The mechanical properties of light-weight concrete (LWC) in fire are known to be better than those of normal-strength concrete (NSC), both at high temperature (hot properties) and after cooling (residual properties). The objective of this paper is to increase the knowledge of LWC's residual properties by testing a number of mixes containing expanded clay as light-weight coarse aggregate.An experimental program was carried out, in which one normal-weight concrete mix and two lightweight aggregate mixes containing different amounts of LECA were used to fabricate 72 concrete cylinders and 36 concrete prisms. All mixes contained silica fume as a supplementary cementitious material. The specimens were tested at the ambient temperature and after exposure to temperatures of 250, 500, and 750 C to obtain their compressive and tensile strength, modulus of elasticity, and stress-strain response. Results indicate that exposure to temperatures up to 250 C has no significant effect on the mechanical properties of concrete containing LECA just as in normal weight concrete.However, with increasing the temperature, increasing the lightweight aggregate content of the mix resulted in better strength retention after exposure to elevated temperatures. The experimental data are also used to develop equations to evaluate the residual mechanical properties of concrete.

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The present research is focused on developing efficient, durable flexural members by combining the use of lightweight concrete (LWC), fiber‐reinforced polymer (FRP) bars, and prestressing. The use of LWC reduces the structural weight while providing suitable thermal insulation whereas using FRP bars instead of steel reinforcement provides corrosion resistance, light weight, high tensile strength, and fatigue resistance. Both materials possess smaller moduli of elasticity compared to those in materials within conventional construction, which may cause large deflections and excessive crack widths that are addressed via prestressing. Six LWC beam specimens were fabricated and tested, all of which contained FRP bars. Two specimens were not prestressed, one in under‐reinforced and the other in over‐reinforced conditions. The other four specimens contained different configurations of prestressing steel in addition to FRP bars. The experimental results were used to validate nonlinear finite element models in Abaqus. Results showed that of a prestress level of 6 MPa in concrete reduced the beam deflection at failure by 28% and increased the cracking load by three times. Therefore, a relatively small prestress level could compensate for the increase in deflection and possible cracking, which shows the merits of this combination in providing an optimal solution for the structural members of the future.

This study explores the effects of mixture design parameters on the residual mechanical properties of lightweight expanded clay aggregate (LECA) concrete exposed to elevated temperatures. A total of 30 lightweight concrete mixtures were cast and exposed to three elevated temperatures, namely 250°C, 500°C, and 700°C. The test variables comprised the LECA percentage used as partial volume substitution for natural sand (0%, 25%, 50%, 75%, and 100%), silica fume partial replacement for cement by weight (5%, 7.5%, 10%, 12.5%, and 15%), cement content (300, 400, 500, 600, and 700 kg/m3), and different water‐to‐cement (W/C) ratios (0.25, 0.313, 0.375, 0.438, and 0.5). The compressive and indirect tensile strengths were measured before and after exposure to elevated temperatures. The results indicate that the lightweight concretes incorporating higher contents of cement and silica fume and made with lower W/C ratio exhibited higher initial mechanical properties yet incurred more significant drop in mechanical properties after exposure to 500°C and 750°C.