Showing papers by "Marc-André Bérubé published in 1991"

Behavior of common rock-forming minerals in a strongly basic NaOH solution

Abstract: The pH of the pore solution existing within concretes or lime-treated soils normally exceeds 12. When exposed to a solution witl a pH over 10, several rock-forming and soilforming minerals are unstable, and dissolve with or without precipitation, depending on the nature and concentration of species in solution. In concrete, made with a typical cement containing 0.7a/o to l9o alkalis, after a few days, the composition of the liquid phase is dominated by sodium, potassium and hydroxide ions. In this study, the behavior of several common minerals in a pure sodium hydroxide solution was evaluated by the means of two experiments. First, mineral fragments were immersed in a lN NaOH solution at 23oC for 265 days, then at 80oC for 7 days. The specimens were regularly analyzed with a SEM-EDX system. Secondly, the release of silica by silicate minerals in a lN NaOH solution was measured by means of the Chemical Method ASTM C 289 test (80'C, 24 hours). Of all rhe silicate minerals tested, the microcryslalline variety of silica, chert, was the most unstable phase. Significant quantities of silica also were released by quartz and feldspars. Iron and magnesium silicates were found to be the mosr stable phases in the NaOH solution. Among the other minerals investigated, dolomite, siderite and gypsum are classified as highly reactive in the alkaline solution.

Evaluation du potentiel de réactivité alcaline des granulats à béton produits dans les Basses-Terres du Saint-Laurent du Québec (Canada)

Abstract: Seventy-one samples of aggregates representative of the various sedimentary rock types exploited in the St. Lawrence Lowlands were submitted to standard and experimental laboratory tests to evaluate their potential alkali-reactivity in concrete. Among these, only the Trenton and Black River limestones with more than 6% insoluble residues produced excessive expansion in the concrete prism test, the most reliable method in assessing the alkali-reactivity potential of concrete aggregates. Expansion values of 0.1 and 0.15%, obtained respectively after 14 days in the accelerated mortar bar test (1 M NaOH at 80 °C) and 5 h of autoclave curing (0.17 MPa at 130 °C and 100% relative humidity), can only be used as acceptance limits, since nonexpansive aggregates (as per the concrete prism test) from the Black River, Chazy and Beekmantown Groups induced excessive expansion in these tests. Limiting the reactive alkali content of the concrete mix to 3 kg/m3 or using cements containing between 5 and 10% of condensed si...