Construction and Demolition Waste as Raw Materials for sustainable Cements

In 2014 about four billion tonnes of cement were produced [CEMBUREAU, 2014]. The use of industrial by-products, as a source of raw materials in the manufacture of portland and blended cements, is a research theme of significant relevance to the construction industry. Such industrial by-products can be employed as constituents of the final product or components of the raw feed in a cement kiln. Due to their hydraulic and/or pozzolanic activity, industrial by-products are utilized worldwide. Such by-products also increase durability and reduce costs for producing blended cements. The use of such by-products as raw mixture component for the cement production has received comparatively little attention by researchers and engineers. There is currently an increasing interest towards searching for new categories of by-products, which would be able to provide reactive calcium, silicon, aluminum, and/or iron oxides, for portland cement clinker manufacture. In this regard, construction and demolition waste (C&DW) is worthy of consideration because, when obtained from a properly selective demolition process, they could be employed as alternative raw material for portland clinker production. The present study deals with the use of two different kinds of C&DW, namely concrete waste (CW) and masonry waste (MW). In this study, C&DW is proposed to be employed as partial or total substitute for limestone and clay, respectively, in the portland clinker generating raw mixture. Four ternary mixtures containing limestone, as well as CW and MW, were subjected to laboratory tests in order to evaluate the clinker raw mixture produced and the performance of the related portland cement. A binary mixture, composed of limestone and clay, was used as a reference. All of these different cements displayed similar hydration behavior. Detailed results are presented and discussed.