Effect of foaming agent and admixtures on hydration in ultralight foam concrete with cement-metakaolin binders

Ultralight foam concrete (ULFC) typically exhibit a complex composition, comprising Ordinary Portland cement, potential secondary cementitious materials, and a mix of admixtures to ensure mix stability, high-quality structure, desired consistency, and rapid setting. The rational selection of ULFC composition demands a comprehensive understanding of the interactions among its components and the exploration of the hydration process can facilitate this challenge. Especially, significant importance lies in the interaction between admixtures and the protein-based foaming agent (FA) employed for foam concrete production. This study fills a significant gap in the literature on foam concrete by conducting detailed hydration studies. The research aimed to investigate the relationship between the composition of the base paste and the content of the foaming agent, aiming to reveal their combined impact on the hydration heat of ULFC. Isothermal calorimetry was employed to measure heat emission and heat flow rate over 168 h. It was concluded that the use of a stabilizer (ST) and superplasticiser (SP) in foam concrete extended both the induction period (respectively by 46 % and 35 %) and end of acceleration period (respectively by 6 % and 20 %), and thus acceleration admixture is advised. Simultaneously, compatibility studies are recommended for hardening accelerators (HA) concerning other admixtures and foaming agents. Metakaolin (MK) demonstrated effective acceleration in cement hydration (by 7 % for just cement paste, and 18 % for foam concrete) and its use in foam concrete is strongly recommended. Additionally, restrained use of a foaming agent (FA) is advised due to its retarding effect at higher concentrations, as the induction phase can be prolonged up to 50 % in the presence of FA.