| Popis: |
The use of sustainable concrete mixtures with high content of supplementary cementitious materials requires the understanding of the mechanical behaviour of these mixtures after exposure to damaging events such as fire. Deterioration due to microcracking may cause degradation of the mechanical and mass transport properties, therefore affecting the durability of damaged elements. It is therefore necessary to understand the resilience of concrete mixtures with high contents of supplementary cementitious materials. In this study, the dynamic shear modulus (Gd) and crack density parameter (ε) of five different mixtures with varying proportions of fly ash and silica fume before and after exposure to 150 ℃ (300 ℉) and 300 ℃ (570 ℉) were examined. A w/cm of 0.50 was selected for all mixtures; the control mixture had 100% ordinary Portland cement, all other mixtures had 5 % silica fume cement replacement and increasing fly ash cement replacement of 0%, 20%, 40% and 60%, and labelled as mixtures S0F0 (control), S5F0, S5F20, S5F40 and S5F60, respectively. Gd of thin concrete disks 25 mm (1 in) thick and 100 mm (4 in) in diameter were determined in both wet and air-dry conditions, to estimate ε. Before damage, Gd of mixture S0F0 was 15.0 GPa (2.20 Mpsi), and 14.5 GPa (2.10 Mpsi) for all other mixtures, and ε was 0.235, 0.250, 0.225, 0.230 and 0.255 for mixtures S0F0, S5F0, S5F20, S5F40 and S5F60 respectively. The study found that the exposure to 300 ℃ produced a decrease in Gd and an increase in ε that was statistically significantly higher than companion specimens exposed to 150 ℃ using paired analysis. No statistically significant difference was observed in the decrease in Gd and increase in ε between mixtures for each exposure, indicating similar deterioration of the sustainable mixtures and the control mixture after exposure to moderate temperatures. |
