Effects of freeze-thaw cycles and sustained stress on the durability and long-term deformation behavior of bamboo coarse aggregate concrete

For sustainable construction via crop waste valorization, bamboo aggregate concrete (BAC) was developed using epoxy mortar (EM)-modified bamboo coarse aggregates (BCAs). Plant aggregate concrete shows promise as a green material because of its renewability and carbon reduction, but its durability and long-term deformation behavior are limited by high water absorption and weak bonding. The performance evolution under 100 freeze-thaw (FT) cycles and 360 d shrinkage and creep behavior of BACs were evaluated using multi-scale testing. Nuclear magnetic resonance (NMR) tests showed that BAC exhibited higher water absorption and a higher proportion of free water than natural aggregate concrete (NAC). The mechanical performance loss is positively correlated with the FT cycles and the BCAs replacement rates ( r ). 60 FT cycles marked a critical point for accelerated degradation, at which point the EM on BCAs delaminated, exposing their inherent high water absorption. The macroscopic mechanical losses were closely linked to microstructural damage, including interfacial transition zone (ITZ) thickening, debonding, and progressive microcrack propagation. Computed tomography (CT) scanning tests showed that FT-induced cracks were mainly concentrated in the ITZ around BCAs and propagated radially along the ITZ. 3D pore reconstruction confirmed that pore deterioration positively correlated with FT cycles and r . Compared to NAC, BAC exhibited more pronounced time-dependent deformation characteristics. Both shrinkage and creep magnitudes increased markedly with higher r ; but the creep rate at later stages tended to slow down. ITZ bond weakening and elastic modulus differences caused deterioration in both FT damage and time-dependent deformation. Finally, empirical coefficients related to r were introduced to establish predictive models.