Mechanical properties variations of expandable foam grout containing various alkali-free accelerator contents

Expandable foam grout (EFG) is a cementitious mixture with relatively high flowability, high volume expansion, and low long-term strength. EFG mixtures typically contain water, cement, bentonite, aluminum powder, and an alkali-free accelerator. Aluminum powder induces volume expansion in EFG mixtures through chemical reactions with the cement paste, resulting in hydrogen gas generation in the cement paste. Subsequently, gas retention establishes a porous structure as the mixture loses its flowability through cement hydration (cement setting). The alkali-free accelerator plays a critical role in the activation of cement hydration, depending on the accelerator content. Therefore, it is important to evaluate the effects of the accelerator content on the volume expansion and strength of EFG mixtures because the hydration rates affect these characteristics. This study experimentally observed the evolution of the expansion ratio and compressive strength of EFG mixtures with various accelerator contents. The expansion ratio and compressive strength decreased with an increase in accelerator content, partly because of the shortened setting time. Based on these results, the relationship between the accelerator content of the EFG mixtures and their mechanical properties was established. Furthermore, the relationship between volume expansion and compressive strength was determined.