EVALUATION OF EARLY STRENGTH REQUIREMENT OF CONCRETE FOR SLAB REPLACEMENT USING APT

Full slab replacement is a common method for repair of badly deteriorated concrete pavement slabs in Florida. This type of repair work is typically performed at night, and the repaired slabs are opened to traffic by the next morning. It is essential that this repair work be finished in a minimal amount of time. High early strength concrete is typically used in this application in order to have sufficient strength within a few hours after placement. Florida Department of Transportation (FDOT) currently specifies the slab replacement concrete to have a minimum 6-hour compressive strength of 2200 psi (15.2 MPa) and a minimum 24-hour compressive strength of 3000 psi (20.7 MPa). Due to a lack of research in this area, there are uncertainties on the optimum concrete mixtures to be used in this application. Questions arise as to what are the required curing time and the required early-age properties of the concrete for this application. This research study was conducted to answer these questions. Based on the limited test results from this study, it appears that for a 9-in. slab placed on a strong foundation (as in the case of the asphalt base used in this study) and a maximum temperature differential of +10 deg F in the concrete slab, a minimum required compressive strength of 1100 to 1600 psi for the concrete at the time of application of traffic loads may be adequate. It may be feasible to lower the minimum required compressive strength of 2200 psi at 6 hours, as specified by the current FDOT specifications, to 1600 psi at 6 hours, subject to further testing and verification. Due to the limited scope of this study and the limited amount of testing performed in this study, no recommendation for changes in FDOT specifications for concrete replacement slab is made at this point. Recommendations for further testing and research are made.