• Computers and Concrete
• /
• v.33 no.4
• /
• pp.471-479
• /
• 2024

In urban areas, appropriate backfilling design is necessary to prevent surface subsidence and subsurface cavities after excavation. Expandable foam grout (EFG), a mixture of cement, water, and an admixture, can be used for cavity filling because of its high flowability and volume expansion. EFG volume expansion induces a porous structure that can be quantified by the entrapped air content. This study observed the unit weight variations in the EFG before and after expansion depending on the various admixture-cement and water-cement ratios. Subsequently, the air content before and after expansion and the gravimetric expansion ratios were estimated from the measured unit weights. The air content before expansion linearly increased with an increase in the admixture-cement ratio, resulting in a decrease in the unit weight. The air content after the expansion and the expansion ratio increased nonlinearly, and the curves stabilized at a relatively high admixture-cement ratio. In particular, a reduced water-cement ratio limits the air content generation and expansion ratio, primarily because of the short setting time, even at a high admixture-cement ratio. Based on the results, the relationship between the maximum expansion ratio of EFG and the mixture ingredients (water-cement and admixture-cement ratios) was introduced.

• The Journal of Korean Academy of Prosthodontics
• /
• v.37 no.6
• /
• pp.730-740
• /
• 1999

The purpose of this study was to investigate setting and thermal expansion of dental soldering investments. In order to compare expansion rates and to investigate the effect of water/powder ratio on expansion, setting and thermal expansion of low dental soldering investments were measured under three different water/powder ratio conditions. standard, 20% decreased and 20% increased. Setting expansion of investments was measured by use of dialgauge method. Each measurement was started two minutes later from the beginning of spatulation and recorded every one minute for one hour. Thermal expansion of cylindrical test specimens, 10mm diameter, 50mm length, was recorded in a thermodilatometer at heating rate of $10^{\circ}C$ per minute from $25^{\circ}C\;to\;700^{\circ}C$. The results of this study were obtained as follows: 1. Setting expansion rates under the standard water/powder ratio condition were 0.198% in Speed-E, 0.090% in Deguvest, 0.080% in CM and Hi-temp. Setting expansion of Speed-E was significantly different from those of CM, Deguvest and Hi-temp, and setting expansion of Deguvest was significantly different from those of CM and Hi-temp(p<.05). 2. Under the decreased water/powder ratio condition, there was significant increase in setting expansion of 4 dental soldering investments (p<.05). 3. There were no significant differences in setting expansions of investments except Hi-temp between standard and increased water/powder ratio condition(p<.05). 4. Thermal expansion rates under the standard water/powder ratio condition were 1.923% in Deguvest, 1.629% in Speed-E, 1.619% in Hi-temp and 1.580% in CM. No significant differences in thermal expansions under the standard water/powder ratio condition existed only between Speed-I and Hi-temp(p<.05) 5. Under the decreased water/powder ratio condition, there was significant increase in thermal expansion of CM and Deguvest but decrease in thermal expansion of Speed-E (p<.05). 6. Under the increased water/powder ratio condition, there was significant decrease in thermal expansion of CM, Deguvest and Speed-I but decrease in thermal expansion of Hi-temp(p<.05).

• Journal of the Korean Ceramic Society
• /
• v.37 no.6
• /
• pp.576-582
• /
• 2000

Two type of expanding cement generally referred to as CSA with Hauyne(3CaO 3Al2O3 CaSO4) and Quick lime(CaO). Hauyne is formed to ettringite when there are presented with CaO and CaSO4, and CaO reacts wtih water to form Ca(OH)2. REcently, the mechanism of compensation and expand mortar or concrete tend to same and it has been used improving on its shrink property. The volume of cement paste varies with its water content shrink with drying and re-wetting. Concrete and mortar works are required shrinking compensation and expansion properties to reduce of potential crack. The use of expansion cement may improve on its shrinking volume changes. CSA dosages for shrinking compensation limited by cement weight, but obtained difference expansion rate with varied W/C or inorganic admixture. This paper studies expansion rate according to expansion cement dosages, water and inorganic admixtures as Silica fume. Therefor, the expansion factor has to considered before the application.

• Proceedings of the Korean Association of Geographic Inforamtion Studies Conference
• /
• 1999.12a
• /
• pp.21-25
• /
• 1999

Planning support systems(PSS) add more advanced spatial analysis functions than Geographic information systems(GIS) and intertemporal functions to the functions of spatial decision support systems(SDSS). This paper reports the continuing development of a PSS providing a framework that facilitates urban planners and civil engineers in conducting coherent deliberations about planning, design and operation & maintenance(O&M) of water-distribution networks for urban growth management. The PSS using dynamic optimization model, modeling-to-generate-alternatives, value engineering(VE) and life-cycle cost(LCC) can generate network alternatives in consideration of initial cost and O&H cost. Users can define alternatives by the direct manipulation of networks or by the manipulation of parameters in the models. The water-distribution network analysis model evaluates the performance of the user-defined alternatives. The PSS can be extended to include the functions of generating sewer network alternatives, combining water-distribution and sewer networks, eventually the function of planning, design and O&H of housing sites. Capacity expansion by the dynamic water-distribution network optimization model using MINLP includes three advantages over capacity expansion using optimal control theory(Kim and Hopkins 1996): 1) finds expansion alternatives including future capacity expansion times, sizes, locations, and pipe types of a water-distribution network provided, 2) has the capabilities to do the capacity expansion of each link spatially and intertemporally, and 3) requires less interaction between models. The modeling using MINLP is limited in addressing the relationship between cost, price, and demand, which the optimal control approach can consider. Strictly speaking, the construction and O&M costs of water-distribution networks influence the price charged for the served water, which in turn influence the. This limitation can be justified in rather small area because price per unit water in the area must be same as that of neighboring area, i.e., the price is determined administratively. Planners and engineers can put emphasis on capacity expansion without consideration of the relationship between cost, price, and demand.

• Restorative Dentistry and Endodontics
• /
• v.5 no.1
• /
• pp.29-34
• /
• 1979

The purpose of this study was to measure thermal expansions of dental investments, Biovest(Casting Investment. Dentsply International INC, U.S.A.), Multi-Best (Use for all dental chrome-cobalt alloys, The Ransom & Randolph Co. U.S.A.), Kerr(Inlay Investment. Sybron Kerr, U.S.A.), O. K. (Inlay Investment. Shofu Dental MFG, Co. Japan), Whip-Mix (Cristobalite Inlay Investment. Whip-Mix Corporation. U.S.A.). Thermal expansion of specimens(5mm in diameter and 50mm in length) was measured by a dilatometer at the temperature range from $20^{\circ}C$ to $700^{\circ}C$ by comparing expansion between standardized quartz and experimental specimens with heating rate about $300^{\circ}C$/hr. The following results were obtained. 1. The coefficient of thermal expansion of Biovest was $15{\times}10^{-6}/^{\circ}C$ in the water powder ratio 18/100 and $14{\times}10^{-6}/^{\circ}C$ in the water powder ratio 28/100. Those of Multi-Best were $9{\times}10^{-6}/^{\circ}C$ in the water powder ratio 14/100 and $7{\times}10^{-6}/^{\circ}C$ in the water powder ratio 24/100. 2. The coefficient of thermal expansion of Kerr were $17{\times}10^{-6}/^{\circ}C$ in the water powder ratio 38/100 and $14{\times}10^{-6}/^{\circ}c$ in the water powder ratio 48/100. Those of O. K. were $9{\times}10^{-6}/^{\circ}C$ in the water powder ratio 33/100 and $7{\times}10^{-6}/^{\circ}C$ in the water powder ratio 43/100 3. The coefficient of thermal expansion of Whip-Mix were $14{\times}10^{-6}/^{\circ}C$ in the water powder ritio 40/100 and $12{\times}10^{-6}/^{\circ}c$ Fein the water powder ratio 50/100. Those of Hi-Heat were $11{\times}10^{-6}/^{\circ}c$ in the water powder ratio 28/100 and $10{\times}10^{-6}/^{\circ}c$ in the water powder ratio 38/100.

• Korean Journal of Health Education and Promotion
• /
• v.27 no.4
• /
• pp.113-121
• /
• 2010

Objectives: The study sought to identify the perception of schoolchildren's parents concerning an approval on the expansion implementation of community water fluoridation program in Gimhae, Korea. Methods: Questionnaires were distributed to schoolchildren's parents in Gimhae in 2008. Responses were collected from 1,703 parents. The standard questionnaire of Ministry of Health and Welfare was used and items were socioeconomic variables, water used for drinking and cooking, awareness on the fluoridation program and approval on the expansion implementation of fluoridation program at the region of Myeongdong water plant. Significance was analyzed by chi-square test and multiple logistic analysis. Results: Of parents, 1.9% used plain tap water and 39.8% used boiled tap water for drinking and 50.0% used tap water for cooking. 58.0% of parents were aware of fluoridation program with 27.1% being aware of the implementation of the program in Gimhae. 74.5% approved the expansion implementation of the program to the region of Myeong-dong water plant. Significant variables associated to approving the expansion implementation of program were age, gender, residence period in Gimhae, occupation and awareness of the program. Conclusion: The expansion implementation of fluoridation program in Gimhae is desirable for caries prevention because of the majority of schoolchildren's parents' approval.

• Journal of Korean Society of Environmental Engineers
• /
• v.39 no.12
• /
• pp.733-740
• /
• 2017

'The facilities standards of water supply' issued by the Ministry of Environment in 2004 indicates that expansion joints cannot be used in welding water supply steel pipes. However, their reason is not clear and it is difficult to confirm the stability of the steel pipe for a water supply pipeline. The purpose of this study is to determine whether or not an expansion joint is necessary to improve the stability of water supply in steel pipe through a displacement analysis of the pipework. The test results are as follows. Firstly, it was found that expansion and contraction of the water supply steel pipe (D 2,400 mm) occur repeatedly in 4 cycles per year, and the maximum expansion and contraction amount of the pipe is 13.03 mm in 1.24 km pipelines. Secondly, the thermal stress caused by expansion and contraction of the steel pipe is $13.7{\sim}36.1kgf/cm^2$ according to the burial depth (0~4 m). The main comparison factors to determine the stability of the steel pipe (STWW 400) were the allowable tensile strength and the fatigue limit, which were computed to be $4,100kgf/cm^2$ and $1,840kgf/cm^2$, respectively. Finally, the thermal stress of the steel pipe is very small compared to the allowable tensile stress and fatigue stress. Therefore, thermal stress does not affect the stability of the steel pipe, although the expansion and contraction of the steel pipe occurs by temperature changes. In conclusion, the study demonstrated that expansion joints are not required in water supply steel pipelines.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.11 no.6
• /
• pp.928-936
• /
• 1999

An experimental study was performed to investigate characteristics of an inverter driven water-to-water refrigeration system with a variation of compressor frequencies and expansion devices. The frequency of a compressor varied from 30Hz to 75Hz, and performance of the systems applying three different expansion devices such as capillary tube, thermostatic expansion valve(TXV), and electronic expansion valve(EEV) were measured. The load conditions were altered by varying the temperature of the secondary fluid entering condenser and evaporator with a constant flow rate. When the test conditions were deviated from the standard value(rated value), TXV and EEV showed better performance than capillary tube due to optimum control of mass flow rate and superheat. In the present study, it was observed that the variable area expansion device had better performance than constant area expansion device in an inverter refrigeration system due to active control of flow area with a change of compressor frequency and load conditions.

• Journal of the Korea Concrete Institute
• /
• v.12 no.1
• /
• pp.79-88
• /
• 2000

Usually, the expansive additives is used to prevent the occurrence of drying shrinkage in concrete. However it may sometimes be over-added in field due to the insufficient cognition of constructor's, which may cause the serious problems in concrete structures. In this study the experiments are performed to present the expansion properties of concrete by varying the water to binder ratios, unit contents of expansive additives and curing conditions. By the results, the strength showed an increase with the addition of expansion additives from 30kg/㎥ up to 50kg/㎥, and a great decrease by contraries if the larger amount are added. Also the more the expansion additives were used, the more length change occurred in concrete. In view of the curing conditions, the concrete by air cured appeared a little expansion even the unit expansion additives increased, which showed an opposite inclination of that with standard curing. This could be explained by the less occurrence of hydration in air condition which also lead to the little expansion of concrete. Hence the expansion concrete to be cured in water or moisture condition became an especial important thing. concrete using expansive additives showed that high expansion was taken place with the rise of temperature.

• Water Engineering Research
• /
• v.1 no.1
• /
• pp.63-74
• /
• 2000

This paper presents a two- phase search scheme for optimal pipe expansion of expansion of existing water distribution systems. In pipe network problems, link flows affect the total cost of the system because the link flows are not uniquely determined for various pipe diameters. The two-phase search scheme based on stochastic optimization scheme is suggested to determine the optimal link flows which make the optimal design of existing pipe network. A sample pipe network is employed to test the proposed method. Once the best tree network is obtained, the link flows are perturbed to find a near global optimum over the whole feasible region. It should be noted that in the perturbation stage the loop flows obtained form the sample existing network are employed as the initial loop flows of the proposed method. It has been also found that the relationship of cost-hydraulic gradient for pipe expansion of existing network affects the total cost of the sample network. The results show that the proposed method can yield a lower cost design than the conventional design method and that the proposed method can be efficiently used to design the pipe expansion of existing water distribution systems.