Investigating the physical and chemical characteristics of construction and demolition wastes as filler to regenerate beaches

Abstract

Currently, many countries around the world face serious problems related to coastal erosion. The use of natural fillers extracted from shallow areas as well as from rivers for coastal regeneration and beach nourishment generates additional environmental impacts that affect plants and animal communities, water circulation and coastal dynamics, amongst others. On the other hand, construction and demolition wastes (CDW) are becoming more abundant worldwide, generating additional environmental impacts related to water pollution due to leaching of contaminants, as well as loss of landscape quality. In this work it is proposed that CDW can be better suited to replace natural gravel for coastal erosion management. In addition, the use of CDW for beach regeneration will help to reduce the use of natural sources and thus to reduce the environmental impacts produced by extraction. This study investigates the physical characteristics of some fractions of construction and demolition wastes (CDW), particularly concrete, ceramics, asphaltic, and mixture material, to be used as filler to regenerate beaches, replacing the traditional filler generally used elsewhere. A wet ball milling method was used to adequate the physical characteristics (i.e. such as sphericity, roundness, and roughness) of the aggregates of CDW to be used for beach regeneration. The effects of the water mass to solid mass ratio (W/S), mass of sample to the mass of the balls (S/B), as well as ball milling time on the shape of CDW aggregates were studied. The optimum conditions to generate the required aggregates were W/S = 1, S/B = 0.5 and 1 h of ball milling. As particle size is considered an important parameter to avoid water turbidity, it is recommended to use particles with size greater than 2 mm, and the shape of the generated aggregates was calculated and compared to natural beach gravel. Wet ball milling significantly increased their roundness and contributed to a decrease of surface roughness, thus the final material presented high similarity with standard beach gravel aggregates. The durability of the material was also studied and compared to commercial gravel and beach gravel. The results show that weight loss during durability tests mainly depends on chemical composition of the CDW aggregates assayed. The chemical composition and mineralogical phase identification of CDW show the absence of hazardous elements and the presence of dolomite, quartz and calcite as principal phases. Inorganic composition of the CDW was also determined in order to comply with the Spanish Technical Instruction for the Environmental Management of Marine Extractions to obtain sand. Additionally, leaching tests of organic and inorganic substances were carried out according the European Standard EN12457/4 which specifies a compliance test providing information on leaching of granular wastes and sludges under specified experimental conditions, particularly a liquid to solid ratio of 10 L/kg dry matter for materials with a particle size below 10 mm (without or with limited size reduction). All generated aggregates complied with standard requirements, thus based on the satisfactory results produced by wet ball milling treatment on the physicals characteristics of CDW aggregates as well as on their chemical composition and results of the leaching tests, it is proposed the use of CDW as filler in beach and coastal regeneration.