UC Berkeley

Conventional concrete used for construction has neither the inherent ductility nor durability to meet the requirements of modern infrastructure construction. With ageing highway and bridge infrastructure requiring a significant expenditure of capital, it is prudent to explore utilization of so-called high performance materials that have the potential to outperform and outlast their conventional counterparts. This research program is built around the concept of creating a sustainable material that exceeds the performance of conventional concrete through a characteristic enhanced cracking resistance achieved by the introduction of discrete fiber reinforcement combined with an optimized level of workability.

In an effort to meet the existing demand for high performance materials suitable for modern construction practice, self-consolidating features have been developed for a preexisting high performance hybrid fiber reinforced concrete. A parametric study was employed to maximize the fresh state performance benefits of chemical and supplementary cementitious material additives in conjunction with optimization of the fiber reinforcement to meet the flow criteria of self-consolidating type concrete. The resulting composite, Self-Consolidating Hybrid Fiber Reinforced Concrete (SC-HyFRC), is tested under compression, tension and flexure loading independently and in combination with conventional steel reinforcement to illustrate the mechanical performance gains that can be achieved with such composites. The performance enhancements gained in each manner of loading are then combined in the material's application to a structural element that must be designed to undergo a substantial inelastic (cracked) response.

The intrinsic durability of the SC-HyFRC material is tested against two environmental deterioration mechanisms which plague modern concrete. Due to the enhanced crack resistance present in SC-HyFRC, chloride-induced steel reinforcement corrosion is mitigated during both the initiation and the propagation phases. This mitigation is qualitatively and quantifiably measured by suppression of observable cracking and direct electrochemical measurements of the reinforcing steel surface. Similarly, the cracking resistance feature of SC-HyFRC and similar fiber reinforced cementitious composites is judged for mitigation capacity of alkali-silica reaction. The magnitude of internal cracking accompanying the swelling-induced expansion is measured by relative changes in structurally relevant concrete mechanical properties, compressive strength and elastic modulus, with fiber reinforced restraint of expansion observed to correlate well with mechanical property retention. As reinforcement corrosion and alkali-silica reaction are but two of many deterioration mechanisms that induce damage by way of internal expansion, the positive outcomes of SC-HyFRC testing are expected to be transferable to concrete durability in a holistic sense.

The potential benefit of constructing critical infrastructure elements with such high performance materials is a two-fold gain in overall structural life cycle assessment, being better equipped to deal with multiple facets of loading placed on modern structures. This and similar research of SC-HyFRC and other such materials will hopefully validate the upfront costs necessary to build with materials that can generate outsized long term fiscal savings.