Investigation of shrinkage-compensating cement concrete from material and structural perspectives

Longitudinal joints used to connect adjacent box beams in bridges are known to experience cracks due to a variety of environmental and mechanical stressors, including diurnal temperature changes, hydration, drying shrinkage, restrained shrinkage, and traffic loads. Such cracks can open a direct path for water and deleterious agents to penetrate into the structural system, causing corrosion of embedded steel bars and structural degradation of bridge superstructure and substructure elements. The degradation adversely affects the integrity of the entire bridge, provokes safety and durability concerns, and eventually results in road closures and traffic disruptions due to maintenance and repair requirements. Shrinkage-compensating cement, also known as Type K expansive agent, is a type of calcium sulfoaluminate cement with the ability of volume expansion during the early stages of hardening due to the volumetric formation of ettringite. In this way, shrinkage-compensating cement concrete (SCC-C) can significantly enhance the volume stability of concrete, increase the serviceability of the structure, and thus develop an optimized solution for cracking, especially in adjacent box beam bridges. In this study, a comprehensive experimental program was established to investigate the SCC-C from material and structural perspectives. The ultimate goal of this study is to develop recommendations for the proper use of SCC-C in longitudinal joints for adjacent box beam bridges, especially where the structural components are susceptible to both shrinkage and chloride attack. To meet this goal, a comprehensive testing program was established to evaluate the concretes made with various dosages of Type K expansive agent (i.e., 0%, 7.5%, 15%, and 22.5% by weight of total cementitious materials) subjected to a number of mechanical, transport, and durability assessment experiments, including compressive strength, drying shrinkage, rapid chloride penetration, rapid chloride migration, surface resistivity, absorption of water in hardened concrete, helium porosimetry, and Mercury intrusion porosimetry tests. The results indicated that the resistance of concrete to chloride ions was reduced with increasing the dosage of replacement of Type K cement. While the addition of class F fly ash led to partial mitigation of increased chloride permeability caused by the inclusion of Type K agent, the incorporation of silica fume or class C fly ash were identified as appropriate strategies for addressing the chloride permeability issue. In addition, two full-scale box beams were designed, constructed and connected using a longitudinal joint made with Type K cement, to investigate the structural response under early-age thermal effects and cycles of structural loads. A set of three-dimensional finite-element simulations were also performed to extend the scope of investigations beyond the cases tested in the laboratory. Both experimental and numerical results indicate that the longitudinal Type K joint provides satisfactory performance in resisting joint cracks subjected to both early-age thermal effects and long-term service loads that the bridge experiences during its service life. Results from the finite element models were in a good agreement with the experimental measurements. Also, a parametric study was conducted to investigate the structural response subjected to the AASHTO-specified temperature profiles and the longitudinal joint design parameters, including different bond properties and the effect of joint reinforcement