Dynamic Shear Properties of Recycled Combustion Slag, a Sustainable Material, in Road Construction

Solid waste recycling challenges civil and environmental engineers to use waste from different industries to exceed sustainable development while meeting current material costs. Combustion slag (CS) is the material resulting from the combustion of hard coal in pulverized coal boilers. It is removed by gravity from the furnace chamber and transported by hydraulics through the slugger to the sedimentation chambers and from there to the heaps. The waste combustion slag can be used for land leveling, road building, and sports and leisure facilities. This paper presents the geomechanical characterization of the CS from the “Siekierki” CHP Plant, located in Warsaw, Poland. Particular emphasis was placed on the dynamic properties of combustion slag, including shear modulus (G) and damping ratio (D). Correct estimation of these parameters over a wide strain range is essential for laboratory research and modeling. A laboratory test program was defined to obtain the G-modulus, Gmax-modulus, shear modulus degradation curve G(γ)/Gmax, D-ratio, depending on the mean effective stress and relative density, in the strain range of 10−6 up to 10−3. Stiffness of CS was obtained using laboratory investigations typical for natural soils, namely, standard resonant column tests, and bender element tests. From the many different methods for soil damping estimation, two of the most common were selected: logarithmic decay and half-power bandwidth. The dynamic properties and their changes with strain of the Siekierki combustion slag are in line with general trends for granulated natural soils and other recycled materials. The outcomes of the presented research promote the reuse of CS as aggregate in road construction, which contributes to limiting the extraction of natural aggregate, reducing the filling of lands with this type of waste, and ultimately reducing the transport of materials and consequently lowering greenhouse emissions.