Page 4 - Open Access-June 2019

TECHNICAL PAPER

EFFECt OF tHERMaL

CYCLEs On COMpREssIvE

stREnGtH OF HIGH

stREnGtH COnCREtE

(M 90) COMpaREd tO

nORMaL stREnGtH

COnCREtE (M 30) B. VIDyA, K. SRInIVASA RAO

Abstract the residual properties of concrete at sustained or cyclical high
temperature. This kind of information has become increasingly
With an increased usage of high strength concrete (HSC) in in demand for several reasons. First, advanced industrial
general structural construction and its application in power, applications, in particular for nuclear reactors, require a greater
nuclear and oil industries where structures are subjected to knowledge of the properties of various types of concrete when
elevated temperatures and in the event of accidental fires, it is subjected to complex, sustained or repetitive, mechanical
essential to investigate its behaviour. There is a serious lack of and thermal stress regimes at moderately high temperatures.
fire test data for HSC subjected to thermal cycles and hence it is Second, new concrete constituents and proportions continue to
important to study the mechanical properties of HSC compared become available as some industrial and military applications
to normal strength concrete.
require special concrete that is resistant to specific service
temperature regimes.
This paper presents the study of residual compressive
strength and weight loss of high strength concrete compared
to normal strength concrete of age 28 days subjected to High strength concrete (HSC) used to minimize the space taken
up in buildings/structures by columns and maximize the area
thermal cycles namely 1, 5, 10, 15, 20, 25, 30, 35, 40, 45 and
50 apart from control concrete. Specimens were exposed to that can be utilized. Further, HSC has denser micro-structure
temperatures from 100 to 400°C for 8 hours exposure duration than normal strength concrete resulting in improved durability
and subsequent air cooling for the remaining period of day. in terms of lower-permeability. Because of this property,
Therefore, one thermal cycle consists of 8 hours heating and 16 HSC gives a more pleasing environment as there would be
comparatively no permeation or movement of liquids, gasses
hours cooling. The results obtained can be useful as guidelines
for fire resistant design of the structures subjected to heating etc. These types of concretes used in structures like chimneys
and cooling cycles at elevated temperatures. and nuclear power plants and industrial installation are often
subjected to elevated temperatures and also sometime exposed
to elevated temperature due to fire. Subjecting concretes to
Keywords: Compressive strength, Thermal cycles, Weight loss
elevated temperature due to fire, leads to severe deterioration
and it undergoes a number of transformations and reactions,
1. INTRODUCTION thereby causing reduced strength and durability. The physical
To improve fire resistance in design, or to assess the condition and chemical changes in concrete under elevated temperatures
and possibilities of repair of a structure damaged by fire, more depend not only on matrix composition but also on the type
needs to be known about the mechanical properties of concrete of aggregate, water-to-cementitious material ratio, porosity,
at elevated temperatures and residual properties after slow or humidity, and age of concrete.
quench cooling. It is relatively easy to determine the residual
properties by standard test methods and the results do provide Hence, it is proposed in this work to investigate the behaviour
much of the information needed to determine what can be of normal and high strength concrete exposed to thermal cycles
saved after a fire. However, one has to focus in determining at elevated temperatures. Investigations are proposed on

8 The IndIan ConCreTe Journal | June 2019