Development and Performance of Fiber-reinforced Self-consolidating Concrete for Repair Applications

Download or read book Development and Performance of Fiber-reinforced Self-consolidating Concrete for Repair Applications written by Fodhil Kassimi and published by . This book was released on 2013 with total page 377 pages. Available in PDF, EPUB and Kindle. Book excerpt: The use of self-consolidating concrete (SCC) in the concrete industry in cast-in-place applications, including repair applications, is growing given the various advantages offered in both fresh and hardened states. The present study deals with the design and performance of fiber-reinforced self-consolidating concrete (FR-SCC) as a repair material of concrete infrastructure. The study also considers the use of various steel and synthetic fibers (five fibers in total) that were used to produce FR-SCC and fiber-reinforced self-consolidating mortar (FR-SCM) that can be employed for structural and non-structural repair applications. The study evaluates the effect of material properties and mixture composition of the fibrous concrete and mortar on workability, mechanical, visco-elastic, durability, and structural behavior. The investigation that is presented in this thesis included the testing of 28 full-scale beams under four-point flexural loading. The majority of these beams were repaired by casting concrete to fill a relatively thin section along the tension zone of the beams. The repair technique was based on the FR-SCC characteristics including the maximum fiber volume and length. This technique required mixtures of high range of fluidity. The optimized FR-SCC and FR-SCM mixtures exhibited excellent flow characteristics along the 3.2-m long beams without blockage, segregation, nor debonding at the interface of repair-substrate concrete. Based on the structural characteristics of the composite beams, the overall performance of the beams repaired using the FR-SCC and FR-SCM was similar or higher (up to 2.6 times) than that of monolithic beams made with conventional vibrated concrete (CVC). The use of optimized FRSCC mixtures enabled the replacement of 50% of the tension steel reinforcement in repair sections; i.e., the number of bars in the tension zone decreased from three bars to two bars with the addition of fibers in the SCC without mitigating structural performance. The degree of prediction of crack width, cracking load/moment, ultimate loads, and deflection of various FR-SCC and FR-SCM mixture was evaluated using several design and code models. The results indicate that these code models can provide safe predictions for crack and ultimate loads, as well as crack width of FR-SCC. The deflection of FR-SCC is unsafe but predictable by these code models. In total, 18 large-scale beams were tested in four-point for flexural creep. FR-SCC incorporating steel fibers combined with expansive agent provided overall performance up to 10 times of that obtained with CVC with the same fiber type and volume. The cracking under constant load was reduced by 60% to 80% using self-consolidating fibrous mixtures made with or without expansion agents, compared to SCC without fibers. The best combination to reduce the cracking potential when the restrained shrinkage ring test was employed was obtained with SCC mixtures made with steel fibers and expansive agent. Models were elaborated to predict the time-to-cracking for FR-SCC and FR-SCM mixtures based on mixture modulus of elasticity and drying and autogenous shrinkages. The project involved extensive testing of highly flowable fibrous materials to determine drying shrinkage (nearly 260 prisms), modulus of rupture (nearly 180 prisms), as well as compressive and splitting tensile strengths and elastic modulus (nearly 2100 cylinders). Based on the results, models were proposed to predict these key material properties that affect the performance of FR-SCC and FR-SCM used in repair applications. In addition to FR-SCC, the investigation also was set to evaluate the feasibility of using fiber-reinforced superworkable concrete (FR-SWC) in construction and repair applications. Such highly flowable concrete that requires limited vibration consolidation can represent some advantages over FR-SCC (lower admixtures demand, lower risk of segregation, greater robustness, lower formwork pressure, etc.). The energy needed to ensure proper consolidation, using either vibration or rodding, applied on samples made with FR-SWC was determined. The energy requirement took into consideration the development of mechanical properties, the resistance to segregation, and the development of proper surface quality. The study also demonstrated the higher overall structural performance of optimized FR-SWC compared to the corresponding FR-SCC mixtures. The findings of the thesis on the design and performance of highly workable fiber-reinforced cementitious materials should facilitate the acceptance of such novel high-performance material in infrastructure construction and repair applications.