Characterization of fresh and landfilled cement kiln dust (CKD) and evaluation of potential applications

This research addressed the recycling of cement kiln dust (CKD), a by-product of cement manufacturing. While significant quantities of CKD are generated every year, its utilization in construction has been to this day quite limited. Additionally, the issue of reusing already landfilled CKD has remained almost completely unexplored. The work made use of three fresh CKDs collected at different instances from the same U.S. plant, as well as CKD obtained from different locations in a 12 year old landfill adjacent to the plant. A comprehensive experimental study of the physio-chemical and engineering properties of the CKDs was performed, and the results compared to published data for other CKDs. Differences in the free lime content were observed between different batches of the fresh CKD and were ascribed to changes implemented to the cement plant. Tests performed on the landfilled CKD showed very consistent characteristics and the presence of only traces of free lime. A distinct characteristic of both CKDs is the small particle size (85--95% \u3c10μm). There exist, however, marked differences in particle morphology between the fresh and the landfilled CKD, which have a significant impact on the engineering properties. Hence, the study highlights the potential impact of chemical alteration processes on the properties of reactive byproducts when exposed to the environment in a disposal site. Based on the results of the characterization study, several potential applications for the CKDs were identified. Two of these: soil improvement and controlled low strength materials (CLSM) were selected for additional work. In investigating the use of CKD for soil improvement, only one fresh CKD was found to be sufficiently reactive (thanks to presence of free lime). The results for the other fresh and the landfilled CKD suggest that these materials may be used in combination with limited amounts of Portland cement to treat wet subgrades or water-logged areas. The viability of using the low free lime fresh and landfilled CKDs was assessed through comparison of the fresh and hardened properties to those of fly-ash based mixtures. While all CKD mixtures displayed excellent flow properties, only those manufactured with the highest cement dosage considered (50 kg/m3) had setting times and strength compatible with their practical use in the field