폴리머 콘크리트의 압축 및 휨강도 발현 특성

김남길,연규석 한국농공학회 2018 한국농공학회논문집 Vol.60 No.1

This study experimentally investigated the compressive and flexyral strength development characteristics of polymer concrete using four different type polymeric resins such as unsaturated polyester, vinyl ester, epoxy, and PMMA (polymethyl methacrylate) as binders. The test results show that the average compressive strength of those four different polymer concretes was 88.70 MPa, the average flexural strength was 20.30 MPa. Those test results show that compressive and flexural strengths of polymer concrete were much stronger than compressive and flexural strengths of ordinary Portland cement concrete. In addition, the relative gains of the compressive strength development at the age of 24 hrs compared to the age of 168 hrs were 68.6~88.3 %. Also, the relative gains of the flexural strength development at the age of 24 hrs compared to the age of 168 hrs were 73.8~93.4 %. These test results show that compressive and flexural strengths of each polymer concrete tested in this study were developed at the early age. Moreover, the prediction equations of compressive and flexural strength developments regarding the age were determined. The determined prediction equations could be applied to forecast the compressive and flexural strength developments of polymer concrete investigated in this study because those prediction equations have the high coefficients of correlation. Last, the relations between the compressive strength and the flexural strength of polymer concrete were determined and the flexural/compressive strength ratios were from 1/4 to 1/5. These results show that polymer concretes investigated in this study were appropriate as a flexural member of a concrete structure because the flexural/compressive strength ratios of polymer concrete were much higher than the flexural/compressive strength ratios of Portland cement concrete.

The effects of surface grinding and polishing on the phase transformation and flexural strength of zirconia

Ji-Young Lee,Geun-Won Jang,In-Im Park,Yu-Ri Heo,Mee-Kyoung Son 대한치과보철학회 2019 The Journal of Advanced Prosthodontics Vol.11 No.1

PURPOSE. The purpose of this in vitro study was to evaluate the effect of surface grinding and polishing procedures using high speed zirconia diamond burs with different grit sizes on the phase transformation and flexural strength of zirconia. MATERIALS AND METHODS. Forty disc shape specimens (15 × 1.25 mm) with a cylindrical projection in the center of each disc (1 × 3 mm) were fabricated with 3Y-TZP (Prettau, Zirkonzahn, Italy). The specimens were divided into 4 groups (n=10) according to the grinding and polishing procedures: Control group - grinding (coarse-grit diamond bur), Group 1 - grinding (coarse-grit diamond bur) + polishing, Group 2 - grinding (fine-grit diamond bur) + polishing, and Group 3 - grinding (fine grit diamond bur). Each specimen was analyzed by 3D-OM, XRD analysis, and biaxial flexural strength test. RESULTS. Based on the surface morphology by 3D-OM images, polished specimens showed smoother surface and lower roughness value (Ra). In the result of XRD analysis, partial phase transformation from tetragonal to monoclinic zirconia occurred in all groups. Control group, ground with a coarse grit diamond bur, showed more t→m phase transformation and lower flexural strength than Groups 1 and 2 significantly. CONCLUSION. The flexural strength in all specimens after grinding and polishing showed over 500 MPa, and those were clinically acceptable. However, grinding with a coarse grit diamond bur without polishing induced the phase transformation and low strength. Therefore, surface polishing is required for the occlusal adjustment using a high speed zirconia diamond bur to reduce the phase transformation and to prevent the decrease of flexural strength of zirconia. [ J Adv Prosthodont 2019;11:1-6] PURPOSE. The purpose of this in vitro study was to evaluate the effect of surface grinding and polishing procedures using high speed zirconia diamond burs with different grit sizes on the phase transformation and flexural strength of zirconia. MATERIALS AND METHODS. Forty disc shape specimens (15 × 1.25 mm) with a cylindrical projection in the center of each disc (1 × 3 mm) were fabricated with 3Y-TZP (Prettau, Zirkonzahn, Italy). The specimens were divided into 4 groups (n=10) according to the grinding and polishing procedures: Control group - grinding (coarse-grit diamond bur), Group 1 - grinding (coarse-grit diamond bur) + polishing, Group 2 - grinding (fine-grit diamond bur) + polishing, and Group 3 - grinding (fine grit diamond bur). Each specimen was analyzed by 3D-OM, XRD analysis, and biaxial flexural strength test. RESULTS. Based on the surface morphology by 3D-OM images, polished specimens showed smoother surface and lower roughness value (Ra). In the result of XRD analysis, partial phase transformation from tetragonal to monoclinic zirconia occurred in all groups. Control group, ground with a coarse grit diamond bur, showed more t→m phase transformation and lower flexural strength than Groups 1 and 2 significantly. CONCLUSION. The flexural strength in all specimens after grinding and polishing showed over 500 MPa, and those were clinically acceptable. However, grinding with a coarse grit diamond bur without polishing induced the phase transformation and low strength. Therefore, surface polishing is required for the occlusal adjustment using a high speed zirconia diamond bur to reduce the phase transformation and to prevent the decrease of flexural strength of zirconia. [ J Adv Prosthodont 2019;11:1-6]

Effects of relining materials on the flexural strength of relined thermoplastic denture base resins

Yunhan Sun,So-Yeon Song,Ki-Sun Lee,Jin-Hong Park,Jae-Jun Ryu,Jeong-Yol Lee 대한치과보철학회 2018 The Journal of Advanced Prosthodontics Vol.10 No.5

PURPOSE. The aim of this study was to evaluate the effects of relining materials on the flexural strength of relined thermoplastic denture base resins (TDBRs). MATERIALS AND METHODS. For shear bond strength testing, 120 specimens were fabricated using four TDBRs (EstheShot-Bright, Acrytone, Valplast, Weldenz) that were bonded with three autopolymerizing denture relining resins (ADRRs: Vertex Self-Curing, Tokuyama Rebase, Ufi Gel Hard) with a bond area of 6.0 mm in diameter and were assigned to each group (n=10). For flexural strength testing, 120 specimens measuring 64.0×10.0×3.3 mm (ISO-1567:1999) were fabricated using four TDBRs and three ADRRs and were assigned to each group (n=10). The thickness of the specimens measured 2.0 mm of TDBR and 1.3 mm of ADRR. Forty specimens using four TDBRs and 30 specimens using ADRRs served as the control. All specimens were tested on a universal testing machine. For statistical analysis, Analysis of variance (ANOVA) with Tukey’s test as post hoc and Spearman’s correlation coefficient analysis (P=.05) were performed. RESULTS. Acry-Tone showed the highest shear bond strength, while Weldenz demonstrated the lowest bond strength between TDBR and ADRRs compared to other groups. EstheShot-Bright exhibited the highest flexural strength, while Weldenz showed the lowest flexural strength. Relined EstheShot-Bright demonstrated the highest flexural strength and relined Weldenz exhibited the lowest flexural strength (P<.05). Flexural strength of TDBRs (P=.001) and shear bond strength (P=.013) exhibited a positive correlation with the flexural strength of relined TDBRs. CONCLUSION. The flexural strength of relined TDBRs was affected by the flexural strength of the original denture base resins and bond strength between denture base resins and relining materials.

Strength Characteristics of the Cement-Stabilized Surface Layer in Dredged and Reclaimed Marine Clay, Korea

Yun, Jung-Mann,Song, Young-Suk,Lee, Jae-Ho,Kim, Tae-Hyung Taylor Francis 2006 Marine georesources & geotechnology Vol.24 No.1

<P>A series of tests in both laboratory and field were performed to investigate the engineering and mechanical properties, especially flexural strength, of cement-stabilized soils. The strength of cement-stabilized soils mainly depends on water-to-cement ratio and curing temperature. The higher curing temperature and the longer curing time, the higher strength in cement-stabilized soils generates. The high ratio of water-to-cement results in lower strength. The compressive strength observed in the field is similar to the strength in the laboratory. Field tests on a cement-stabilized soil layer indicate that the strength is significantly affected by the thickness of the improved layer, which is directly related to the moment of inertia. In addition, the failure shape observed in a cement-stabilized layer in the field looks likes a bending failure type, because the flexural tensile strength, rather than the compressive strength, mainly dominates the failure of cement-stabilized layer. The flexural tensile strength is closely related to the moment of inertia. Therefore, the flexural tensile strength should be considered for determining the thickness and strength in improvement of soft clay.</P>

Flexural Behavior and Prediction Model of Basalt Fiber/Polypropylene Fiber-Reinforced Concrete

Qiang Fu,Zhaorui Zhang,Wenrui Xu,Xu Zhao,Lu Zhang,Yan Wang,Ditao Niu 한국콘크리트학회 2022 International Journal of Concrete Structures and M Vol.16 No.5

The flexural behavior of basalt fiber (BF)/polypropylene fiber (PF)-reinforced concrete (BPRC) was investigated. When the content of BF and PF is 0.1%, the addition of fibers increases the compressive strength of concrete. A BF content of 0.1% has the most obvious effect on improving the compressive strength, but a hybrid fiber content of 0.2% exhibits a negative effect on the compressive strength. The addition of BF and PF can increase the flexural strength and the expansion tortuosity of the fracture cracks, thus enhancing the ductility of concrete. The hybrid fibers with content of 0.1% are most beneficial to increase the flexural strength. However, the ductility of concrete and the tortuosity of fracture crack decrease with the matrix strength, and the improvement proportion of fibers on the flexural strength also decreases. When the BF and PF are mixed, compared to the case of single fiber added, there is no significant change in the damage of BF, whereas the damage of PF is more severe. The flexural toughness index FTδ effectively characterizes the change in the flexural toughness of BPRC. The hybrid fiber contents of 0.1% and 0.2% exhibit the most significant improving effect on FT-l/600 and FT-l/150, respectively. Considering the influence of fibers on the compressive strength, flexural strength and flexural toughness of concrete, a hybrid content of 0.1% is the optimal choice of fiber content. A prediction model for flexural strength of BPRC is proposed based on the composite material theory.

Flexural Strength of a Hybrid Member for Culverts Consisting of Mortar-filled Steel Tubes Laterally Connected by Headed Reinforcements

조선규,김성일,박덕혐,이종민 한국강구조학회 2009 International Journal of Steel Structures Vol.9 No.3

In this study, the temporary structural system for a trenchless method was developed. The developed structural system is a type of hybrid member consisting of mortar-filled steel tubes laterally connected by headed reinforcements. This lateral connection gives this system not only longitudinal but also lateral stiffness. Experimental studies were carried out to evaluate the flexural strength of the developed hybrid structural system. Behaviors of each component of this structural system, such as wing plate, connection plate and headed reinforcement were also studied. Experimental results showed that the developed system had superb flexural strength. The wing plate and connection plate had a positive effect on the flexural strength. Based on the experimental results, a simple design equation to evaluate the flexural strength of the developed structural system was suggested and compared with experimental results. In this study, the temporary structural system for a trenchless method was developed. The developed structural system is a type of hybrid member consisting of mortar-filled steel tubes laterally connected by headed reinforcements. This lateral connection gives this system not only longitudinal but also lateral stiffness. Experimental studies were carried out to evaluate the flexural strength of the developed hybrid structural system. Behaviors of each component of this structural system, such as wing plate, connection plate and headed reinforcement were also studied. Experimental results showed that the developed system had superb flexural strength. The wing plate and connection plate had a positive effect on the flexural strength. Based on the experimental results, a simple design equation to evaluate the flexural strength of the developed structural system was suggested and compared with experimental results.

바잘트 섬유 시트로 보강한 철근콘크리트 보의 휨모멘트 예측식 제안

김대진,서상욱,최기봉 한국복합신소재구조학회 2020 복합신소재구조학회논문집 Vol.11 No.4

Fiber-reinforced polymer (FRP) sheets are utilized in structures because of their ease of manufacture and application. Studies have been conducted to predict the flexural strength of reinforced concrete strengthened with FRP sheets. However, these investigations are mainly limited to carbon fiber and glass fiber. In this study on basalt fiber sheets, the mechanical properties of basalt fiber sheets and flexural strength of reinforced concrete beams strengthened with basalt fiber sheets were investigated by mechanical property tests and flexural tests, respectively. Furthermore, a new equation for predicting the flexural strength of reinforced concrete beams strengthened with basalt fiber sheets is proposed. The flexural strength was predicted using the strength design method, and the American Concrete Institute (ACI) design code. The values of the experimentally-to-predicted flexural strength ratios by the strength design method, ACI design code, and Park (2005) are 0.88, 0.92, 0.97, respectively. These prediction methods overestimate the flexural strength, whereas, the proposed equation predicts an experimental-to-predicted flexural strength ratio of 1.00, and predicts a more reliable flexural strength. FRP 시트(Sheet)를 활용한 보강 공법은 제작 과정에서의 간편함과 시공의 용이성으로 현장에서 다수 적용되고 있으며, 기존 연구자들은 FRP 시트로 보강한 철근콘크리트의 휨강도를 예측하기 위한 연구를 진행하였다. 그러나 이는 주로 탄소섬유와 유리 섬유에 한정되어 있었다. 이 연구에서는 바잘트 섬유시트의 역학적 성질을 파악하기 위하여 물성 시험을 수행하였으며, 바잘트 섬유시트로 보강한 철근콘크리트 보의 휨실험을 수행하였다. 또한 그 결과 값을 비교 분석하여 기존 연구를 바탕으로 바잘트 섬유 시트로 보강한 철근콘크리트 보의 휨모멘트 예측식을 제안하였다. 강도설계법, ACI440.2R (2017) 그리고 Park et al. (2005)의 예측값을 검토한 결과, 강도설계법은 실험값과 예측값의 비가 0.88로나타났으며, ACI440.2R (2017) 설계식은 0.92, Park et al. (2005)은 0.97로 나타나 기존의 해석 방법은 휨모멘트를 과대평가하는 것으로 나타났다. 본 연구의 제안식은 실험값과 예측값의 비가 1.00으로 나타나 휨모멘트를 안전측으로 예측하는 것으로 나타났다.

Relationship between flexural or splitting tensile strength and compressive strength of roller-compacted concrete

Chhorn Chamroeun,Han Seung Hwan,Chon Beom Jun,Lee Seung Woo 한국도로학회 2015 한국도로학회 학술발표회 논문집 Vol.2015 No.10

More Roller-compacted concrete (RCC) is a dry concrete consisted of same materials as conventional concrete with different proportioning which requires compaction effort in order to reach its final form. Thus, both hydration and aggregate interlock play important roles in its strength augmentation. Flexural strength, an important factor in pavement design and fatigue cracking resistance, can be difficult to be obtained at in-situ and may be subjected to high variability. Even though its compressive strength is relatively high compared to conventional concrete with similar binder content, the relationship between compressive strength and flexural or tensile strength were not well defined. The goal of this research is to compare the relationship between compressive strength and flexural strength as well as the relationship between compressive strength and splitting tensile strength of RCC with those of conventional concrete using various equations suggested in other researches and also to determine new regression equations for estimating RCC’s flexural and splitting tensile strength. The positive result of RCC’s flexural strength was found; it was higher than majority of predicted values from conventional concrete for the same compressive strength. In contrast, RCC’s splitting tensile strength was relatively low compared to that of conventional concrete for the same compressive strength. Power equations were learned to be suitable for relationship between compressive and flexural strengths as well as relationship between compressive and splitting tensile strengths.

COMPARISON OF MECHANICAL PROPERTIES OF VARIOUS POST AND CORE MATERIALS

Ahn Seung-Geun,Sorensen John A. The Korean Academy of Prosthodonitics 2003 대한치과보철학회지 Vol.41 No.3

Statement of problem: Many kinds of post and core systems are in the market, but there are no clear selection criteria for them. Purpose: The purpose of this study was to compare the flexural strength and modulus of elasticity of core materials, and measure the bending strength of post systems made of a variety of materials. Material and Methods: The flexural strength and elastic modulus of thirteen kinds core buildup materials were measured on beams of specimens of $2.0{\times}2.0{\times}24{\pm}0.1mm$. Ten specimens per group were fabricated and loaded on an lnstron testing machine at a crosshead speed of 0.25mm/min. A test span of 20 mm was used. The failure loads were recorded and flexural strength calculated with the measured dimensions. The elastic modulus was calculated from the slopes of the linear portions of the stress-stram graphs. Also nine kinds commercially available prefabricated posts made of various materials with similar nominal diameters, approximately 1.25mm, were loaded in a three-point bend test until plastic deformation or failure occurred. Ten posts per group were tested and the obtained data were anaylzed with analysis of variance and compared with the Tukey multiple comparison tests. Results: Clearfil Photo Core and Luxacore had flexural strengths approaching amalgam, but its modulus of elasticity was only about 15% of that of amalgam. The strengths of the glass ionomer and resin modified glass ionomer were very low. The heat pressed glass ceramic core had a high elastic modulus but a relatively low flexural strength approximating that of the lower strength composite resin core materials. The stainless steel, zirconia and carbon fiber post exhibited high bending strengths. The glass fiber posts displayed strengths that were approximately half of the higher strength posts. Conclusion: When moderate amounts of coronal tooth structure are to be replaced by a post and core on an anterior tooth, a prefabricated post and high strength, high elastic modulus core may be suitable. CLINICAL IMPLICATIONS In this study several newly introduced post and core systems demonstrated satisfactory physical properties. However when the higher stress situation exists with only a minimal ferrule extension remaining a cast post and core or zirconia post and pressed core are desirable.

이형 콘크리트 블록의 강도 평가방법에 관한 연구

임무광,박대근,류성우,조윤호 한국도로학회 2014 한국도로학회논문집 Vol.16 No.2

PURPOSES: This study aims to develop a strength test method for irregularly shaped concrete block paver. METHODS : Ten (10) different types of concrete block pavers including porous and dense blocks were tested for strength capacities. Destructive and non-destructive methods were used to develop a strength test method for irregularly shaped concrete block paver. The flexuralstrength evaluation was conducted in accordance to KS F 4419, while compressive strength was conducted with a 45.7mm-diameter corespecimen. The impact echo test method was used to evaluate the elastic modulus. Finally, regression analysis was used to investigate therelationship between flexural strength, compressive strength and elastic modulus based on their corresponding test results. RESULTS : The flexural strength of the tested block pavers ranged from 4MPa to 10MPa. At 95% confidence level, the coefficients ofdetermination between compressive-flexural strength relationship and compressive strength-elastic modulus relationship were 0.94 and 0.84,respectively. These coefficients signified high correlation. CONCLUSIONS : Using the test method proposed in this study, it will be easier to evaluate the strength of irregularly shaped concreteblock pavers through impact echo test and compressive test, instead of the flexural test. Relative to the flexural strength requirement of 5MPa,the minimum values of compressive strength and elastic modulus, as proposed, are 13.0MPa and 25.0GPa, respectively.