Recycling of construction and demolition waste containing mixtures of fired clay and gypsum implies a separation process which aims to obtain individual fired clay and gypsum aggregates. This paper presents a method to quantify very small amounts of gypsum that still adhere at the fired clay bricks surface after the separation process. This may require a single or several steps. Leaching studies were carried out on mixed fired clay bricks and gypsum powder, by measuring the electrical conductivity of the water. Results show that maximum electrical conductivity of mixed fired clay and gypsum powder in contact with water can be correlated to gypsum content present in corresponding mixture. Therefore, electrical conductivity could be a method to evaluate the amount of gypsum which still remains at the surface of fired clay bricks after separation.

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