Environmental sustainability of fly ash and recycled crushed glass blends: an alternative to natural clay for masonry bricks production

Abstract

Waste utilization as an alternative for masonry bricks has proven to compensate for the dwindling natural construction materials particularly clay. Currently, South African municipalities are struggling to update their effective waste management techniques. Improper waste management is one of the major constraints affecting the natural environment due to the associated environmental waste pollution. This constraint fostered the motivation to the present study, which reported on the findings obtained from the masonry bricks produced from blends of recycled crushed glass (RCG) and fly ash (α-FA) with the inclusion of ordinary Portland cement (OPC) at varying percentages. The masonry bricks were produced with 5%, 10%, and 15% inclusion of OPC to the combined weight of α-FA and RCG. The produced bricks rendered significant compression strength resistance compared to the fired clay bricks that are 3.8% higher on average. However, the compressive strength of all the produced bricks in this study satisfied the South African National Standard SANS 227 Code requirements (i.e., 7 MPa) for individual load-bearing masonry brick. The scanning electron microscopy (SEM) analysis confirmed that the identified void spaces within the microstructure of the brick specimens with 5% OPC were the major cause of the low strength resulting from the incomplete pozzolanic reaction. Also, the effects of sulphate salt were significantly resisted on the surface of all the tested bricks incorporating α-FA and RCG, due to the presents of aluminosilicates compounds that triggered pozzolanic reactions within the brick’s matrix. The stiffness of the investigated bricks portrayed brittle characteristics due to the developed strength after production. This revealed the existence of a great proportionality between the dynamic modulus and ultrasonic pulse velocity (UPV) revealed a coefficient of determination (R2) equivalent to 90% because of the percentages of RCG particles.