Réalisation des bétons à matrice mixte et étude de leurs propriétés

Résumé

L'incorporation au liant hydraulique de petites quantités de résine a deux conséquences:

• -avant son complet durcissement, elle fixe la chaux libérée par la pâte de ciment et freine l'évaporation de l'eau: l'hydratation et le retrait des mortiers sont alors fortement ralentis.

• -après son durcissement, elle améliore notablement les propriétés mécaniques du mortier.

L'addition de résine n'améliore que faiblement les résistances mécaniques des bétons légers car les granulats ne sont pas renforcés; il est donc nécessaire d'imprégner les granulats par une résine fluide et qui polymérisera avant le malaxage du béton.

Summary

The making of lightweight concrete from an organic matrix offers important technical advantages but serious disadvantages too: a bad fire resistance and a dubious behaviour when aging on one hand, a greater handicap because of a high price on the other hand.

It was a great temptation to incorporate small amounts of resin with the hydraulic binding so as to rectify the main failings of the concrete without making its price grow too much.

In order not to block the hydration of the paste, it is advisable to add a resin hardening in a basic environment, which leads to two phenomena:

• -before its complete hardening, the resin fixes the lime which has been released from the concrete paste and restrains the water evaporation. The hydratation and shrinkage of the mortar are then extremely slackened;

• -after its hardening, it considerably improves the mechanical properties of mortars.

On the other hand, the making of lightweight concretes from a joint matrix does not improve their mechanical characteristics much because the resin does not penetrate into the aggregates owing to a suction phenomenon produced by the paste.

The lightweight aggregates remain weaker than the matrix and their destruction produces the failure of concrete.

Then it is advisable to reinforce the aggregates before they are mixed with the paste; the resin should be fluid enough to penetrate into the pores of the aggregates without their weight changing much and with a resin which is no longer required to be compatible with the concrete.