About the research
High performance concrete (HPC) is increasingly used in bridge deck and deck overlays because of its high strength, low permeability, and excellent durability. However, due to its high cementitious content, low water-to-binder ratio (w/b), and use of various admixtures, HPC can have a high risk for shrinkage cracking. Cracks weaken structures and permit water and harmful chemical ingress into concrete, thereby accelerating deterioration and corrosion of reinforcement (Shah et al 1997). Shrinkage also causes concrete slabs to curl and warp, which affects the girder-to-deck composite action, ultimately decreasing load-carrying capacity of the bridge (Tarr 2008). In addition, shrinkage may bring about stress loss in prestressed concrete structures and affect camber and deflection and load carrying capacity of bridge girders.
Over the past decade, many states have reported cracking on HPC bridge decks at early ages (Wan 2010 and Whiting et al 2000), and this problem is also a great concern in Iowa. Recently, the Iowa Highway Research Board (IHRB) sponsored Project TR-633, Investigation into Shrinkage of High Performance Concrete Used for Iowa Bridge Decks and Overlays (Phase I). In this study, autogenous, free drying, and restrained ring shrinkage of 11 typical Iowa HPC mixes were monitored over time. The mechanical properties (such as elastic modulus and compressive and splitting tensile strength), creep coefficients, and cracking potentials of these concrete mixes were evaluated. The results indicated that among these 11 mixes studied, three mixes were identified as having high cracking potential and five mixes as having medium cracking potential.
The researchers have suggested that the shrinkage behavior of the mixes identified as having high cracking potential could be modified by using the state-of-the art shrinkage reduction and control technologies, such as use of shrinkage-reducing agents (SRAs), shrinkage compensating admixtures (SCAs), and internal curing (IC). The shrinkage behavior of the mixes identified as having medium cracking potential can be tailored through the balance between the w/b, cementitious content, and tensile strength.
This field study will monitor and compare the performance of the high and low shrinkage cracking mixes used in Iowa. To verify and implement the research results obtained from the Phase I study, the Phase II, TR-663, study will further investigate and identify the most functional, practical, and cost-effective method for controlling shrinkage cracking potential of HPC in Iowa bridge decks and overlays.