Stabilization of plastic soils for use in pavement layers with wood ash at different treatment steps

Abstract

The combustion of biomass, which is a renewable energy source, generates ashes with potential for reuse in pavement construction, particularly in the stabilization of soils for the development of more cost-effective and environmentally sustainable pavements. This research evaluated the potential use of calcium-rich wood ash, subjected to different treatment steps, as a stabilizing agent for plastic soils for use in pavement layers. The ash, produced by an industry located in the Metropolitan Region of Cariri (Ceará, Brazil), underwent a series of laboratory-scale treatments, such as sieving, washing with heated water, calcination, and hydration, each aimed at modifying its chemical and physical properties. The treated ashes were incorporated into two clayey soils in order to assess changes in plasticity, expansiveness, saturation behavior, mechanical performance, and environmental safety. The study also included the design of a hypothetical pavement section using the most promising mixture, followed by a comparative cost feasibility analysis between a alternative solution (Soil-ash) and a conventional pavement structure typically employed in the region. Laboratory analyses comprised compaction tests, unconfined compressive strength (UCS), mini-CBR, consistency limits, CBR, and resilient modulus (MR) tests, conducted at different curing times (0, 28, and 90 days). Indirect tensile strength and fatigue tests were also carried out, in addition to leaching tests and physicochemical characterization of the ashes through particle size analysis, X-ray fluorescence (XRF), and X-ray diffraction (XRD).Although the addition of ash, regardless of the processing level, reduced the plasticity and expansiveness of the mixtures, improved saturation stability and the highest mechanical strength gains were observed in mixtures incorporating calcined ashes and commercial lime. From an environmental standpoint, the ashes were classified as hazardous due to their corrosivity, except for the washed ash. However, the adopted treatment processes significantly reduced the leaching potential of toxic elements. It is concluded that calcium-rich wood ashes can be transformed into effective binders through simple treatment procedures, contributing to waste reuse and promoting the circular economy within the pavement sector.