Waste clay brick binders for rigid pavement subbase and base concretes

Abstract

Both base and subbase layers of rigid pavements are currently constructed with concrete based on ordinary Portland cement (OPC). The OPC manufacturing process is heavily carbon intensive and has severe negative impacts towards the environment and sustainability. Geopolymer as an alternative is promising, in terms of both performance and sustainability. This study used waste clay bricks (WCB) blended with fly ash and slag precursors to produce one-part geopolymer binderswith the aim of replacing OPC in pavement concrete. One-part binders were prepared by combining activators and the precursor at a 1:9 ratio by weight.Within the precursor, fly ash content was varied at 0%, 10%, 20% and 30% by weight. In the remaining precursor, WCB was replaced with slag at 20%, 40%, 60% and 80% replacements. All blends of WCB with fly ash and slag showed significantly higher strengths than their unblended counterparts. The highest 28-day compressive strength of 92 MPa was recorded for the sample with 30% fly ash and with 80% replacement of WCB with slag on the remaining precursor. Additionally, the WCB based geopolymer binders showed a high early strength development, achieving more than 50% of its 28-day compressive strength within 72 h. Aggregates were then introduced to the selected binders to prepare geopolymer concrete (GPC). The compressive strength of GPC samples was recorded after 28 days of aging. Initial GPC trial mixes were able to achieve compressive strengths up to 41 MPa, demonstrating the feasibility of using WCB based binders for developing pavement concretes.