Proposal for limitation and control of fines in calcareous sands based upon their influence in some concrete properties

The development and final conclusions of a research programme which has gone on for four years are explained here. The products of Basque Country quarries have been analysed, studying also the influence of calcareous and clay fines in mortars, as well as in crushed calcareous aggregate concretes, this being the objective of the present article. 42 different concrete mixes in duplicate, with the same workability, have been made, taking the contents of fines and clay in sand and the cement content as variables. This process has involved handling a total of 14 tonnes of aggregate and the manufacturing of more than 900 standardized cylinders. It is concluded that up to 15% of fines in calcareous and ground sand are admissible, provided that the proportion of clay fines is controlled by means of a sand equivalent sight test and, even better, by the methylene blue test method. This research work has been the basis for the new text of the corresponding paragraphs in the recent Spanish Concrete Standard EH-88, but could be, a reference for others with a similar type of aggregate.