Quantitative Effect on Water Demand of Absorption and Fine Particles Content of Recycled Concrete Sands

Recycled sands demand a large amount of water, affecting the consistency of mortars and concretes. For this research, recycled concrete sands were used in mortars to assess the quantitative effect of their fine particles content and absorption coefficient on water demand. Thirteen different samples of recycled concrete sands were tested, covering a wide range of behaviours. Experimental results show the dominant influence of absorption rather than fines on the consistency of mortars when the sands are used dry. Numerical relationships between these properties of the recycled sands and their water demand were established allowing to calculate the expected increase of water/cement ratio when using recycled sands of the categories included in European standards. As a final practical conclusion, recycling processes that minimize the absorption of the sands are advisable, removing attached paste as much as possible, even at the expense of increasing the fines content.