A New Bond Degradation Model for Freeze–Thaw-Damaged Reinforced Concrete

Abstract

Freeze–thaw cycles (FTCs) are one the most serious causes of damage in RC structures in cold regions affecting both concrete and bond behavior. In this paper, after a comprehensive review on the effects on concrete and bond of freeze–thaw degradation for ordinary concrete, a new constitutive bond stress-slip law is formulated in the framework of a coupled mechanical-environmental damage model. This law is developed exploiting the versatility of Bezier curves and using an optimization process based on genetic algorithms to select the best form among some options (composite quadratic, composite cubic, and a single fourth-order curve). Moreover, a comprehensive enhanced freeze–thaw degradation (E-FTD) model is developed including the effect of FTCs on bond behavior, by means of a new environmental damage parameter included in the proposed bond stress-slip law. The whole model is formulated, calibrated, and validated referring to all the available experimental data to the authors’ knowledge both for compressive and pull-out tests for ordinary concrete. The comparison with the experimental results showed the proposed E-FTD model is able to predict bond strength degradation fairly well and generally on the safe side, capturing also the overall bond-slip curves, making it particularly appealing for the structural analysis of RC elements subjected to FTCs according to an engineering-oriented approach.