Bond Strength of UHPC Overlays on Aging Concrete: Effects of Surface Preparation and Moisture Conditioning

Abstract This study investigates the tensile bond performance between ultrahigh-performance concrete (UHPC) overlays and aged normal concrete (NC) substrates under varying surface preparation methods and moisture conditions. A total of 96 laboratory specimens were tested using direct tensile pull-off testing in accordance with ASTM C1583, with 92 specimens retained following outlier screening. Results indicate that substrate moisture condition significantly affects bond performance, with saturated surface conditions increasing system pull-off capacity by approximately 33% relative to dry substrates. Surface preparation methods also played a critical role: abrasive blasting and scarification improved pull-off capacity strength by approximately 30% and 21%, respectively, compared with untreated surfaces. Abrasive blasting combined with saturated surface dry (SSD) conditions produced the highest system bond performance, yielding a 56% improvement over untreated, dry substrates. When macrodamage to coarse aggregate occurred, such as through spalling or scarification, moisture conditioning had minimal influence on bond performance. Exposure to simulated winter conditions and deicing salts further degraded substrate properties, reducing the effectiveness of surface preparation. The findings demonstrate the coupled influence of surface preparation and moisture conditioning on UHPC–NC bond performance and provide practical guidance for mitigating delamination risks in UHPC overlay applications for aging infrastructure.