Retrait et adhérence du béton modifié au latex

Résumé

Le béton de ciment modifié avec un latex à base de styrène-butadiène est un matériau de réparation utilisé depuis plus de 30 ans, bien que ses propriétés ne soient pas encore très bien connues. Un programme de recherche est présentement en cours pour évaluer la pertinence d’un ajout de latex dans un béton de réparation. Des essais de retrait et d’adhérence au béton durci, entre autres, ont été faits avec des bétons contenant respectivement 0,7,5 et 15% de latex. Ces essais ont été effectués pour trois valeurs du rapport eau ciment, soit 0,30, 0,35 et 0,40. Les résultats démontrent que la présence de latex réduit de façon significative le retrait durant les premières semaines, mais que le retrait à long terme du béton au latex est du même ordre de grandeur que celui du béton sans latex. Les résultats montrent aussi que l’adhérence au béton durci est supérieure en présence de latex.

Summary

Concrete modified with styrene-butadiene latex has been in use for more than thirty years as a repair material even though its properties have not yet all been investigated in depth. A research programme is presently being carried out at Laval University to evaluate the relevance of an addition of such latex in concrete used for repairs.

This paper presents the results of shrinkage and bonding tests performed with concretes containing 0, 7.5 and 15% latex. For each latex content, two concrete mixtures were prepared at each one of the three selected values of the water/cement ratio (0.30, 0.35, 0.40). The test results show that latex reduces the drying shrinkage during the first weeks, but the value after 30 weeks of drying is of the same order of magnitude for both latex-modified and plain concrete. This is in contradiction with other results showing a reduction of the final shrinkage for latex-modified concrete.

Shear slant tests (ASTM C882) were performed to evaluate the influence of latex on the bonding of fresh concrete to hardened concrete. The high variability obtained with many series of ten specimens indicates that this procedure cannot be used as a reliable routine test to evaluate the resistance of the bond. The results show only little improvement of the mechanical resistance of the bond when latex is added, but the variability is significantly reduced with latex. The durability of the bonding, however, is an essential quality for a repair material and it remains to be seen if latex also improves this important characteristic.

Other tests, such as the de-icer salt scaling resistance, are presently being performed to establish the overall utility of a latex addition in good-quality concrete.