About the research
Rutting, caused by a depression or groove of traveling wheels worn into a road, is a major problem of conventional asphalt or flexible pavements, and is primarily due to plastic deformation of the asphalt concrete near the pavement surface. To overcome this problem, a hybrid, made with asphalt (flexible) pervious concrete filled with Portland cement (rigid) mortar, called casting cement asphalt mixture (CCAM), has been developed.
During the development process, various CCAMs were made with Iowa concrete materials. Experiments were conducted to gauge optimal porosity of asphalt pervious concrete and optimal flowability of mortar for CCAMs. The basic engineering properties of these CCAMs, such as strength, shrinkage, and freeze-thaw durability, were evaluated.
The results show that CCAMs can be produced successfully by using pervious concrete of 25% porosity and rapid set cement grout with very high flowability. The calcium sulphoaluminate cement grout used in this study attained strength greater than 18 MPa (2,600 psi) in less than 12 hours. Therefore, a CCAM pavement could open to traffic at a much earlier time than a conventional Portland cement concrete roadway. While asphalt concrete displayed a 9 mm rut after being subjected to 10,000 wheel track cycles during a wheel track rutting test, the CCAM showed a less than 1 mm rut. However, as the CCAM is neither asphalt nor Portland cement concrete, a big project challenge was to find appropriate test methods for evaluating key properties of CCAM, especially the method for testing its freeze-thaw durability.
Although CCAM has attracted a great deal of attention in Europe and Asia, most applications have been in warm climate regions. Few applications of CCAM have been conducted in the US, especially in cold climate regions. Further investigation needs to be done on the CCAM freeze-thaw durability before this new material is applied to Iowa pavements.
Iowa Department of Transportation
Iowa Highway Research Board ($45,000.00)
Mid-America Transportation Center
Contract Number: DTRT13-G-UTC37