Cement kiln dust (CKD) is a fine powder that is a by-product of the manufacture of cement that is classified as a waste. Whilst not considered a hazard if handled properly, it is preferable not to send it to landfill and a possible use is as the added filler in asphalt mixtures, as was done in the 1970s. To investigate the potential, two laboratory studies were undertaken, the first using five different mixture types manufactured both with CKD and limestone filler and the second concentrating on workability and water sensitivity together with the composition of three sources of CKD (of which only one complied with the requirements for filler in BS EN 13043). Overall, these laboratory studies showed a mixed justification to encourage the adoption of using CKD as the filler. Nevertheless, a pilot-scale trial was undertaken involving the plant manufacture and laying of both binder course and surface mixtures with and without CKD as the filler. The trial demonstrated that asphalt mixtures can be produced and laid without exceptional problems to produce a good looking mat. The overall conclusion of the work is that CKD can be successfully used as the added filler in routine asphalt mixtures, but that it varies as a product between sources (the extent of the consistency of properties from a single source has not been investigated). To facilitate the acceptance of this use, a Quality Protocol has been drafted and is included as an Appendix to the report. (Author/publisher)
Abstract