About the research
Concrete is made of multiple ingredients that begin in a plastic phase and become solid over time. Additionally, it is well established that concrete is exposed to various stressors from the initial hours of pouring, making it prone to cracking. The multiphase nature of concrete along with these stressors require the consideration of several factors, especially for the design of concrete bridge decks that are exposed to aggressive environmental and mechanical stressors simultaneously. Due to the low early-age strength of concrete, even small-scale tensions can result in cracking and consequently decrease the longevity of the concrete structure.
In order to address these issues, a three-stage framework was designed for this project. In Stage 1, multiple binder compositions were investigated for their performance in terms of early-age plastic shrinkage by recording capillary pressure development, monitoring crack width, and determining strain development by means of digital image correlation. After binder modification, in Stage 2 different dosages of microfibers were added to concrete mixtures to compensate for the concrete’s low tensile strength and control cracking during the life of the concrete. To measure the efficiency of the microfibers, drying shrinkage, compressive and splitting tensile strength, and rapid chloride migration tests were carried out to determine the cracking potential and mechanical and durability properties of fiber-reinforced concrete (FRC). In Stage 3, three types of macrofibers (i.e., polypropylene [PP], alkali-resistant [AR] glass, and polyvinyl alcohol [PVA]) were incorporated at multiple dosages into FRC that already contained microfibers to enhance the post-peak strength of the concrete. The compressive, splitting tensile, and flexural strengths of the concretes were recorded as the pre-peak mechanical properties, and the toughness and residual flexural strength were recorded as the post-peak mechanical properties.
The results show that Class F fly ash, as opposed to silica fume and Type K (expansive) cement, contributes most to the early-age cracking resistance of concrete. Furthermore, increasing PP microfiber content significantly reduced the cracking potential and enhanced the mechanical properties and chloride resistance of concrete. In the case of hybrid FRC (FRC containing both microfibers and macrofibers), AR glass macrofibers introduced superior performance compared to PP and PVA macrofibers, in terms of pre- and post-peak mechanical properties.