Bond properties of basalt fiber reinforced polymer (BFRP) bars in recycled aggregate thermal insulation concrete under freeze-thaw cycles

In this study, recycled aggregate thermal insulation concrete (RATIC) with good frost resistance and basalt fiber reinforced ploymer (BFRP) bars were used to overcome the corrosion of recycled aggregate concrete (RAC). First, the influence of recycled coarse aggregate (RCA) and glazed hollow beads (GHBs) on the basic mechanical properties of concrete under freeze-thaw (FT) cycles was studied. Second, through FT cycle tests, the freeze--thaw resistance of four kinds of concrete (normal concrete, RAC, GHB thermal insulation concrete, and RATIC) was determined and the apparent morphology, mass loss rate, relative dynamic elastic modulus, and durability coefficient were obtained and analyzed. Finally, the bond performance between BFRP bars and four kinds of concrete under different FT cycles was investigated by center pull-out tests. The effects of RCA and GHBs on the failure mode, ultimate bond strength, peak slip, and bond slip curve of concrete were analyzed. The research results show that RCA has adverse effects on the mechanical properties, freeze-thaw resistance, and bond properties of RAC. The reasonable addition of GHB can compensate for the adverse effects of RCA and signifi-cantly improve the freeze-thaw resistance of concrete. GHB can also improve the bond properties between BFRP bars and RAC under freeze-thaw cycles. The combined use of BFRP bars and recycled aggregate thermal insu-lation concrete is an important way to effectively solve the problem of steel bar corrosion in structural engi-neering in severely cold areas.