Emulsified cold recycled mixtures using cement kiln dust and coal waste ash-mechanical-environmental impacts

Cold recycling is a widely recommended asphalt pavement rehabilitation technology with potentially significant economic and environmental benefits. One of the advantages of cold recycling is that its operations are performed at ambient temperature. However, there are still some concerns regarding the use of emulsified cold recycled mixtures (ECRMs). These pavements are susceptible to problems such as raveling, stripping, low initial strength, and long curing time, which are often countered by the use of additives. This study examined the mechanical outcomes and environmental implications of using cement kiln dust (CKD), which is a byproduct of cement production plant, and coal waste ash (CWA), which is obtained by igniting coal waste, in ECRMs as additives. The effects were compared with the additive-free or reference mixture and the mixtures with 1% and 2% cement content. To evaluate the mechanical properties, Marshall stability, indirect tensile strength and moisture susceptibility tests were performed on the specimens of different ages at different temperatures. Environmental impact was assessed using the modified toxicity characteristic leaching procedure (MTCLP) test. Finally an economical-environmental analysis was performed on designed pavements with each type of ECRM. The results showed that the combined use of CKD and CWA improved the mechanical properties, especially after prolonged curing periods. In some cases, this improvement was even greater than the improvement resulting from the addition of cement. The results of the MTCLP test showed that even after five extractions, the concentration of heavy metals in the leachate of CKD- and CWA-containing mixtures remained below the regulatory levels. Overall, it was found that using CKD and CWA as additives in ECRMs had remarkable economical and environmental benefits, especially if they are employed together.