Comparison of the strength and durability performance of normal- and high-strength pozzolanic concretes at elevated temperatures

The strength and durability performance of normal- and high-strength pozzolanic concretes incorporating silica fume, fly ash, and blast furnace slag was compared at elevated temperatures up to 800°C. The strength properties were determined using an unstressed residual compressive strength test, while durability was investigated by rapid chloride diffusion test, mercury intrusion porosimetry (MIP), and crack pattern observations. It was found that pozzolanic concretes containing fly ash and blast furnace slag give the best performance particularly at temperatures below 600°C as compared to the pure cement concretes. Explosive spalling occurred in most high-strength concretes (HSCs) containing silica fume. A distributed network of fine cracks was observed in all fly ash and blast furnace slag concretes, but no spalling or splitting occurred. The high-strength pozzolanic concretes showed a severe loss in permeability-related durability than the compressive strength loss. Thirty percent replacement of cement by fly ash in HSC and 40% replacement of cement by blast furnace slag in normal-strength concrete (NSC) was found to be optimal to retain maximum strength and durability after high temperatures.