Synthesis of a CKD modified fly ash based geopolymer cementitious material for enhancing pumpable roof support

Pumpable roof supports have been increasingly used as secondary support in longwall mining to provide a safe mining environment.This study examines the feasibility of using class F fly ash (FFA) with added cement kiln dust (CKD) to synthesize a geopolymer cementitious material (GCM) that will address the limitations of current cementitious materials (CMs) for building pumpable roof supports. The GCM is designed to be a combination of two individual pumpable grout streams: stream 1 being a slurry composed of FFA, CKD, superplasticizer and water, and stream 2 being an alkaline solution prepared with sodium silicate (SS) and sodium hydroxide (SH). When the two streams stay alone, they remain as a slurry and a solution, respectively, and can be easily handled and transported. When they are mixed together, a GCM is formed. The study systematically analyzed the influence of different factors on pumpability, setting time, and mechanical performance of the GCM. The results show that stream 1 can be designed to be pumpable for a long distance within a certain period of time simply by adjusting the water to solid ratio and superplasticizer content. Stream 2 is an alkaline solution containing SH and SS and can be easily pumped. The setting time can be effectively adjusted by including CKD. Furthermore, the GCM shows much higher peak and residual strength than the pumpable CMs currently used in practice.