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[en] A common basic assumption in civil engineering is that rainwater is chemically neutral (pH = 7.0). However, even under pristine conditions, rainwater is often more acidic due to natural emissions of organic acids. Even natural rain acidity may be very aggressive against natural stones and concrete. A harmful impact of UV radiation on the concrete durability was discussed by the authors for the first time in 2006. The objective of the current research was the characterization of weathering processes occurred in the wet cast concrete subjected to the normal acidic rain and UV radiation, and the evaluation of their possible effect on the reinforced concrete durability. It was revealed that organic acids contained in rain of the natural acidity promote an intense concrete carbonation, even when a permeability of concrete looks to be low.
[en] Our goal was to reconstruct soil recovery from Acid Rain based upon removal of stemflow at beech (Fagus sylvatica) stands of known historic and recent soil status. Fourteen beech stands in the Vienna Woods were selected in 1984 and again in 2012 to study changes in soil and foliar chemistry over time. A part of those stands had been strip cut, and to assess reversibility of soil acidification, we analyzed soils around beech stumps from different years of felling, representing the years when acidic stemflow ceased to affect the soil. Furthermore, it was hypothesized that changes of soil chemistry are reflected in the stemwood of beech. Half-decadal samples of tree cores were analyzed for Ca, Mg, K, Mn, Fe, and Al. Soil analyses indicated recovery in the top soil of the stemflow area but recovery was delayed in the between trees areas and deeper soil horizons. Differences in soil pH between proximal and distal area from beech stumps were still detectable after 30 years indicating that soils may not recover fully from acidification or do so at a rather slow rate. Stemwood contents indicated mobilization of base cations during the early 80s followed by a steady decrease thereafter. Backward reconstructions of soil pH and soil nutrients, building on regressions between recent stemwood and soil chemistry, could not be verified by measured soil data in 1984, but matched with declining cation foliar contents from 1984 to 2012. Dendrochemical reconstructions showed highest values in the 1980s, but measured soil exchangeable cation contents were clearly lower in 1984. Hence, we conclude that our reconstructions mimicked soil solution rather than soil exchanger chemistry.
[en] A temperature stepped-combustion method for separating soil organic carbon (SOC) fractions and their 14C ages was developed to investigate SOC fixation and stability in soils. After acid-leaching, SOC was sequentially oxidized, and extracted from three temperature intervals: (1) 25-400 °C, (2) 400-600 °C, and (3) 600-900 °C. The acid-soluble carbon and SOC released below 600 °C are labile components, with relatively younger 14C ages, while the SOC released above 600 °C is stable with older 14C ages. We applied this method in a grassland, maize cropland and forest nursery cropland, to assist in understanding the stability of carbon in soils under different land use conditions. (author)
[en] Chemicals leached from concrete are an important way that urban stormwater can influence water quality. In this study, we evaluated the weathering properties of sidewalk samples and tested how carbonation (exposure to elevated levels of gaseous CO2) can be used to simulate natural aging of concrete. The experiments focused on acid neutralizing capacity (ANC), which is known to be released by concrete in large amounts, and Cr(VI), because of its established carcinogenicity and prevalence in concrete. Chemical weathering of crushed sidewalk samples was measured with upflow recirculating columns carrying simulated acid rain. The weathering rate of ANC from four different samples was found to decrease after 1 week of exposure to a 5% carbon dioxide atmosphere and to remain constant thereafter through 8 weeks of carbonation treatment. In contrast, weathering of chromium (VI) increased after exposure to a 5% carbon dioxide atmosphere for 1 week, though it also remained stable from then through 8 weeks of carbonation. Almost all ions approached steady state after 2.5 h in the recirculation columns irrespective of carbonation time. The main contributor of ANC was Ca2+ ion, though this was partly balanced by an unexpectedly high amount of SO42−. A notable exception to the temporal leaching pattern was largely un-ionized Si, which continued to increase in concentration for at least 3 days of recirculation. Si levels were also higher than is generally observed for aluminosilicate weathering in small watersheds, a novel finding.
[en] Recycled tires are often shredded for use in a variety of consumer-related products. The rubber so used may contain a number of compounds known to be deleterious to human and environmental health. We obtained nine samples of shredded tire material sold over the counter to the general public for home use, as well as six samples used for infill in synthetic turf athletic fields. After thorough cleaning and grinding, samples were extracted with either organic solvent (dichloromethane), strong acid, or simulated acid rain, or allowed to degas passively. Compounds released by these multiple methods were then identified, and in some cases quantified. Solvent extraction yielded 92 separate compounds, of which only about half have been tested for human health effects. Of these, nine are known carcinogens and another 20 are recognized irritants, including respiratory irritants that may complicate asthma. Strong acid extraction released measurable amounts of Pb and Cd and relatively large amounts of Zn. These three metals were specifically targeted for analysis, and others may be present as well, but were unmeasured. Simulated acid rain extracted only Zn in significant quantities. Passive volatilization yielded detectable amounts of 11 compounds. Results demonstrate that recycled tire materials contain and can release a wide variety of substances known to be toxic, and caution would argue against their use where human exposure is likely.
[en] The building stones are affected by pollution. Since 1980s, the actions to reduce the greenhouse gas emissions led to the inversion of the SO2/NOx proportions in the atmosphere. This study aims at estimating the effects of nitrogen and sulfur compounds on stones by assessing the changes of three building limestones and one reconstituted stone submitted to acid attacks. Two of these stones were already contaminated with sulfates, while the two others were fresh quarried. Two different types of accelerated aging tests were used: (1) the exposition to two mixed acid and saturated atmospheres (HNO3 and H2SO3) to simulate the ancient and current pollutants ratio and (2) the immersion in a mixed acid solution (HNO3 and H2SO4) and in rainwater (pH 5 and 5.9), with and without agitation to simulate stagnant water and storm runoff water. Macroscopic, binocular and SEM observations, variations of color, weight, porosity, salt content and dissolved calcium were assessed over time. The sulfur amount influences the esthetic alterations such as color changes due to the salt precipitation and the oxidation of metallic compounds. During the immersion tests, the dissolution in the acid solution was more efficient than in the rainwater, due to the combination of the acidity and the karst effects. In the mixed acid atmospheres, the behavior of the porous network depends on the pore size distribution while in the immersion tests it is the open porosity. The high initial sulfur content of the contaminated stones increases the dissolution rate and limits the crystallization.
[en] Room-temperature-vulcanized silicone rubber (RTV-SiR) is an excellent polymer for the coatings of high voltage outdoor insulators. However, like other polymers it also degrades by environmental stresses and lessens its service life. Silica-based composites may improve this behavior. To investigate the effect of multiple environmental stresses such as acid rain, heat, UV radiations, salt fog, etc., on silica-based composites, we prepared a sample neat SiR, two SiR nano-composites (5% and 2.5% nano-silica loading), an SiR micro-composite (15% micro-silica loading) and a hybrid composites (2% nano 10% micro-silica loading). The prepared samples are subjected to accelerated multistress environment for a long term. Dielectric strength, leakage current and siloxane backbone are analyzed periodically during entire aging period. Composites showed improved characteristics and service life. Silicone rubber nano-composite with 5% nano-silica loading (SNC-5) showed longest estimated service life of 29 lab years in comparison with 19.8 lab years of neat silicone rubber. Similarly, after aging 17 kV/mm of dielectric of SNC-5 was highest among the all samples. Siloxane backbone also showed improved intactness in the case of SNC-5.
[en] Increased concern over regional and international aspects of air pollution, acid deposition and accidental releases has created a need for air pollution dispersion model development and evaluation. Under the framework of the US-China Peaceful Uses of Nuclear Technologies (PUNT) Agreement, a program to carry out an Asian tracer experiment was proposed. In this paper, the long range tracer experiments conducted internationally and evaluation of long range dispersion models were reviewed and a preliminary planning on the former several aspects was analyzed and discussed. (author)