• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.287-295
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• 2010

In this study, ordinary Portland cement was used and the air void was minimized by using minute quartz as the filler. In addition, steel fibers were used to mitigate the brittle failure problem associated with high strength concrete. This study is in progress to make an Ultra-high strength powdered concrete (UHSPC) which has compressive strength over 300 MPa. To increase the strength of concrete, we have compared and analyzed the compressive strengths of the concretes with different mix proportions and curing conditions by selecting quartz sand, dolomite, bauxite, ferro silicon which have diameters less than 0.6 mm and can increase the bond strength of the transition zone. Ultra-high strength powdered concrete, which is different from conventional concrete, is highly influenced by the materials in the mix. In the study, the highest compressive strength of the powdered concrete was obtained when it is prepared with ferro silicon, followed in order by Bauxite, Dolomite, and Quartz sand. The amount of ferro silicon, when the highest strength was obtained, was 110%, of the weight of the cement. SEM analysis of the UHSPC showed that significant formation of C-S-H and Tobermorite due to high temperature and pressure curing. Production of Ultrahigh strength powdered concrete which has 28-day compressive strength upto 341MPa has been successfully achieved by the following factors; steel fiber reinforcement, fine particled aggregates, and the filling powder to minimize the void space, and the reactive materials.

• Journal of the Korea Concrete Institute
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• v.27 no.3
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• pp.253-263
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• 2015

Ultra-high strength concrete which have 100 MPa compressive strength or higher can be developed applying RPC(Reactive Powder Concrete). Preventing brittle failure under compression and tension, ultra-high strength concrete usually use the steel fibers as reinforcements. For the effective use of steel fiber reinforced ultra-high strength concrete, estimation of tensile strength is very important. However, there are insufficient research results are available with no relation between them. Therefore, in this study, correlation between compressive strength and tensile strength of ultra-high strength concrete was investigated by test and statistical analysis. According to test results, increasing tendency of tensile strength was also shown in the range of ultra-high strength. Evaluation of test results of this study and collected test results were carried out. Using 284 splitting test specimens and 265 flexural test specimens, equations suggested by previous researchers cannot be applied to ultra-high strength concrete. Therefore, using database and test results, regression analysis was carried out and we suggested new equation for splitting and flexural tensile strength of steel fiber reinforced ultra-high strength concrete.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.6
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• pp.2195-2209
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• 2013

The effective strength of concrete struts must be determined accurately for the reliable strut-tie model analysis and design of structural concrete. In this study, the equations of the effective strength, which are useful for the three types of determinate and indeterminate strut-tie models of reinforced concrete deep beams employed in current design codes, are proposed. The effects of shear span-to-effective depth ratio, compressive strength of concrete, and flexural and shear reinforcement ratios are reflected in the development of the proposed equations. To examine the appropriateness of the proposed equations, the strengths of 241 reinforced concrete deep beams, all tested to shear failure, are evaluated by using the three types of strut-tie models with the existing and proposed equations.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.1-10
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• 2013

In this study utilize industry product for OPC(ordinary portland cement) and BFS(blast furnace slag) mixing concrete early age compressive strength elevation and executed study for high strength binder. Association ratio of industry product for high strength binder manufacture is Titanogypsum (4) : Limestone (3) : Waterworks Sludge by ratio of (3) as it is proper move. high strength binder mixing rate appeared that (7~9) % are proper via preliminary test. Could confirm that display high compressive strength incidence rate in early age than plain harmony according as mix high strength binder mixing concrete compressive strength high strength binder. Also, high strength binder generality that give function than high strength binder used in existing displayed more excellent intensity, and compressive strength displayed result that multiply single breadth according as high strength binder substitute that give function increases.

• Journal of Korean Society of Steel Construction
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• v.23 no.3
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• pp.385-395
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• 2011

The flexural strength of composite HSB hybrid I-girders under positive moment is investigated by the moment-curvature analysis method to evaluate the applicability of the current AASHTO LRFD design specification to such girders. The hybrid girders are assumed to have the top flange and the web fabricated from HSB600 steel and the bottom flange made of HSB800 steel. More than 6,200-composite I-girder sections that satisfy the section proportion limits of AASHTOL RFD specifications are generatedby the random sampling technique to consider a statistically meaningful wide range of section properties. The flexural capacities of the sections are calculated by the nonlinear moment-curvature analysis in which the HSB600 and HSB800 steels are modeled as an elastoplastic, strain-hardening material and the concrete as CEB-FIP model. The effects of ductility ratio and compressive strength of concrete slab on the flexural strength of composite hybrid girders make of HSB steels are analyzed. Numerical results indicated that the current AASHTO-LRFD equation can be used to calculate the flexural strength of composite hybrid girders fabricated from HSB steel.

• Journal of the Korea Concrete Institute
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• v.28 no.1
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• pp.105-113
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• 2016

Most studies on mechanical properties of concrete with recycled aggregate was focused on the concrete with compressive strength of less than 40 MPa. Therefore, this paper concerns the compressive strength and mechanical properties of concrete with compressive strength of greater than 40 MPa containing recycled coarse aggregate (RCA). The experimental parameters were compressive strength level and replacement ratio of RCA. Compressive strength level was 45 and 60 MPa, and replacement ratio of RCA was 30, 50, 70 and 100%. The results of the test were discussed: compressive strength, elastic modulus, split tensile strength and modulus of rupture. Test results of elastic modulus were compared to the design code predictions. The design code predictions for elastic modulus overestimated the experimental results. However, the design code predictions for modulus of rupture were generally in agreement with the measured values.

• Fire Science and Engineering
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• v.23 no.4
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• pp.1-6
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• 2009

High Strength Concrete has a disadvantage of the brittle failure under fire due to the spalling. It is reported that spalling is caused by the vapor pressure under fire and polypropylene (PP) fiber has an important role in protecting from spalling. The silica fume which is essentially mixed in high strength concrete decrease the permeability of concrete, and this will increase the degree of spalling. The fire resistance characteristics of high-strength reinforced concrete columns with various contents of PP fiber and silica fume were investigated in this study. In results, the ratio of unstressed residual strength of columns increases as the content of PP fiber increases from 0% to 0.2% and the ratio decreases as the content of silica fume increases from 7% to 21%.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.4
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• pp.305-311
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• 2005

Shotcrete adhesive strength in large section tunnels in jointed rock masses plays an important role in preventing rock block from falling and shotcrete debonding due to blasting vibration. Nevertheless, it has not been considered as a major factor such as shotcrete compressive strength in design and construction. For this reason, the purpose of this study is to analyze the effect on shotcrete adhesive strength for large-sectioned tunnels. First, the parametric study using numerical model similar to Holmgren's punch-loaded test was executed for various range of adhesive strength. It shows that the shotcrete bearing capacity is linearly proportioned to the adhesive strength between shotcrete layer and blocks. And then, distinct element analysis of a jointed rock tunnel for an adhesive strength of 1 MPa and a conventional fully-bonded condition between the shotcrete layer and the excavation face was compared in order to evaluate the effect of the shotcrete adhesive strength.

• Composites Research
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• v.16 no.5
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• pp.15-20
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• 2003

In this paper, the fracture strength of the surface damaged laminates was predicted by applying the fracture strengths of the unflawed and flawed laminates. For prediction, the theoretical equation about the fracture strength of laminates was simplified applying classical laminate theory and was applied to the surface damaged laminates. Lagace's and Tsai's experimental data were used for verifying the theoretical equation. Moreover, to verify the theoretical prediction, an experiment was performed. Surface unflawed laminate and flawed laminates were fabricated and the experiments were made and these results were compared with theoretical predictions. The specimens' fiber direction was same to the tensile direction and the theoretical predictions and the experimental results were showed good agreement. Therefore, by this equation, the fracture strength of structures made of composites will be able to be predicted when the surface of the structures was damaged.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.1
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• pp.127-135
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• 2005

Recently, as the concrete structures are becoming bigger, higher, longer and more special, high strength concrete is demanded. But the fracture behavior of high strength concrete is shown more brittle than that of the normal strength concrete. Therefore, in order to improve the brittle fracture behavior and crack propagation resistance, ACI Committee363 has been recommend the use of fiber reinforced concrete which showed superior property against the crack propagation resistance. On the other hand, bridges, concrete pavements and railroads etc. have been exposed to the repetition loading at least several million times during the service life. Therefore, fatigue load is dominantly most of all, but it is very difficult to estimate the suitable fatigue strength calculated by fatigue load. In this research, in order to examine the fatigue behavior of hybrid fiber reinforced high strength concrete, the static and fatigue tests were carried out. And from these results, it was estimated the fatigue strength of hybrid fiber reinforced high strength concrete.