• Advances in concrete construction
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• v.7 no.4
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• pp.219-229
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• 2019

This paper presents an experimental study on the structural performance of an innovative ultra-high performance fiber reinforced concrete (UHPFRC) deck with coarse aggregate of composite bridge under shear force. Test parameters included curing method and shear span-to-height ratio. Test results indicated that more short fine cracks developed beside the existing cracks due to the randomly dispersed fibers, resulting in re-distributing and homogenizing of the concrete stress beside cracks and allowing for the occurrence of more cracks with small spacing compared to normal strength concrete beams. Curing methods, incorporating steam curing and natural curing, did not have obvious effect on the nominal bending cracking strength and the ultimate strength of the test specimens. Shear reinforcement need not be provided for UHPFRC decks with a fiber volume fraction of 2%. UHPFRC decks showed superior load resistance ability after the appearance of cracks and excellent post-cracking deformability. Lastly, the current shear provisions were evaluated by the test results.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2004.10a
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• pp.542-549
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• 2004

The compressive strength of concrete is commonly used criterion in producing concrete. However, the tests on the compressive strength are complicated and time-consuming. More importantly, it is too late to make improvement even if the test result does not satisfy the required strength, since the test is usually performed at the 28th day after the placement of concrete at the construction site. Therefore, accurate and realistic strength estimation before the placement of concrete is being highly required. In this study, the estimation of the compressive strength of concrete was performed by probabilistic neural network (PNN) on the basis of concrete mix proportions. The estimation performance of PNN was improved by considering the correlation between input data and targeted output value. Adaptive probabilistic neural network (APNN) was proposed to automatically calculate the smoothing parameter in the conventional PNN by using the scheme of dynamic decay adjustment algorithm. The conventional PNN and APNN were applied to predict the compressive strength of concrete using actual test data of a concrete company. APNN showed better results than the conventional PNN in predicting the compressive strength of concrete.

• Journal of the Korea Concrete Institute
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• v.12 no.1
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• pp.33-44
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• 2000

Since the mechanism of chloride diffusion and its ratio in concrete depend on structural conditions and concrete as a micro-structure, if these are analyzed quantitatively, the long-term ageing of structures can be predicted. Although, a quantitative analysis of concrete micro-structure, in which the results are affected by various parameters, is very difficult, this can be done indirectly by the durability test of concrete. In this study, the compressive strength, void ratio and air permeability of concrete. In this study, the compressive strength, void ratio and air permeability of concrete are chosen as the parameters in concrete durability test, and these effects on test results are analysed according to changes of mixing properties. The relationships between parameters and chloride diffusion velocity is used for prediction models of chloride diffusion. The developed prediction models for the chloride diffusion according to mixing and physical properties, can be used to estimate the service life and corrosion initiation of reinforcing bars in marine structures.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.390-393
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• 2006

LB-DECK is used for both of permanent formwork and structural component with cast-in place concrete of concrete bridge decks. Current Korean design code recommends that concrete bridge deck with precast concrete panels have to be designed only using conventional flexural design method and does not allow the empirical design method which is based on punching shear strength of bridge deck. This paper present experimental test results of punching shear strength of concrete bridge decks with LB-DECKs. Six full-scaled concrete bridge decks, which are designed with the empirical design method, are fabricated with variation of girder spacings. Test results are presented in the paper and compared with the code predictions of ACI 318, CEB-FIP MC90. Based on the test results, it is proposed that LB-DECK is suitable to apply the empirical design method for concrete bridge decks.

• KCI Concrete Journal
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• v.11 no.3
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• pp.99-107
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• 1999

In designing the Prestressed concrete box-girder bridge. dead load, prestressing force, creep and shrinkage of concrete are the main factors which influence the camber and deflection of segmental concrete structure under construction. Among these factors the creep and shrinkage are the functions of the time-dependent property which. therefore, must be considered with time. The prediction model for estimating creep and shrinkage of concrete has been suggested by ACI, CEB/FIP, JSCE and KSCE design code and EMM, AEMM, RCM, IDM and SSM has been suggested for analytical method in consideration of time-dependent characteristics. In this study the creep test was carried out for four different curing ages of concrete which were applied to the Prestressed concrete structure at the construction site, and the results of test were compared with the values of creep prediction proposed by the design code. Also the creep test was performed with step-wise incremental stresses and the results were compared to the analytical values.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.707-710
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• 2004

This paper reported the results of mock-up test on mass concrete for transfer girder using setting time difference of super retarding agent(SRA). According to test results, two mock-up structures were made. Plain concrete without placing layer reached maximum temperature after 24hours since placement and caused surface hydration cracks at top section. However, concrete with placing layer reached maximum temperature after 72hours and surface temperature was higher than center temperature, which did not cause surface crack. After form removing, no crack was observed at side surface of plain concrete, while concrete using SRA at mid section had surface scaling and settling crack. According to coring results, concrete with placing layer had a penetration crack from top section to bottom section. Therefore, the setting time difference method to reduce hydration heat will have difficulty in applying the mass concrete for transfer girder.

• Computers and Concrete
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• v.23 no.6
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• pp.399-408
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• 2019

Structural health monitoring is important for the safety of lives and asset management. In this study, numerical models were developed for the piezoresistive behavior of smart concrete based on finite element (FE) method. Finite element models were calibrated with experimental data collected from compression test. The compression test was performed on smart concrete cube specimens with 75 mm dimensions. Smart concrete was made of cement CEM II 42.5 R, silica fume, fine and coarse crushed limestone aggregates, brass fibers and plasticizer. During the compression test, electrical resistance change and compressive strain measurements were conducted simultaneously. Smart concrete had a strong linear relationship between strain and electrical resistance change due to its piezoresistive function. The piezoresistivity of the smart concrete was modeled by FE method. Twenty-noded solid brick elements were used to model the smart concrete specimens in the finite element platform of Ansys. The numerical results were determined for strain induced resistivity change. The electrical resistivity of simulated smart concrete decreased with applied strain, as found in experimental investigation. The numerical findings are in good agreement with the experimental results.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.13-16
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• 2005

This study is aimed to investigate the strength variation of fire-damaged reinforced concrete column by non-destructive test. It is studied to infer the recovery degree of residual strength of fire-damaged concrete. For measuring the surface hardness of RC columns. Schmidt hammer test is used. Testing is performed three-times: before fire test, directly after fire test and after 20 days.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.185-186
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• 2010

For Mega foundation, concrete must have high strength and high flowability. Especially in marine environment, concrete durability becomes a significant property. In this study, high durable concrete, under marine environment, was developed. And to estimate its performance, the world's biggest Mock Up test, $4m{\times}4m{\times}4m$ size, was performed.

• Journal of the Korea Concrete Institute
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• v.11 no.4
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• pp.117-127
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• 1999

In concrete incorporating high volume ground granulated blast-furnace slag that has frozen at early age, to evaluated the results of resistance to freezing and thawing is very difficult because the hydration of the concrete increases over the duration of rapid freezing and thawing test. Hence, the dynamic modulus of elasticity of specimens after freezing and thawing will be favorable results unless the hydration effect is taken into consideration. In this study, a method of evaluating to the resistance to freezing and thawing of concrete subjected freezing at early age, in which the effect of hydration is modified for its increase during rapid freezing and thawing test, is investigated.