Benoit Durand

Evaluation Protocol for Concrete Aggregates Containing Iron Sulfide Minerals

Several cases of concrete deterioration involving sulfide-bearing aggregates have been reported over the years. However, no specific guidelines are currently available to enable making a precise decision on the deleterious potential of aggregates containing iron sulfide minerals. The aim of this paper is to provide an innovative assessment protocol to evaluate the potential deleterious effects of iron-sulfide-bearing aggregates prior to their use in concrete. The findings of this paper are based on tests developed within the past few years as part of a major research project. The protocol is divided into three major phases: 1) total sulfur content measurement; 2) oxygen consumption evaluation; and 3) an accelerated mortar bar expansion test. Tentative limits are proposed for each phase of the protocol, which still need to be validated through the testing of a wider range of aggregates.

Effect of Curing on Shrinkage and Expansion of Surface Repair Mortars

Hydro-Quebec has undertaken a major study on the evaluation of repair materials for concrete surfaces damaged by erosion. Shrinkage-expansion and compressive tests, among others, were carried out on 36 different products: 12 cementitious mortars and grouts, eight cement-based mortars containing styrene-butadiene rubber (SBR), four cement-based mortars containing acrylics, and 12 epoxy mortars. For each mix, four 25 by 25 by 275-mm bars and six 51 by 51 by 51-mm cubes were prepared for shrinkage-expansion and compressive-strength tests, respectively. Specimens were demolded after 24 h and placed at 21°C and 100% relative humidity for another 24 h. After that, half the bars were put in lime-saturated water, the other half in air at 50% relative humidity (both cured at 21°C). With respect to the cubes, half were placed in air at 21°C and 50% relative humidity, the others in a moisture chamber. Among the 35 products tested, two cementitious grouts made with special cement and artificial aggregates showed the lowest shrinkage-expansion behavior and the highest compressive strength (over 80 MPa). Two polymer-modified cement-based mortars containing SBR had shown large water expansion and air shrinkage, whereas another cement-based mortar containing SBR showed little shrinkage expansion and high compressive strength. Four of the 12 high sand: epoxy ratio mixes exhibited very large water expansion, whereas most products showed little air shrinkage.