Hyoung-Seok So

Analysis of Influence Factors for the Pozzolanic Activity and Material Characteristic of the Calcined Paper Sludge

The purpose of this study is to investigate the influencing factors for pozzolanic activity and material characteristics of calcined paper sludge. Calcined paper sludge (CPS) was produced by various parameters such as temperature and time of calcination, cooling methods, basicity and fineness, and its chemical and mineral characteristics were investigated using X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses. The pozzolanic activity of the CPS was also investigated by using an API (assessed pozzolanic activity index) test. From the results of XRD, new phases such as anorthite and gehlenite by crystallization of CAS appeared at CPS above 800 °C. These new phases have higher chemical and thermal stability than calcite or kaolinite. This may have a negative effect on the pozzolanic activity of CPS. The results of the API (%) test clearly showed that the pozzolanic activity of CPS was highest at a calcination temperature of 700 °C, a calcination time of 2 hours and the cooling method of water quenching.

Pozzolanicity of Calcined Sewage Sludge with Calcination and Fineness Conditions

This study discussed the pozzolanic properties of calcined sewage sludge (CSS) according to calcination and fineness conditions. The chemical and mineralogical analysis of CSS according to calcination temperature and time were carried out and compared with that of the existing pozzolanic materials such as fly-ash, blast furnance slag and meta-kaolin. Various mortars were made by mixing those CSS and Ca(OH)2 (1:1 wt. %), and their compressive strength and hydrates according to experimental factors such as fineness of CSS and curing age were also investigated in detail. The results show clearly the potentiality of calcined sewage sludge (CSS) as an admixture materials in concrete, but the CSS should be controlled by calcination temperature and time, and fineness etc. In this experimental condition, the calcination temperature of 800°C, calcination time of 2 hours and fineness of 5,000 cm 2 /g were optimum conditions in consideration of the mechanical properties and economic efficiency of CSS. The compressive strength of CSS mortars was higher than that of fly-ash mortars and blast furnace slag mortars, especially at the early ages. Then, the utilization of CSS in construction fields was greatly expected.

Antifungal Activity of Antifungal Mortars with Various Organic/Inorganic Antifungal Agents

This study discuss the antifungal performance of antifungal mortars with various organic and inorganic antifungal agent on the five kinds of mold: Chaetomium globosum, Aspergillus niger, Aureobasidium pullulans, Gliocladium virens and Penicillium pinophilum, which can be easily discovered in the interiors and exteriors of buildings. Various antifungal mortars using organic and inorganic antifungal agents were made in this study, and the antifungal performance, the durability of antifungal activity and chemical stability of them were investigated. As the results, the antifungal mortar with 10% Df-45 of organic antifungal agent exhibited the outstanding antifungal activity as well as the durability of antifungal activity. The antifungal mortars with inorganic antifungal agents presented overall the low antifungal activity and durability of antifungal activity, relatively.

Influence of Temperature on Chloride Ion Diffusion of Concrete

The long term integrity of concrete cask is very important for spent nuclear fuel dry storage system. However, there are serious concerns about early deterioration of concrete cask from creaking and corrosion of reinforcing steel by chloride ion because the cask is usually located in seaside, expecially by combined deterioration such as chloride ion and heat, carbonation. This study is to investigate the relation between temperature and chloride ion diffusion of concrete. Immersion tests using 3.5% NaCl solution that were controlled in four level of temperature, i.e. 20, 40, 65, and 90℃, were conducted for four months. The chloride ion diffusion coefficient of concrete was predicted based on the results of profiles of Cl- ion concentration with the depth direction of concrete specimens using the method of potentiometric titration by AgNO3. Test results indicate that the diffusion coefficient of chloride ion increases remarkably with increasing temperature, and there was a linear relation between the natural logarithm values of the diffusion coefficients and the reciprocal of the temperature from the Arrhenius plots. Activation energy of concrete in this study was about 46.6 (W/C = 40%), 41.7 (W/C = 50%), 30.7 (W/C = 60%) kJ/mol under a temperature of up to 90℃, and concrete with lower water-cement ratio has a tendency towards having higher temperature dependency.

Influence of Mixtures and Curing Conditions on Strength and Microstructure of Reactive Powder Concrete Using Ternary Pozzolanic Materials

This study discussed the influence of mixtures and curing conditions on the development of strength and microstructure of RPC using ternary pozzolanic materials. Through pilot experiment, various RPC was manufactured by adding single or mixed ternary pozzolanic materials such as silica fume, blast furnace slag and fly ash by mass of cement, up to 0~65%, and cured by using 4 types of method which are water and air-dried curing at , steam and hot-water curing at . The results show that the use of ternary pozzolanic materials and a suitable curing method are an effective method for improving development of strength and microstructure of RPC. The unit volume of cement was greatly reduced in RPC with ternary pozzolanic materials and unlike hydration reaction in cement, the pozzolanic reaction noticeably contributes to a reduction in hydration heat and dry shrinkage. A considerable improvement was found in the flexural strength of RPC using ternary pozzolanic materials, and then the utilization of a structural member subjected to bending was expected. The X-ray diffractometer (XRD) analysis and Scanning Electronic Microscope (SEM) revealed that the microstructure of RPC was denser by using the ternary pozzolanic materials than the original RPC containing silica fume only.

The Use of Galvanostatic Pulse Transient Techniques for Assessing of Corrosion Rate of Reinforcing steel in Concrete

An electrochemical transient response technique was used to study the corrosion of reinforcing steel bar in the concrete. Analysis of the transient electrochemical potential response in a corrosion interface to an applied current has enabled the separate components that make up the measured transient response to be isolated. These components display a range of resistances and capacitances, dependent on the corrosion conditions of the reinforcing steel, which may be attributed to the corrosion process, to effects within the concrete cover or to film effects on the surface of the concrete. In this technique, the corrosion rate was evaluated by summing all of the resistances in the separate components to obtain an aggregated corrosion resistance. However, it is possible that not all resistances identified are associated with the corrosion process. The results obtained show that the corrosion rates are significant dependent on the assignment of the separate components to either corrosion or to other processes. The assignment of resistive components associated with the corrosion rate can be clearly identified by taking a series of the transient measurement at different lateral distances from the corroding reinforcing steel. An inappropriate selection of measurement time however may result in an additional resistance, which is not associated with corrosion, being included or part of the resistance associated with corrosion being left out.