Water transport in binary eco-cements containing coal mining waste

Abstract

This study explores certain indirect, water transport-related durability indicators for mortars made with cement in which 20% or 50% of the ordinary portland cement (OPC) is replaced by thermally activated coal mining waste (ACMW). The valorisation of ACMW is triply beneficial, environmentally speaking, for it reduces waste stockpiling and its processing emits less CO2 and requires less fossil fuel-based energy than OPC manufacture. Its addition was observed to generate a finer pore structure and a larger volume of pores accessible to water. In mortars with 50% ACMW, pore volume rose by approximately 30%, lowering density and consequently mechanical strength. Total water absorption declined by 13% and capillary absorption by 24% in mortars with 20% ACMW, whilst no significant variations in either parameter relative to the OPC reference were found in the materials with 50% replacement ratios. Permeability to water penetration under pressure rose substantially in both blended mortars, although as the maximum and mean depth values lay within the limits specified in Spain's structural concrete code, the materials would be classified as impermeable. The mortars with 20% replacement exhibited no greater drying shrinkage than the OPC materials, whereas the mortars bearing 50% ACMW shrank by approximately 50% more than the reference.