Josée Duchesne

The effectiveness of supplementary cementing materials in suppressing expansion due to ASR: Another look at the reaction mechanisms part 2: Pore solution chemistry

Abstract Pore solution chemistry (high pressure extraction method) of cement pastes made with two condensed silica fumes, three pulverized fly ashes and one ground granulated blast furnace slag was measured after 7, 28, 84, 182, 364 and 545 days of curing (38°C and 100% R.H.). Results were compared to expansions obtained for a 2 year time period in the CAN/CSA A23.2-14A Concrete Prism Method for concrete specimens made with two very alkali-silica reactive aggregates and tested at the same conditions and water/cement/SCM. A long-term threshold in alkali hydroxide concentration was observed around 0.65N, below which no significant expansion occurred in corresponding concretes. The lower the SCM alkali content and the concrete alkali content as well, and the higher the SCM content, the easier this limit is satisfied.

Laboratory assessment of alkali contribution by aggregates to concrete and application to concrete structures affected by alkali–silica reactivity

Abstract In Phase I, particles from 17 different aggregates, 1.25–5 mm in size, were immersed in continuously agitated solutions at 38 °C: distilled water, Ca(OH)2-saturated solution, 0.7 M NaOH (measurement of K supply), and 0.7 M KOH (measurement of Na supply). These solutions were periodically analysed for K and/or Na up to 578 days. More alkalies were released in alkaline solutions than in lime-saturated solution, with lower values in water. After 578 days, the aggregates released between

Carbon sequestration kinetic and storage capacity of ultramafic mining waste.

Mineral carbonation of ultramafic rocks provides an environmentally safe and permanent solution for CO(2) sequestration. In order to assess the carbonation potential of ultramafic waste material produced by industrial processing, we designed a laboratory-scale method, using a modified eudiometer, to measure continuous CO(2) consumption in samples at atmospheric pressure and near ambient temperature. The eudiometer allows monitoring the CO(2) partial pressure during mineral carbonation reactions. The maximum amount of carbonation and the reaction rate of different samples were measured in a range of experimental conditions: humidity from dry to submerged, temperatures of 21 and 33 °C, and the proportion of CO(2) in the air from 4.4 to 33.6 mol %. The most reactive samples contained ca. 8 wt % CO(2) after carbonation. The modal proportion of brucite in the mining residue is the main parameter determining maximum storage capacity of CO(2). The reaction rate depends primarily on the proportion of CO(2) in the gas mixture and secondarily on parameters controlling the diffusion of CO(2) in the sample, such as relative saturation of water in pore space. Nesquehonite was the dominant carbonate for reactions at 21 °C, whereas dypingite was most common at 33 °C.

Long-term effectiveness of supplementary cementing materials against alkali-silica reaction

Abstract The long-term effectiveness of six supplementary cementing materials (SCM) were tested according to the CSA-A23.2-14A Concrete Prism Method in the presence of two very alkali–silica reactive aggregates from Canada. Three fly ashes, two silica fumes, and one ground granulated blast furnace slag (GGBFS) were selected based on their elemental composition in order to represent a wide range of composition. The performance of SCMs in suppressing expansion due to alkali–silica reaction was compared with that obtained by a low-alkali cement. Pore solution composition of the mixtures was also determined. Results show that expansion curves flatten out after 2 years of curing. This phenomenon was due to alkali leaching from the concrete prisms and alkali binding by the alkali aggregate reaction products in the presence of the very reactive aggregates used, which was supported by very low alkali ion concentrations measured on concrete samples at the end of the experiment. A 2-year expansion limit is then suggested when using the CAN/CSA-A23.2-14A method to evaluate mixtures containing SCM. The proportion of SCM and total alkali content of the concrete are very significant factors controlling concrete expansion.

The effectiveness of supplementary cementing materials in suppressing expansion due to ASR: Another look at the reaction mechanisms; Part 1: Concrete expansion and portlandite depletion

Abstract Portlandite content (TGA) of cement pastes made with two condensed silica fumes, three pulverized fly ashes and one ground granulated blast furnace slag was measured up during a 1 year time period. Results were compared to expansions obtained for a 2 year time period in the CAN/CSA A23.2-14A Concrete Prism Method for concrete specimens made with two very alkali-silica reactive aggregates and tested at the same conditions and water/cement/SCM. No correlation was obtained between reduction in concrete expansion and the portlandite depletion which appears to be only a consequence of pozzolanic reaction.

CO2-depleted warm air venting from chrysotile milling waste (Thetford Mines, Canada): Evidence for in-situ carbon capture from the atmosphere

We have discovered diffuse warm air vents at the surface of a chrysotile milling waste heap at the Black Lake mine, Thetford Mines, Quebec, Canada. The venting areas are inconspicuous, except in winter when the vents form snow-free areas of unfrozen ground, each with a surface area of 1–15 m 2 . The temperature and chemical composition of the warm air vents have been monitored from March 2009 to July 2010. The temperature of the warm air and ground surface at the venting sites ranged from 6.6 to 20.0 °C, whereas that of the ambient air ranged from −13.2 to 20.0 °C. The difference between atmospheric and vent air temperatures is greater in cold-weather months. The warm air has low CO 2 content, but has otherwise normal atmospheric gas composition. Warm air volumetric flow varies from 2.1 to 19.9 L/m 2 /s in winter, when it contains between 2 . In summer, the venting areas are more diffuse, with volumetric flow rates ranging from 0.5 to 1.5 L/m 2 /s, and are less depleted in CO 2 (260–370 ppm). Frozen ground is likely focusing airflow in winter compared to summer. We present a conceptual model in which air enters the steep flanks of the chrysotile milling waste heap, into which CO 2 reacts with Mg-rich minerals, stripping CO 2 from air by exothermic mineral carbonation reactions. Considering the surface area of summer and winter venting areas, flow rates, and concentration of CO 2 in warm air vents, we estimate that the Black Lake mine heap passively captures at least 0.6 kt CO 2 per year.

Removal of Metals from Contaminated Soils by Mineral Processing Techniques Followed by Chemical Leaching

A contaminated soil was exhaustively sampled at various depthson a rectangular sampling grid of 12 by 15 m (107 samples).Four metal contaminated soil samples were submitted to physicaltreatment methods followed by chemical leaching. The treatmentflowsheet consisted of crushing the 2–10 mm contaminatedfraction, various sieving and use of a wet magnetic separatorprocess for the >63 μm size fraction (SF). Subsequently theWilfley shaking table was applied to the 63-850 μm SF while ajig gravimetric separator was used on the SF >850 μm. Themagnetic separator had a small removal efficiency. Out of fourSF, one was successfully decontaminated by the Wilfley table andtwo other SF were successfully decontaminated by the jig; bothtreatments removed a significant part of metals from all soils.Chemical leaching using hydrochloric and acetic acids at atemperature of 37 °C was performed on 9 SF out of 12. After completion of the treatment, soils were recombined and tested with the Toxicity characteristics leaching procedure (TCLP) of the United States Environmental Protection Agency anda gastric juice simulation test (GJST). Untreated small size particles leach more metals with the GJST than coarse particles.Decreases in Pb concentrations varied from 33.9 to 82.5%, thehighest values corresponding to the most heavily contaminated soils. Decreases in Pb TCLP between 54.1 and 99.5% were observedand the maximal value for a treated soil was 1.53 mg Pb L-1.The GJST decrease varied from 48.5 and 92.5% (highest leachingpotential before treatment). No problematic levels of leachingoccurred, as leaching of Pb, Cu, Zn and Sn after treatment wasrelatively low. The amount of soil to be treated was estimated from a micro and macro characterization. For an heterogeneous soil like the one studied here, the estimated cost for a 100 000 metric tons project on a 2 year span is relatively low at nearly 60

A simple and fast screening test to detect soils polluted by lead.

CDN/mt.

Evaluation of the validity of the pore solution expression method from hardened cement pastes and mortars

Lead pollution is an environmental priority. The evaluation of contaminated soils was often based on the results of the toxicity characteristic leaching procedure (TCLP) or the synthetic precipitation leaching procedure (SPLP). This paper presents a simple and fast screening test to detect soil contaminated by lead. The test is based on the chemistry of the stomach (Cl- concentration, pH 2, T = 37 degrees C) and simulates the incidental oral ingestion of soil by young children. The gastric juice simulation test (GJST) and the TCLP were applied to six size fractions from five soils. The GJST solubilized more Pb (up to 169 mg/l) than the TCLP especially for the smallest size fraction. Particle size had less effect on the TCLP. The percentage of lead released with the GJST, was most significant for the <63 microm size fraction and varied from 18 to 74% of the total lead content. Lead leached during the TCLP as a function of the total lead content showed poor linear regression coefficient (R) values for soils <250 microm. R values were significant for all size fractions with the GJST. The pH of approximately 5 in the TCLP limits the solubilization of lead in the small size fractions. The five soils exceeded the toxicity threshold of 10 microgPb/dl of blood for a significant fraction of children between 0 and 36 months using the EPAs IEUBK model (Integrated Exposure Uptake Biokinetic). But the TCLP did not detect lead contamination in two of these five soils. The GJST proved to be a better estimator of lead bioaccessibility in the gastrointestinal tract.

LABORATORY AND FIELD INVESTIGATIONS OF THE INFLUENCE OF SODIUM CHLORIDE ON ALKALI-SILICA REACTIVITY

Abstract Pore solution was expressed from cement pastes made with various supplementary cementing materials (SCM) under various pressure intervals (0–560, 0–200 and 200–560 MPa). The alkali concentrations measured after 7 and 28 days at 38°C and 100% R.H. were not affected by the pressure at which the samples were expressed. Comparisons were also made between the pore solution from cement pastes and mortar samples made with alkali-silica reactive and non reactive aggregates, and the same water:cement:SCM ratio. The alkali concentrations measured after 7 and 28 days were not affected by the presence of aggregate. The results confirm that the pore solution expression method is a good tool for investigating the solid-liquid chemical interactions in mortars and concretes.