• Journal of the Korea Institute of Building Construction
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• v.23 no.6
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• pp.683-692
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• 2023

This research assesses the mechanical properties of concrete, utilizing both normal and lightweight aggregates, through measurements of compressive strength and ultrasonic pulse velocity. The study observed that concrete with normal aggregates exhibited higher compressive strength in its initial stages, whereas concrete with lightweight aggregates showed increased strength over time, likely attributed to the higher water absorption rate of lightweight aggregates. Ultrasonic pulse velocity generally registered higher in normal aggregate concrete, barring a specific duration, presumably due to variations in the internal pore structure of the aggregates. The correlation coefficient(R²) for the strength prediction equation, derived from the relationship between compressive strength and ultrasonic pulse velocity, exceeds 0.95. This high correlation suggests that the predictive equation based on these experimental findings is a reliable method for estimating concrete strength.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.11a
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• pp.34-35
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• 2013

In this study, the ultra high strength concrete which have 80, 130, 180MPa took the heat from 20℃ to 700℃ and the 0, 20% stress in normal condition's to evaluate stress-strain, residual compressive strength and thermal expansion deformation were evaluated. The heating speed of specimen was 0.77℃/min 20~50℃, 50℃ before the target temperature, and the other interval's heating speed was 1℃/min. As a result, the stress-strain curve of non-load specimen showed the liner behavior at high temperature when the specimen's strength increased more. If ultra high strength concrete got loads, its compressive strength tended to decrease different from the normal strength concrete. The thermal expansion deformation was expanded from a vitrification of quartz over 500℃. however, over the 600℃, it was shrinked because of the dehydration of the combined water.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.507-512
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• 2002

Prestressed concrete I-girders were used in the bridge applications in the early 1950s. During the last four decades, the most widely used girder length of bridges have been below 30 meters. The main objective of this study is to develope the alternative section for widely spaced girder of 30 meters span bridge. Girder spacing, the number of strands and compressive strength of concrete are major parameters for widely spaced girders. The optimal girder spacing is determined through the parameter studies of design using widely spaced girders. 30m span bridges of widely girder spacing must use high-strength concrete. Although the basic unit cost of concrete is higher for high-strength concrete, it may be partially or even fully offset by reduced quantities of concrete as result of the smaller number of girders used. High-strength concrete girders have more prestressing strands per girder, but the total number of strands for all of the girders is less than that required for the larger number of normal-strength concrete girders. It could design PSC-I Birdge with widely spaced girder owing to high-strength concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.589-592
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• 1999

This paper is experimental study on the flexural strength and ductility capacity of reinforced high-strength concrete beams using fly ash artificial lightweight concrete beams and five reinforced high-strength normal concrete beams with different tensile reinforcement ratio were tested to investigate their behavior. Test result show that the ratio of flexural strength between experimetal results and those by ACI code decrease as the compressive strength of concrete increase. Also, The reinforced concrete beams behave more brittly than those with equal reinforcement ratio($\rho$/$\rho$b) as the compressive strength of concrete increase.

• Computers and Concrete
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• v.30 no.6
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• pp.377-391
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• 2022

The use of carbon fiber-reinforced polymers (CFRP) has widely increased due to its enhancement in the ultimate strength and ductility of the reinforced concrete (RC) structures. This study presents a prediction model for the axial compressive strength and strain of normal-strength concrete cylinders confined with CFRP. Besides, soft computing approaches have been extensively used to model in many areas of civil engineering applications. Therefore, the genetic expression programming (GEP) models to predict axial compressive strength and strain of CFRP-confined concrete specimens were used in this study. For this purpose, the parameters of 283 CFRP-confined concrete specimens collected from 38 experimental studies in the literature were taken into account as input variables to predict GEP based models. Then, the results of GEP models were statistically compared with those of models proposed by various researchers. The values of R² for strength and strain of CFRP-confined concrete were obtained as 0.897 and 0.713, respectively. The results of the comparison reveal that the proposed GEP-based models for CFRP-confined concrete have the best efficiency among the existing models and provide the best performance.

• Fire Science and Engineering
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• v.25 no.1
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• pp.78-84
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• 2011

Recent researches of the fire resistance in concrete focus on how to secure relevant functions in the high strength concrete. However, the demand of normal strength concrete less than 40 MPa takes most of the total concrete demand. Therefore, fire resistance study needs to cover not only high strength concretes but also normal strength concretes. This study evaluated the fire resistance performance of 40 MPa concrete columns, taking the concrete covering thickness and the size of section as variables. Consequently, the fire resistance performance improved as the section size and the covering thickness became larger.

• International Journal of Highway Engineering
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• v.19 no.3
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• pp.11-18
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• 2017

PURPOSES : This study investigates the effect on concrete pavement accordance with the curing methods in cool weather and supports the best method in the field. METHODS : Two field tests evaluated the curing methods of concrete pavement in cool weather. Firstly, five curing methods were tested, including normal curing compound, black curing compound, bubble sheet, curing mat, and curing mat covered with vinyl. Concrete maturity was compared from temperature data. Secondly, normal curing compound and curing mat with vinyl, which showed the best performance, were compared in terms of maturity and join condition index. RESULTS:From the field tests, it is an evident that curing mat with vinyl accelerated the concrete strength. Therefore, it is possible to conduct saw-cut works in cool weather, which minimizes damage on concrete at joint. CONCLUSIONS : For concrete pavement in cool weather, using curing mat with vinyl as the curing method could overcome the strength delay. Therefore, strength and durability problems on concrete at joint due to cool weather would be fewer in the future.

• Journal of Ocean Engineering and Technology
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• v.14 no.3
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• pp.66-71
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• 2000

The main objectives of this study are to carried out in order to evaluate strength development of Fly Ash concrete containing various amounts of Fly Ash such as 0%, 10%, 20% and 30%. The experimental variables included in this test program consist of content of Fly Ash, concrete strength and chemical activation. As Fly Ash increases, air content, strength development of concrete and slump loss of normal strength concrete were gradually decreased. The inclusion of Na$_2$SO$_4$increased the short-term strength of concrete that contains Fly Ash. In addition, the strength development of concrete that contains Fly Ash and Na$_2$SO$_4$were improved.

• Structural Engineering and Mechanics
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• v.69 no.1
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• pp.77-93
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• 2019

Although much research has been carried out using recycled aggregates sourced from normal strength concrete, most of the buildings to be demolished are constructed with low strength concrete. Therefore, the properties of the concrete incorporating recycled aggregates, sourced from the waste of structural elements cast with low strength concrete, were investigated in this study. Four different concrete mixtures were designed incorporating natural and recycled aggregates with and without fly ash. The results of the mechanical and durability tests of the concrete mixtures are presented. Additionally, full-scale one-way reinforced concrete slabs were cast, using these concrete mixtures, and subjected to bending test. The feasibility of using conventional reinforced concrete theory for the slabs made with structural concrete incorporating recycled aggregates was investigated.

• Journal of the Korean Society of Safety
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• v.20 no.2 s.70
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• pp.84-90
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• 2005

This study is to use results of the experiment on the influence to the strength by mixing powders of wasted tires into regular remicon within a range of little effectiveness in durability, applicability, economic aspect, and workability, to put it to practical use and to apply as basic data from a view of recycling wasted tires as construction materials. And the concrete, which was mixed with 10mm particles with ratio of $0.5\%\;and\;1.0\%$ respectively at 270 of mixing strength, was reduced by $27\%$ in compressive strength compared to normal concrete, whereas concrete mixed with other than 10mm particles showed lower decrease ratio compared to the former by reducing only $1.0\%\~1.5\%$. it is found that as strength increases, the less in quantity of aggregate and the more increase in quantity of cement. When considered to the above result, it is estimated that concrete mixed with wasted tire particles could be better used in conditions of compressive force rather than tensile force, and could also be used for structures with flexural strengths as well. In conclusion, higher strengths could be made using waste tire mix.