No abstract

No abstract

Interest in exploring the use of seawater as the mixing water for preparing concrete is increasing due to the lack of freshwater in some coastal regions and remote islands, where seawater is more accessible. However, up to now, the mechanism of the accelerating effect of seawater on the hydration of portland cement (PC) remains unclear. In this study, alite, a major clinker phase in PC, was hydrated with common salt solutions (NaCl, Na2SO4, and MgCl2) in seawater to explore the mechanism of acceleration. The heat release peaks of the salt-added systems shifted to an earlier hydration time with a higher peak value, which indicated the faster hydration rate of alite pastes compared to the deionized (DI) water system. The addition of the single salts was found to increase the concentration of Ca species in solutions, contributing to the increased formation of calcium–silicate–hydrates (C–S–H) and portlandite at early ages. In the Na2SO4 system, gypsum was the new hydration product, while brucite was formed in MgCl2 systems, which caused the sharp decrease of Mg species in the solution. The morphology of the early formed C–S–H was changed with the addition of the salts, and the C–S–H were characterized as thinner and longer fibers. At later ages, the incorporation of the single salts lowered the polymerization degree of C–S–H, but no noticeable morphological change was observed.

Plastic productions continue to grow, and improper management of plastic wastes has raised increasing concerns. This reflects the need to explore the microplastics in water bodies. Microplastics have been regarded as emerging pollutants in water systems. In recent years, large numbers of studies across the world were conducted to investigate the distribution, behavior and the integrated impacts of microplastics in both the marine environment and the freshwater environment. Compared with the marine environment, the migration and transformation of microplastics in inland water systems seem more informative as they may reach the marine environment as one of their final destinations. Based on the updated literature, this review aims at overviewing the migration and transformation processes/behavior of microplastics in rivers, lakes and reservoirs. As for the migration, the microplastics’ fate is from manufacturing, consuming, discarding to migrating and returning to the human society which could form a closed though complicated circle. For transformation, microplastics experience five stages of their fate in inland water systems. These include changing into suspending pieces; ending up deposited as the sediment; resuspending under various changing conditions; ending up via burying into the soil as the part of the riverbed; reaching the marine environment; and being ingested by organisms and also becoming entangled with aquatic plants, etc. It is highly expected that this review can provide a valuable reference for better understanding microplastics’ migration and transformation mechanisms and a guide for the future study of microplastics in an inland water environment.

No abstract

No abstract

No abstract

No abstract