View into the testing furnace during fire testing of lightweight mortars based on alkali-activated fly ash.
Source: BAM divisions Technology of Construction Materials, Technical Properties of Polymeric Materials and Building Materials
Alkali-activated fly ashes (AAFAs) are novel binders with a better stability at high temperatures than conventional cements. This makes AAFAs promising materials for fire protection systems, e.g. for road tunnels and steel structures. However, several aspects of their stability and their deterioration when exposed to fire are still poorly understood. In a collaboration of BAM with the University of Bologna, the processes that take place when AAFAs and lightweight mortars based on these binders are exposed to high temperatures were studied using fire testing coupled with acoustic emission analysis as well as microstructural analyses. It was found that significant cracking on heating occurred exclusively during loss of pore water in the temperature range ~90–360 °C, while no further cracking was detected via acoustic emission measurements up to temperatures of 1100 °C. However, considerable cracking was observed on cooling if the materials had previously been heated to 600 °C or higher; this was attributed to local sintering and partial melting in the materials above this critical temperature and subsequent quenching of the affected regions. These results have implications for the design of AAFA-based fire protection systems and particularly for the interpretation of scanning electron micrographs, which are usually captured after cooling, in studies of the heat resistance of AAFAs and related materials.
Acoustic emission study of heat-induced cracking in fly ash-based alkali-activated pastes and lightweight mortars
L. Carabba, Stephan Pirskawetz, Simone Krüger, Gregor Gluth, M.C. Bignozzi
published in Cement and Concrete Composites, Vol. 102, pages 145 - 156, 2019
BAM divisions Technology of Construction Materials, Technical Properties of Polymeric Materials and Building Materials