Use of waste materials in the construction industry

A Symposium by Correspondence has been organised on behalf of RILEM on the use of waste materials and industrial by-products in the construction industry. 18 countries (excluding the UK for which the authors are providing information) submitted contributions and in this paper these contributions are summarised and analysed. Information about individual materials has been extracted from the national contributions and a chapter devoted to each waste in turn. The properties, occurrence, present uses and possible future applications of each waste are described. Blastfurnace slags and pulverised fuel ashes are the two materials which are being used to the greatest extent. Blastfurnace slags are used overall to some 80% of their production and in several countries virtually all that is produced is used and the slags are regarded as a highly satisfactory material. Pulverised fuel ashes are about 20% used overall but up to 70% is used in some countries. Much of these two materials is used as fill but many more sophisticated uses are developing. These materials can make a particular contribution in conserving energy in the manufacture of cementitious materials and of lightweight aggregates. Overall however the proportion of mineral wastes which is used is only about 5% of the production and most is used in relatively low grade applications such as fill in roads and embankments. The most influential factor in determining whether or not a waste material or by-product is used is the economic cost in comparison with the alternative natural material in a particular application. These costs are primarily made up by handling, processing and transport but the social benefits of using a waste, for example avoiding the dereliction associated with the tipping of a waste material or the quarrying of a natural, should not be forgotten. Possible disbenefits such as pollution arising during processing or a less well proven technical performance should also be taken into account. Adequate knowledge of the properties of the waste materials and products containing them are therefore essential to enable a balanced judgement to be made on the overall advisability of using a waste material in a particular situation.