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Chloride attack severely impacts the performance of reinforced concrete. The total and free chloride ion concentration (CIC) of self-compacting concrete (SCC) prepared with three supplementary cementitious materials (SCM) – fly ash (FA), blast furnace slag (BS) and silica fume (SF) – were measured by accelerated salt immersion tests. The apparent chloride diffusion coefficient (CDC) at any exposure time and erosion depth were calculated using the Boltzmann–Matano method. The influence of the type and content of SCM, the water–binder ratio (W/B) and the type of salt solution on CIC and CDC were investigated. Both the introduction of SCM and the reduction of W/B effectively reduced the CIC. The SCM that most effectively reduced CIC was SF, followed by BS and then FA. Free CIC was reduced to a greater degree than total CIC in FA and BS concrete, but the opposite was true for SF concrete. The presence of calcium chloride in salt solution increased total CIC while reducing free CIC. Apparent free CDC dropped over exposure time and initially increased with erosion depth but eventually stabilised. A model of apparent free CDC considering time–depth dependency was created, which shows that time reduction factors of CDC is greater in SCC containing SCM than in control SCC. [ABSTRACT FROM AUTHOR]

Landfill leachate has a high chloride (Cl−) content. Because it is highly mobile, and cannot be sorbed or transformed bio-chemically, it is important to have detailed information about how it migrates in landfill sites. In this study, we set up four lab-scale simulated landfills, including an anaerobic landfill (AL), an anaerobic landfill with leachate recirculation (RAL), an anaerobic/semi-anaerobic landfill with leachate recirculation (RASL), and an anaerobic/semi-aerobic landfill (ASL), to explore how, when regulated, moisture and air affected the migration of chlorine. We found that water and air had a strong influence on the release of Cl−. Leachate obviously promoted Cl− dissolution in refuse when recirculated. When air was introduced into landfill, thereby changing it from anaerobic to semi-aerobic, the leachate Cl− concentration increased sharply from around 4–9 g L−1 (RASL) and 18 g L−1 (ASL), respectively. In principle, Cl− is released continuously when leachate is recirculated in landfills (RAL and RASL), but it can also be found a terminal when the leachate recirculation stops (AL and ASL). Cumulative amounts of 64, 66, 27, and 53 g of Cl− were released from the AL, RAL, RASL, and ASL, respectively. Lower COD/Cl and N H 4 + -N/Cl ratios in ASL and RASL after day 175 indicated that lower Cl− pollution risk than that in AL and RAL. [ABSTRACT FROM AUTHOR]

The chloride ion (Cl − ), a very common monatomic anion, has high ecological toxicity at high concentrations because of its non-biodegradability, and can easily migrate from landfill site into the surrounding environment. Four lab-scale landfill simulation reactors were established to investigate Cl − release behavior: the anaerobic landfill mode (R1), the semi-aerobic landfill mode (R2), the anaerobic landfill with leachate re-circulation mode (R3), and the semi-aerobic landfill with leachate re-circulation mode (R4). The landfill operation modes had a great influence on the release of Cl − . In 256 days, the cumulative release amounts of Cl − in the four reactors were 64.52, 132.07, 56.10, and 33.1 g for R1–R4, respectively. Once air enters anaerobic landfill, the leachate Cl − concentration may sharply increase. The highest leachate Cl − concentrations were 6.6 g L −1 in anaerobic reactor and 18 g L −1 in semi-aerobic reactor. However, the leachate re-circulation can maintain the release of Cl − at dynamic equilibrium state. Theoretically, the Cl − release behavior from anaerobic landfill with leachate re-circulation (R3) will be continuous. In contrast, under the other conditions, it can be anticipated to occur once the leachate recirculation stops (R1) or when the landfill encounters air incursion (R2 and R4). The semi-aerobic operation modes had significantly lower COD/Cl and NH 4 -N/Cl ratios than the anaerobic modes. This indicates that the Cl − pollution risk from semi-aerobic modes is lower than that from anaerobic modes. [ABSTRACT FROM AUTHOR]