Essais systématiques de validation de formulations de sable sénégalais pour l'élaboration d'un sable normalisé

Résumé.

Au Sénégal, pays en voie de développement, le sable normalisé employé pour la détermination des classes de résistance des ciments est importé. Un inventaire des ressources locales en sable a été conduit pour rechercher un produit de substitution au sable de Leucate. La première phase de l'étude a permis sur la base d'essais d'orientation, de mettre au point un mélange ternaire composé de deux sables roulés et d'un sable de concassage qui remplit les critères requis pour un "sable normalisé CEN". Dans la deuxième phase de l'étude, des essais systématiques croisés ont été menés à Rennes et à Dakar, ils confirment les résultats des essais d'orientation et les valident d'un point de vue statistique.

Abstract

The aim of this study is to elaborate a sandy material from the Senegalese basin which would be appropriate for use in place of the standardised European sand necessary for the determination of the mechanical strength of cements and defined by the European norm CEN EN 196 1 (1990). (In particular, the Leucate sand fits with this norm and presently has to be imported from France.)

The study began with an inventory of the main sandy formations of the Senegalese basin: a beach sand and a dune sand in the north of Dakar and an alluvial sand from the River Senegal were considered. It was shown that mortars of cements using these natural sands exhibit a mechanical strength lower than that of mortars using the standardised Leucate sand. Beach and dune sands are very fine and poorly graded, which results in mortars of cement with a low density. Alluvial sands are well graded, but they contain a high percentage of iron oxides and hydroxides which results in mortars of cement with a low mechanical strength.

In order to improve the mechanical strength of mortars of cements and come close to the results obtained with the Leucate sand, a crushed basaltic sand was used from a quarry which provides high-resistance aggregates. Different mixtures of natural sands and crushed sands were tested to obtain mortars of cements that exhibit mechanical strengths similar to those obtained with the Leucate sand. An artificial sand, which is a mixture of two rounded sands and a crushed sand, was produced to replace the Leucate sand for the determination of the mechanical strength of cements. In a second stage, systematic crossed tests were implemented at Rennes (France) and Dakar (Senegal), considering different types of cements and sand mixtures.

The conclusion was that for the determination of the mechanical strength of cements, the artificial sand produced from Senegalese materials was appropriate to replace the Leucate sand (which has to be imported into Senegal), with large financial benefits.