Engineering properties of effective microorganism-based tin slag mortar

Abstract

Lately, there has been a global trend of the use of waste materials in construction. Industrial wastes such as tin slag are found in large quantities at landfills in Asia. Their removal will birth a safer environment since these deposits contain metals and radionuclides. Moreover, the use of waste aggregates may significantly affect the properties of mortar. Insufficient strength of mortar produced by natural fine aggregates has necessitated its replacement with other materials such as tin slag. The smoothness and roundness of natural fine aggregate reduces its bond and overall strength of mortar. Therefore, tin slag; with its superior aggregate properties was used as a natural aggregate substitute in this study. However, tin slag contains toxic metals and radionuclide’s, which make the material unfit for use without remediation. Effective microorganisms were incorporated in mortar mixes as additive. Independent variables considered are; replacement levels of 0%, 25%, 50%, 75% and 100%, dilution ratios of EM1, molasses and water, EM type (EM1, EM2) and EM to water ratio (EM/W). Hardened properties were determined by compressive strength, flexural strength, tensile strength, water absorption, ultrasonic pulse velocity and expansion tests. The optimum concentrations of EM that maximally improved mortar properties and reduced the concentration of radionuclides were determined. Fresh properties of tin slag mortar indicate that mortar flow increases as tin slag replacement increases. Mechanical properties testing show that optimum replacement is 50% of tin slag. The valorisation of tin slag in mortar reduced concentration of metals drastically below permissible limit, while inclusion of EM as additive further reduces the concentration of metals and radionuclides. EM1 and EM2 performed optimally in terms of mechanical properties and remediation of tin slag, respectively. Mortar mix containing 50% tin slag, 30% fly ash, 10% EM and cured at 50 ºC produced optimum strength.