Evaluation of High Performance Fiber-Reinforced Concrete for Bridge Deck Closure Pours

Connections and closure pours in bridges are often a source of irreversible damage to bridges due to the penetration of harmful agents into cracks that can lead to costly repairs. These cracks are caused by shrinkage, the application of service loads after the concrete has hardened, and poor bonding of these poured sections to bridge deck sections at the bond interface, where wide cracks allow the ingress of water and other compounds. This causes damage to the bridge deck sections as well as the bridge substructure, where the penetration of harmful solutions causes the corrosion of reinforcing steel, as well as alkali-silica reactions, sulfate attack, and freeze-thaw damage in concrete. Problems such as these can also occur in situations where joints are to be eliminated to create joint-less bridge structures, and subsequent shrinkage and flexure of these connections can cause wide cracks in the concrete. In these situations, bridge joints are removed and sections of the deck are cut away. The moving joint systems are then replaced with a link slab that rigidly connects adjacent deck sections. When normal concrete is used, cracks that allow corrosive compounds to damage the underlying beams and piers may occur in the link slab. Two major issues with closure pours and connections are cracking in the sections and separation at the bond surfaces. When fibers are added to a conventional concrete matrix, cracking may be minimized, but the sizes of these cracks still permit the intrusion of harmful solutions. When using high performance fiber-reinforced concrete (HPFRC), multiple very tight cracks (< 0.1 mm wide) may occur when the material is placed in flexure instead of one larger localized crack. Tight cracks do not allow ingress of water and other harmful solutions as larger cracks do. Thus HPFRC offers a potential solution to damage of bridge connections.
In this project, four different high-performance fiber-reinforced systems were tested for properties that relate to their ability to produce tight cracks in flexure and bond to typical bridge deck concrete. These systems include of High-Performance Fiber-Reinforced Concrete (HPFRC), which encompasses Hybrid Fiber-Reinforced Concrete (HyFRC), and High-Performance Fiber-Reinforced Cementitious Composite (HPFRCC) mixtures, which include Engineered Cementitious Composites (ECC). Of these systems, ECC displayed the highest deflection hardening capacity, while UHPC exhibited the most desirable results in flexural toughness and bond strength tests. The overall material properties of ECC and UHPC were the most desirable, but a cost benefit analysis was completed to determine which mix is the most cost-effective option for closure pours and joints. It was concluded from this study that HyFRC using only synthetic discontinuous fibers provides the most cost efficient option for a material that will not only deflection harden, but will also provide adequate bond strength to typical A4 bridge deck concrete.