Iowa State University
Iowa Department of Transportation
Guidelines, Pavement performance, Portland cement concrete, Sawing, Setting (Concrete), Stripping (Pavements), Ultrasonic pulse velocity
At present there is little fundamental guidance to assist contractors in choosing when to start sawing joints in slabs on grade. Too early and there is a risk of raveling, but too late and there is a risk of random cracking. Failures may lead to disputes between agency and contractor as to who is responsible and what remedial action can be taken, leading to increased costs to both parties due to slabs having to be replaced or patched. Guidance and proactive is often based on subject tests such as scratching the surface with a "calibrated" penknife or assessing the depth of a footprint. It is also common for crews to start attempting to saw relatively early and assess the degree of raveling. It is believed that a fundamentally sound approach to assessing when sawing should start will improve the overall quality of pavements in place, and at the same time, save money. Pilot tests of an approach using ultrasonic pulse velocity (UPV) (p-wave) indicate that the method has the potential to meet this need. The device is used to measure the initial set of the mixture in the environmental condition at the site. It is believed that this information can be used to predict the start of the sawing window. The aim of the work described in this proposal is to conduct additional work to evaluate the relative effectiveness of the UPV approach along with thermal based systems to measure initial set of mixtures in-situ and so to predict sawing time.