Cement replacement materials are commonly used in concrete technology. Several researchers have examined high-performance concrete after adding mineral admixtures to it, but further studies are still needed to provide the optimum dosage of these materials for instance fly ash and silica fume. This study compares three types of concrete and the mechanical properties (compressive strength, flexural strength, and splitting tensile) of these types at the age of 28 and 90 days. The test results designate that adding the mineral admixtures commonly affects the mechanical properties of all the tested types. However, silica fume is more operative than fly ash. Furthermore, adding the fly ash and silica fume in the same concrete type slightly improves the mechanical properties.
If all concrete is to be recycled in a future scenario, recycled concrete will be needed. Usually concrete recycling causes loss of properties, but this does not have to be truth for all the mixtures. This paper shows a comprehensive knowledge about the improving methods used to keep the properties of the recycled aggregate concrete (RAC). In the reviewed literature several kinds of RAC were tested with various replacement ratios. The effect of adding steel fibres, silica fume or fly ash to the mixture were also examined both separately and together. Most of the experiments demonstrated excellent mechanical properties of the RAC compared with ordinary concretes. Based on these results the ideal RAC composition can be deduced and a future can be imagined when concrete can be recycled multiple times (MRAC).
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