Setting control of completely recyclable concrete with slag and aluminate cements

A completely recyclable concrete (CRC) is designed to have a chemical composition equivalent to the one of general raw materials for cement production. By doing so, this CRC can be used at the end of its service life in cement manufacturing without the need for ingredient adjustments. In one of the designed CRC compositions, blast-furnace slag cement (BFSC) was combined with calcium aluminate cement (CAC), which resulted in fast setting. In an attempt to control this fast setting, different retarders and/or the combination of lime and calcium sulfate were added to the system. The workability (slump and flow), setting time (ultrasonic transmission measurements and Vicat), strength development (compressive strength tests), and hydration behavior (isothermal calorimetry) were studied. It was found that the combined addition of lime and calcium sulfate results in a workable mixture that becomes even more workable if a retarder is also added to the system.

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