• Journal of Industrial Technology
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• v.23 no.A
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• pp.165-173
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• 2003

The purpose of this paper is to analysis of initial behavior of concrete pavement with initial measurement strain gauge for concrete pavement at field, and to investigate the field test results for field applicability testing. The early-age behaviors of concrete pavement slabs were measured using the strain gauges. From the slab depths and positions, the outputs from each gauges were recorded at initial curing period. The initial measurement of concrete pavement and check of crack at the joint were performed, the results could be summarized as follows. From the results of concrete strength, compressive strength and flexural strength were showed $271kgf/cm^2$, $43kgf/cm^2$ respectively. From the tests of early-age strain measurement, it was found that the strain varied at the maximum value of $150{\mu}{\varepsilon}$ and early behavior of concrete slab was showed a tensile strain. However, for long-term was showed a compressive strain due to dry-shrinkage.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.741-744
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• 2008

Quality control of early age concrete significantly influences the long term performance. Primary factors for early age concrete quality control should include the relative humidity and temperature variation, and these are more important as structures become massive and huge. Temperature raise due to cement hydration causes stress, which can develop to cracking with internal and/or external restraints. Exposure conditions including ambient temperature, humidity and wind also significantly affect the cracking behavior of early age concrete. Among many of studies on the early age concrete behavior, investigation on the variation of temperature and relative humidity internal of concrete is not common. That is in part because the difficulties in measuring the relative humidity and temperature inside the concrete. This study used a digital sensor with an appropriate logger to measure internal temperature and relative humidity. This direct measuring method is expected to provide more reliable and comprehensive data acquisition on the early age behavior of concrete.

• Journal of the Korea Concrete Institute
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• v.14 no.3
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• pp.331-340
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• 2002

In this paper, finite element analysis is applied for simulation of cracks due to restraining autogenous and drying shrinkage at early-age concrete. A micro-level heat hydration model and a shrinkage prediction model along with a moisture diffusion model are adopted for the finite element analysis. Then, an axial restraint test is carried out for concrete specimens containing different amounts of chloride ions to evaluate stress development and cracking due to the restraining shrinkages at early ages. Test results show that the increase of contents of chloride ions increases restrained stress, but does not increase strength. By this increase of shrinkage strain at early-age, time to occur the crack is accelerated. Finally, stress development and cracking of concrete specimens containing different amount of chloride ions we simulated using the finite element analysis. Results of the analysis using the Proposed model are verified by comparison with test results.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.806-809
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• 2004

The early-age cracks have bad effects on the diffusion movement of chloride ions and oxygen. In this study, a corrosion analysis algorithm for cracked concrete is proposed to examine the influence of early-age cracks on corrosion of RC structures. For different environmental exposure conditions of RC structures, a corrosion model is combined with models for activation polarization and concentration polarization. From the finite element corrosion analysis using the proposed algorithm and the models, the effects of early-age cracks to the corrosion is simulated.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.569-570
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• 2009

An improvement of the test method is proposed to more accurately measure early-age autogenous shrinkage in concrete particularly within first 24 hours after casting. Experiments were conducted considering existing and improved method. In improved method, hydration temperature was artificially controlled to prevent thermal deformations. Test results indicate that the autogenous shrinkage calculated by existing approach is underestimated which might be due to the wrong assumption of considering the thermal dilation coefficient to be constant (equal to 10 ${\times}$ $10^{-6}/^{\circ}C$) at early-age. We recommend that the proposed method should be adopted to better assess precise value of autogenous shrinkage or an appropriate method of determining the time-evolution of thermal dilation coefficient be considered.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.409-410
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• 2023

In this study, the compressive strength and ultrasonic pulse velocity were evaluated according to the elapsed time on concrete mixed with normal and lightweight aggregates at early age. For evaluation in various strength ranges, the design compressive strength was set to 30, 45, and 60MPa and evaluated. As a result of the experiment, the compressive strength of concrete mixed with lightweight aggregates developed 5MPa earlier compared to normal aggregate concrete, and the UPV showed a similar tendency.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.5
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• pp.63-71
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• 2010

This paper is about a research of steam curing which is one of the curing methods for accelerating the early-age strength of pre-cast concrete. With cylinder mold and mock-up specimen, the research was executed to study the best cycle of steam curing temperature through quantifying cycle of steam curing and maximum temperature, while the required strength is developed under the early-age. Moreover, causes and measurements for the high temperature of concrete, which is due to the steam curing, and the crack, which occurs when removing steel form, are stated. Ultimately, the economical method of producing, which satisfies early-age strength development and quality assurance while manufacturing PC structure, is stated.

• Journal of the Korea Concrete Institute
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• v.22 no.2
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• pp.237-245
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• 2010

Recently, deflection of the slab during construction periods becoming one of the important issues because of increasing the large-span structures. Early removing the form and support of the slab to achieve the rapid construction cause falling-off in quality of the structures. To reduce these deterioration and make rapid construction, construction of strength and stiffness gain model is needed by the research about the early-age concrete properties. Previous research results indicated that concrete model in existing design codes could not provide the mechanical properties of early age concrete. This paper carried out the concrete compressive strength tests on the curing age at early age stage. Evaluation of the accuracy of compressive strength and modulus of elasticity gain formula in existing various design codes was performed based on this test results, and new design model was proposed. This new model will be useful to develop the new rapid construction methods or prevent the deterioration of the deflection at construction periods. Material tests were performed at 1, 3, 7, 14, 28 curing days, total 159 cylinder style specimens were tested. Based on analyzing the test results, the relationship between compressive strength and modulus of elasticity at early age was proposed.

• Journal of the Korea Concrete Institute
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• v.12 no.6
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• pp.67-74
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• 2000

The usage of nondestructive testing on early-aged concrete leads to enhacned safty and allows effective scheduling of construction, thus making it possible to maximize the time and cost efficiencies. In this study, a reliable nondestructive strength evaluation method for early-aged concrete using the longitudinal wave velocity is proposed. Compression tests were performed to examine factors influencing the velocity-strength relationship of concrete, such as water-cement (w/c) ratio, fine aggregate ratio, curing temperature, and curing condition. The test results show that a change in the w/c ratio and curing temperature has minor effect on the velocity-strength relationship/ However, curing condition significantly influences the velocity-strength relationship of early-aged concrete. Moreover, the longitudinal wave velocity increases with decreasing fine aggregate ratio. It is concluded from this study that the strength evaluation of early-age concrete can be achieved by a nonlinear equation which considers the effects of curing condition and fine aggregate ratio.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.813-822
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• 2002

The purpose of the present study is first to refine the mathematical material models for moisture and temperature distributions in early-age concrete and then to incorporate those models into finite element procedure. The three dimensional finite element program developed in the present study can determine the degree of hydration, temperature and moisture distribution in hardening concrete. It is assumed that temperature and humidity fields are fully uncoupled and only the degree of hydration is coupled with two state variables. Mathematical formulation of degree of hydration Is based on the combination of three rate functions of reaction. The effect of moisture condition as well as temperature on the rate of reaction is considered in the degree of hydration model. In moisture transfer, diffusion coefficient is strongly dependent on the moisture content in pore system. Many existing models describe this phenomenon according to the composition of mixture, especially water to cement ratio, but do not consider the age dependency. Microstructure is changing with the hydration and thus transport coefficients at early ages are significantly higher because the pore structure in the cement matrix is more open. The moisture capacity and sink are derived from age-dependent desorption isotherm. Prediction of a moisture sink due to the hydration process, i.e. self-desiccation, is related to autogenous shrinkage, which may cause early-age cracking in high strength and high performance concrete. The realistic models and finite element program developed in this study provide fairly good results on the temperature and moisture distribution for early-age concrete and correlate very well with actual test data.