Investigation on the setting time improvement of geopolymer cementitious material developed for pumpable roof supports

A novel geopolymer cementitious material (GCM) has recently been developed at the University of Arizona for the construction of pumpable roof supports (PRSs) in underground coal mines. The newly developed GCM not only demonstrated superior mechanical properties but also addressed the cracking issues of the traditional CM when exposed to air. However, during the full-scale production and performance evaluation of the GCM, it was observed that the GCM encountered a self-supporting issue. Specifically, the setting time of the GCM was longer than anticipated, leading to slight buckling during the production of the PRSs. The present study explores different additives to adjust the setting time of the GCM, aiming to improve its self-supporting capacity at the very beginning. To achieve the goal, systematic laboratory experiments were conducted to investigate the setting time and self-supporting capacity of the GCM containing different types and dosages of additives. The rheology, compressive strength, tensile strength, and toughness of the GCM at different conditions were evaluated. X-ray diffraction (XRD) analyses were also performed to study the effect of the additives on the phase composition of the GCM. The results show that with the addition of free lime up to a certain amount, the GCM achieves good self-supporting while maintaining its superior mechanical properties and durability.