Kiln Dust for Stabilization of Pavement Base and Subrade Materials

INTRODUCTION The purpose of this synthesis of available information was to provide the Texas Department of Transportation (TxDOT) with a concise document on the state of the practice regarding the use of kiln dusts for stabilization of subgrade soils or granular base materials in highway pavements. This document should assist TxDOT in making decisions related to allowing the use of kiln dusts and the development of associated specifications, design procedures, construction practices, and evaluation processes. This review of current information should also help TxDOT develop relevant research programs. According to Chesner et al. (1998), both cement kiln dust (CKD) and lime kiln dust (LKD) can be used as activators in pozzolanic stabilized base mixtures. Depending on its reactivity, CKD may have potential for use as the sole cementitious material in stabilized base mixtures. Most research and construction with kiln dusts, however, has involved combinations of kiln dusts and coal fly ash as the cementitious component of the mixture. The strength of kiln dust-fly ash-aggregate base and subbase materials is dependent on three factors: the kiln dust, the fly ash, and the aggregate. Either pozzolanic or self-cementing fly ash can be used as part of stabilized base mixtures, although precautions may be necessary when using a self-cementing fly ash, because, with self-cementing fly ashes, no activators are needed. (2003), who has done significant work in this area, stated that the use of kiln dusts to stabilize bases and soils is a mature technology. However, according to Collins and Ciesielski (1994) kiln dust was not included in any state highway agency (SHA) specifications in 1994. Although CKD is not without potential usefulness for purposes other than paving, the quantities of CKD that are generated are sufficient to present the cement industry with serious disposal or storage problems (Miller et al., 1980). Kiln dusts have been used for slope stabilization, drainage from mines, among other things (Miller et al., 1997). This synthesis will only deal with pavement subgrade stabilization and modification and base stabilization 3 ORIGINS OF KILN DUSTS Production of lime and portland cement results in the annual generation of more than 20 million tons of kiln dust in north America, mostly cement kiln dust (Collins and Emery, 1983). As the name implies, kiln dusts are fine powder-like by-products of portland cement and lime production. They are collected from the stacks of high-temperature rotary kilns by the federally mandated dust collection systems …