This issue of Waste and Resource Management illustrates the different environmental forces that are affecting the construction and construction products industries. Increasingly stringent definitions of hazardous waste and restrictions on its disposal are leading to innovative solutions in land remediation that minimise off-site disposal. Baylis and Allenby (2010) use three case studies of industrial sites to illustrate how techniques such as bioremediation, in-situ and ex-situ solidification and stabilisation, and in-situ chemical oxidation can be used to treat and retain a greater proportion of material on site compared to the ‘dig and dump’ strategies that have historically been common with these heavily contaminated sites. The wastes successfully treated included typical gas works chemicals such as tars, phenols and cyanides; hydrocarbon oil refinery wastes, complicated by the occurrence of asbestos-containing insulation materials; and aromatic and chlorinated chemicals. A final case study concerns a site investigation to confirm the prior decontamination of a chemical warfare agent site, demanding sophisticated containment and risk management approaches.
The increasing consideration of techniques such as stabilisation and solidification for hazardous wastes means that test methods are required in order to determine the likely leaching characteristics of these wasteforms and the deterioration in the mechanical properties of the solidified material. A series of experiments reported by Dyer (2010) uses a synthetic electrochemical plating waste incorporated into a sintered glass matrix, and air pollution residues from a municipal waste incinerator incorporated into a cementitious matrix. The studies show that although small sample sizes leach faster, they show more variability, as do samples that have been subject to acid leaching. A technique based on curve fitting to predict strength deterioration is proposed, as well as a modelling approach for describing the loss of mass from the wasteform.
As well as the increasing restriction on landfill, the use of waste materials to create more sustainable products is discussed in this issue. Products can be used as a ‘sink’ for waste products, displacing other more valuable and resource-intensive virgin raw materials. Al-Otaibi et al. (2010) examine the use of recycled concrete from the construction and demolition industry in Kuwait as a raw material in lime–silica bricks. They demonstrate that crushed concrete fines can be used in such products and that their performance can be improved by using ground blastfurnace slag or additional lime. Construction products that take less energy to manufacture – and are hence less carbon-intensive and usually cheaper – can also be facilitated by the use of waste materials. Unfired products made from natural clay soils are receiving increasing interest in the UK, not just from niche manufacturers of ‘green’ products, but also from mainstream construction product manufacturers. They form an interesting example of reinvention or reinterpretation of an old technology, brought up to date for environmental reasons. In the case of unfired clay bricks, Oti et al. (2010) investigate the addition of slags as latent hydraulic binders to improve their freeze–thaw stability. Since water saturation of clay products is a common problem, freeze–thaw stability is a necessary property of structural clay components. The swelling associated with sulfate-containing clays can be inhibited with a lime-activated latent hydraulic binder, allowing clay soils (in this case Lower Oxford Clay) to be formed into bricks that meet the appropriate British Standards for freeze–thaw.
