Alkali-activated aluminosilicate composite with heat-resistant lightweight aggregates exposed to high temperatures: Mechanical and water transport properties

A lightweight composite material with alkali-activated aluminosilicate binder is investigated. The intended use of this material is the high-temperature applications, such as the fire-protecting layers for Portland-cement based structures. Therefore, a heat-resistant mixture of expanded vermiculite and electrical porcelain is used as aggregates. Basic physical characteristics, mechanical properties and water- and water vapor transport properties are studied as functions of previous heat treatment up to 1200 °C. Experimental results show that the studied material has very good high-temperature properties which are quite superior to Portland-cement concrete. The open porosity increases only up to 7% between room temperature and 1000 °C. The material keeps 35% of its original compressive strength and 66% of its flexural strength even in the worst case of 800 °C pre-heating. After pre-heating to 1200 °C the compressive strength is found 30% higher and flexural strength three-and-half times higher than in the reference state. Liquid moisture diffusivity is after the heat treatment up to three orders of magnitude higher than in reference room-temperature conditions. The water vapor transport parameters allow fast removal of water vapor and other gaseous compounds over the whole studied heat-treatment range.