SHRINKAGE, CREEP, AND FATIGUE BEHAVIOR OF CSA CEMENT CONCRETE AND UHPC INCORPORATING INTERNAL CURING

Abstract

This dissertation consists of four studies investigating the impact of internal curing on the performance of advanced concrete materials. The first chapter introduces the research by presenting its background, motivation, objective and organization. The second chapter focused on Ultra-High Performance Concrete (UHPC), an advanced cementitious material with superior mechanical properties compared to conventional concrete; however, its high cementitious material content results in significant early-age autogenous shrinkage. This study evaluated internal curing using presoaked lightweight sand (LWS) to improve the performance of UHPC. The quantity of LWS varied to supply 0, 1, 2, and 3 lb of internal curing water per 100 lb of total cementitious material. Early-age shrinkage was measured using vibrating wire strain gauges (VWSGs) embedded in 6 in. × 12 in. UHPC cylinders, while calorimetry testing was conducted to evaluate setting time and hydration heat. The results indicate that autogenous shrinkage significantly decreased with increasing LWS, whereas compressive strength, setting time, and hydration heat were not significantly affected. Bridge deck deterioration is a primary contributor to poor bridge condition ratings in the United States. The third chapter investigated the effects of internally cured UHPC overlays on the flexural capacity of beams simulating bridge decks. Beam specimens were tested under third-point bending, and fresh and hardened properties of UHPC with varying LWS contents were evaluated. The addition of the overlay enhanced the load-bearing capacity while maintaining composite action with the substrate. Incorporation of LWS reduced shrinkage strain, resulting in lower residual interfacial shear stresses and enhanced load-carrying capacity. Calcium sulfoaluminate (CSA) cement is a viable alternative binder that can partially or fully replace portland cement because of its rapid strength gain, reduced shrinkage, and lower environmental impact. The fourth chapter investigated the use of internal curing provided by presoaked LWS to improve the shrinkage, creep, and mechanical properties of Belitic Calcium Sulfoaluminate (BCSA) and Type K CSA-based cements. A portion of conventional sand was replaced with LWS, and its influence was evaluated through compressive strength, modulus of rupture (MOR), creep, and shrinkage tests using ASTM C157 and VWSGs. The results were used to identify the optimal amount of LWS for enhanced performance. Finally, the fatigue behavior of CSA cement concretes, including expansive BCSA and Type K cement, was evaluated in the fifth chapter. A total of 88 beams with dimensions of 6 in. × 6 in. × 21 in. and 14 beams with dimensions of 8 in. × 8 in. × 30 in. were tested under different stress levels and loading frequencies. LWS was used to provide internal curing and reduce shrinkage. The results of the S-N curve indicate that the 8 in. × 8 in. specimens provided more reliable fatigue behavior with higher R² values and reduced scatter. The addition of LWS significantly enhanced the fatigue strength of Type K cement concrete, and a higher R2 value of the S-N curve compared to both portland cement and expansive BCSA mixtures.