• Computers and Concrete
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• v.25 no.1
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• pp.83-94
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• 2020

The use of fly ash in modern-day concrete technology aiming sustainable constructions is on rapid rise. Fly ash, a spinoff from coal calcined thermal power plants with pozzolanic properties is used for cement replacement in concrete. Fly ash concrete is cost effective, which modifies and improves the fresh and hardened properties of concrete and additionally addresses the disposal and storage issues of fly ash. Soft computing techniques have gained attention in the civil engineering field which addresses the drawbacks of classical experimental and computational methods of determining the concrete compressive strength with varying percentages of fly ash. In this study, models based on soft computing techniques employed for the prediction of the compressive strengths of fly ash concrete are collected from literature. They are classified in a categorical way of concrete strengths such as control concrete, high strength concrete, high performance concrete, self-compacting concrete, and other concretes pertaining to the soft computing techniques usage. The performance of models in terms of statistical measures such as mean square error, root mean square error, coefficient of correlation, etc. has shown that soft computing techniques have potential applications for predicting the fly ash concrete compressive strengths.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2006.05a
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• pp.19-22
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• 2006

The quantity of Recycled concrete powder is increased, because it hal been ever so often crushing for production of a good quality recycled aggregates This Study is on the Development of Concrete-Product by Using Recycled Concrete Powder and alto for know performance of concrete-producted having low water contents and it is to know for all of performance of concrete-producted having low water contents The conclusions of this study are following. The use of replacement cement is not effective, because it has strengh of less than 10MPa But It is possible to develop high strength concrete-producted having 39MPa above compressive strength by using recycled concrete powder. Because strength enhancement effects by recycled concrete powder are responsible to optimum grading. The conclusions of this study are following. The use of replacement cement is not effective, because it has strengh of less than 10MPa. It is possible to develop high strength concrete-producted having 39MPa above compressive strength by using recycled concrete powder. Because strength enhancement effects by recycled concrete powder are responsible to optimum grading.

• KCI Concrete Journal
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• v.14 no.4
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• pp.139-144
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• 2002

Concrete filled FRP tube has lately attracted attention as the member that can substitute the conventional reinforced concrete. Glass fiber and carbon fiber are some of available materials for FRP tube. Carbon tube is filament wound with specified winding angle to meet the appropriate capacity demands. Confinement effect of carbon tube is varied according to winding angle. In this study, a total 4 of large scale circular specimens of 30cm diameter and 60cm height is tested. To estimate the effect of winding angle and thickness of carbon tube on the increased confined compressive strength, the test tube are wound with $\pm45^{\circ}\;and\;\pm30^{\circ}$ with two types of thickness, 2mm and 3mm, respectively. It is shown that effectively increased confined strength and ductility are observed from the specimens with $\pm45^{\circ}$ winding angle than $\pm30^{\circ}$ winding angle. Increasing thickness is not as effective as adjusting winding angle for the confinement of concrete core.

• Computers and Concrete
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• v.16 no.1
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• pp.179-190
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• 2015

An experimental program has been carried out to investigate the effect of edge-slope on compressive strength of concrete specimens. In this study, effect of such slope was investigated by testing 100 standard cylinder specimens and 40 standard cubes. When molds are put on a slanted place, wet concrete starts to flow through the open end of mold. It keeps flowing until it reaches to a parallel surface with the place over which it was placed. That creates a sloped surface over the loading area. Experimental results revealed significant relationships between failure loads and slope of loading surface for cylinders. Angled cracks occurred in sloped cylinder specimens. Tension cracks occurred in cube specimens. Fracture mechanisms were also evaluated by using finite element analyses approach. Experiments yielded an exponential curve with bandwidth for cylinders. Average value of curve is $y={\frac{\pi}{2}}e^{-cf}$ between slope and compressive strength. Inclination is much effective parameter for cylinders than cubes.

• Proceedings of the Korea Concrete Institute Conference
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• 1992.10a
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• pp.155-160
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• 1992

In this study , the size effect on diagonal shear failure of reinforced high strength concrete beams was investigated, For this purpose, ten singly reinforced high strength concrete beams without web reinforcement were tested for five different dimensions of effective depth which were varied from 67mm to 915mm. The compressive strength of concrete used in this study was 53.7 MPa. One type of reinforcing bar with nominal yield strength of 400 MPa was used. Test results were analyzed and compared with strength predicted by ACI code equation, Zutty's equation and Bazant &Kim's equation. As the results, ACI code equation was seriously unconservative for beams with d of 915mm. Bazant & Kim's equation predicted well the trend of test data. Within the scope of this study, there was no clear difference in size effect with variation of compressive strength of concrete.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.122-129
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• 2015

In this study, a prediction model for the effective compressive strength of corner columns with intervening normal strength concrete slabs was developed. A structural analogy between high-strength concrete column-normal strength concrete slab joint and brick masonry was used to develop the prediction model. In addition, the aspect ratio of slab thickness to column dimension was considered in the models. The reliability of the new prediction model was evaluated by comparison with experimental results and its superiority was demonstrated by comparison with previous models proposed by design codes and other researchers. As a result, with average test-to-predicted ratios of 1.09, a standard deviation of 0.15, the newly developed equation provided superior predictions in terms of accuracy and consistency over all of the existing effective strength prediction approaches including KCI structural concrete design code (2012).

• Proceedings of the Korea Concrete Institute Conference
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• 1994.04a
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• pp.203-208
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• 1994

These tests were conducted to get a device high strength concrete products in factory using admixtures for high strength concrete. The superplasticzer was used to compensate low slump of base concrete keeping its slump up about $6\pm1cm$. To examine the property for strength revelation of concrete using admixtures for high strength concrete, steam and standard curing were compared each other. Test results show that admixtures for high strength concrete is effective in steam curing and compressive strength 500kgf/$\textrm{cm}^2$ is obtained at one day, 650kgf/$\textrm{cm}^2$ at 28days as added to concrete at the ratio of 10-15%, and 740kgf/$\textrm{cm}^2$ at the ratio of 30%. Therefore admixtures for high strength concrete is effective in steam curing and make it possible to get high strength concrete using only steam curing not using autoclave curing.

• Steel and Composite Structures
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• v.39 no.3
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• pp.307-318
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• 2021

Utilizing fibers is an effective way to avoid the brittle behavior of the conventional concrete and can enhance its ductility. In particular, propylene fibers can improve concrete properties, including energy absorption, physical and mechanical properties, controlling shrinkage cracks. The increase of fiber density leads to an increase of the overlapping surface of the fiber of concrete and, in turn, a decrease of cracks developed in the concrete. However, the workability of fiber reinforced concrete tends to be lower than the conventional concrete owing mainly to the hairline thickness and excessive concentration of fibers. The low slump of concrete impedes the construction of reinforced concrete members. In this research, we study if the utilization of magnetic water can alleviate the workability issue of young fiber reinforced concrete. To this end, the compressive and flexural strength of four types of concrete (conventional concrete, fiber reinforced concrete, magnetic concrete, magnetic fiber-reinforced concrete) is studied and compared at three different ages of 7, 14, and 28 days. In order to study the influence of the fiber density and length, a study on specimens with three different fiber density (1, 2, 5 kg of fiber in each cubic meter of concrete) and fiber length (6, 12, 18 mm) is undertaken. The result shows the magnetic fiber concrete can result in an increase of the flexural and compressive strength of concrete at higher ages.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.1789-1795
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• 2007

Railroad, the structure maintenance and restoration project was increased and widely performed in concrete pavement road and airport, building at downtown area, bridge abutment, and other concrete structures. Especially, the ground reinforcement technique by quick-reaction expansible resins is the most effective countermeasures against differential settlement and undesired deformation of structure. In this paper, the unconfined compressive strength and some environmental related tests were conducted to evaluate compressive strength and environmental effect of quick-reaction expansive resins and soil mixtures. Also, three case histories of concrete structure and railroad restoration project are presented. Based on the laboratory test, the quick-reaction expansible resins and soil mixture represent the sufficient compressive strength and the leachate material is satisfied the environmental regulation limits. As a result of this study, the structure restoration technology using quick-reaction expansible resins is very effective for restoration of differential settlement and deformation, and it is environmentally sustainable technology.

• Journal of The Korean Society of Agricultural Engineers
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• v.52 no.3
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• pp.9-17
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• 2010

This study aims to evaluate a porous concrete using hwang-toh, blast furnace slag and blast furnace slag (BFS) cement instead of type I cement. The tests that were carried out to analysis the properties of porous hwang-toh BFS cement concrete included compressive strength, continuous void ratio, absorption rate, and pH value, repeated freezing and thawing test were conducted. Test results indicated that the performance in porous hwang-toh concrete are effective on the kaoline based binder materials. The pH value were shown in about 9.5 ~ 8.5. The compressive strength was increased and void ratio was decreased with increasing the kaoline based binder materials, respectively. The void ratio and compressive strength were in the range of about 21 ~ 30 %, 8 ~ 13 MPa, respectively. The increased in void ratio of more than 25 % is showed to reduce the resistance of repeated freezing and thawing. Also, the resistance of repeated freezing of thawing and the compressive strength of porous hwang-toh BFS cement concrete are independent with hwang-toh content and BFS cement amount. But, the void ratio was decreased with increasing the high volume hwang-toh contents (more than 15 %).