There is an established tradition for salvaging and recycling building and construction materials. For hundreds of years after the end of the Roman empire, later groups plundered their buildings as a source for new materials, often skilfully worked stone masonry and fired clay products were thus incorporated into altogether cruder new buildings.
Demolition waste has long been broken down and used as foundations and sub-bases for new construction, roads and other pavements. There is now a movement towards, and encouragement for, recycling old concrete as crushed aggregate for new concrete, although there can be legitimate concerns and certainly more caution must be exercised with respect to fine aggregate.
More valued building elements, such as ashlar blocks, bricks, roofing slates or tiles, lintels, flooring tiles and various decorative items, have long been recovered and re-used. In recent times, as we have become ever more sensitive to the need to minimise waste and maximise re-use, this trade has organised itself into centres where these items can be sold, sorted and purchased.
Alongside this admirable recovery and re-use of earlier construction materials, there has also been a gradually increasing role for finding gainful re-employment by the construction industry of redundant or waste products. Large quantities of industrial wastes and by-products, such as various slags, have found extensive and largely beneficial uses in construction and this trend is increasing.
Civil engineers will be aware of many other examples of this happily growing endeavour to consume waste or previously-used products as an alternative to extracting or making new construction materials. However, it is a constantly changing situation, partly because the availability of wastes or by-products can and does fluctuate.
Two extremely popular construction materials in common usage worldwide, blast-furnace slag by-product from the iron and steel industry, in its ground granulated form, and fly ash waste (including pulverised-fuel ash) from coal-burning furnaces, might face at least regional supply shortages going forward.
Some of the former large producers of iron and steel, including the UK, are increasing focusing on specialist rather than bulk production, with consequently reduced slag outputs, although interestingly and relevantly, there could soon be a new lease of life from the processing of recycled iron and steel materials. In the case of fly ash and other types of produced ash (such as rice husk ash), this possible shortage could be more profound worldwide as there is a global move away from coal and other carbon-burning for environmental reasons