Hyun Ju Kang

The Effects of Sepiolite on the Properties of Portland Cement Mortar

Shrinkage crack is a major concern for cement materials, especially for flat structures such as Korean On-Dol floor system, flooring for garages, and wall. One of the methods to reduce the adverse effects of shrinkage cracking is to reinforce cement materials with shot randomly distributed fibers. The efficiency of inorganic fibrous material to arresting cracks in cementitious composites was studied. Cement materials reinforced with five different qualities of inorganic fibrous material were tested. Contents of inorganic fibrous material were 1.0 ㎏, 1.5 ㎏, 2.0 ㎏, 2.5 ㎏, 3.0 ㎏ by weight of cement mortar and C : S types of cement mortar were 1 :3 and 1: 4. W/C were 60% and 80%. Cement mortar of inorganic fibrous material reinforcement showed an ability to reduce the crack width and crack length significantly as compared to unreinforced cement mortar. 40%~60% drop in shrinkage crack of 1: 4 cement mortar with 1.5 ㎏ over was observed.

Effect of Superplasticizer on the Early Hydration Ordinary Potland Cement

To improve concrete quality one of the most widely used chemical admixtures is polycarboxylate type superplasticizer. Unlike lignosulfonate and naphthalene-sulfonate, it has high dispersion property and excellent sustainable dispersion property for cement and concrete. Thus, polycarboxylate type superplasticizer has been widely used as a high-performance water reducing admixture together with silica fume in high-performance concrete and other applications for the dispersion of high-strength concrete over 100 ㎫. However, even though there have been many studied on the dispersion of concrete by the structure of polycarboxylate type superplasticizer, there have a few studied that clarified the relationships between its rheological properties and microstructure properties in the early hydration behavior of ordinary portland cement. To investigate the correlations between the rheological properties and microstructure of cementitious materials with polycarboxylate type superplasticizer, this study experimented on the rheology, pore structure, heat evolution, and consistency in early hydration as well as on the compressive strength by early dispersion characteristics.

Solidification of Heavy Metal Ions Using Magnesia-phosphate Cement

Since 1980s, many mines have been closed and abandoned due to the exhaustion of deposits and declining prices of international mineral resources. Because of the lack of post management for these abandoned mines, Farm land and rivers were contaminated with heavy metal ions and sludge. We studied on the solidification/stabilization of heavy metal ions, chromium ions and lead ions, using magnesia-phosphate cement. Magnesia binders were used calcined-magnesia and dead-burned magnesia. Test specimens were prepared by mixing magnesia binder with chromium ions and lead ions and activators. We analyzed the hydrates by reaction between magnesiaphosphate cement and each heavy metal ions by XRD and SEM-EDAX, and analyzed the content of heavy metal ions in the eruption water from the specimens for the solidification and stabilization of heavy metal ions by ICP. The results was shown that calcined magnesia binder is effective in stabilization for chromium ions and dead-burned magnesia binder is effective in stabilization for lead ions.

The Properties of Repair Cement Mortar with Insulation Performance under the Composite Deterioration Conditions

In this study, we studied on the durability of restorative cement mortar for deteriorated concrete at complex deteriorated conditions as variation of temperature and of humidities. We made a comparison between restorative materials with insulation function and restorative materials without insulation function in items of compressive and bending strength and permeability of water, durability for carbonation, salt damage, diffusion coefficient of salt at complex deterioration conditions like change of temperature, change of humidity, For insulation, we used close-pore type Alumino-Silicate lightweight aggregate and substituted 12 wt% and 15 wt% out of original restorative cement mortar without insulation function.As a result, it was found that original restorative cement mortar without insulation function fail to meet Korean Standard on polymer modified cement mortar for maintenance in concrete structure, but restorative cement mortar with insulation function is in contentment Korean Standard to meet excellent than restorative materials without insulation function for durability at complex deteriorated conditions.

The Effect of Magnesia-Phosphate Cement on the Stabilization of Colluvium Soil

ABSTRACT This study investigated the increased strength and permeability of colluvium soil as soil cement using phosphate magnesia cement for the purpose of strengthening soft ground by increasing the strength of colluvium soil which has very weak soil quality. The experiment results show that when colluvium soil, which has been solidified using phosphate magnesia cement, was applied to soft ground with a high water content, the evaporation of water could be accelerated by hydration heat. Therefore, it is expected to be effective for the solidification and stabilization of soft ground. Furthermore, when phosphate magnesia cement was used for colluvium soil, at the uniaxial compressive strength of 0.05MPa, the uniaxial compressive strength at the age of 28 days increased approximately 40 times to 2.16MPa. An ordinary colluvium soils permeability coefficient of 1.0×10−6cm/sec, and the soil with phosphate magnesia cement of 40wt% changed to impermeable solid with a permeability coefficient increased to 1.4×10−8cm/sec.

The Effect of Sorel's Cement on the Solidification/Stabilization of Heavy Metal Ions

ABSTRACT Since the 1980s, many mines have been closed and abandoned due to the exhaustion of deposits and the declining prices of international mineral resources. Because of the lack of post management for these abandoned mines, rivers have been contaminated with heavy metal ions and sludge. We studied the solidification/stabilization of heavy metal ions, chromium ions and lead ions, using Sorels cement. Specimens prepared by the mixing and reacting of chromium ions and lead ions with Sorels cement were analyzed by XRD and SEMEDAX to investigate the products and crystal shapes. Furthermore, ICP analysis was used to analyze the content of heavy metal ions in the eruption water from the specimens to check the solidification and stabilization of heavy metal ions. This experiment found that Sorels cement had excellent solidification effects for chromium ions and lead ions with solidification rates of 99.9% and 99.7%, respectively.