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There are several cases worldwide wherein sulfide-bearing aggregates in concrete elements/structures have undergone oxidation and caused extensive damage. Signs of observed deterioration include map cracking, pop-outs, and secondary products that were generated from swelling. Unfortunately, it takes years to detect these signs visibly. Thus, in this study, a new methodology is proposed to activate and accelerate the potential oxidation reaction of iron sulfide minerals in concrete aggregates using chloride ions as activators or catalysts for the oxidation reaction. To promote the rapid penetration of chloride ions through concrete specimens, an electrochemical treatment is proposed consisting of two main phases, namely chloride impregnation in the specimen and impressed voltage treatment. Concrete specimens each 100 mm in diameter and 200 mm in length were made using aggregates with or without iron sulfide minerals and a mix design resembling the one used for building house foundations in the Trois-Rivières case, Canada. The results showed that chloride ions could activate the reaction and act as catalysts for the oxidation reaction of sulfide-bearing aggregates under a constant current (impressed voltage). Finally, traces of iron oxides/hydroxides and the formation of secondary sulfates (i.e., gypsum and ettringite) were observed in the concrete made with sulfide-bearing aggregates. This new procedure is promising for evaluating the oxidation potential of concrete with sulfide-bearing aggregates over a reasonable testing period. [ABSTRACT FROM AUTHOR]

Currently, in Ontario, Canada, around 21.7% of the total hazardous waste (HZW) collected by municipalities is waste paint. Waste latex paint (WLP) alone constitutes 12% of the total HZW. It is estimated that only 10–30% of this waste is presently being collected but this proportion is growing with public education efforts. In addition, due to increasingly more stringent environmental regulations on volatile organic compounds (VOCs), more latex-based paints will be produced compared to solvent- and oil-based alkyds. This will result in more WLP being generated annually in Ontario and across North America. The disposal cost of such waste currently varies between Can$0.90 and Can$1.40 per litre. This study was conducted in collaboration with the City of London, Ontario and the Ontario Paints and Coatings Association and aims at investigating the benefits of recycling WLP in concrete with a special focus on concrete sidewalks. WLP was used in concrete mixtures both as a partial replacement for virgin latex and for mixing water. This paper demonstrates that concrete mixtures incorporating WLP can have improved workability, higher flexural strength, lower chloride ion penetrability, better resistance to deicing salt surface scaling and can be more economic because they require less water-reducing and air-entraining admixtures. The results also indicate that the annual urban concrete sidewalk construction could use the yearly production of WLP while producing sidewalks with enhanced properties and durability. [Copyright &y& Elsevier]

With the implementation of the Clean Air Act Amendments of 1990 in the U.S. and similar emission reduction measures in Canada, sulfur dioxide (SO 2) and nitrogen oxides (NO x = NO + NO 2) emissions in the eastern U.S. and Eastern Canada declined significantly during the period 1989–2016. Correspondingly, air quality over the region improved tremendously and sulfate, nitrate and acidity in precipitation decreased significantly. In this study, we analyzed measurement data in the eastern U.S. and Eastern Canada from the two national long-term wet deposition networks, the National Atmospheric Deposition Program/National Trends Network (NADP/NTN) in the U.S. and the Canadian Air and Precipitation Monitoring Network (CAPMoN) in Canada, to reveal the spatial-temporal trends of precipitation concentrations and wet deposition of sulfate, nitrate, ammonium and acid in the eastern part of North America (broken into 4 different regions) for the period of 1989–2016. Comparing 2014–2016 to 1989–1991, the results show that the acid, sulfate and nitrate wet deposition decreased by 78%, 69% and 46% for 1989–2016, and decreased annually at rates of −2.8~-3.6% yr−1, -2.5~-2.9% yr−1, and -1.6~-2.0% yr−1 over different regions, respectively. It also revealed that there were no statistically significant trends for the annual mean wet concentrations of ammonium (NH 4 +) in precipitation in the Midwest and the Mid-Atlantic of the U.S. (P >0.4 respectively). However, there were statistically significant increasing trends of annual wet deposition of NH 4 + over these latter two regions (P = 0.01–0.13) with an annual rate of increase of 0.6% and 0.4%, respectively. The increasing trends of wet deposition of NH 4 + in these regions were mostly due to increasing annual precipitation amounts, as indicated by positive correlation coefficients between them (R = 0.67–0.77), and a statistically significant increasing trend of the precipitation amount during the period. The annual mean wet concentration of chloride ion (Cl−) in precipitation in the above two regions had a clear decreasing trend of −1.5% annually (P < 0.001). In 20 years (2010–2014 vs. 1990–1994), the frequency of acidic rain with pH < 5 was reduced from 72% to 49% in the Northeast U.S. and Eastern Canada, 88% to 37% in the Midwest, 97% to 60% in the Mid-Atlantic and 79% to 49% in the Southeast. The imbalance between the measured cations and anions increased over the years from 2009 to 2016 with the anions dropping lower than the cations in all regions. This can be attributed to the increased dissociation of weak organic acids, i.e., the free H+ contributed from these weak acids increased as the acidity of the precipitation decreased, but the corresponding conjugate bases were not measured and not included in the calculation of total anions. This pH buffering effect needs to be taken into account in assessing the reductions in acid deposition following the implementation of the Clear Air Act Amendments (CAAA) of 1990 in the U.S. and measures to reduce the emissions of SO 2 and NO x in Canada. • A new statistical method was proposed to eliminate potential biases in deriving long-term trends. The trends derived with the proposed method are more robust than some previously published ones. • Comparing 2014-2016 to 1989-1991, the acid, sulfate and nitrate wet deposition in the eastern U.S. and Eastern Canada decreased by 78%, 69% and 46% for 1989-2016, and decreased annually at rates of -2.8~-3.6% yr-1, -2.5~-2.9% yr-1, and -1.6~-2.0% yr-1 over different regions, respectively. • The imbalance between measured cations and anions increased after 2009, and it was attributed to the increased dissociation of weak organic acids. • The trends of the wet concentration of NH 4 + remained flat when less H+ was contributed from SO 4 2- and NO 3 -, as H+ dissociated from carbonic acid and weak organic acids compensated for the loss of H+ from SO 4 2- and NO 3 - in the formation of NH 4 + in precipitation. • An explanation was proposed for the lack of trends in the wet concentration of NH 4 + during the study period. NH x (NH x = NH 3 + NH 4 +) was shown to have a flat trend for 2008–2016 in the Midwest despite the partitioning of NH x having changed with emission reductions of SO 2 and NO x. [ABSTRACT FROM AUTHOR]

• Adding slag improved the compressive and split-tensile strengths. • Adding slag increased the flexural strength and enhanced post-cracking behavior. • SEM images suggest that PVA fibres exhibit frictional debonding in slag ECC mixture. • Slag was effective in reducing the chloride ion penetration and water sorptivity. • The ASR expansion of all ECC mixtures was rated as harmless as per ASTM C1260. The need for sustainable power generation resources is increasing day after day. Among many countries around the world, Canada is considering elimination of coal plants. This is causing a shortage in the supply of good quality fly ash minerals. Recent research on the production of engineered cementitious composites (ECC) focused on utilizing of Class F Fly Ash. Hence, this study was designed to experimentally investigate the influence of partial and full replacement of slag with fly ash on the mechanical and durability performance of ECC mixtures through a comprehensive experimental program. Test results from this study showed that slag containing mixtures exhibited strain-hardening behaviour and a comparable or similar ductility characteristics as fly ash containing mixtures. Moreover, incorporating slag in the mixtures were found to be effective in reducing permeability in terms of rapid chloride penetration, sorptivity, and water absorption at both 28 and 90 days. However, mixtures containing slag had higher drying shrinkage strains when compared to fly ash mixtures. [ABSTRACT FROM AUTHOR]