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Mortar and concrete may contain small amounts of trace elements as well as organic substances deriving from additives and admixtures. The hardened cement paste is a good encapsulating and binding matrix for these components and therefore the release rates of these substances to the environment are on a low level.

The use of recycled crushed sands contributes to closing the material cycles in the building materials industries that process non-metallic minerals. The potential that arises from the processing of mineral demolition waste for the production of resource-conserving concretes was investigated in the "R-Beton" joint research project. Investigations by VDZ gGmbH showed that the production and use of clinker-efficient cements that contain finely ground crushed sand as a main cement constituent can represent an alternative recycling route. Crushed sand from railway sleepers, railway ballast, crushed concrete, bricks, tiles and masonry was used in the project. In Germany, the recycling of crushed sand in this way involves proof of usability in accordance with building regulations law. In addition to the environmental compatibility of the crushed sands and the technical performance of the cements containing crushed sand as specified in DIN EN 197-1 it is also necessary to comply with the approval-relevant durability for the concretes to be produced with these cements (so-called R-cements) and fulfil building inspectorate requirements. The investigations in the project have shown, for example, that concretes made with R-cements containing 10 or 30 mass % crushed masonry with a high clay brick content can pass all the durability tests safely, in contrast to cements made with crushed sand of different origin. When the results obtained in the project are considered as a whole it can be stated that R-cements made with up to 30 mass % crushed sand could, at least, be used for internal component concretes but external components in building construction also appear to be possible. The investigations carried out on crushed sands with respect to their effects on soil and water have shown that the environmental analysis requirements for solids and eluates as specified in DIN 4226-101 can be fulfilled. [ABSTRACT FROM AUTHOR]