Paper by EICKSCHEN SIEBEL from ISCR 8th 1998 Lisbon Portugal
In the domain of road building, recycled aggregate made from old concrete road pavings has been used in the construction of new concrete pavings for quite some time. Generally only the coarse fractions of more than 4 or 2 mm, respectively, are used as recycled material. Most of the recycled sand produced has been used in frost protection layers and in hydraulically bound sub-base courses so far. In order to permit its use in the highest-grade concrete applications possible, e.g. in bottom layer concrete of new road pavings, investigations were carried out by the Research Institute of the German Cement Industry. The main focus was placed on the properties of fresh and hardened concrete in relation to the crushed sand proportion metered. It turned out that, in line with an increase in the proportion of crushed sand, higher quantities of superplasticizer and air entraining agents had to be added to ensure sufficient workability and a sufficient air content. Investigations of hardened concrete have shown that an increase in the proportion of recycled sand has only marginal effects on strength properties and the resistance to freeze-thaw attack with de-icing salt, while it may in some cases cause a considerable increase in shrinkage and swelling.
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