Reflective crack mitigation guide for flexible pavements.

PDFTech ReportIHRB Project TR-641InTrans Project 11-424Flexible pavementsReflection crackingRehabilitation (Maintenance)Hot mix paving mixturesPavement performanceBituminous overlaysCrack and seat treatmentRuttingComminutionFalling weight deflectometersIowaIowa State University. Institute for TransportationWilliams, R. ChristopherChen, CanBuss, AshleyIowa State University. Institute for TransportationIowa. Dept. of TransportationIowa. Highway Research BoardUS Transportation CollectionReflective cracks form in pavements when hot-mix asphalt (HMA) overlays are placed over jointed and/or severely cracked rigidand flexible pavements. In the first part of the research, survival analysis was conducted to identify the most appropriaterehabilitation method for composite pavements and to evaluate the influence of different factors on reflective crack development.Four rehabilitation methods, including mill and fill, overlay, heater scarification (SCR), and rubblization, were analyzed usingthree performance indicators: reflective cracking, international roughness index (IRI), and pavement condition index (PCI). It wasfound that rubblization can significantly retard reflective cracking development compared to the other three methods. Nosignificant difference for PCI was seen among the four rehabilitation methods. Heater scarification showed the lowest survivalprobability for both reflective cracking and IRI, while an overlay resulted in the poorest overall pavement condition based onPCI. In addition, traffic level was found not to be a significant factor for reflective cracking development. An increase in overlaythickness can significantly delay the propagation of reflective cracking for all four treatments. Soil types in rubblization pavementsites were assessed, and no close relationship was found between rubblized pavement performance and subgrade soil condition.In the second part of the research, the study objective was to evaluate the modulus and performance of four reflective crackingtreatments: full rubblization, modified rubblization, crack and seat, and rock interlayer. A total of 16 pavement sites were testedby the surface wave method (SWM), and in the first four sites both falling weight deflectometer (FWD) and SWM wereconducted for a preliminary analysis. The SWM gave close concrete layer moduli compared to the FWD moduli on aconventional composite pavement. However, the SWM provided higher moduli for the rubblized concrete layer. After thepreliminary analysis, another 12 pavement sites were tested by the SWM. The results showed that the crack and seat methodprovided the highest moduli, followed by the modified rubblization method. The full rubblization and the rock interlayer methodsgave similar, but lower, moduli. Pavement performance surveys were also conducted during the field study. In general, none ofthe pavement sites had rutting problems. The conventional composite pavement site had the largest amount of reflective cracking.A moderate amount of reflective cracking was observed for the two pavement sites with full rubblization. Pavements with therock interlayer and modified rubblization treatments had much less reflective cracking. It is recommended that use of themodified rubblization and rock interlayer treatments for reflective cracking mitigation are best