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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]

The corrosion resistance of concrete strengthened with three types of fibre-reinforced polymer (FRP) sheets (unidirectional carbon-FRP (CFRP), unidirectional basalt-FRP (BFRP) and bidirectional BFRP) was evaluated under chloride attack and the combined attack of chloride and ultraviolet radiation. After different corrosion durations, powder samples were collected from various depths of the concrete specimens to measure the total chloride ion concentrations (CICs). Scanning electron microscopy (SEM) was conducted to analyse the microscale morphology changes of the concrete surface layer, FRP fibre layer and resin matrix layer before and after combined attack. The results showed that all three types of FRP sheet provided significant chloride ion resistance, with the barrier effect of CFRP being better than that of BFRP under the same conditions. The total CIC of the FRP-strengthened concretes was higher under the combined attack than under chloride attack alone. The SEM observations showed that the resin matrix and fibre filaments of the FRP layer under combined attack were damaged, resulting in an increase in the permeability of the FRP-strengthened concretes. Finally, a time-varying model of CIC inside the FRP-strengthened concrete under chloride attack was established. [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]