Study of the Deterioration of Concrete Incorporating Sulfide-Bearing Aggregates

In the Trois-Rivières area (Québec, Canada), several hundred foundations of private houses, apartment and public buildings were built using concrete incorporating an anorthositic gabbro coarse aggregate containing sulfide minerals. A large number of those concrete structures developed serious deterioration within 3 to 5 years after their construction, which triggered, in many cases, their demolition/replacement. To help understanding the deterioration mechanisms and the conditions most prone to the development of premature damage, as well as quantifying the rate of deterioration, concrete blocks, 1 m x 1 m x 0.225 mm in size, were extracted from housing foundations just prior to their demolition. The blocks were disposed on an outdoor exposure site where they were monitored for the development of cracking and expansion over a five-year period. More than three hundred cores were extracted at different depths in eight housing foundations. A variety of tests including in-situ relative humidity measurements, petrographic, physical, mechanical and chemical tests on those cores were conducted for a full condition assessment of the concrete. A good correlation was observed between the monitoring of crack and the development of expansion in concrete foundation walls of different initial damage degree. Deterioration was also found to be largely influenced by the exposure conditions and RH conditions within the concrete. The determination of the total sulfur content of the concrete is a way to estimate the amount of sulfide minerals in the aggregate but significant variability was observed on values measured on different core samples from the same foundation

The effect of wood ash as a partial cement replacement material for making wood-cement panels

The aim of this study was to consider the use of biomass wood ash as a partial replacement for cement material in wood-cement particleboards. Wood-cement-ash particleboards (WCAP) were made with 10%, 20%, 30%, 40%, and 50% of wood ash as a partial replacement for cement with wood particles and tested for bending strength, stiffness, water absorption, and thermal properties. Test results indicate that water demand increases as the ash content increases, and the mechanical properties decrease slightly with an increase of the ash content until 30% of replacement. On the other hand, the heat capacity increases with the wood ash content. The WCAP can contribute to reducing the heat loss rate of building walls given their relatively low thermal conductivity compared to gypsum boards. The replacement of cement to the extent of approximately 30% by weight was found to give the optimum results

Supplementary Cementitious Materials for Concrete: Characterization Needs

peer reviewedA wide variety of materials are currently used as supplementary cementitious materials (SCMs) for concrete, including natural materials and byproducts from various industries. Historically, natural SCMs, mostly derived from volcanic deposits, were common in concrete. In recent years, the dominant SCMs have been industrial by-products such as fly ash, ground granulated blast furnace slag (GGBFS), and silica fume. There is currently a resurgence of research into historic and natural SCMs, as well as other alternative SCMs for many reasons. The primary benefits of SCM use in improvement of long-term mechanical performance, durability, and sustainability are widely accepted, so local demand for these materials can exceed supply. This paper describes some of the SCMs that are attracting attention in the global research community and the properties and characteristics of these materials that affect their performance. Special attention is paid to the importance and demands of material characterization. Many SCMs do not necessarily lend themselves to characterization methods used in standardized test methods, which sometimes fail to describe the properties that are most important in predicting reactivity

Passive Mineral Carbonation of Mg-rich Mine Wastes by Atmospheric CO2

Mg-rich process tailings and waste rocks from mining operations can react spontaneously with atmospheric CO2 to form stable carbonate minerals by exothermic reactions. Over the last decade, we have conducted a number of laboratory and field experiments and surveys on both mine waste rocks and different types of mine tailings from Ni-Cu, chrysotile, and diamond mines. The experiments and surveys cover a wide range of time (103 to 108 s) and mass (1-108 g) scales. Mine waste rich in brucite or chrysotile enhances the mineral carbonation reactions. Water saturation, but more importantly, watering frequency, are highly important to optimize carbonation. Adjusting the chemical composition of the interstitial water to favour Mg dissolution and to prevent passivation of the reaction surfaces is crucial to ensure the progress of the carbonation reactions. Preservation of the permeability structure is also critical to facilitate water and CO2 migration in the rock wastes and tailings. In field experiments, CO2 supply controled by diffusion in the mining waste is slower than the reaction rate which limits the capture of atmospheric CO2. Industrial implementation of passive mineral carbonation of mine waste by atmospheric CO2 can be optimized using the above parameters

Reactivity tests for supplementary cementitious materials: RILEM TC 267-TRM phase 1

A primary aim of RILEM TC 267-TRM: “Tests for Reactivity of Supplementary Cementitious Materials (SCMs)” is to compare and evaluate the performance of conventional and novel SCM reactivity test methods across a wide range of SCMs. To this purpose, a round robin campaign was organized to investigate 10 different tests for reactivity and 11 SCMs covering the main classes of materials in use, such as granulated blast furnace slag, fly ash, natural pozzolan and calcined clays. The methods were evaluated based on the correlation to the 28 days relative compressive strength of standard mortar bars containing 30% of SCM as cement replacement and the interlaboratory reproducibility of the test results. It was found that only a few test methods showed acceptable correlation to the 28 days relative strength over the whole range of SCMs. The methods that showed the best reproducibility and gave good correlations used the R3 model system of the SCM and Ca(OH)2, supplemented with alkali sulfate/carbonate. The use of this simplified model system isolates the reaction of the SCM and the reactivity can be easily quantified from the heat release or bound water content. Later age (90 days) strength results also correlated well with the results of the IS 1727 (Indian standard) reactivity test, an accelerated strength test using an SCM/Ca(OH)2-based model system. The current standardized tests did not show acceptable correlations across all SCMs, although they performed better when latently hydraulic materials (blast furnace slag) were excluded. However, the Frattini test, Chapelle and modified Chapelle test showed poor interlaboratory reproducibility, demonstrating experimental difficulties. The TC 267-TRM will pursue the development of test protocols based on the R3 model systems. Acceleration and improvement of the reproducibility of the IS 1727 test will be attempted as well

Le rôle des ajouts minéraux face aux réactions alcalis-granulats dans le béton : mécanismes de réaction, performance et essais d'évaluation de la performance

Québec Université Laval, Bibliothèque 201

Recommendation of RILEM TC 258-AAA: RILEM AAR-8: determination of potential releasable alkalis by aggregates in concrete

The test method AAR-8 is intended to be used for assessing the potential amount of alkalis released by aggregates in field concrete in the long-term. This is done by measuring the amounts of sodium and potassium ions released from the fine graded (< 4 mm) aggregate immersed in (0.7 M) KOH and NaOH solutions, respectively, at elevated temperature when in contact with excess calcium hydroxide. It is of great importance to realise that this accelerated test method must be considered as a mere indication of potential (maximum) alkali release by the aggregates, rather than a quantification used for the alkali inventory calculations

Chemical and petrographic characterization of aggregates used in the 1st AAR-8 Round Robin Test

Most of the types of rocks commonly used as aggregates contain minerals in which composition Na andlor K are present. Fe/dspar, fe/dspathoid, as we/1 as sorne mica, zeo/ites and amphibo/e are examples of minerals present in aggregates that contain a/kalis. Studies published in the /ast decades show that certain types of aggregates cou/d re/ease significan! amounts of a/kalis over time, when exposed to high pH environment, additionally providing Si and Alto the so/ution, which are high/y soluble al high pH conditions. Therefore, aggregates containing these minerals have been investigated dueto the suspicion that they might increase the a/ka/is content in cement paste and contribute to the development of a/ka/i-aggregate reactions in concrete. The rate and amount of a/kalis re/eased depends on generic exposure conditions such as pH and temperature but also on diverse properties of the actual aggregate, e.g. partic/e size, bu/k litho/ogical composition, mineral grain size, mineral modal content, total alkali content and bonding of mineral constituents related to degree of alteration, and their spatial distribution in terms of microstructure, fabric or texture, as we/1 as interna/ porosity and permeability of the aggregate partic/e. In order to create an international recommendation conceming the re/ease of alkalis, the test method AAR-8 was developed in the scope of RILEM TC 258-AAA activities. The first Round Robín Test (RRT1) of AAR-8 was performed using five aggregate types and further investigation took place as RRT2 /eading to the final version of AAR-8 recommendation that wi/1 be published soon

Élaboration, implantation et évaluation d’une formation à l’enseignement de l’offre active pour les professeurs et formateurs d’université

Les professeurs et les formateurs des programmes de formation dans les domaines de la santé et des services sociaux ont la responsabilité d’enseigner le concept d’offre active, ses enjeux et les comportements qui y sont associés aux futurs professionnels de ces secteurs qui travailleront auprès des populations francophones vivant en contexte minoritaire. Cet article porte sur les résultats d’une recherche-développement visant l’élaboration, l’implantation et l’évaluation d’une formation à l’enseignement de l’offre active destinée aux professeurs et aux formateurs de ces domaines. Le programme de formation mis en place sera présenté et les pistes d’amélioration découlant de son évaluation seront proposées. Finalement, la discussion soulignera l’importance de facteurs tels que le temps, l’engagement et le soutien de l’administration, la souplesse, le partage des expériences, le soutien du formateur ainsi que les perspectives d’avenir lors de l’élaboration d’un tel programme.Health and social service professors and instructors teaching future health and social service professionals who will work with Francophone populations living in a minority context have a responsibility to teach the concept of active offer, issues surrounding it, and associated behaviours. This article addresses the results of a research and development project on the development, implementation and evaluation of active offer teaching training for professors and instructors in these fields. The training program and its evaluation are presented, along with proposed avenues for development. Lastly, the discussion will highlight the importance of factors such as time, administrative engagement and support, flexibility, experience sharing, professor/instructor support, as well as program development prospects