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The recent boom in infrastructural development in Bangladesh has triggered the exceptional demand for clay burnt brick aggregate as the country's supply of natural aggregates cannot meet the high demand. However, the production process of brick creates significant environmental issues. On the flip side of the construction industry, the increase of industrial by-products and waste (e.g., coal fly ash (CFA), sewage sludge ash (SSA), and incinerated medical ash (IMA), constantly taking up virgin lands for disposal, mainly through landfills. The recycling of the above-mentioned three ashes reduces the environmental impact in terms of soil contamination, and air and water pollution. Geopolymer coarse aggregate (GCA) can provide an effective solution that simultaneously reduces the production of bricks and promotes sustainable hazardous waste management, which has pozzolanic capacity.
GCA was produced by geopolymerization process from a combination of waste materials consisting of 50% SSA, 45% CFA, and 5% IMA using alkaline activator (e.g. Sodium hydroxide (NaOH) and Sodium silicate (Na2SiO3)). In this study, concrete specimens were prepared by utilizing GCA as a replacement of brick coarse aggregate (BCA) at five different GCA replacement ratio of 0%, 25%, 50%, 75%, and 100%. Different fresh, physical, mechanical, and durability properties of geopolymer aggregate concrete (GAC) were investigated. Microstructural analysis, failure modes, cost and CO2 footprint analysis were also evaluated. Simplified regression equations have been proposed to predict various mechanical properties of GAC mixtures.
Total incorporation of GCA in concrete decreased the slump value of fresh concrete up to 36.4%. However, GAC remains high degree workable. The compressive strength decreased with an increase in GCA percentage. Higher than 30 MPa concrete can be produced by using 100% GCA content, and it can be 40 MPa if the GCA content is limited to 50%. Furthermore, when the specimens are heated to 400°C the compressive strength was drastically reduced from 42% to 61%. Though all the GAC specimens provide comparatively lower splitting tensile and flexural strengths, the 50% GCA content presented a marginal reduction of 8.7% and 8.5%, respectively, compared to the control one. All the GAC mixes have a lower density than the BAC mix and fall within the limiting value of lightweight concrete.
The leaching behavior of the specified heavy metals (Pb, Cr, Cd, Cu, and Ni) has been analyzed using the Toxicity Characteristics Leaching Procedure (TCLP). The heavy metal concentrations obtained from the TCLP test results for all GCAs and GACs are far below the USEPA regulatory limits. The strength-CO2 analysis results showed that all the GAC specimens provide more strength in terms of CO2 footprint compared to control specimens. Overall, the findings presented in this study will aid in advancing sustainable artificial aggregate concrete as well as mitigate the environmental and economic burden of waste. |
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