National Concrete Pavement Technology Center

Project description

A common pavement rehabilitation technique for rutted or cracked hot - mixed asphalt concrete roadways is to mill the surface and then overlay with up to 6 inch es of a portland cement concrete (PCC) layer. More recent advancements in research has proven that a feasible top wearing surface can be made at this 2 inch (50 mm) thin layer if it is comprised of f iber reinforced c oncrete (FRC). FRC has increasingly being used in UTW overlays since it has been proven through experimental lab and field testing improve the fatigue life and reduce deflections of jointed concrete overlay slabs. Cracking and debonding of the overlay structure can initiate as a result of drying shrinkage, and temperature shrinkage, slab settlements, or external load. Temperature - induced curling and cracking has been researched many times and is currently recognized as one of the major failure mechanisms in concrete pavements. Slabs are designed to have joints cut at spacing sizes proportional to the thickness. These jo ints are cut in order to provide a specific location for thermal and humidity - induced cracking while also keeping net curling lift - off deflections to a minimum. It has experimentally been verified that with FRC overlays and pavements, not every joint crack s upon the first thermal cycle. Yet the few joints that do crack at early ages produce the lowest load transfer efficiency and widest crack widths at later ages. There are no known publications or research performed which has studied why or how the addition of fiber - reinforcement in a thin concrete overlay affects the joint cracking and slab curling. A full - scale test pavement of a 50 mm thick FRC overlay was constructed in July 2009, which has been subjected only to environmental loading since then.. This is a unique pavement section as well because it has no mid - panel slab cracking except in pre - placed constructed debonding zones. The cracking of joints was monitored at early ages between 3 and 20 days as well as climatic temperature data of the air and in 4 depths within the pavement structure. Existing temperature and joint opening models overpredict the actual crack widths measured from the field. The proposed research will attempt to improve prediction of crack width for thermally - loaded FRC pavements. The early - age properties of FRC as measured in this research will be utilized in a co hesive zone finite element analysis of the same The main objective of this research is to perform experimental tests to determine the hardened properties of fiber- reinforced concrete as they change with time at early-ages. These properties and their function with time can be implemented into finite element modeling to improve overlay prediction at early ages.