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Bottom-up cracking may be due to CSL surface raveling or fatigue of the CSL, as follows:(a) Bottom-up cracking due to CSL surface raveling Based on accelerated pavement testing, studies show that the surface of a stabilized base layer can ravel, creating a layer of loose material between the HMA and base CSL (Figure A-8). Raveling of the base increases the strain level at the bottom of the HMA, which can result in alligator cracking. In addition, pumping was observed in these cases. The pumping is caused by the loss of fines in the loose material layer. This phenomenon may be linked to the erodibility of stabilized materials, which often happens when relatively fine raw materials are treated (De Beer 1985). reported the loose layer is about 0.8 in. thick and is believed to be due to shear failure within the CSL as a result of horizontal loading, which in turn causes alligator cracking.

In-place recycling of asphalt pavement materials is a sustainable rehabilitation method. Existing hot-mix asphalt (HMA) layer is pulverized and blended with some or the entire base course and possibly some subgrade to form a broadly graded material referred to as recycled pavement material (RPM). The RPM is then compacted as the new base course and overlaid by a new layer of HMA. In some occasions, additives are added to increase the strength of RPM base course, such as cement, emulsion, fly ash. It is plausible to utilize high calcium high carbon fly ash, as the high level of carbon prevents fly ash from being used in concrete. A series of laboratory tests were conducted to evaluate the performance of these materials, including crushed aggregate, untreated RPM, and treated RPM with high carbon fly ash. The tests included compaction, California Bearing Ratio, resilient modulus, and unconfined compressive strength for treated RPM. The engineering properties of these materials were compared.

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