Characteristics of fine processed construction and demolition waste in Japan and method to obtain fines having low gypsum component and wood contents

Plaster board waste (PBW) - A potential fluoride leaching source in soil/water environments and, fluoride immobilization studies using soils

Plaster board waste generated from industries, usually contains major proportion of calcium as calcium sulfate. In addition, fluoride is remarkably one among the constituents of this waste material which leaches off into the soil and aquatic environments and causes fluoride pollution. In order to simulate how the dumping of PBW causes fluoride contamination in soil and water sources, shaking and stirring based batch-mode leaching studies were conducted. These studies explored the leaching of fluoride as a function of particle size, agitation time, pH of the leaching solvent (distilled water), L/S (water: PBW) ratio, temperature and electrolytes. It was explored that 1 g of plaster board waste contains18.54 mg F per gram of PBP. High leaching of 3.72 mg F per liter was studied at pH 6.02 with Ca²⁺ and TDS contents of 1050 mg L^-1 and1640 mg L^-1 respectively. The influence of sodium electrolytes such as chloride, nitrate, hydrogen carbonate, carbonate, sulfate, borate, phosphate and acetate on the leaching of fluoride from PBW was studied. The influence of fluoride leaching by sodium phosphate recorded a high value of 12.75 mg L^-1 with no detectable amount of calcium ions. The influence of eight electrolytic mixtures each containing five sodium electrolytes on fluoride leaching corroborated the highest leaching in mixtures containing phosphate followed by hydrogen carbonate/carbonate. Solutions of calcium and aluminium chloride and their mixture were used to measure the rate of leachable fluoride in solution. Furthermore, the fluoride leaching at different temperatures and acids was studied. Naturally occurring soils when blended with PBW were observed to immobilize fluoride and lessened the amount of leaching fluoride in water. Various characterization studies such as FTIR, Raman, FESEM (with EDS), XRD and XPS were carried out for PBW and its treated samples using different electrolytes. Fluoride leaching proportionate to the precipitation of carbonate and phosphate was recorded in the case of appropriate electrolyte and mixtures.

Physical process to sort construction and demolition waste (C&DW) fines components using process water

Modern societies are generating considerable volume of Construction and Demolition Wastes (C&DW) annually. Most recycling facilities offers viable sorting and recycling options for the coarser particles of the different materials found in those wastes. However, usual dry mechanical sorting and human sorting are not efficient on C&DW fines particles (C&DF, <10 mm) representing the third of the C&DW produced and being composed of similar materials. Recent environmental issues related to the landfilling of C&DF have pointed out the need to develop innovative alternative and adapted recycling paths for the C&DF. This study presents an efficient sorting process train based on physical separation steps used in the mining and the soil treatment industries. The use and recirculation of process water allowed to segregate and concentrate the gypsum from the 2-12 mm C&DF into a specific fraction (55-65% gypsum content) representing 40% of the total mass. Other constituents were sorted based on their relative density, size and shapes; thanks to hydraulic classification and physical sorting forming four more fractions with high recycling potential: coarse aggregates (15%), fine aggregates (9.4%), organic and inorganic fibers (10.8%) and light organic compounds (24.8%). The process has been designed to be integrated in existing sorting facilities and the process costs were evaluated to 38 CAN$/t.

Chemicals of concern in construction and demolition waste fine residues: A systematic literature review

Despite the increasing use of chemical additives in construction and their potential threat to the environment and human health, many C&DW studies lack a comprehensive view of chemicals of concern (COC) in C&DW. This study systematically reviewed published studies from 2010 to August 2021 using a keyword search methodology to explore COC in C&DW fine residues based on 73 articles identified from 5 prominent databases. Results show that trace/heavy metals (As, Cr, Cu, Cd, and Pb) as well as high concentrations of toxic gasses (methane, hydrogen sulphide and mercury vapour) have been reported in landfills. Besides, organic chemicals such as polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and brominated flame retardants have been found in landfill leachates in the Netherlands and widely detected in landfill leachates in Sweden, Japan, and Canada. The potential of these contaminants to cause health complications has also been reported. Carcinogenicity, liver and kidney damage, cumulative damage, neurological disorders and foetal damage were reported as associated health implications of exposure to COC from C&DW. A waste disposal lens was used to explore the factors that influence the environment and human health impacts (pH, gypsum and organic content, size fraction, atmospheric exposure and liquid infiltration rate). Despite environmental and health issues relating to C&DW fine residues, the ultimate destination for C&DW fine residues remains in general landfills. Although significant efforts in managing C&DW have been implemented at various levels, those specifically targeting C&DW fine residues remain sparse.

Valorization of Fine Recycled Aggregates Contaminated with Gypsum Residues: Characterization and Evaluation of the Risk for Secondary Ettringite Formation

Fine recycled aggregates (FRA) (0/4 mm) are up to now not valorized on a high enough level because of characteristics like an elevated water absorption, higher fines content, and the presence of contaminations. Leftover gypsum residues from the construction site can cause internal sulfate attack when FRA are incorporated into new structures. Concern about this deteriorating reaction plays an important role in the rejection of FRA. In this study, samples of FRA from different recycling centers were characterized and incorporated into mortars. They were then subjected to swelling tests in order to evaluate the development of sulfate attack. Reference materials with different amounts of sulfates were used as a comparison. Results showed a variable sulfate content in industrial FRA, depending heavily on the source of the materials. In all but one case, the total amounts surpassed the acceptable sulfate contents specified in the European standard EN 206, meaning the FRA would be rejected for reuse in concrete. Nevertheless, swelling tests demonstrated that these contamination levels did not pose a risk for sulfate attack. These results indicated that the incorporation of FRA leads to acceptable mechanical performances and that the sulfate limit could be reviewed to be less strict.

Recycled blocks with improved sound and fire insulation containing construction and demolition waste

The environmental problem posed by construction and demolition waste (C&D waste) is derived not only from the high volume produced, but also from its treatment and disposal. Treatment plants receive C&D waste which is then transformed into a recycled mixed aggregate. The byproduct is mainly used for low-value-added applications such as land escape restoration, despite the high quality of the aggregate. In the present work, the chemical composition properties and grading curve properties of these aggregates are defined. Furthermore, the resulting recycled concrete with a high proportion of recycled composition, from 20% to 100% replacement of fine and coarse aggregate, is characterized physically and mechanically. An environmental study of the new construction material when all aggregates are substituted by C&D waste shows a low toxicity level, similar to that of other construction materials. The new material also has improved properties with respect to standard concrete such as high fire resistance, good heat insulation, and acoustic insulation.