (2015) investigated on the
Sixty eight cubes were exposed to a varied number of 24- effect of thermal cycles on the strength properties of glass fibre
hour thermal cycles ranging from 0 to 90 and subsequently self compacting concrete using alkaline glass fibres in various
were tested in a wedge splitting configuration. The maximum proportions of controlled mixes of grade M 30 to M 65. The
temperature was then maintained for another 8 hours before the improvements in compressive, split tensile, flexural strength
beams were cooled down to the room temperature in a further of self compacting concrete and glass fibre self compacting
16 hours. The specimens were exposed to 30 and 90 thermal concrete mixes in comparison with zero thermal cycles are
cycles. The mechanical and fracture properties of normal observed to be varied from 40 to 60 % at 50oC and 20 to
strength and high strength concretes are substantially improved 30 % at 100oC for 28, 90 and 180 thermal cycles. Glass fibre
after 30 thermal cycles, but less so after 90 thermal cycles both self compacting concrete mixes are observed to give higher
in isolation and when bonded to an ultra-high performance strengths than self compacting concrete mixes when exposed
(UHP) fibre-reinforced cement-based composite. The increase to thermal cycles. The variation in strengths of glass fibre self
in these properties after 30 thermal cycles is probably due to compacting concrete mixes is observed to be 15 to 20% when
the continued hydration of unhydrated cement. However, the compared with self compacting concrete.

The IndIan ConCreTe Journal | June 2019 9