Improvement of Cold Recycled Mixture Performance Based on Improved Density Test Method and RAP Characteristics

The available test methods for optimal moisture content of cold recycled mixture (CRM) as well as its bulk specific gravity, and theoretical maximum relative density were analyzed in this work. Some test improvements were suggested to improve test control of the CRM road performance based on the discovered flaws. Besides, the properties of reclaimed asphalt pavement (RAP), including the content of old asphalt, penetration index, passing rate of 4.75 mm sieve, and gradation change rate after extraction, were examined. The effects of RAP characteristics on splitting tensile strength, water stability, the high- and low-temperature performance of emulsified asphalt CRM were studied. The results show that the optimum moisture content of CRM should be determined when the compaction work matches the specimen’s molding work. Among the analyzed methods of bulk specific gravity assessment, the dry-surface and CoreLok methods provide more robust and accurate results than the wax-sealing method, while the dry-surface method is the most cost-efficient. The modified theoretical maximum relative density test method is proposed, which can reduce the systematic error of the vacuum test method. The following RAP-CRM trends can be observed. The lower the content of old asphalt and the smaller the change rate of gradation, the smaller the voids and the better the water stability of CRM. The greater the penetration of old asphalt, the higher the fracture work and low-temperature splitting strength. The greater the penetration, the higher the passing rate of 4.75 mm sieve after extraction, and the worse the high-temperature performance of CRM.