USE OF RE-CON ZERO FOR CONCRETE CONTAINING ADMLXTURES

摘要

Recycling of returned fresh concrete using the common treatments such as washing, retarding the hydration reaction for days or even crushing the hardened concrete for reuse is effortful and therefore costly. An innovative alternative procedure has been developed by Mapei S.p.A. A two-component powder is used to granulate the returned fresh concrete in the truck mixer. The granulate can directly be used as recycled concrete aggregate. The two components are a superabsorbent polymer and an accelerating agent. The absorbent reduces viscosity of the fresh concrete while the accelerator gives a high early strength of the resulting granulate. The aim of this study was to evaluate the effects of different admixtures in the original concrete on the accelerating reaction and the properties of the produced granulate. The use of superplasticisers or retarders may affect the hardening reaction and the granulate properties. A series of tests has been carried out using different types of superplasticisers and retarding agents. The reaction kinetics with and without the addition of the accelerator has been evaluated by means of heat flow calorimetry, ultrasonic speed measurements and x-ray diffraction. Exemplary results are presented in this paper. The granulate properties and the characteristics of fresh and hardened concrete containing the recycled aggregate were tested. The results show the good performance of the aggregate produced with Re-Con Zero. However water absorption has to be taken into account when using the recycled aggregate at higher substitution levels.