No abstract

No abstract

The effectiveness of two different management schemes to dispose of heavy metal-contaminated sediments from Ulsan Bay, South Korea, soil washing and solidification/stabilization, were evaluated through a series of analyses. NaOH proved to be an effective washing reagent for As, extracting 75% of the As in sediment samples. EDTA was found to significantly enhance the extraction of Cu, Pb and Zn. However, complete removal of any metals was not achieved even after application of 100 mM concentrations of washing reagents. Therefore, a solidification/stabilization technique was applied to dredged sediment samples using ordinary Portland cement (1-40%) and fly ash ($20%). Solidified sediments did not release meaningful amount of the metals via leaching tests. Our results suggest that solidification/stabilization is a better option for effective disposal of heavy metal-contaminated sediments than soil washing. A legal framework for the treatment of hazardous wastes and contaminated soils in Korea is discussed.

The performance of commercial wood chip (WC) and biosolid (BS) biochars available in bulk from carbonization processes in South Korea was examined via determination of sorption capacity from batch experiments and evaluation of carbon sequestration using biochar-mortar composites according to construction and environmental properties. Compared with rice straw (RS) biochar synthesized in a laboratory, the sorption capacities of WC and BC biochars are determined by the types of contaminants, the properties of the biochar, and sorption mechanisms. BS and WC biochars are competitive as sorbents for nitro explosives and chlorinated phenols. Characterization of biochar-mortar composites showed that 3-5 wt% biochar inclusion did not significantly change the composites' engineering properties, including flowability, compressive strength, and thermal conductivity. As the biochar content increased in the biochar-mortar composites, the benzene and toluene concentrations in air were accordingly reduced, suggesting that biochar inclusion may be favorable to remove volatile toxic contaminants that cause sick building syndrome. The toxicity characteristics leaching procedure (TCLP) and Micotox ® bioassay tests showed that biocharmortar composites were not toxic. These results suggest that BS and WC biochars in South Korea are competitive as sorbents for some organic contaminants and that biochar-mortar composites may be environmentally friendly carbon-sequestering construction materials.

As the amount of construction wastes increase, reuse of demolished concrete is being considered in research areas. Reflecting these interests, this experiment was performed to clarify concrete's mechanical property and workability using recycled aggregate as a coarse aggregate. Eleven cases of concrete specimens were produced by changing the rates of replacement of coarse recycled aggregate, replacement of fly ash, design strength, and moisture state of coarse aggregate. Compressive and tensile split strength tests were taken to study the mechanical properties of hardened concrete. To verify flowability of fresh concrete, a slump test and a flow curve test using ICAR Rheometer were performed. It was found that using recycled aggregate and fly ash leads good workability by testing slump and flow curve. The yield stress of fresh concrete decreased with increase of recycled aggregate substitution rate. Through the test, it was confirmed that there is inversely proportional relationship between the slump and yield stress roughly. Recycled aggregate concrete containing fly ash has considerably lower plasticity viscosity than not containing fly ash. Strength test results showed that recycled aggregate tended to decrease compressive and tensile strength of concrete, when recycled aggregate was used as a coarse aggregate. Using over 30% recycled aggregate caused significant decreases in compressive and tensile strength. Replacing 30% cement with fly ash was helpful to improve the long-term strength of concrete.