Investigation of waste clay brick as partial replacement of geopolymer binders for rigid pavement application

Waste clay brick (WCB) is identified as a feasible alternative cementitious material for producing geopolymer binders to replace ordinary Portland cement (OPC). This study investigated mechanical properties and environmental impacts of one-part geopolymer binders at ambient curing conditions, employing binary blends of WCB with fly ash or slag, while using anhydrous solid sodium metasilicate as the sole activator. WCB was replaced separately with fly ash and slag at 20%, 40%, 60% and 80% by mass to obtain the aluminosilicate precursors. Combination of the aluminosilicate precursors and the solid activator was considered as the total binder. The effect of the alkali activator content, particle size and water-to-binder ratio on compressive strength development were investigated. The strengths of the geopolymers were compared with minimum concrete strength requirements indicated in Australian pavement design guidelines and American Association of State Highway and Transportation Officials (AASHTO) guidelines. The experimental results indicated an optimum activator content of 10% by mass of the total binder for all binary geopolymer systems. Compared to WCB alone and WCB-fly ash blends, binary geopolymer systems of WCB-slag blends showed higher compressive strengths. WCB-slag blends showed high early strength gain and achieved more than 22% and 48% of its corresponding 28day strength within 24 h and 72 h, respectively. Highest 28-day compressive strength of 81.8 MPa was achieved for the binder with 40% WCB and 60% slag in the precursor. The strength further improved to 96.8 MPa by reducing WCB particle size from 150 mu m-passing to 75 mu m-passing. Additionally, the environmental impacts associated with the different blends were evaluated considering carbon dioxide emission and energy consumption during their production. These values were subsequently compared with those of OPC manufacturing. The comparison showed that WCB based geopolymer binders can reduce carbon emissions up to 78% and energy consumption up to 85%.