• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.657-660
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• 2006

Recently, very-early strength latex-modified concrete(below ; VES-LMC) has been developed for repairing and overlaying the old concrete bridge deck. Early-age defects in high-performance concrete due to thermal and autogenous deformation shorten the life cycle of concrete structures. Thus, it is necessary to examine the behavior of early-age concrete at the stages of design and construction. The purpose of this study was to evaluate the autogenous shrinkage of VES-LMC, having an experimental variables such as retarder and water-cement ratio. The greater the retarder content in VES-LMC, the greater the expansion at early-age. This recommend the small retarder content as possible. The effect of water-cement ratio on early-age behavior is very small, because of the wrapped specimen in order to prevent water evaporation.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.463-468
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• 2003

A finite element formulation to predict the flexural behavior of composite girder is presented in which the early-age properties of concrete are specified including maturing of elastic modulus, creep and shrinkage. The time dependent constitutive relation accounting for the early-age concrete properties is derived in an incremental format by expanding the total form of stress-strain relation by the first order Taylor series with respect to the reference time. The total potential energy of the flexural composite member is minimized to derive the time dependent finite element equilibrium equation. Numerical applications are made for the 3-span double composite steel box girders which is a composite bridge girder filled with concrete at the bottom of the steel box in the negative moment region. The numerical analysis with considering the variation of concrete elastic modulus are performed to investigate the effect of it on the early-age behavior of composite structures. The one dimensional finite element analysis results are compared with the analytical method based on the sectional analysis. Close agreement is observed among the two methods.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.281-286
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• 2002

To study of binder and fine aggregate a lot of replacement fly-ash concrete, initial characteristics, standard environment of curing temperature $20^{\circ}C$, hot-weather environment of curing temperature $35^{\circ}C$, . Flesh concrete tested slump. air contest and Hardening concrete valuated setting period of form, day of age 1, 3, 5. 7, 10, 28 compression strength in sealing curing. Purpose of study is consultation materials in field that variety of fly-ash replacement concrete mix proportion comparison and valuation. (1) Experiment result age 28day compression strength more higher plan concrete then standard environment in curing temperature $20^{\circ}C$, , most strength F43 is hot-weather environment in curing temperature $35^{\circ}C$, replacement binder 25%, fine aggregate 15%. (2) Hot-weather environment replacement a mount of fly-ash is a same of plan concrete setting period of form. Age 28day compression strength replacement a mount of fly-ash more hot-weather concrete then plan concrete.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.559-562
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• 2000

This study is about the compensation of early age strength on mortar and concrete admixed with blast-furnace slag powder. For study, we have used fine powder of gypsum and kiln dust from cement factory. According to the test results, we have obtained proper mixing ratio of slag powder, gypsum and kiln dust for the compensation of early age strength on mortar and concrete property.

• 한국농공학회논문집
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• 제60권1호
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• pp.101-110
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• 2018

This study experimentally investigated the compressive and flexyral strength development characteristics of polymer concrete using four different type polymeric resins such as unsaturated polyester, vinyl ester, epoxy, and PMMA (polymethyl methacrylate) as binders. The test results show that the average compressive strength of those four different polymer concretes was 88.70 MPa, the average flexural strength was 20.30 MPa. Those test results show that compressive and flexural strengths of polymer concrete were much stronger than compressive and flexural strengths of ordinary Portland cement concrete. In addition, the relative gains of the compressive strength development at the age of 24 hrs compared to the age of 168 hrs were 68.6~88.3 %. Also, the relative gains of the flexural strength development at the age of 24 hrs compared to the age of 168 hrs were 73.8~93.4 %. These test results show that compressive and flexural strengths of each polymer concrete tested in this study were developed at the early age. Moreover, the prediction equations of compressive and flexural strength developments regarding the age were determined. The determined prediction equations could be applied to forecast the compressive and flexural strength developments of polymer concrete investigated in this study because those prediction equations have the high coefficients of correlation. Last, the relations between the compressive strength and the flexural strength of polymer concrete were determined and the flexural/compressive strength ratios were from 1/4 to 1/5. These results show that polymer concretes investigated in this study were appropriate as a flexural member of a concrete structure because the flexural/compressive strength ratios of polymer concrete were much higher than the flexural/compressive strength ratios of Portland cement concrete.

• 콘크리트학회논문집
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• 제17권1호
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• pp.11-18
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• 2005

온도 및 수분의 변화로 인하여 초기재령 콘크리트에서 발생하는 응력을 합리적으로 예측하기 위해서는 초기재령 콘크리트의 경화특성을 실제적으로 표현할 수 있는 컴플라이언스 함수가 필요하다. 그러나, 기존의 컴플라이언스 함수는 경화된 콘크리트의 데이터로부터 도출되어 초기재령 콘크리트의 특성을 합리적으로 표현하지 있지 않다. 또한 탄성 컴플라이언스를 측정하는 기존의 실험에서는 하중도달시간이 존재하므로 탄성 컴플라이언스와 크리프 컴플라이언스의 구분이 모호해지며 탄성 컴플라이언스에 크리프의 영향이 존재하는 문제점이 있다. 본 연구에서는 먼저 순간 컴플라이언스 함수를 실제적으로 추정할 수 있는 실험적 방법론을 제시하였다. 제시된 실험적 방법론을 이용하여 다양한 하중도달시간과 재령에 대하여 준-순간 컴플라이언스를 실험적으로 측정하여 순간 컴플라이언스를 제시하였다. 또한 초기재령 콘크리트에 대하여 크리프 실험을 수행하였다. 이로부터 고체화 이론에 기초하여 콘크리트의 컴플라이언 함수를 표현하는 B3 모델을 초기재령 콘크리트에 합리적으로 적용될 수 있도록 수정하여 제시하였다. 따라서 본 연구에서 제안된 컴플라이언스 함수는 초기재령 콘크리트의 시간에 따른 응력을 합리적으로 평가하는데 유용하게 활용될 수 있을 것으로 사료된다.

• International Journal of Concrete Structures and Materials
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• 제2권1호
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• pp.63-68
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• 2008

High performance concrete (HPC) is widely used in civil engineering due to its high durability and low permeability etc. Compared with ordinary concrete, HPC may develop much higher AS (autogenous shrinkage) at early age due to the relative low water cement (w/c) ratio and adding of mineral admixtures, which is one of the main reasons for early age micro-cracking of HPC structures. This paper studies the early age property of HPC columns under similar construction-site surroundings by embedded strain transducers. Results show that for HPC structure, early-age autogenous shrinkage especially within the first day after concrete pouring is pretty large. AS within the first day are 60% larger than those for 14 days in this research for all specimens. Therefore it should be taken into account for structure durability. By comparison of PHPC (plain HPC column) and RHPC (reinforced HPC column) specimens, the effects of reinforced bars on AS and temperature distribution have been analyzed. Also the influence of w/c ratio on AS is demonstrated.

• Steel and Composite Structures
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• 제28권1호
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• pp.39-49
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• 2018

The concrete bridge decks are usually precast and in-situ assembled with steel girders with post-pouring joint in the construction practice of super-wide steel-concrete composite beam. But the difference of concrete age between the precast slabs and the post-pouring joint has been not yet considered for the long-term performance analysis of this kind composite beam. A simply supported precast-assembled T-shaped beam was taken as an example to analyze the long-term performance of steel-concrete composite beam with post-pouring joint. Based on the deformation coordination conditions of the old-new concrete deck and steel girder, a theoretical model for the long-term behavior of precast-assembled composite beam is proposed in this paper according to age-adjusted effective modulus method. Then, the feasibility of the proposed model is verified by the available test data from the Gilbert's composite beams. Parametric studies were preformed to evaluate the influences of the cross-sectional area ratio of the post-pouring joint to the whole bridge deck, as well as the difference of concrete age between the precast slabs and the post-pouring joint, on the long-term performance of the composite beam. The results indicate that the traditional method without considering the age difference would seriously underestimate the effect of creep and shrinkage of concrete bridge decks. The concrete age difference between the precast slabs and the post-pouring joint should be demonstrated for the life cycle design and long-term performance analysis of precast-assembled steel-concrete composite beams.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1994년도 가을 학술발표회 논문집
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• pp.93-98
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• 1994

The property of concrete at different places in mass concrete is affected by the age under the same curing temperature. For more accurate analysis of thermal stress in mass cocnrete, it is necessary to obtain the property of concrete with age and curing temperature. In this study, the effects of curing temperature and age (Maturity) on the development of the property of concrete were investigated by using concrete specimens made with type I cement. The curing temperatures are 23$^{\circ}C$, 5$0^{\circ}C$, and 8$0^{\circ}C$, respectively. As the maturity increases, the strength of concrete was increased. The results obtained experimentlly was compapred with the previous models, and good agreements was obtained.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.781-784
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• 2005

Concrete structures often present volumetrical changes particularly due to thermal and moisture related shrinkages. Volumetric instability is detrimental to the performance and durability of concrete structures because structural elements are usually restrained. These restrained shrinkages develope tensile stresses which often results in cracking in combination with the low fracture resistance of concrete. Early-age defects in high-performance concrete due to thermal and autogenous deformation shorten the life cycle of concrete structures. Thus, it is necessary to examine the behavior .of early-age concrete at the stages of design and construction. The purpose of this study was to propose a shrinkage models of VES-LMC (very-early strength latex-modified concrete) at early-age considering thermal deformation and autogenous shrinkage.