Environmental effects of concretes produced from partial replacement of cement and sand with coal ash

Abstract

Environmental effects of concretes produced from partial replacement of cement and sand with coal ash were investigated. Oxide composition of coal ash and cement was determined with X-ray fluorescence spectrometer, while particle size and shape were determined using scanning electron microscope. Concrete mixtures were produced by replacing cement and sand with coal ash at 10, 20, 30 and 40%. Their workability, setting times and compressive strengths were obtained using iron cube mold, Vicat apparatus and compression testing machine, respectively. Biochemical oxygen demand (BOD) and pH of curing water were analyzed. Pollution potential of the cement and concretes produced by partially replacing cement with coal ash was evaluated using CO2 emission simulation. Concretes in which sand was replaced with coal ash (CAS) had better slumps and compressive strengths than those in which cement was replaced with coal ash (CAC). Setting times increased as more coal ash was added but were lower for CAS. BOD analysis of curing water showed it was safe for livestock consumption and body contact during recreational use. CO2 emissions and concrete carbonation analysis showed blending of cement with coal ash reduced emissions which ranged from 0.22 to 0.33 kg but was 0.37 kg in conventional concrete. CAC-40:60 had the lowest emission of CO2 from cement. CO2 uptake after 50-year service life showed that CAC-30:70 had the highest absorption-to-emission ratio of 38.5%. Secondary application of coal ash in concrete production should be encouraged as concretes of similar strengths were obtained with reduction in environmental pollution.