Stiffness and Fatigue Behavior of Emulsified Cold Recycled Mixture Containing Waste Powder Additives: Mechanical and Microstructural Analysis

In recent years, due to economic and environmental considerations, the use of waste additives has been highly regarded in pavements. In the case of emulsified cold recycled mixtures (ECRMs), waste additives with pozzolanic properties can accelerate the emulsion setting rate and improve the technical specifications of mixtures. The present study aimed to introduce a new additive in ECRM to achieve a mixture with satisfactory mechanical properties: a combination of cement kiln dust (CKD), a cement production waste, and coal waste ash (CWA), a pozzolanic waste additive. The indirect tensile strength, resilient modulus, and indirect tensile fatigue (ITF) properties of these mixtures were studied at different temperatures and curing periods. The mixtures were also compared with a nonadditive mixture and a mixture containing cement as a conventional ECRM additive. The relationship between mechanical behavior and microstructure of ECRMs was investigated through field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The results showed that the mixture containing the new additive had a denser and stiffer structure and better ITF behavior, especially at lower strain levels, than the nonadditive mixture due to effective reaction between CKD and CWA in the presence of water and the formation of calcium silicate hydrate (C-S-H). It had a comparable behavior with cement-containing mixture. According to the experimental results, this ECRM can be recommended for use in the base layer of road pavements.