A coupled thermal-analytical and mechanical approach to investigate the behavior of bonded anchors cured at sub-zero temperatures

In post-installed connection in reinforced concrete structures, bonded anchors are commonly adopted when elevated mechanical performances are required. Such performances may be significantly impaired by adverse service conditions, above all temperature variations with respect to room ambient one. It is also generally acknowledged that the curing temperature may impact on the anchor performances, to the extent that all the main existing qualification procedures assess the anchor behavior when cured at different temperatures, in particular below zero Celsius degree. However, among the few investigations focusing on the impact of a low curing temperature on the long term behavior of an anchor, a low effort exists in addressing the relationship between the anchor mechanical behavior and the thermal properties of the bonding agent. The paper proposes a coupled thermal-analytical and mechanical approach to detect potential critical issues in the long term mechanical behavior of the anchor as a function of the adhesive behavior, as investigated by thermal or thermo-mechanical analyses. To the scope, a wide investigation on two adhesives is carried out comprising MDSC, DMA, pull-out and sustained load tests. On the basis of the obtained results, it is concluded that some thresholds in the variations of degree of conversion and phase transition temperatures may indicate a negligible impact of a low curing temperature on the anchor mechanical behavior, but also that existing qualification procedures are not able to capture the anchor behavior, when cured at low temperatures and subjected, during its service life, to temperatures higher than room ambient one.