Damage behavior of geopolymer composites exposed to elevated temperatures

This paper presents a study on geopolymers and geopolymer/aggregate composites made with class F fly ash. Samples were heated up to 800 degrees C to evaluate strength loss due to thermal damage. The geopolymers exhibited strength increases of about 53% after temperature exposure. However, geopolymer/aggregate composites with identical geopolymer binder formulations decreased in strength by up to 65% after the same exposure. Test data from dilatometry measurements of geopolymers; and aggregates provides an explanation for this behavior. The tests show that the aggregates steadily expanded with temperature, reaching about 1.5-2.5% expansion at 800 degrees C. Correspondingly, the geopolymer matrix undergoes contraction ofabout 1% between 200 degrees C and 300 degrees C and a further 0.6% between 700 degrees C and 800 degrees C. This apparent incompatibility is concluded to be the cause of the observed strength loss. This study presents the results of 15 different geopolymer combinations (i.e. mixture proportions, curing and age) and four different aggregates. (C) 2008 Elsevier Ltd. All rights reserved.