Use of Coal Mine Overburden as Sustainable Fine Aggregate in Cement Mortar

Abstract

The natural aggregate crisis is an alarming concern for the construction industry worldwide. This study provides a detailed investigation of coal mine overburden (OB) from opencast mine dumps, to evaluate its potential as a sustainable alternative to natural aggregate. The microproperties, including mineralogy, morphology, and chemistry, were evaluated, and the macroproperties, including alkali–aggregate reaction, soundness, durability, flow value, ultrasonic pulse velocity, and other mechanical properties of crushed OB, OB-based mortar, and concrete, were determined. OB was found to be mineralogically more stable (55%–77% SiO2), mechanically comparable, and durable (volume change 3%–8%) than other alternatives of natural aggregate. The toxicity characteristic due to leaching was found to have no hazardous effects on local and regional soil and water quality. The cement mortar prepared using OB had similar performance in terms of fresh and hardened density, flowability (>0.6 w/c), and durability [slake durability index (SDI) >95%] as other industrial by-products. The compressive strength of the mortar with OB was found to be comparable to that of mortar with river sand. OB-based mortar and concrete were found to have good corrosion resistance. For bulk utilization of OB, a pilot-scale study is recommended to assess its performance under real-world exposure conditions.