Influence of High Temperatures on Flexural Strength of Foamed Concrete Containing Fly Ash and Polypropylene Fiber

In this study, the high temperature flexural strengths of lightweight foamed concrete (LFC) containing fly ash (FA) and polypropylene fiber (PF) was investigated experimentally and statistically. The variables included were temperature (in the range 20 to 600 degrees C), LFC densities of 600, 800, 1000, 1200 and 1400 kg/m(3) and additive content. Two mixes were made by replacing 15% and 30% of cement mass with FA. In another two series 0.2vol% and 0.4vol% of PF was added to LFC mix, and finally, one controlled mixture without additives was produced. After being subjected to high temperatures, the flexural strengths of LFC were investigated. The reduction of LFC flexural strength at high temperature may be principally due to the formation of micro cracks at temperatures above 93 degrees C, since the flexural strength is adversely influenced by cracks so that a severe strength loss was observed at 600 degrees C and the flexural strength was only about 40% of its original value. Flexural strength of LFC with higher density achieved a higher value regardless to temperature. LFC flexural strength exposed to high temperature increased by contribution of FA and PF and this relative improvement for all series was the most pronounced for LFC with higher density and higher additive content. In addition, the applicability of some suggested models for normal concrete was examined for the flexural strength prediction of LFC incorporating different percentages of FA and PF at high temperature and the most reliable model was recommended for future researches.