Characterization of Freeze-Thaw Resistance of New-to-Old Concrete Based on the Ultrasonic Pulse Velocity Method

Abstract The adhesive interface in new-to-old concrete widely occurs in the concrete structure, and the adhesion assessment for freeze-thaw (F-T) resistance is hardly focused on. To evaluate the F-T resistance of adhesive interfaces in new-to-old concrete with a nondestructive method, this experiment was conducted with ultrasonic pulse velocity (UPV). Specimens with the same natural roughness were obtained using three-dimension printing technology. The surface roughness was measured via the sand replacement method. The traditional evaluation that the decrease of relative dynamic elastic modulus under 60 % represents the failure of concrete F-T resistance has a limitation in new-to-old concrete structures. A new characterization method of F-T resistance in adhesive interface for new-to-old concrete was proposed based on the variation trend of UPV in parallel direction (UPV-PD) and vertical direction (UPV-VD). The UPV-VD loss ratio had a three-stage characteristic and a steady phase, which was different from the loss ratio of splitting tensile strength in numerical value. The results showed that the UPV-PD loss ratio grew linearly in the process of F-T cycles. Moisture content was the dominant influence on the numerical difference. This difference can be eliminated based on a correction method. The variation trend of the UPV loss ratio in adhesive interfaces was similar to that of splitting tensile strength, and the obvious turning points appeared after similar F-T cycles. The characterization method of F-T resistance proposed in this article is applicable to evaluate the F-T resistance of adhesive interfaces in new-to-old concrete, which is also proved by splitting tensile test results.