High-strength self-compacting concrete produced with recycled clay brick powders: Rheological, mechanical and microstructural properties

Abstract

High-strength self-compacting concrete (HSSCC), which has superior workability and filling ability compared to conventional concrete, is increasingly used in modern densely reinforced structures in the construction industry. However, HSSCC is more costly to produce than conventional concrete and can result in higher carbon emissions due to higher cement usage. On 6 February 2023, the devastating Kahramanmaraş earthquakes in Türkiye created a serious environmental problem. In this context, recycling and utilizing construction demolition waste (CDW), which creates a serious environmental problem after devastating earthquakes and urban transformations, can contribute to the economy of countries and environmental waste problems. In this study, to produce HSSCC more economically, sustainably, and environmentally, HSSCC series were produced using fly ash (FA) and recycled clay brick powders (RCBP) obtained from CDWs in certain proportions by weight instead of cement. For this purpose, seven different series of HSSCC were produced. FA and RCBP were used separately in the mixtures at 0% (control), 10%, 15%, and 20% by weight instead of cement. The fresh HSSCC series were then subjected to workability tests and cured for 28, 56, and 90 days. At the end of the curing period, physical and mechanical property tests and internal structure analyses by scanning electron microscopy (SEM) were performed on the HSSCC series. In addition, sensitivity analysis was performed using multiple linear model analysis to determine which parameters affect which properties in HSSCC designs. Although the highest workability loss in fresh HSSCCs was in the blend series where 20% RCBP was used, all of the blends provided fresh SCC properties by the standards. In general, the increase in FA and RCBP used in the HSSCC series decreased the 28-day compressive strengths (except RCBP10), while the strength losses gradually decreased as the curing age increased and at the end of 90 days; the compressive strengths of FA10 (71.9 MPa with 1.6% increase), RCBP10 (74.8 MPa with 5.6% increase) and RCBP15 (71.5 MPa with 1% increase) series were obtained above the control series (70.8 MPa). SEM analyses performed at the end of the study showed that HSSCC specimens with 10% RCBP replacement contained more intense hydration products and fewer pores than the other series.