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

In this study, the elevated 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 the temperature degrees (in a range of 20 to 600°C), LFC densities of 600, 800, 1000, 1200 and 1400 kg/m3 and additive content. Two mixes were made by replacing 15% and 30% of cement mass with FA and in other two series; PF was added to LFC mix, respectively by 0.2% and 0.4% of binder volume, one controlled mixture without additives was also produced. After being subjected to high temperatures, the flexural strengths of LFC have been investigated. The reduction of LFC flexural strength in temperature may be principally due to the formation of micro cracks at temperature above 93°C since the flexural strength is adversely influenced by cracks so that a severe strength loss was observed at 600°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 elevated temperature and the most reliable model was recommended for future researches.