응력조건에 따른 고결모래의 강도정수 평가

이문주,최성근,추현욱,조용순,이우진 한국지반공학회 2007 한국지반공학회논문집 Vol.23 No.5

The factors affecting the geotechnical properties of cemented sands are known to be relative density, cementation level, stress level, and particle characteristics such as particle size, shape and surface conditions. It has been widely accepted that the friction angle of cemented sands is not affected by cementation while the cohesion of cemented sands was significantly influenced by cementation. The cementation that is a critical component of the strength of cemented sands will be broken with increasing confining pressure and great caution is required in evaluating the cohesion of cemented specimens due to their fragilities. In this study, a series of drained shear tests were performed with specimens at various cementation levels and confining stresses to evaluate the strength parameters of cemented sands. From the experiments, it was concluded that the cohesion intercept of cemented sand experiences three distinctive zone (cementation control zone, transition zone, and stress control zone), as the cementation level and the confining stress varies. In addition, for accurate evaluation of the strength parameters, the level of confining stress triggering the breakage of cementation bond should be determined. In this study, the relationship between the maximum confining stresses capable of maintaining the cementation bond intact and unconfined compression strength of the cemented sand was established.

고결정도와 응력조건에 따른 고결모래의 배수전단거동

이문주(Lee Moon Joo),최성근(Choi Sung Kun),김승한(Kim Seung Han),이우진(Lee Woo Jin) 대한토목학회 2007 대한토목학회논문집 C Vol.27 No.3

본 연구에서는 삼축압축시험을 통해 고결정도와 응력조건에 따른 고결모래의 강도특성과 변형특성을 파악하였다. 동일한 상대밀도의 모래에 대해 석고함유율을 조절하여 시료를 조성한 후, 50~200㎪까지 단계적으로 구속압을 조절하여 배수전단 시험(CID)을 실시하였다. 실험결과에 의하면, 고결정도가 증가할수록 모래의 전단강도가 증가하고 파괴양상이 취성적으로 변하며 전단시 팽창이 크게 발생한다. 동일한 구속압에서 약한 고결모래의 팽창경향은 미고결모래에 비해 현저히 감소하지만, 고결정도가 증가하면 팽창경향이 증가한다. 또한 동일한 고결정도에서 구속압이 증가할수록 전단강도는 증가하지만 구속압에 의한 고결결합 파괴시 거동이 연성적으로 변하며, 고결정도가 큰 시료에서는 큰 구속압에 의해 전단시 압축이 발생한다. 고결결합이 파괴된 이후에 나타나는 극한상태에서는 고결모래의 극한강도 및 유효응력비가 미고결 모래와 유사하며, 고결모래의 점착력은 모두 사라지고 미고결 모래와 동일한 마찰력에 의해 저항한다. 또한 미고결 모래의 변형계수는 구속압 영향을 상대적으로 크게 받는 반면, 고결모래의 변형계수는 결합이 파괴되기 전에는 구속압의 영향이 상대적으로 작았다. 미고결모래와 고결정도가 약한 모래의 할선탄성계수와 전단강도 비는 구속압이 증가할 수록 감소하는 반면, 고결정도가 더 큰 모래의 할선탄성계수와 전단강도 비는 구속압과 함께 증가하는 경향을 보였다. In this study, a series of cm tests were performed on gypsum-cemented specimens to evaluate the strength and the modulus of cemented sand having various degrees of cementation and stress levels. It was shown that, with increasing cementation level, peak shear strength increases; specimen fails in brittle fashion; and the tendency of dilation becomes greater. At the same confining stress level, the dilation of weakly cemented sand is less than that of uncemented sand, whereas the stronger tendency of dilation is observed with increasing degree of cementation. In addition, with increasing confining stress, the shear strength of the specimen increases and a relatively ductile failure is developed once confining pressure causes the bonding breakage. Under high confining stress, volumetric contraction was observed even for strongly cemented sands. When the cementation is completely destroyed, the shear strength and the effective stress ratio of cemented sand converge to those of uncemented sand. Cohesion intercept of the cemented sand disappears after the breakage of cementation bond and intrinsic variables seem to dominate the shear behavior at ultimate state. While Young's modulus of uncemented sand is affected by confining pressure significantly, that of cemented sand is slightly affected until confining pressure breaks the cementation bonds. The ratio of secant Young's modulus and peak strength for uncemented and weakly cemented sands decreases with increasing confining pressure, while that of strongly cemented sand increases with increasing confining pressure level.

Effects of a relined fiberglass post with conventional and self-adhesive resin cement

Santos Junior Wilton Lima dos,Santi Marina Rodrigues,Lins Rodrigo Barros Esteves,Martins Luís Roberto Marcondes 대한치과보존학회 2024 Restorative Dentistry & Endodontics Vol.49 No.2

Objectives This study was conducted to evaluate the mechanical properties of relined and non-relined fiberglass posts when cemented to root canal dentin using a conventional dual-cure resin cement or a self-adhesive resin cement. Materials and Methods Two types of resin cements were utilized: conventional and self-adhesive. Additionally, 2 cementation protocols were employed, involving relined and non-relined fiberglass posts. In total, 72 bovine incisors were cemented and subjected to push-out bond strength testing (n = 10) followed by failure mode analysis. The cross-sectional microhardness (n = 5) was assessed along the root canal, and interface analyses (n = 3) were conducted using scanning electron microscopy (SEM). Data from the push-out bond strength and cross-sectional microhardness tests were analyzed via 3-way analysis of variance and the Bonferroni post-hoc test (α = 0.05). Results For non-relined fiberglass posts, conventional resin cement exhibited higher push-out bond strength than self-adhesive cement. Relined fiberglass posts yielded comparable results between the resin cements. Type II failure was the most common failure mode for both resin cements, regardless of cementation protocol. The use of relined fiberglass posts improved the cross-sectional microhardness values for both cements. SEM images revealed voids and bubbles in the incisors with non-relined fiberglass posts. Conclusions Mechanical properties were impacted by the cementation protocol. Relined fiberglass posts presented the highest push-out bond strength and cross-sectional microhardness values, regardless of the resin cement used (conventional dual-cure or self-adhesive). Conversely, for non-relined fiberglass posts, the conventional dual-cure resin cement yielded superior results to the self-adhesive resin cement.

시멘트 유지형 임플란트 보철물의 유지력에 시멘트의 종류와 열순환이 미치는 영향에 관한 연구

조재호,정창모,전영찬,Cho Jae-Ho,Jeong Chang-Mo,Jeon Young-Chan 대한치과보철학회 2003 대한치과보철학회지 Vol.41 No.4

Statement of problem : In cemented implant-supported porstheses, it is still controversy what kind of cement to use. However, the effect of thermocycling on retentive strength of cemented implant-supported prostheses has not been well investigated. Purpose : This study was tested to evaluate the effects of various cements and thermocycling on retentive strengths of cemented implant-supported prostheses. Material and methods : Prefabricated implant abutments, height 5mm, diameter 6mm, 3-degree taper per side, with light chamfer margins were used. Ten specimens of two-unit fred partial denture were fabricated. The luting agents used for this study were three provisional luting agents which were Temp bond, Temp bond NE, IRM and four permanent luting agents which were Panavia F, Fuji-cem, Hy-bond Zinc cement, Hy-bond Polycarboxylate cement. 24 hours after cementation. the retentive strengths were measured by the universal testing machine with a cross-head speed of 0.5mm/min. Then cementation procedures were repeated and specimens were thermocycled 1000 times at temperature of $5^{\circ}C$ and $55^{\circ}C$. After thermocycling, the retentive strengths were measured. Results : Before thermocycling, the retentive strengths were decreased with the sequence of Panavia F. Fuji-cem. Hy-bond Zinc cement. Hy-bond Polycarboxylate cement, IRM, Temp bond NE and Temp bond, and there were significant differences among each groups(p<0.05). After thermocycling, the retentive strengths were decreased with the sequence of Panavia F. Fuji-cem, Hybond Zinc cement, Hy-bond Polycarboxylate cement, IRM, Temp bond NE and Temp bond, and there were no significant differences among Panavia F, Fuji-cem and Temp bond NE, Temp bond(p>0.05). The retentive strengths before and after thermocycling showed significant differences in Hy-bond Zinc cement. IRM, Temp bond NE and Temp bond(p<0.05). Conclusion : Within the limitation of this study, thermocycling do not affect the retentive strengths of permanent luting agents but the retentive strengths of temporary cements were reduced significantly after thermocyling.

Property Analysis of Aerosol Containing NORM in Cement Manufacturing Industry for Radiological Risk Assessment

Jong Hyeok Park,Byung Min Lee,Seong Yeon Lee,Kwang Pyo Kim 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.2

Cement is widely used as representative industrial material. In Korea, about 50 million tons of cement are consumed every year. In the manufacture of cement, raw materials containing NORM such as fly ash and bauxite are used. Therefore, the workers can be subjected to radiation exposure. The major exposure pathway in NORM industries is internal exposure due to inhalation of aerosol. Internal radiation dose due to aerosol inhalation varies depending on physicochemical properties of the aerosol. Therefore, the objective of this study was to investigate aerosol properties influencing inhalation dose in cement industries. In this study, aerosol properties were measured for two cement manufacturers. A particulate size distribution and concentration at various processing areas in cement manufacturing industries in Korea were analyzed using a cascade impactor. The mass density of raw materials and byproducts were measured using pycnometer. Shape of particulates was analyzed using SEM. The radioactivity concentration of Ra-226, Ra-228 for U/Th decay series was measured using HPGe. Particulate concentration by size was distributed log-normally with maximum at particle size about 7.2 μm in manufacturer A and 5.2 μm in manufacturer B. The mass density of fly ash and cement were 2.3±0.06, 3.2±0.02 g/cm3 respectively in manufacturer A. In manufacturer B, the mass density of bauxite and cement were 3.4±0.02, 2.9±0.01 g/cm3 respectively. The shape of particulates appeared as spherical shape in manufacturer A and B regardless of sampling area. Thus, a shape factor of unity could be assumed. The radioactivity concentrations of Ra-226, Ra-228 were 82±9, 82±8 Bq/kg for fly ash, and 25±4, 23±3 Bq/kg for cement in manufacturer A. In manufacturer B, the radioactivity concentrations of Ra-226, Ra-228 were 344±34, 391±32 Bq/kg for bauxite, and 122±13, 145±12 Bq/kg for cement. The radioactivity concentrations of Ra-226, Ra-228 in cement were less than raw materials such as fly ash and bauxite. It is because the dilution of the radioactivity concentration occurred during mixing with other raw materials in cement production process. This study results will be used as database for accurate dose assessment due to airborne particulate inhalation by workers in cement industries.

Effects of a relined fiberglass post with conventional and self-adhesive resin cement

Wilton Lima dos Santos Junior,Marina Rodrigues Santi,Rodrigo Barros Esteves Lins,Luis Roberto Marcondes Martins The Korean Academy of Conservative Dentistry 2024 Restorative Dentistry & Endodontics Vol.49 No.1

Objectives: This study was conducted to evaluate the mechanical properties of relined and non-relined fiberglass posts when cemented to root canal dentin using a conventional dual-cure resin cement or a self-adhesive resin cement. Materials and Methods: Two types of resin cements were utilized: conventional and self-adhesive. Additionally, 2 cementation protocols were employed, involving relined and non-relined fiberglass posts. In total, 72 bovine incisors were cemented and subjected to push-out bond strength testing (n = 10) followed by failure mode analysis. The cross-sectional microhardness (n = 5) was assessed along the root canal, and interface analyses (n = 3) were conducted using scanning electron microscopy (SEM). Data from the push-out bond strength and cross-sectional microhardness tests were analyzed via 3-way analysis of variance and the Bonferroni post-hoc test (α= 0.05). Results: For non-relined fiberglass posts, conventional resin cement exhibited higher pushout bond strength than self-adhesive cement. Relined fiberglass posts yielded comparable results between the resin cements. Type II failure was the most common failure mode for both resin cements, regardless of cementation protocol. The use of relined fiberglass posts improved the cross-sectional microhardness values for both cements. SEM images revealed voids and bubbles in the incisors with non-relined fiberglass posts. Conclusions: Mechanical properties were impacted by the cementation protocol. Relined fiberglass posts presented the highest push-out bond strength and cross-sectional microhardness values, regardless of the resin cement used (conventional dual-cure or self-adhesive). Conversely, for non-relined fiberglass posts, the conventional dual-cure resin cement yielded superior results to the self-adhesive resin cement.

단섬유를 사용한 시멘트 혼합토의 일축압축강도 특성

박성식(Park Sung-Sik),김영수(Kim Young-Su),최선규(Choi Sun-Gyu),신시언(Shin Shi-Eon) 대한토목학회 2008 대한토목학회논문집 C Vol.28 No.4

시멘트로 고결된 사질토의 일축압축강도와 취성적인 거동을 개선하기 위하여 단섬유를 사용한 혼합토에 관한 연구를 수행 하였다. 낙동강 모래에 포틀랜드시멘트와 콘크리트 보강재로 많이 사용되고 있는 폴리비닐알코올 섬유를 무작위로 보강하였다. 낙동강 모래에 시멘트와 섬유를 최적함수비로 잘 섞은 다음 5층 다짐으로 공시체를 만든 후 7일간 양생시켰다. 적은 양의 시멘트를 혼합하여 시멘트의 고결효과보다는 섬유의 인장력으로 인한 보강효과에 중점을 두었다. 8% 이하의 시멘트비를 가진 약하게 고결된 혼합토에 섬유비를 다르게 공시체를 제작하여 일축압축시험을 실시하였다. 섬유비와 시멘트비에 따른 일축압축강도의 특성을 비교하였으며, 일축압축강도는 시멘트비가 2%인 경우 섬유비의 증가에 따라 최대 6배까지 증가하였다. 섬유의 인장력으로 공시체의 연성이 증가하여 최대응력 시의 축변형률이 시멘트비가 2%인 경우 섬유비에 따라 최대 7% 정도 증가하였다. 시멘트비가 2%인 혼합토에 1%의 섬유 보강으로 인한 효과를 마찰각의 증가와 점착력의 증가로 분리하여 해석하였으며, 마찰각의 증가로 해석한 경우 섬유로 전달되는 응력은 수직응력의 8% 정도로 계산되었다. A study on cemented sand reinforced with short fibers was carried out to improve its unconfined compressive strength and brittle behavior. Nak-dong River sand was mixed with Portland cement and polyvinyl alcohol (PYA) fibers. A PYA fiber widely used for concrete reinforcement is randomly distributed into cemented sand. Nak-dong River sand, cement and fibers with optimum water content were compacted in 5 layers and then cured for 7 days. The effect of fiber reinforcement rather than cementation was emphasized by using a small amount of cement. Weakly cemented sand with a cement/sand ratio less than 8% was fiber-reinforced with different fiber ratios and tested for unconfined compression tests. The effect of fiber ratio and cement ratio on unconfined compressive strength was investigated. Fiber-reinforced cemented sand with 2% cement ratio showed up to six times strength to non-reinforced cemented sand. Because of ductile behavior of fiber-reinforced specimens, an axial strain at peak stress of specimens with 2% cement ratio increases up to 7% as a fiber ratio increases. The effect of 1% fiber addition into 2% cemented sand on friction angle and cohesion was analyzed separately. When the fiber reinforcement is related to friction angle increase, the 8% of applied stress transferred to 1% fibers within specimens.

A practical method for estimating maximum shear modulus of cemented sands using unconfined compressive strength

Choo, Hyunwook,Nam, Hongyeop,Lee, Woojin Elsevier 2017 Journal of applied geophysics Vol.147 No.-

<P><B>Abstract</B></P> <P>The composition of naturally cemented deposits is very complicated; thus, estimating the maximum shear modulus (<I>G<SUB>max</SUB> </I>, or shear modulus at very small strains) of cemented sands using the previous empirical formulas is very difficult. The purpose of this experimental investigation is to evaluate the effects of particle size and cement type on the <I>G<SUB>max</SUB> </I> and unconfined compressive strength (<I>q<SUB>ucs</SUB> </I>) of cemented sands, with the ultimate goal of estimating <I>G<SUB>max</SUB> </I> of cemented sands using <I>q<SUB>ucs</SUB> </I>. Two sands were artificially cemented using Portland cement or gypsum under varying cement contents (2%–9%) and relative densities (30%–80%). Unconfined compression tests and bender element tests were performed, and the results from previous studies of two cemented sands were incorporated in this study. The results of this study demonstrate that the effect of particle size on the <I>q<SUB>ucs</SUB> </I> and <I>G<SUB>max</SUB> </I> of four cemented sands is insignificant, and the variation of <I>q<SUB>ucs</SUB> </I> and <I>G<SUB>max</SUB> </I> can be captured by the ratio between volume of void and volume of cement. <I>q<SUB>ucs</SUB> </I> and <I>G<SUB>max</SUB> </I> of sand cemented with Portland cement are greater than those of sand cemented with gypsum. However, the relationship between <I>q<SUB>ucs</SUB> </I> and <I>G<SUB>max</SUB> </I> of the cemented sand is not affected by the void ratio, cement type and cement content, revealing that <I>G<SUB>max</SUB> </I> of the complex naturally cemented soils with unknown in-situ void ratio, cement type and cement content can be estimated using <I>q<SUB>ucs</SUB> </I>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Unconfined compressive strength (q<SUB>ucs</SUB>) and shear wave velocity were measured. </LI> <LI> Factors affecting the maximum shear modulus (<I>G<SUB>max</SUB> </I>) and <I>q<SUB>ucs</SUB> </I> were investigated. </LI> <LI> Relationship between <I>G<SUB>max</SUB> </I> and <I>q<SUB>ucs</SUB> </I> is not affected by cement type and cement content. </LI> <LI> <I>G<SUB>max</SUB> </I> of complex naturally cemented soils can be estimated with <I>q<SUB>ucs</SUB> </I>. </LI> </UL> </P>

손상 없이 영구 접착 보철물을 제거할 수 있는 cementation type 임플랜트 지대주 개발에 관한 연구

최진호,이재봉,Choi Jin-Ho,Lee Jai-Bong 대한치과보철학회 2004 대한치과보철학회지 Vol.42 No.5

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.

Numerical investigation on tortuosity of transport paths in cement-based materials

Xiao-Bao Zuo,Wei Sun,Zhi-Yong Liu,Yu-Juan Tang 사단법인 한국계산역학회 2014 Computers and Concrete, An International Journal Vol.13 No.3

Based on the compositions and structures of cement-based materials, the geometrical models of the tortuosity of transport paths in hardened cement pastes, mortar and concrete, which are associated withthe capillary porosity, cement hydration degree, mixture particle shape, aggregate volume fraction andwater-cement ratio, are established by using a geometric approach. Numerical simulations are carried out to investigate the effects of material parameters such as water-cement ratio, volume fraction of the mixtures, shape and size of aggregates and cement hydration degree, on the tortuosity of transport paths in hardened cement pastes, mortar and concrete. Results indicate that the transport tortuosity in cement-based materials decreases with the increasing of water-cement ratio, and increases with the cement hydration degree, the volume fraction of cement and aggregate, the shape factor and diameter of aggregates, and the material parameters related to cement pastes, such as the water-cement ratio, cement hydration degree and cement volume fraction, are the primary factors that influence the transport tortuosity of cement-based materials.