Performance of Cement–Fly Ash Masonry Mortar with Sand from Mine Overburden as an Environment-Friendly Alternative to Conventional Fine Aggregate

There is an increasing demand for fine aggregate for use in concrete and mortar. In this study, sand extracted from mine overburden from two locations through the wet-sieving process was used as alternative fine aggregate in mortar. The behavior has been benchmarked with mortar using conventional river sand and coarse and fine sand obtained from crushed stone. Combination mortar with ordinary portland cement and Class C fly ash was used as a binder. The sand-to-binder ratio was fixed as 3, as per ASTM C270-19ae1, Standard Specification for Mortar for Unit Masonry, whereas the fly ash–to–cement ratio was varied from 0.75 to 3. The water required to achieve a constant flow value of 110 ± 5 % was determined. The water retention of fresh mortar and dry density, compressive strength, and drying shrinkage of hardened mortar were determined. Mortar mixtures with sand from mine overburden with a fineness modulus of 2.36 conformed to the water retention requirement of ASTM C91/C91M-18, Standard Specification for Masonry Cement, whereas very fine sand did not satisfy. Masonry mortar with different mixture proportions and fineness modulus of fine aggregate resulted in a range of compressive strengths, satisfying a wide range of mortar designations as per ASTM C270-19ae1, BS EN 998-2, Specification for Mortar for Masonry - Part 2, and IS 2250, Code of Practice for Preparation and Use of Masonry Mortars. For mortar with a fine aggregate of different origins (river sand, crushed stone coarse sand, sand from overburden with fineness modulus 2.67, 3.01, and 2.36, respectively), a marginal variation in drying shrinkage across strength was observed. The maximum drying shrinkage of the higher fly ash–to–cement ratio of the mixture with finer sand was 1,600 microstrain.