Durable and sustainable overlay with ECC

While Portland cement concrete (PCC) overlay has been increasingly used as a rehabilitation technique for deteriorated PCC pavements in the last decade, reflective cracking places a major limit on its durability performance. The use of ultra ductile concrete named Engineered Cementitious Composite (ECC) should arrest such failure mode and greatly enhance the long term performance of the overlaid pavements. In this paper, we introduce and demonstrate this novel concept via experimental study on the reflective cracking resistance of small-scale ECC overlaid concrete beam. The ECC specimens totally eliminate the reflective cracking mode by developing extensive micro-cracks under flexural fatigue loading, in addition to a much enhanced MOR compared to controlled concrete specimen. Based on FEM analysis of the overlay system and fatigue performance of the ECC beam, a simplified design chart for ECC overlay is presented for use in practice and LCALCC analysis. The proposed ductile overlay approach should greatly enhance the durability and sustainability of the future pavement overlay. Introduction Unbonded concrete overlay and HMA overlay are two major rehabilitation methods used for deteriorated rigid pavements (MDOT 2005). In both cases, reflective cracking acts as a major limitation on the service life of overlays (Tayabji and Okamoto 1985; Huang 2004). Under repeated traffic loading, the preexisting joints/cracks in the substrate concrete tend to reflect through the overlay, ultimately leading to the termination of service life of the overlaid concrete pavement. The overlay material responds brittlely under high stress concentration induced by the preexisting joint/crack in the substrate concrete. A number of techniques addressing the reflective cracking problem have been attempted with varying degrees of success. Current Techniques to Addressing Reflective Cracking and Limitations. Current techniques may be grouped into at least three broad categories in relation to their different approaches to address reflective cracking: concrete slab fracturing, stressrelieving (crack relief) interlayer, and modified overlay. Concrete slab fracturing techniques include rubblization, crack and seat (for plain concrete pavement), and break and seat (for reinforced concrete pavement). By creating small pieces of concrete, fracturing technique minimizes one of the main mechanisms of reflective cracking, i.e., the horizontal movement of concrete substrate due to temperature and moisture changes (Huang 2004). The second broad category involves paving fabric, geogrid, and specially modified HMA interlayer. These interlayers are used in between the concrete substrate and the HMA overlay and/or concrete overlay to 1 ACE-MRL, Dept. of Civil and Environ. Engineering, University of Michigan, MI 48109, USA 2 Now at Microlab, Dept. of Civil Eng. and Geoscience, T U Delft, 2600 GA, Delft, The Netherlands 3 CSS, School of Natural Resources and Environ., University of Michigan, MI 48109, USA 9th International Conference on Concrete Pavements, San Francisco, California, August 17-21, 2008