Abstract—This paper presents the results of an experimental study on the effects of elevated temperature on compressive and flexural strength of Normal Strength Concrete (NSC), High Strength Concrete (HSC) and High Performance Concrete (HPC). In addition, the specimen mass and volume were measured before and after heating in order to determine the loss of mass and volume during the test. In terms of non-destructive measurement, ultrasonic pulse velocity test was proposed as a promising initial inspection method for fire damaged concrete structure. 100 Cube specimens for three grades of concrete were prepared and heated at a rate of 3°C/min up to different temperatures (150, 250, 400, 600, and 900°C). The results show a loss of compressive and flexural strength for all the concretes heated to temperature exceeding 400°C. The results also revealed that mass and density of the specimen significantly reduced with an increase in temperature. Keywords—High temperature, Compressive strength, Mass loss, Ultrasonic pulse velocity. I. INTRODUCTION ONCRETE is the most widely used construction material in the world. Although concrete engineering is more than one hundred years old and concrete is thought to be a well- understood construction material. In recent years, high performance concrete (HPC) is becoming an attractive to traditional normal strength concrete (NSC). HPC exhibits significantly higher mechanical strengths as well as superior performances under severe conditions in comparison with normal strength concrete (NSC). The alleged HPC is generally defined as high fluidity and high durability concrete, moreover, high performance water reducer and superfine mineral admixtures are absolutely necessary ingredients. The dense microstructure of HPC ensures a high strength and a very low permeability, which is essential to obtain good durability in severe exposure conditions where there are aggressive agents. However, the dense microstructure of HPC seems to be a disadvantage, when compared to NSC, in the situation where concrete is exposed to fire. Fire represents one of most sever risks to buildings and structures. Being a primary construction material, the properties of concrete after exposure to high temperatures have gained a great deal of attention since the 1940s [1]–[3]. S. Hachemi is with Civil Engineering and hydraulic Laboratory LARGHYDE, University of Biskra, 07000, Algeria, (phone: 213-557534498; e-mail: samia_hachemi4@yahoo.fr). A. Ounis is foreman Civil Engineering and hydraulic Laboratory LARGHYDE, University of Biskra, 07000, Algeria, (e-mail: safidin@ yahoo.fr). S. Chabi is with Civil Engineering and hydraulic Laboratory LARGHYDE, University of Biskra, 07000, Algeria. The behavior of NSC under elevated temperatures has been clearly understood [4]–[6]. In recent years, there have been many research studies to determine the thermal behavioral differences between HSC and NSC [7]–[16]. The mechanical properties of concrete at high temperature degrade mainly because of two relevant mechanisms: mechanical and physic-chemical damage [17]–[23]. In the case of elevated heating conditions, the dehydration of CSH gel, the thermal incompatibility between the aggregate and cement paste and the pore pressure within the cement paste are the main detrimental factors. To investigate the effect of high temperature and to obtain necessary information for evaluating the structural safety and establishing reparation methods, the residual strength and properties of concrete that has been exposed to high temperatures should be determined. In this experimental investigation, the effect of elevated temperatures on the physical and mechanical properties of concrete mixtures produced by different water/cement (w/c) ratios and different types of aggregates were extensively examined. In the tests, temperatures of 20, 150, 250, 400, 600 and 900°C were chosen for ease of observation of the test results. II. EXPERIMENTAL STUDY The cement used in this study was Portland cement (CPJ CEM II/A 42.5). Its chemical composition is presented in Table I. Natural siliceous river sand with a maximum grain size of 5mm was used as a fine aggregate (fineness modulus of 2.65). Coarse aggregate was crushed calcareous (diameter ranging from 5mm to 20mm). The specific gravity of the aggregate was 2600 kg/m 3 . TABLE I CHEMICAL, PHYSICAL AND MECHANICAL PROPERTIES OF CEMENT USED Chemical composition (%) Physical properties CaO Al2O3 SiO 2 Fe 2 O 3 MgO Na2O K2O Cl - SO 3 60.41 5.19 21.91 2.94 1.60 0.16 0.54 0.02 2.19 Specific gravity (kg/m 3 ) Initial setting (h:mn) Final setting (h:mn) 3000 2 h : 06’ 3 h : 03’ Compressive strength (MPa) 2 days 7 days 28 days 19.03 44.93 53.41 100mm cube specimens were prepared for three grades of concrete named NSC, HSC and HPC, respectively. The mix proportions of each concrete are given in Table II. The concretes specimens were cast in the moulds for 24h at room temperature of (20±2)°C. After demolding, specimens were S. Hachemi, A. Ounis, S. Chabi Evaluating Residual Mechanical and Physical Properties of Concrete at Elevated Temperatures C World Academy of Science, Engineering and Technology International Journal of Civil, Architectural, Structural and Construction Engineering Vol:8 No:2, 2014 176 International Scholarly and Scientific Research & Innovation International Science Index Vol:8, No:2, 2014 waset.org/Publication/9997531