Substitution of Low-Calcium Fly Ash for Partial Portland Cement in Underground Backfilling Mining

The ordinary Portland cement (OPC) as usual binder is widely used for the backfilling in the Zijinshan Copper mine of Fujian province, whereas it leads to high cost of cemented paste backfill (CPB) every year. The main objectives of this study were to investigate the effect of low-calcium fly ash (LCFA) substituting for OPC on the compressive strength of CPB samples, through treating LCFA with mechanical and chemical action method to improve its pozzolanic activity. The experiment results show that the compressive strength of CPB samples is not increased when the non-treated LCFA is added into substitute for partial OPC. However, the compressive strength is obviously improved by the replacement of partial OPC with treated LCFA. When the substitution ratio of treated LCFA is 29.8%, the 28-day compressive strength of CPB samples with binder/tailing ratio of 1:6 achieves 3.9 MPa, and is 1.95 times higher than that of CPB samples with OPC as sole binder under the same condition. The economic analysis result exhibits a partial replacement (29.8%) of OPC with treated LCFA can save 28.7% of cemented backfill cost, indicating great economic benefit for underground backfilling mining.