Additives for improving paste backfill mixes

Paste backfill mixtures exhibit high water demands due to high surface area, mineralogical composition and state of dispersion of the fine particles. A reduced water content results in a loss of flow unless an additive is used to compensate. Several additives have been tested to determine the water reduction attainable while maintaining the same flow of a “model” paste backfill mixture without additives. In addition, the compressive strength of the low binder-content backfill mixtures was monitored. In these tests, the binder was composed of 90% slag and 10% portland cement. The results show that specific additives can reduce the water requirements (2% to 28%) without sacrificing the original flow properties. Reducing the water content in the paste can significantly increase its compressive strength (5% to as much as 100%), as long as the additive type and amount does not cause excessive retardation.