Experimental Assessment of Fly-Ash Stabilized and Recycled Mixes

Abstract

Abstract The use of fly-ash stabilizers, materials from fluidized combustion fly-ash, and other solid coal-burning residues, which are called coal combustion by-products (CCB), have good potential for application in subgrade structures and roadbed materials of roads as well as in the structural pavement layers. One of the many factors limiting the application of some CCB sorts is the relatively low resistance in repetitive contact with water, volumetric changes, and the risk of partly unsatisfactory hygienic and environmental parameters. With respect to the aforementioned negative characteristics of CCB, which occurred primarily under the repetitive impact of water and freezing, the experimental examination focused on improving CCB resistance to frost and water, verification of volumetric changes, and improvement of pozzolana characteristics of CCB by increasing the percentage of fine particles in the original material (e.g., by means of mechanical and/or chemical activation, including combination of both types). At the same time, the road construction industry strives to find a suitable substitute for the traditionally applied hydraulic binders as well as expand the existing base of the binders applied. The experience with using CCB as a binder or binder component has not been as extensive so far as to allow any generalisation of conclusions. Therefore, the possibilities of applying alternative additives as a replacement for the binders traditionally applied have been researched. Another application of the coal combustion by-products tested was in cold recycling mixes. In this case, the fly-ash from fluidized combustion is used as a substitute for the hydraulic binder. The fly-ash tested was subjected to mechanical activation, while the parameters of the mix under scrutiny reflected the impact on the strength and deformation parameters of the mix; last but not least, the water susceptibility indicator was also monitored. From the environmental perspective of practical applicability of the mixes a chemical analysis and leaching tests have been done.