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 pozzol anic concretes incorporating silica fume, fly ash, and blast furnace slag w as compared at elevated temperatures up to 800 degreesC. The strength prope rties were determined using an unstressed residual compressive strength tes t, while durability was investigated by rapid chloride diffusion test, merc ury intrusion porosimetry (MIP), and crack pattern observations. It was fou nd that pozzolanic concretes containing fly ash and blast furnace slag give the best performance particularly at temperatures below 600 degreesC as co mpared to the pure cement concretes. Explosive spalling occurred in most hi gh-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 concr etes showed a severe loss in permeability-related durability than the compr essive strength loss. Thirty percent replacement of cement by fly ash in HS C and 40% replacement of cement by blast furnace slag in normal-strength co ncrete (NSC) was found to be optimal to retain maximum strength and durabil ity after high temperatures. (C) 2001 Elsevier Science Ltd. All rights rese rved.