Comparative Evaluation of Potential Impacts of Agricultural and Industrial Waste Pozzolanic Binders on Strengths of Concrete

Concrete is one of the most widely used construction material in the world which uses aggregates and cement as a binder. Use of cement concrete and mining/ transportation of raw materials makes the construction industry the biggest emitter of CO2 by contributing up to 7-10% of global emissions. The waste materials from different industries and agriculture contribute to 90% of waste disposal/ recycling effort in the world. This research has focused to use a selection of waste materials as supplementary cementitious materials (SCM) to minimize the emission of CO2 and recycling/ absorption of waste from other industries to construction industry to make it more sustainable. The contemporary research has established use of pulverized fly ash (PFA), silica fume (SF), metakaolin (MK) and granulated ground blast furnace slag (GGBS) as suitable SCMs. This study has focused on using two established industrial waste SF and MK and two agricultural wastes, rice husk ash (RHA) and palm ash (PA), to determine and compare their potential use as pozzolanic SCMs and to expand the family of alternative pozzolanic binders in addition to PFA and GGBS. The w/c (w/b) ratio was 0.4 with an intended design mix strength classification of C50/60. The chemical composition of all the materials was determined through x-ray spectrometry/ diffraction test to ascertain the chemistry. All four materials satisfied the ASTM constituent criteria for pozzolans. In comparison to the control mix (100% cement content), all these materials improved the compressive strength from 2.5% to 30% and enhanced tensile strength from up to 17%, indeed all the SCM mixes had a higher compressive strength than the control. RHA exhibited the best performance in agricultural waste with 10% optimum quantity to give maximum compressive strength of 83 MPa and PA exhibited the optimum performance with 2.5% content and gave maximum compressive strength of 78 MPa. The addition of MK progressively increased the compressive strength with 20% content mix giving a strength of 84 MPa. The SF performed the best at optimum quantity of 2.5% and exhibited the highest compressive strength of 90 MPa. The results suggest that these SCM based concrete are recommended for formulation of high-strength concrete applications, i.e., 60+ MPa. Furthermore, all the SCMs had at least one mix which satisfied the C60/75 classification without reducing the w/b ratio below 0.4; this has significant positive ramifications for the development of sustainable high-performance concrete. The absorption of waste materials from industrial and agricultural fields can substantially reduce waste disposal and more pertinently facilitate in reducing the CO2 emission associated with the construction industry.