• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.237-243
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• 2001

The prediction model is proposed to estimate the variation of compressive strength of fly ash concrete with aging. After analyzing the experimental result with the model, the regression results are presented according to fly ash replacement content and water-cement ratio. Based on the regression results, the influence of fly ash replacement content and water-cement ratio on apparent activation energy was investigated. According to the analysis, the model provides a good estimate of compressive strength development of fly ash concrete with aging. As the fly ash replacement content increases, the limiting relative compressive strength and initial apparent activation energy become greater. The concrete with water-cement ratio smaller than 0.40 shows that the limiting relative compressive strength and apparent activation energy are nearly constant according to water-cement ratio. But, the concrete with water-cement ratio greater than 0.40 has the increasing limiting relative compressive strength and apparent activation energy with increasing water-cement ratio.

• Computers and Concrete
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• v.5 no.5
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• pp.491-501
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• 2008

The present study verifies compressive strength, ultrasonic pulse velocity, electrical resistance,permeable ratio, and shrinkage from waste glass controlled low strength materials (WGCLSM) and early-high-strength WGCSLM specimens, by replacing the sand with waste glass percentages of 0%, 10%,20%, and 30%. This study reveals that increasing amounts of waste LCD glass incorporated into concrete increases WGCLSM fluidity and reduces the setting time, resulting in good working properties. By increasing the glass to sand replacement ratio, the compressive strength decreases to achieve low-strength effects. Furthermore, the electrical resistance also rises as a result of increasing the glass to sand replacement ratio. Early-high-strength WGCSLM aged 28 days has twice the electrical resistance compared to general WGCSLM. Early-high-strength WGCSLM aged 7 days has a higher ultrasonic pulse velocity similar to WGCSLM aged 28 days. The variation of length with age of different compositions is all within the tolerance range of 0.025%. This study demonstrates that the proper composition ratio of waste LCD glass to sand in early-high-strength WGCSLM can be determined by using different amounts of glass-sand. A mechanism for LCD optical waste glass usage can be established to achieve industrial waste minimization, resource recycling, and economic security.

• Computers and Concrete
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• v.9 no.2
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• pp.153-169
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• 2012

The contribution of steel fibers on the 28-day compressive strength of high-performance steel fiber reinforced concrete was investigated, is presented. An extensive experimentation was carried out over water-cementitious materials (w/cm) ratios ranging from 0.25 to 0.40, with silica fume-cementitious materials ratios from 0.05 to 0.15, and fiber volume fractions ($V_f$= 0.0, 0.5, 1.0 and 1.5%) with the aspect ratios of 80 and 53. Based on the test results of 44 concrete mixes, mathematical model was developed using statistical methods to quantify the effect of fiber content on compressive strength of HPSFRC in terms of fiber reinforcing index. The expression, being developed with strength ratios and not with absolute values of strengths, is independent of specimen parameters and is applicable to wide range of w/cm ratios, and used in the mix design of steel fiber reinforced concrete. The estimated strengths are within ${\pm}3.2%$ of the actual values. The model was tested for the strength results of 14 mixes having fiber aspect ratio of 53. On examining the validity of the proposed model, there exists a good correlation between the predicted values and the experimental values of different researchers. Equation is also proposed for the size effect of the concrete specimens.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.1
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• pp.140-144
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• 2010

In recent years there has been a growing interest for the use of natural fibers in composite applications due to their low cost, environmental friendliness, and good mechanical properties. The purpose of this study is to determine the characteristic of bending strength on bamboo fiber reinforced polymer composites. The parameters of RTM process depend on the weight ratio of bamboo fiber and resin, the number of bamboo ply and amount of hardening agent. Besides the existence of pore in composites according to vacuum time investigated a effect on mechanical properties of reinforced polymer composites. Test result shows that compressive strength was a maximum(approximately 1,840kgf/$cm^2$) value when weight ratio of resin was 12%.

• Economic and Environmental Geology
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• v.23 no.4
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• pp.411-424
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• 1990

Mechanical, physical and petrographic properties of seventeen marble specimens collected from ten marble mines in Korea were investigated. Studied marbles were mainly composed of calcite, dolomite, and various amounts of serpentine, tremolite, olivine, quartz and opaque minerals. Complete and sutured textures were dominant. Compressive strength measured normal to the bedding plane is larger almost two times than that measured parallel to the bedding plane. From the results of Shore hardness test on marbles, water content was an important factor to decrease Shore hardness values. Engineering geological properties, especially, compressive strength, Young's modulus, wear resistance and water absorption could be controlled by the presence of quartz, and the type of marble texture. Water absorption-porosity, compressive strength-Young's modulus, and impact strength index-Los Angeles abrasion couples show good correlation. According to the comparative utility as commercial stone, it could be concluded that marbles from the Banglim mine, Songbo mine, Kwangdeok mine and Bongjeong mine were superior to that of other studied marbles.

• Computers and Concrete
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• v.19 no.5
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• pp.477-488
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• 2017

In this paper, an innovative technique for finite element (FE) modeling of steel tube-confined concrete (STCC) columns with active confinement under axial compressive loading is presented. In this method, a new constitutive model for the stress-strain relationship of actively-confined concrete is proposed. In total, 14 series of experimental STCC stub columns having active confinement were modeled using the ABAQUS software. The results obtained from the 3D model including the compressive strength at the initial peak point and failure point, as well as the axial and lateral stress-strain curves were compared with the experimental results to verify the accuracy of the 3D model. It was found that there existed a good agreement between them. A parametric study was conducted to investigate the effect of the concrete compressive strength, steel tube wall thickness, and pre-stressing level on the behavior of STCC columns with active confinement. The results indicated that increasing the concrete core's compressive strength leads to an increase in the compressive strength of the active composite column as well as its earlier failure. Furthermore, a reduction in the tube external diameter-to-wall thickness ratio affects the axial stress-strain curve and the confining pressure, while increasing the pre-stressing level has a negligible effect on the two.

• Advances in concrete construction
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• v.5 no.6
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• pp.563-573
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• 2017

Transparency, excellent toughness, thermal stability and a very good dimensional stability make Polycarbonate (PC) one of the most widely used engineering thermoplastics. Polycarbonate market include electronics, automotive, construction, optical media and packaging. One alternative for reducing the environmental pollution caused by polycarbonate from electronic waste (e-waste), is to use it in cement concretes. In this work, physical and chemical characterization of recycled polycarbonate from electronic waste was made, through the analysis by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and scanning electron microscope (SEM). Then cement concrete was made with Portland cement, sand, gravel, water, and this recycled polycarbonate. Specimens without polycarbonate were produced for comparison purposes. The effect of the particle sizes and concentrations of recycled polycarbonate within the concrete, on the compressive strength and density was studied. Results show that compressive strength values and equilibrium density of concrete depend on the polycarbonate particle sizes and its concentrations; particularly the highest compressive strength values were 20% higher than that for concrete without polycarbonate particles. Moreover, morphological, structural and crystallinity characteristics of recycled polycarbonate, are suitable for to be mixed into concrete.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.36 no.2
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• pp.127-136
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• 2020

Prism compressive strength is the most influential parameter to evaluate the seismic performance of non-structural concrete brick masonry walls, and is affected by the practice and workmanship of masonry workers. This study experimentally investigates the influence of workmanship on prism compressive strength throughout the compressive test with prism specimens constructed according to masonry workmanship. To do this, the workmanship is categorized into good, fair, and poor conditions which are statistically evaluated with thickness and indentation depth of bed-joints. Then, the effect of workmanship on the structural properties of masonry prisms is evaluated by investigating relations between properties such as their compressive strength, elastic modulus and numerical parameters such as thickness, filling of bed-joints. This study demonstrates that the indentation depth is more important parameter for structural properties of masonry prisms and masonry prisms with loss in bed-joint area less than of 7% can be in fair condition.

• Magazine of the Korea Concrete Institute
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• v.11 no.2
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• pp.95-103
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• 1999

The reduction phenomena of concrete compressive strength with the size of specimens have been extensively investigated, but till now the adequate analysis technique is not fixed. The existing research results show that the bigger the member size, the smaller the strength. This means the nonlinear fracture mechanics theory is needed in order to analyze the fracture behaviors of concrete and the size effect. There is a few model equations that is to predict the size effect of compressive strength of standard and non-standard cylindrical specimen. However, theses equations did not considered the difference of fracturing mechanism which depends on the strength level. In this paper, model equations to predict compressive strength of concrete considering the size effect and strength level are suggested. The size effect model suggested in this paper shows good prediction compared with the existing test data of various concrete size and strength level.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.145-148
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• 2006

Schmidt hammer and ultra-sonic method are commonly used for crushed sand concrete compressive strength test in a construction field. At present, various of equations for prediction of strength are present, which have been used in a construction field. The purpose of this study is to evaluate the correlation between prediction strength by presentation equations and destructive strength to test specimen, and find out which is a suitable equation for the construction site, In this study, a strength test was carried out destructive test by means of core sampling and traditional test. Non-destructive test was conducted Schmidt hammer and ultra-sonic method, the experimental parameter were concrete age, curing condition, test method and strength level. It is demonstrated that the correlation behavior of crushed sand concrete strength in this study good due to the perform analysis of correlation between core, destructive strength and non-destructive strength.