• Restorative Dentistry and Endodontics
• /
• 제22권1호
• /
• pp.156-169
• /
• 1997

This study was designed to evaluate the influences of evaporation of liquid of dental cements by drying during long term using. Zinc phosphate cement, polycarboxylate cement, and glass ionomer cement were used, and evaluated the properties as follows; consistency, setting time, film thickness, solubility, and compressive strength according to the ADA specification. The specimens of control group were made by mixing the newly opened liquid using the powder-liquid ratio recommended by the manufacturer, and the specimens of ES groups were made by mixing the 10% evaporated liquid by drying with the powder-liquid ratio recommeded by the manufacturer, and the specimens of EM group were made by mixing the 10% evaporated liquid with the powder-liquid ratio modified for standard consistency. The following conclusions were drawn ; 1. The viscosity of mixture of all kinds of cements were increased by the evaporation of liquid, especially the viscosity of glass ionomer cement were influenced significantly. 2. The amount of liquid should be increased to get a standard consistency at the using of evaporated liquid of cement, the most significant increase of liquid amount was required on Ketac-Cem. 3. The setting times were increased at both cases of mixing of evaporated liquid with powder - liquid ratio recommended by manufacturer or modifided through consistency test. 4. At an experimental group of mixing of the evaporated liquid with powder-liquid ratio recommended by manufacturer, solubility was decreased and film thickness was increased. 5. By the result of evaporation of cement liquid, the compressive strength of polycarboxylate cement was increased slightly and it of glass ionomer cement was increased, however, by the increase of amount of liquid to be possible to manipulate the compressive strength were decreased.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 1997년도 가을 학술발표회 논문집
• /
• pp.190-195
• /
• 1997

The purpose of this study was to use daily waste incinerated ash, which was reclaimed worthlessly, as substitutes of fine aggregates in concrete. Various kinds of admixture was utilized to strengthen the cement mortar mixed with waste incinerated ash, and altered the curing condition to diminish the rate of expansion. By the results of this experiment, it was possible to produce the lightweight concrete, charactered with the gravity below 1.5 and over 160kg/$\textrm{cm}^2$ compressive strength by replacing all fine aggregates with waste incinerated ash. It was also observed that the low temperature curing condition, lessoned gas exhausts, was effective to increase the strength of cement mortar.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 1997년도 가을 학술발표회 논문집
• /
• pp.117-124
• /
• 1997

In this study, mechanical properties of type V cement concrete with different curing temperature were investigated. The tests for mechancial properties, i.e., compressive strength and modulus of elasticity, were carried out on two kinds of type V cement concrete mixes. concrete cylinders cured at 10, 23, 35 and 50℃ were tested at 1, 3, 7 and 8 days. The 'rate constant model' was used to described the combined effects of time and temperature on compressive strength development. Test results show that concrete subjected to high temperature at early age attains greater strength than concrete to low temperature but eventually attains lower later-age strength than that. With type V cement concrete, the linear and Arrhenius rate constant models both accurately describe the development of relative strength as afunction of the equivalent age.

• Restorative Dentistry and Endodontics
• /
• 제25권3호
• /
• pp.321-337
• /
• 2000

Dental caries, one of the most frequent dental disease, become larger because it can be thought as a simple disease. Further more, it can progress to unexpected root canal therapy with fabrication of crown that needs reduction of tooth structure. Base is required in a large caries and ZOE, ZPC, glass ionomer are used frequently as base material. They, with restorative material, can affect the longevity of the restoration. In this study, we assume that the mandibular 1st molar has deep class I cavity. So, installing the 3 base material, 3 kinds of fillings were restored over the base as follows; 1) amalgam only, 2) amalgam with ZPC, 3) amalgam with ZOE, 4) amalgam with GI cement, 5) gold inlay with ZPC, 6) gold inlay with GI cement, 7) composite resin only, 8) composite resin with GI cement. After develop the 3-dimensional model for finite element analysis, we observe the distribution of stress and temperature with force of 500N to apical direction at 3 point on occlusal surface and temperature of 55 degree, 15 degree on entire surface. The analyzed results were as follow : 1. Principal stress produced at the interface of base, dentin, cavity wall was smallest in case of using GI cement as base material under the amalgam. 2. Principal stress produced at the interface of base, dentin, cavity wall was smaller in case of using GI cement as a base material than ZPC under gold inlay. 3. Composite resin-filled tooth showed stress distributed over entire tooth structure. In other words, there was little concentration of stress. 4. ZOE was the most effective base material against hot stimuli under the amalgam and GI cement was the next. In case of gold inlay, GI cement was more effective than ZPC. 5. Composite resin has the small coefficient of thermal conductivity. So, composite resin filling is the most effective insulating material.

• 콘크리트학회논문집
• /
• 제13권4호
• /
• pp.354-361
• /
• 2001

폴리카르본산계 고분자는 분산성이 양호하고 시멘트계 재료에서 분산 유지성이 뛰어나므로 최근 콘크리트용 혼화제로 크게 주목을 끌고 있다. 따라서 본 연구에서는 시멘트콘크리트용 분산제로서 수평균 분자량(Mn)이 적당한 poly(acrylate-co-methyla-crylate)를 합성하여 시멘트 모르타르의 분산성과 기계적 물성에 미치는 영향에 대하여 연구하였다. 폴리카르본산계 고분자의 수평균 분자량이 2,000~3,000 보다 5,000 정도로 비교적 큰 polycarboxylate가 시멘트계 재료의 물성을 크게 향상시키며, 최적 첨가량은 시멘트 중량의 0.6% 이다. 그러나 poly(acrylate-co-methylacrylate)계 고분자는 시멘트 모르타르 반죽에서 흐름도의 경시변화가 큰 것으로 나타났으며, 이러한 현상은 폴리카르본산계 서방성 고분자가 시멘트계 재료에 사용되었을 때, 알칼리성 분위기에서 카르복실기의 서방성에 의해서 분산성이 지속적으로 유지된다는 기존의 이론과 다르다.

• 자원리싸이클링
• /
• 제3권3호
• /
• pp.27-31
• /
• 1994

포항제철소에서 발생되는 석회석슬러지의 유효이용의 일환으로 포틀랜드 시멘트 혼합재로서 첨가반응효과에 대한 연구를 행하였다. 즉 포틀랜드 시멘트-석회석슬러지계 경화체에 관하여 수화반응속도, 비증발 수분량, 압축강도등의 실험을 통해 포틀랜드 시멘트-석히석 슬러지계에서의 슬러지 미분말 첨가반응효과에 대하여 실험을 하였다. 석회석슬러지를 10% 첨가한 계에서는 포틀랜드 시멘트 단독의 경우와 별차이가 없으나 5% 첨가계에서는 수화 반응속도가 크게 나타났으며 이는 석회석슬러지의 미분말 효과의 영향으로 사료된다. 한편 경화 시멘트 페이스트의 압축강도는 석회석슬러지 5% 첨가한 계에서 약간 높게 나타났으며 물성도 좋게 나타났다. 수화반응물은 주로 $Ca(OH)_2$와 칼슘실리케이트 수화물이며 석회석슬러지를 첨가한 계의 28일 시료에서는 calcium carbonate hydrate가 생성되었다.

• 대한치과보철학회지
• /
• 제42권5호
• /
• pp.597-607
• /
• 2004

Purpose: This study was peformed to investigate the retrievability of the cemented crown from the cementation type implant abutment. Material and method: The cementation type implant abutments (NEOBIOTECH implant abutment regular, 3 degree taper, 10mm length, 4mm diameter, Ti grade III, machined surface. Hwasung, Kyunggi-do) and cemented crowns were divided into 3 groups, depending on their hole angles formed in the crowns for their retrievability. The abutments and crowns were luted with 4 kinds of cements and separation test using metal wedge was executed with Instron 4465 Universal Testing Machine and the maximum impact force of the modified crown ejector was measured. Results and conclusion : 1. All of the cementation type implant abutments and cemented crowns were separated with relatively small force by metal wedge. 2. The retrieving force was minimum when the metal wedge was applied perpendicular to the axis of abutment. 3. The force for retrieving crowns from abutments was maximum in resin cement group, and reduced in orders of zinc phosphate cement, glass ionomer cement and zinc oxide eugenol cement. 4. The maximum force obtained by the crown ejector was higher than the retrieval force in ZOE and GI cement and lower than that in ZPC and resin cement. 5. If it has similar conditions clinically, the cemented crowns luted with 2 types of cements (ZOE, GI cement) can be safely retrieved from the cementation type implant abutments by the modified crown ejector.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2000년도 봄 학술발표회 논문집
• /
• pp.163-168
• /
• 2000

In this paper, removal times of from from concrete using OPC( Ordinary Portland Cement) and BSC(Blast-furnace Slag cement) are suggested by appling logistic curve, which evaluates the strength development of concrete with maturity. W/B, kinds of cement and curing temperatures are selected as test parameters. According to the results, the estimation of strength development by logistic curve has a good agreement between calculated values. As for the removal time of from suggested in this paper, as W/B increase, curing temperature decrease and BSC in used, removal they times of from are shown to be kept longer. Removal times of from from concrete using OPC suggested in this paper are shorter by about 2~3day than those of standard specifications provided in KCI in the rang of over $20^{\circ}C$, while they takes 4~5 day shorter compared with those of standard specifications Provided in KCI in the range of 10~$20^{\circ}C$. Removal times of from for concrete using OPC are longer than those using BSC by about 1 day.

• International Journal of Concrete Structures and Materials
• /
• 제9권1호
• /
• pp.55-60
• /
• 2015

In this study, influence of different stone powders (SP), including limestone powders (LP), quartzite powders (QP), and granitic powders (GP), on the hydration behaviors of portland cement, for example, setting time, hydration heat, and hydration products, were discussed. The initial and the final setting time both shorten when the content of LP is 5 %, however, they are slightly delayed by the other two SPs. The LP has no obvious influence on the arrival time of the first peak in the exothermal curves, and it makes the peak value decrease; the other two SPs postpone the appearance of the first peak, and they also make the peak value decrease. For the second peak, LP shifts the peak position to the left, QP has no effect on this peak position, and GP makes the appearance of this peak delayed by 143 min. Similarly, three kinds of SPs have different influence on the hydration products of portland cement. The LP precipitates the formation of hydrated calcium carbo aluminate, the QP the formation of hydrated garnet, and the GP makes the amount of Tobermorite increase.

• 콘크리트학회논문집
• /
• 제12권3호
• /
• pp.47-55
• /
• 2000

Protections from the frost damage at early ages are one of the serious problems to be considered in cold weather concreting. Frost damage at early ages brings about the harmful influences on the concrete structures such as surface cracks and declination of strength development. Therefore, in this paper, protecting periods of frost damage at early ages according to the standard specifications provided in KCI(Korean Concrete Institute) are suggested by appling logistic curve, which evaluates the strength development of concrete with maturity. W/B, kinds of cement and curing temperatures are selected as test parameters. According to the results, the estimation of strength development by logistic curve has a good agreement between calculated values and measured values. As W/B and compressive strength for protecting from frost damages at early ages increase, it is prolonged. It shows that the protecting periods of FAC(Fly Ash Cement) and BSC(Blast-furnace Slag Cement) concrete are longer than those of OPC(Ordinary Portland Cement) concrete. The protecting peridos from frost damage at early age by JASS are somewhat shorter than those by this paper.