Characterization of unsaturated properties of recycled materials

Substantial amounts of waste from industry and construction are produced every day around the world. Much of the wastes consist of concrete aggregate, asphalt shingle, steel slag and copper slag which can be reused as construction materials. Many studies have been carried out to investigate the characteristics of recycled materials under saturated conditions. However, only few studies have been performed to investigate the Water-Characteristic Curve (WCC), permeability and shear strength of these recycled materials under unsaturated conditions. In addition, the use of these recycled materials as construction materials using the principles of unsaturated soil mechanics has not been fully studied. Therefore, this paper focuses on the unsaturated properties, i.e. the drying and wetting WCCs and permeability function of Recycled Concrete Aggregate (RCA), Reclaimed Asphalt Pavement (RAP), Steel Slag (SS), Copper Slag (CS) as well as the unsaturated shear strength of RCA and RAP. In addition, the application of RCA and RAP in Capillary Barrier System (CBS) as a slope cover system is also presented. The experimental results indicated that RCA, RAP, SS and CS have similar characteristics with natural aggregates under saturated and unsaturated conditions. The RCA, RAP, SS and CS with smaller particle sizes, have higher air-entry value, higher water-entry value and lower permeability as compared to those with larger particle sizes. The shear strengths of the RCA and RAP exhibit non-linear behavior with respect to net normal stress. Therefore, nonlinear shear strength equations are used to model the shear strength of the RCA and RAP. The experimental results also showed that the RCA and RAP with smaller particles sizes have lower values of φ′ and φ^b as compared to those of the coarser RCA and RAP. The results of the numerical analyses also showed that CBS with RCA and RAP is effective in reducing the rainwater infiltration and maintaining the stability of slope, indicating that the RCA and RAP can be used to replace natural aggregates within CBS.