Sables calcaires à fines calcaires et argileuses: influence et nocivité dans les mortiers de ciment: Fid-Bau Portal

Sables calcaires à fines calcaires et argileuses: influence et nocivité dans les mortiers de ciment

Ramirez, J. L. / Barcena, J. M. / Urreta, J. I.

Abstract On a réalisé un programme de recherches assez exhaustif dans le but de rassembler des données pour une prochaine révision de la Norme Espagnole du Béton sur la teneur en fines des sables, actuellement fixée, sans exception, à 5%. On présente les résultats de l'influence des différentes teneurs en fines calcaires et argileuses sur les propriétés mécaniques des mortiers, prélablement à l'étude de cette influence sur des bétons confectionnés avec des granulats calcaires de broyage. Cette phase est en cours d'exécution à l'heure actuelle. Avant de se livrer à ces travaux expérimentaux, on a réalisé une prospection générale de toutes les carrières de broyage de calcaire dans la zone nord-est de la péninsule correspondant au Pays Basque. D'après les résultats obtenus, il semble que la limite pourra s'élever jusqu'à 12 à 15%, à condition d'assurer la présence d'argile à un taux défini par des essais.

Summary To obtain data for the next revision of the Spanish Concrete Standard, with regard to the content of sand fines, presently set at 5%, an exhaustive research project was undertaken. The results show the influence of different contents of calcareous and clay fines in the mechanical properties of mortars made with crushed limestone sand, prior to studying the corresponding influence on concrete prepared with this type of aggregate, which is presently being examined. Prior to this research work, a general survey was carried out of all the quarries with crushed limestone in the northwest of the peninsula corresponding to the Basque Country. From these analyses carried out in 44 quarries, an average value of 13%, taken from a range between 7 and 23%, was deduced for its contents in fines, the most frequent value being between 11 and 12%. In this study, we have seen that for clay contents in sand below 2%, 20% of total fines can be achieved with a tendency to increase resistance in cement mortars of equal plasticity. For any set contents of total fines, the increase in proportion of clay in the sand is what really makes the resistance to mortar compression drop noticeably and linearly. It has been verified for example, that a jump of 2% in the contents of clay in sand influences the resistance just as much as a modification in the contents of fines from 3 to 20%. In short, it is important to limit the contents of clay in sand, either by the sand equivalent or methylene blue (analogous to NF P 18-301, Dec. 1983). In this way, calcareous crushed sands with fines much higher than the present 5% specified could be allowed. We think that this amount could be set between 12 and 15% after carrying out the present tests on concrete.