Journal of Multidisciplinary Engineering Science Studies (JMESS) ISSN: 2458-925X Vol. 3 Issue 9, September - 2017 www.jmess.org JMESSP13420401 2084 Physical properties and compressive strength of concrete exposed to progressive heat A. P. Adewuyi* Department of Civil Engineering Federal University of Agriculture Abeokuta, Nigeria O. A. Olaniyi Department of Civil Engineering Ladoke Akintola University of Technology Ogbomoso, Nigeria K. A. Ibrahim Department of Civil Engineering Kebbi State University of Science & Technology Birnin-Kebbi, Nigeria D. D. Babalola Department of Civil Engineering Ladoke Akintola University of Technology Ogbomoso, Nigeria *Corresponding Author: adewuyiap@funaab.edu.ng Abstract—Exposure of concrete to harsh environmental conditions has varying degrees of influence on the performance and service life of structures. The present work reports the results of an experimental investigation conducted to evaluate the influence of ambient laboratory temperature and stepwise elevated temperature of 100°C, 200°C, 300°C, 400°C, and 500°C at a rate of 1°C/min on the physical properties and compressive strength of concrete specimens. The concrete cubes were made in accordance to BSI standards. Unstressed residual thermal effects such as physical appearance, mass loss, and change in compressive strength were investigated via laboratory experimentation. Compared to the ambient exposure, the results showed that loss of pore water and strength reduction were mild up to 100°C, while remarkable deterioration trend was recorded at higher temperatures. Keywords—Concrete, compressive strength, unstressed thermal load, mass loss, deterioration, durability I. INTRODUCTION The fundamental aim of structural design is to realize an acceptable probability that proposed structures will not only perform satisfactorily during the intended life, but also be able to sustain all the loads and deformations with adequate durability and resistance to the effects of misuse and fire [1], [2]. One of the prime requirements in terms of safety of a structure is that the structure should provide enough protection to the occupants in case of fire. Concrete is a major construction material once believed to be an eternal construction material [3], but are often threatened by aging, usage-dependent fatigue, and deterioration due to harsh environment and other external and internal stressors. Concrete is a composite material with aggregate as inclusions and cement paste as matrix. The two phases have different thermal and mechanical properties and thus respond differently under elevated temperature. Due to its low thermal conductivity a layer of concrete is frequently used for fireproofing of steel structures which is vulnerable to damage by fire. However, the binding material can decompose if heated to too high a temperature, with consequent loss of strength. Being a porous substance bound together by water-containing crystals, loss of moisture at elevated temperature causes shrinkage and expansion of aggregates thus leading to cracking and spalling of the concrete. In the past two decades, extensive experimental studies have been conducted on various properties of concrete especially physical, chemical and micro- structural evolution of the binding phase under high temperature [4 – 7]. Pioneer studies conducted on this subject concluded that the residual strength of all the concrete at all elevated temperatures fell below the ambient strength [8], [9]. It was also reported that residual strengths in compression and tension, as well as elastic modulus of concrete dropped drastically at elevated temperature up to 500°C [10] . Khoury et al. [11] found that compressive strength of concrete at high temperature was largely affected by individual constituent of concrete, sealing and moisture conditions, loading level during heating period, operational exposure conditions, rate of heating or cooling cycle and duration thermal loading. Morita et al. [12] conducted unstressed residual strength tests and revealed that high strength concrete (HSC) has higher rate of reduction in residual compressive strength than the normal strength concrete (NSC). Castillo and Durani [13] investigated thermal effects on the strength and load-deformation behavior of HSC and NSC under stressed and unstressed test conditions. In the unstressed experiment in the range of 100-300°C, HSC showed a 15 - 20% loss of compressive strength, while NSC recorded negligible strength loss. HSC recovered its strength between 300- 400°C, reaching a maximum value of 8 - 13% above the strength at room temperature. At temperature above 400°C, both NSC and HSC progressively lost compressive strength to about 30% of the room temperature strength at 800°C. Furumura et al. [14]