A study on spalling behaviour of geopolymer mortars using ring restraint test

Abstract

This paper presents the spalling behaviour of two types of geopolymer mortars (fly ash geopolymer and fly ash-slag geopolymer) using ring restraint specimens and is compared with normal cement mortar and polymer cement mortar. All mortar specimens are exposed to fire according to RABT 30 fire curve. Spalling depth, area and volume of all mortar specimens are measured to grade the spalling performance according to Japan Concrete Institute (JCI) spalling evaluation guide. Restraint stress, vapour pressure and temperatures at various depths from heated surface of all mortar specimens are also measured to evaluate the spalling behaviour. Results show that the fly ash-slag geopolymer mortar, normal cement mortar and polymer cement mortar spall compared to no spalling of fly ash geopolymer mortar. However, micro cracking is observed on the heated surface of fly ash geopolymer mortar specimen. Among the three mortars which showed spalling, the fly ash-slag geopolymer mortar took longer time to spall. The moisture content of both geopolymer mortars is lower than that of normal cement mortar and polymer cement mortar and this might be the reason for better spalling behaviour of former than that of latter mortars. Based on JCI spalling evaluation criteria the fly ash geopolymer mortar exhibited much better performance than the other mortars. Sharp increase in vapour pressure and sudden drop of vapour pressure are observed in all three mortar specimens which showed spalling behaviour, except the fly ash geopolymer mortar where no such sudden drop in vapour pressure is observed.