Laboratory investigation into the compressive strength of cemented paste tailings aggregate fills

Abstract

The use of backfill has now become a component of underground mining operations. In terms of mining methods, the top-down method would be less expensive than the bottom-up method, irrespective of the rock mass hardness. However, the implementation of the top-down method requires a high compressive strength ( 4 MPa) of backfill. The addition of aggregates (e.g. crushed waste rock) to the tailings could achieve this targeted strength. This paper investigates the effect of adding aggregates (crushed waste rock) on the compressive strength development of cemented paste tailings aggregate fill (PAF). Two types of waste rock were crushed to two aggregate sizes (0/10 and 0/15 mm) and their proportion in PAF mixtures varied from 10 to 50 %v/v (by cumulative volume of dry crushed waste rock and tailings). These are oxidised acid generating waste rocks (AG) and non-acid generating waste rocks (NAG). The binder type used is a blend of 20% general use Portland cement (type GU) and 80% of ground granulated blast furnace slag (GBFS) at 5 wt% (by total dry mass of aggregates and tailings). The unconfined compressive strength was determined at seven, 28 and 90 days of curing. The results show that the addition of crushed development waste rock to the cemented paste backfill increases significantly its compressive strength. The strength gain varies in the range 2893% at 28 days and 544% at 90 days of curing in drained conditions. However, the strength development is influenced by the aggregate class of size, the volume and the mineralogy of the aggregates in the mixture.