Internal Curing of High-Strength Concrete by Clay-Burnt Brick Fines: A Comprehensive Study

Abstract

This study investigates the synergistic effect of internal curing and pozzolanic activity in both mortar and high-strength concrete (HSC) through the incorporation of clay-burnt brick fines (CBBF) as a sustainable alternative. The investigation comprises two phases, each targeting specific aspects of mortar and concrete properties. In Phase 1, mortar specimens were prepared by substituting a portion of fine aggregate with pre-wetted CBBF (up to 20% v/v) and replacing cement with clay-burnt brick powder (CBBP) (up to 27% v/v). Two sand-to-cement ratios (S/C) of 1.2 and 1.6 were used. Compressive strength tests indicated an enhancement of up to 13.58% at 12% CBBF content for S/C = 1.6, while for S/C = 1.2, the optimal replacement level was 4% v/v of CBBF. Microstructural analysis via scanning electron microscopy (SEM) demonstrated a denser matrix attributed to internal curing and pozzolanic reactivity of CBBF. The potential of CBBF as an internal curing agent for high-strength concrete (HSC) was investigated in Phase 2, examining various parameters including grain sizes (4.75mm to 2.36mm, 4.75mm to 75μm, and <75μm), water-to-binder ratios (w/b) (0.28, 0.32, and 0.38), and substitution percentages of fine aggregate by CBBF (up to 16%). An optimal CBBF content of 8% has been identified in terms of mechanical properties of concrete. Ultrasonic pulse velocity and SEM analysis revealed enhanced microstructure around CBBF particles. Additionally, concrete shrinkage was reduced by up to 34.4% with 16% CBBF content at w/b = 0.28. Moreover, a significant reduction in internal temperature and improved resistance to chloride ion penetration were observed with the increase of CBBF content. Overall, the study highlights the promising efficacy of CBBF as an internal curing agent in enhancing the mechanical properties and durability of both mortar and HSC, thereby offering a sustainable solution for construction materials.