Bond performance between BFRP bars and alkali-activated seawater coral aggregate concrete

Abstract

Alkali-activated materials (AAMs) or geopolymers as substitutes for ordinary Portland cement (OPC) contributed to reduced greenhouse-gas emissions and energy consumption. This paper examines the applicability of employing well-durable AAMs instead of OPCs to develop alkali-activated seawater coral aggregate concrete (AACAC) and explores their bond characteristics with basalt fiber-reinforced polymer (BFRP) bars. The effects of the rib height (0.2 and 0.6 mm), bond length (50, 70, and 100 mm), and stirrup constraints on the bond performance between the BFRP bars and AACAC were considered, and cement-based CAC was also selected as the reference group. Furthermore, a scanning electron microscopy (SEM) was applied to observe the interfacial microstructures between the slurry matrix and the aggregate. The tested results indicated that the utilization of AAMs can improve interfacial microstructures, thus resulting in a higher elastic modulus and splitting tensile strength of AACAC than CAC. Increasing the rib height of the bars and stirrup constraints can effectively enhance the bond strength and bond stiffness. Compared with the specimens with a rib height of 0.2 mm, the bond strengths of AACAC and CAC specimens with a rib height of 0.6 mm increased by about 8 % and 7 %, respectively. Nevertheless, the bond strength and bond stiffness of the specimens gradually decreased with increasing bond length due to the non-uniform distribution in bond stress along with the embedment length. In addition, compared to the cement-based CAC specimens, AACAC specimens possessed greater bond strength, bond stiffness, and residual bond stress. There were approximately 6 % and 15 % improvements in the bond strength for AACAC specimens with rib heights of 0.2 mm and 0.6 mm, respectively, and their bond stiffness at a slip value of 0.02 mm increased by about 38 % and 39 %, respectively, compared to the CAC specimens.