Development of optimal deflection hardening cementitious composites mixture for highway bridge decks to address shrinkage cracking problem

The bridge deck concrete tends to crack more than other concrete structures due to shrinkage. This behavior is attributed to the fact that the shrinkage increases whenever the surface to-volume ratio increases. The production of High Performance Fiber Reinforced Concretes (HPFRC) based on a maximal amount of coarse aggregates and increasing use of industrial by-products (without sacrificing the deflection-hardening behavior) is the purpose of present study to contribute enhancing the mechanical and durability performance with increasing the cracking resistance. After a preliminary study, 24 HPFRC mixtures with a maximum aggregate size of 12 mm were developed with maximal variation in coarse aggregate contents without compromising deflection-hardening behavior. Three different fibers were used at a maximum of 2% of volume in single or hybrid systems: polyvinyl-alcohol (P), hooked-end steel (S) and nylo-mono (N) fibers. To function synergistically with different fiber types and high amounts of coarse aggregates, matrix properties were optimized by varying the proportions of fly ash to Portland cement (FA/PC ratios of 0.20, 0.45, and 0.70, by weight) and aggregate to binder (A/B ratios of 1.0, 1.5, and 2.0, by weight). The produced HPFRC mixtures were evaluated to find their performances under different tests such as bending, compression, free and restrained shrinkage, impact, slab panel, and freezing- thawing tests. Based on the obtained results from the above performed tests, all of produced mixtures were ranked depending on the performances rank analysis. The results revealed that, the overall mixtures' performance was clearly increased as mixtures having three types of fibers (i.e. hybrid fiber system with three types of fibers). The increasing trend in mixtures' performance was improved throughout increasing the A/B ratios especially at A/B ratio of 2.0. Keywords: Deflection-hardening; HPFRC; Cracking Resistance; Coarse Aggregates; Impact Resistance; Energy Absorption.