High reclaimed asphalt pavement (RAP) contents in hot recycling present compaction challenges, insufficient blending of aged and virgin binders, nonuniform RAP dispersion, and unstable mixture performance. This research investigated calcium sulfate dihydrate whiskers (CSDW) derived from municipal solid waste incineration (MSWI) fly ash as a foaming warm mix promoter for increasing RAP incorporation in high-RAP plant mixed hot recycling. The warm mix mechanism, compaction behavior, mesostructural evolution, engineering performance and production-stage cost were evaluated against mixtures containing Evotherm® M1. CSDW exhibited typical gypsum whisker characteristics with good crystallinity and released about 21% crystallization water, with a peak release temperature of approximately 140 °C, providing a stable basis for the warm mix effect within the practical compaction temperature range. CSDW promoted the warm mix effect through physical foaming together with improved dry-state wetting and aggregate coating. The modified mixtures showed improved compactability and better internal homogeneity during compaction. They maintained satisfactory rutting and cracking performance, while moisture resistance showed only a slight reduction and still met the specification requirement. Production-stage cost analysis further showed that CSDW is cost-effective. This approach provides an economical pathway to increase RAP utilization while upgrading an MSWI fly ash derived by-product into a value-added pavement material.
Gong et al. (Tue,) studied this question.