Bond responses and anchorage length of GFRP bar in precast recycled aggregate concrete

Precast recycled aggregate concrete (PRAC) employs precast reject-derived recycled aggregates (PRAs) and exhibits mechanical properties on par with or superior to those of natural aggregate concrete (NAC). Nevertheless, the durability of PRAC is hampered by aged mortar. To address this issue, integrating high durability glass fiber reinforced polymer (GFRP) bars into PRAC emerges as a potential solution for constructing enduring structures. Building upon this context, the study focuses on the bond responses between PRAC and GFRP bars, an area with limited existing research. Three main tasks were conducted: Firstly, a comprehensive test program involving 108 pullout samples was conducted to investigate the key variables' effects on bond failure mode and stress-slip relationship. Subsequently, an equation was developed to determine the peak bond strength of recycled aggregate concrete (RAC) based on available test data. Additionally, reliability analyses were performed to discuss the anchorage length of GFRP bar embedded in RAC. The findings are as follows: (a) The PRAC's bond capacity initially increased then decreased with rising PRA content. At full replacement, PRAC's bond strength was 28.3% lower than NAC. However, a two stage mixing approach restored PRAC's bond capacity to NAC levels. (b) Helical wrapping of the GFRP bar consistently exhibited the highest bond capacity, with an average bond strength 51% greater than a sand coated GFRP bar and 21% higher than a GFRP bar treated with both helical wrapping and sand coating. (c) Current codes specifying the critical anchorage length for FRP bar in NAC were often unsafe for RAC. Hence, a new expression, factoring in RA content, type and RAC mixing method, was proposed to determine the suitable anchorage length.