Seong Uk Hong

Transport of blowing agents in polyurethane

Desorption experiments are conducted for several blowing agents in polyurethane at room temperature and with various blowing agent pressures. The diffusivity and solubility data for blowing agents are compared with the corresponding values for chlorofluorocarbon 11 (CFC 11). In addition, the solubility and diffusivity for these blowing agents in polyurethane are explained in terms of the solubility parameter and van der Waals volume, respectively. The calculated permeabilities based on the measured diffusivities and solubilities indicate that among the nine blowing agents investigated in this study, eight blowing agents can be possible candidates for substitutes of CFC 11 in polyurethane foams.

Embossed superhydrophobic polymer surfaces with topological variances

AbstractIn this report, we compare hot and ultraviolet (UV) embossing processes to fabricate hydrophobic surfaces with topological variance. In the hot embossing process, polypropylene was pressurized on a nickel mold with heat, while UV-curable polyurethane acrylate (PUA) was dispensed on the mold followed by UV exposure during the UV embossing process. Cylindrical micro-pillars were successfully replicated using two types of embossing processes with the same mold. The contact angles were then compared at various pillar diameters and with different embossing processes. Although the materials and embossing techniques were different, we achieved a contact angle (CA) enhancement of about 40%. The water contact angle of a transferred substrate, fabricated by the UV embossing process, was 138°. This was much higher than that of flat UV-cured PUA (78°). In addition, we fabricated reverse pillar-shape packing materials for good wettability and then compared the CA values. With the reverse-shape model, we were able to enhance the wettability and decrease the degree of hydrophobicity. This will be beneficial for lipophilic packing materials. This oleophilic characteristic demonstrates enhanced lubrication capabilities as a retort curry packing material.

Modeling and simulation for acrylamide polymerization of super absorbent polymer

In view of the scale up of a batch reactor for super absorbent polymer (SAP), a dynamic mathematical model of a commercial scale batch reactor was developed with mass balance, energy balance, and complex polymerization kinetics. The kinetic parameters of the polymerization were estimated on the basis of the established mathematical model and reference data. Simulation results were validated with less than 10% marginal error compared with reference data. A case study was executed in terms of dynamic simulation for eight different initial concentrations of initiator and monomer to analyze the influence of initial concentration and predict the operation condition for desired product. The results were compared with various reference data, and good agreement was achieved. From the results, we argue that the methodology and results from this study can be used for the scale up of a polymerization batch reactor from the early stage of design.

Estimation of Compressive Strength of Concrete Member Using Ultrasonic Pulse Velocity Method

This study uses the ultrasonic pulse velocity method, one of the non-destructive testing methods that do not damage the structure, to analyze the correlation of wave velocity and compressive strength of normal strength and high strength concrete to propose an estimation formula. And a concrete member is produced to estimate the compressive strength, and provide elementary data for establishing a site-applicable standard for strength estimation formula. In order to analyze the correlation of concrete compressive strength and wave velocity, total of 144 specimens were produced per age, and six concrete members were produced for wave velocity measurement. In this study, the Ultrasonic Pulse Velocity method was used to propose a compressive strength estimation formula of normal strength and high strength concrete, which was applied to concrete members for verification, and the following conclusion was obtained. The correlation between wave velocity and compressive strength was found to be Fc=0.0952VP3.5, R2=0.82 for normal strength concrete, and Fc=0.0028VP6.1, R2=0.83 for high strength concrete. Result of comparing the estimated strength of the concrete member of the relative error rate was standard strength 18.7% on average, the high-strength 8.7%

Estimation of Compressive Strength of Recycled Aggregate High Strength Concrete Using Ultrasonic Pulse Velocity

This study used the ultrasonic pulse velocity method, one of the non-destructive test methods that does not damage the building for maintenance of to-be-constructed concrete structures using recycled aggregates in order to estimate the compressive strength of high strength concrete structure using recycled coarse aggregate and provide elementary resources for technological establishment of ultrasonic pulse velocity method. 200 test pieces of high strength concrete 40, 50MPa using recycled coarse aggregate were manufactured by replacement rates (0, 30, 50, 100%) and age (1, 7, 28, 180days), and air curing was executed to measure compressive strength and wave velocity. As the result of compressive strength measurement, the one with age of 180day and design strength of 40MPa was 43.69MPa, recycled coarse aggregate replacement rate of 30% 50% 100% were 42.82, 41.22, 37.35MPa, and 50MPa was 52.50MPa, recycled coarse aggregate replacement rate of 30% 50% 100% were 49.02, 46.66, 45.30MPa, and while it could be seen that the test piece substituted with recycled aggregate was found to have lower strength than the test piece with natural aggregate only, but it still reached the design strength to a degree. The correlation of compressive strength and ultrasonic pulse velocity was found and regression analysis was conducted. The estimation formula for compressive strength of high strength concrete using recycled coarse aggregate was found to be Fc=0.069Vp4.05, R2=0.66

Bond of High Strength Concrete with Recycled Coarse Aggregate and Reinforcing Bar

This study conducted a comparative evaluation of bond behavior according to the steel reinforcing type and substitution rate of recycled coarse aggregate. Mixed as high-strength concrete of design strength 50MPa in order to verify the applicability of recycled coarse aggregate concrete as a structural member. Total of 24 specimens were manufactured with variables of recycled aggregate substitution rate (0%, 30%, 50%, 100%), steel reinforcing arrangement direction (vertical, horizontal top·bottom) and steel reinforcing types (SD400 D16, D19). The specimen was produced according to CSA S802-02 and ASTM 234. specimens using D16 reinforcing, the vertical reinforcing showed similar bond stress regardless of the recycled aggregate substitution rate and slip amount, and for the horizontal reinforcing, the bottom specimen showed similar bond stress as the vertical reinforcing and slip amount. The top specimen showed slightly less bonds tress than vertical and horizontal bottom specimens. This is thought to have been caused by the subsidence of the aggregate. The specimen using D19 reinforcing showed similar bond stress in vertical · horizontal top · bottom, horizontal top reinforcing maximum bond stress, horizontal bottom reinforcing maximum bond stress and showed no difference due to aggregate subsidence like in D16. As the result, Bond stress in this study is larger than 2.0fck, the value proposed by CEB-FIP code. The specimen using D16 reinforcing bar showed 4.5fck and the specimen using D19 reinforcing bar was near 3.9fck. Therefore, since the standard value is satisfied regardless of replacement rate of recycled aggregate, natural aggregate in high strength concrete can be substituted by recycled aggregate.

Estimation of Thickness of Concrete Slab Members Using Impact Echo Method

Recently, the interest in maintenance and repair of existing concrete structures have increased, and it is typical to use non-destructive testing methods such as rebound hardness test or ultrasonic pulse velocity method to execute maintenance and repair of structures efficiently. Many non-destructive testing methods are being used in practice such as at construction sites, but verification for site applications are quite inadequate. Thus, this study intends to evaluate the applicability of Impact Echo Method which is one of the non-destructive testing methods using stress wave. Total of four specimens were planned and produced. The thickness of concrete slab members was estimated using I.E(OLSENs Freedom Data PC with Win.TFS Software Version 2.5.2). The estimated materials of concrete members by IE was found to be IE-1 specimen 178mm, IE-2 specimen 197mm, IE-3 specimen 191mm, and IE-4 specimen 263mm, and the error rate was found to be 4.22%~18.67% (average 9.6%), showing that they are relatively well in agreement. In this study, the experiments were executed with the objective of estimating the thickness of concrete slab members using Impact Echo Method. Through this study, the applicability of thickness estimation in concrete slab members using impact echo method could be confirmed.

Estimation of Steel Rebar Position and Thickness in Concrete Members Using Impact Echo Method

Non-destructive testing methods, unlike typical destructive testing methods that deconstruct or cut the building in case of issues such as pores, heterogeneous material, cracks or any such equivalent issues inside/outside the building. And refer to the testing methods for pores, heterogeneous material, or defectiveness occurring in the specimen without changes or destruction of internal structure using ultrasound, radiation, electromagnetism, fluid, heat, or light. In this study, among such non-destructive testing methods, the impact echo method was used for an experiment to estimate the steel rebar location and thickness in the concrete mock member. The mix was made with design standard strength of 30MPa, and for the steel rebar, diameter 22mm was used on the specimen of 300×370×200 to install spacer on the ground surface, and after separating by 40mm, it was arranged with 130mm and 150mm from the top of the specimen to the top of the rebar in 1 column and 3 rows. The specimen for thickness estimation was manufactured with total length of 1800×300 and 6 varying thicknesses of 150mm, 180mm, 210mm, 240mm, 270mm, and 300mm. As the result of rebar location estimation, the maximum resonant frequency was found to be 11269Hz, 9453Hz,and the rebar location estimates were 127.8mm and 151.8mm, which was relatively accurate with error rate of 1.72% and 1.19% from the actual value. In case of thickness estimation specimen, the error rates comparing actually measured thickness and the average value were 2.2%, 2.2%, 4.6%, 0.9%, 3.8%, and 4.7%, which were relatively accurate with average of 3.1%. Through this study, the applicability of steel rebar location and thickness estimation in concrete members using impact echo method could be confirmed.

Estimation of Depth of Concrete Column Members Using Impact Echo Method

In order to maintain the existing concrete structures in a safe and usable state, an overall maintenance management is necessary regarding structure aging from quality management of new construction. Thus, non-destructive testing is needed to estimate the structure damage, defect, or proper construction without damaging the structure. In U.S., there is a standard for non-destructive test (ACI 228.2R-98), and also in Japan, the non-destructive test method and compressive strength estimation manual was prepared by the Architectural Institute of Japan in 1983, and there are active researches in the ground field, but it lacks verification in architecture field. Thus, in this study, a technique that can estimate the depth of concrete column member using the Impact Echo method which is one of the non-destructive test methods shall be reviewed and evaluated for applicability to the architecture field. The specimen was mixed with design strength of 30MPa. The equipment used in testing is Freedom Date Pc Platform Win.TFS 2.5.2 by company Olson of U.S., and the experiment involved leveling the top surface of the concrete member, installing the equipment and applying impact 9 times, and taking the average of the reverberation values obtained. The estimated average depth of concrete column member using Impact Echo method was 304mm for IEC-300, 398mm for IEC-400, and 484mm for IEC-500, and the relative error rate compared to the actual size was 1%~3%. Through this study, the applicability of estimation of depth in concrete column members using impact echo method could be confirmed.

Improved grain dryer based on the principle of an ‘Ondol’: Application to Cambodian rural areas

Cambodia took green growth as their national strategy. In relation to that, the country has adopted several legal plans for the development of green growth. In this vein, we found out that conducting a pilot project of inventing and applying a grain dryer, which is environmentally friendly and tailored to the specific local needs, can be recognized as one of the green growth bottom-up elements. This pilot project was implemented during the year of 2012 funded by the ASEM SMEs Eco-Innovation Center (ASEIC), in collaboration with the Global Green Growth Institute and Cambodian government. Facilities to dry cereal crops were adapted from the incineration facilities developed in 2011 by using the heat generated from incineration to heat up the floor. The drying facilities are divided into two types depending on use. An open-type green house is used for drying large quantities and a closed-type with a solar collector (brick) used for cereals that can dry without sunshine.