Détérioration de fondations de pylones d'ancrage de lignes de transport d'électricité par des réactions alcalis–granulats, performance mécanique et réparation du béton

Abstract

A number of concrete tower foundations that support power lines over the St. Lawrence River in the Quebec City area were showing deterioration related to alkali–aggregate reactions. The aggregates involved are siliceous limestones commonly exploited in the area. Many foundations have been cored down to the rock basement and samples were taken all along the cores for petrographic examination and mechanical testing. These studies show that the concrete presents some mechanical weaknesses but only in the first decimeters close to the surface, even if the entire mass of the concrete foundations is affected by alkali–aggregate reactions. The results also suggest that the deterioration is isotropic in the concrete and that the compressive strength is affected as much as the tensile (Brasilian) strength. Various types of corrective measures were applied to the deteriorated components: sealing of cracks, removing of the deteriorated concrete and replacement with a new concrete containing silica fumes in addition to a low alkali cement, insertion and posttensioning of steel rods in some components, application of water-tight elastomer liners on the exposed concrete surface, etc. Key words: concrete, aggregate, cement, alkali–aggregate reaction, expansion, mechanical strength, repair, protection.