Factors affecting the expansion ratio and flow consistency of expandable foam grout for subsurface improvement

Highly porous cementitious materials have been utilized in various geotechnical applications, such as filling subsurface cavities, backfilling, and enhancing loose layers. In particular, expandable foam grout (EFG) has significant potential for cavity filling owing to its unique characteristics such as volume expansion and high flowability. Various EFG samples were prepared by mixing water, cement, aluminum powder, bentonite, and an accelerator at various ratios. Cementitious materials with various mixing ratios have different volume expansion and flowability, and each ingredient causes different impacts on their properties. This study investigated the effects of aluminum and bentonite contents on volume expansion and flowability. Expansion ratios and flow consistencies were estimated from expansion and flow tests. The results show that the expansion ratios increased with increasing aluminum content regardless of the water-cement ratio while slightly decreased with increasing bentonite content within a given range of ingredient contents. Moreover, the flow consistency increased with increasing water-cement ratio and decreasing aluminum and bentonite contents. The properties were evaluated using EFG mixtures containing relatively high bentonite contents to observe the effects of bentonite on a wide range of cementitious materials with varying bentonite contents. The expansion ratios and flow consistencies of the EFG mixtures containing relatively high bentonite contents decreased steeply with increasing bentonite content. Finally, the ingredient effects on volume expansion and flowability were discussed to design the mixture depending on its purpose.