Thermal and mechanical properties of light-weight concrete exposed to high temperature

The extensive studies devoted so far to normal-strength light-weight aggregate concrete (LWAC orLWC) have exhaustively clarified its behaviour in ordinary conditions. However, the introduction of high-performance light-weight aggregate concrete (HPLWAC or HPLWC), containing such pozzolanic components as microsilica and fly ash, raises some concerns, for instance about the behaviour at high temperature and after cooling. To investigate the temperature-induced mechanical damage, both in compression and tension, of silicafume HPLWCs, a systematic research program was carried out at the Politecnico di Milano on materials residual behaviour (testing after cooling down to room temperature). Three concrete mixes (Normal-Strength Concrete =NSC, fc20 = 30MPa; Light-Weight Concrete =LWC, fc20 40MPa; and High-Performance Light-Weight Concrete =HPLWC, fc20 60MPa), five temperature levels (20, 105, 250, 500 and 750 C, no loads applied during heating), one thermal state (after cooling), three nominally-equal tests for each case (for repeatability) were planned, bringing the total number of specimens to 120 (45 tested in compression, 45 in direct tension and 30 in indirect tension by splitting). At the same time, the thermal diffusivity of the materials was evaluated up to 750 C (4 specimens). The results show that HPLWC is somewhat more temperature-sensitive than both NSC andLWC, but this extra sensitivity is counterbalanced by HPLWC’s lower diffusivity. Its better insulation properties are advantageous for the concrete in axially-loadedmembers and for the tension bars in the beams, as demonstrated by the thermo-mechanical analyses of three typical R/C sections (rectangular, T and slab sections) carried out in the second part of the paper.