• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.909-912
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• 2001

This paper presents the validities of the removal time of side forms considering the relationship between rebound number of P type schmidt hammer and compressive strength. According to test results, compressive strength of 40% of W/C at 12 hours shows 16kgf/$cm^{2}$ and 50% of W/C at 15 hours, 13kgf/$cm^{2}$. Rebound number at 9 hours after casting shows 13 and 9 (W/C 40% and W/C 50%). According to the regression analysis, rebound number of P type schmidt hammer to gain 50kgf/$cm^{2}$ of is estimated 20.1. It is thought that desirable rebound number of P type schmidt hammer to gain 50kgf/$cm^{2}$ is determined 25 considering safety factor.

• 한국구조물진단유지관리공학회 논문집
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• 제3권2호
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• pp.177-183
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• 1999

The major object of this study is to investigate experimentally the experimental equation by the non-destructive testing methods of ultrasonic pulse velocity, rebound number, combined method of ultrasonic pulse velocity and rebound number, maturity which are applicable to the evaluation of compressive strength of concrete at early ages. Also test result of mix are statistically analyzed to infer the correlation coefficient between the maturity and the compressive strength of concrete. The results show good application of Logistic curve for estimating strength development under various curing temperature. The relation between ultrasonic pulse velocity, rebound number, combined method of ultrasonic pulse velocity and rebound number and compressive strength of concrete have low correlation coefficient, but maturity method show good correlation coefficient.

• 한국안전학회지
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• 제32권4호
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• pp.53-58
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• 2017

The rebound hammer test and the measurement of ultrasonic pulse velocity(UPV) have been widely used for the physical properties & condition evaluation of reinforced & prestressed concrete structures for a long time, but the acoustoelastic effects by the prestressing in the prestressed concrete structures on the rebound number and ultrasonic pulse velocity have not been studied clearly. Therefore, this study investigated the data distribution of the rebound numbers and ultrasonic pulse velocities in reinforced and prestressed concrete slabs of $3000{\times}3000mm$ with a thickness of 250 mm. Also, the Kolmogorov-Smirnov goodness-of-fit test was done in order to identify statistical consistency and reliability. The statistical analysis results show that the rebound number and ultrasonic pulse velocities increased about 1.9% and 2.5%, respectively when prestressing was applied. As expected, the UPV shows better statistical reliability and potential for in situ evaluation than the RB because the RB are more sensitive to testing posture, surface condition, temperature and humidity so on. The experimental data in this study can be used for the condition assessment of reinforced and prestressed concrete structures by the rebound number and ultrasonic pulse velocity.

• 콘크리트학회논문집
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• 제16권6호
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• pp.833-840
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• 2004

비파괴 검사에 의한 콘크리트 압축강도 시험법 중에서 반발도법과 초음파 속도법은 가장 널리 사용되는 방법이다. 그러나 국내에서 사용되고 있는 비파괴 강도 시험법은 대부분이 외국의 시험법을 적용하고 있어서 국내의 콘크리트 구조물에 직접 적용하는 데는 무리가 따른다고 할 수 있다. 반발도법의 경우, 일본건축학회 등의 제안에 자라 20개의 타격점을 표준으로 채택하고 있으나 표준편차에 대한 고려를 하지 않고 있는 실정이다. 또한, 초음파 속도법에 의한 시험은 압축강도를 추정하는데 필요한 측정횟수의 규정이 없다 따라서 본 연구에서는 카이검증을 이용하여 비파괴 검사법에 의한 콘크리트 압축강도의 타격횟수의 신뢰도를 검토하고 최소시험 횟수를 제안하였다. 그 결과, 반발도법과 초음파 속도법으로 추정한 콘크리트 압축강도 값이 만족할 만한 신뢰범위에 들기 위한 최소시험횟수는 각각 11회와 7회로 분석되었다. 다만, 실구조물의 품질변동을 고려하여 이상치의 결측처리와 시험군의 격자 배열을 전제로 한다면, 반발도법은 국내의 관행에 따라 20회로, 음파 속도법은 9회로 규정하는 것이 바람직하다고 판단된다.

• Structural Engineering and Mechanics
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• 제65권5호
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• pp.601-609
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• 2018

Steel bolts are used in the construction industry for a large variety of applications that range from fixing permanent installations to temporary fixtures. In the past much research has been focused on developing destructive testing techniques to estimate their pull-out load carrying capacity with very little attention to develop non-destructive techniques. In this regards the presented research work details the combined use of ultrasonic pulse velocity and Schmidt hammer tests to identify anchor bolts with faculty installation and to estimate their pull-out strength by relating it to the Schmidt hammer rebound value. From experimentation, it was observed that the load capacity of bolt depends on its embedment length, diameter, bond quality/concrete strength and alignment. Ultrasonic pulse velocity test is used to judge the quality of bond of embedded anchor bolt by relating the increase in ultrasonic pulse transit time to the presence of internal pours and cracks in the vicinity of steel bolt and the surrounding concrete. This information combined with the Schmidt hammer rebound number, R, can be used to accurately identify defective bolts which resulted in lower pull-out strength. 12 mm diameter bolts with embedment length of 70 mm and 50 mm were investigated using constant strength concrete. Pull-out load capacity versus the Schmidt hammer rebound number for each embedment length is presented.

• 한국구조물진단유지관리공학회 논문집
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• 제12권3호
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• pp.199-207
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• 2008

최근 구조물이 노후화되면서 기존 구조물과 시공품질을 관리하는 비파괴검사 평가의 요구가 증가되고 있다. 콘크리트 구조물의 압축강도 추정의 중요성이 건설업계에서 또한 점차적으로 증대되고 있는 실정이고, 시공관리와 품질관리에 있어서 중요한 요소이다. 본 연구는 콘크리트의 압축강도를 비교하기 위한 비파괴 검사법 중 슈미트해머 시험과 충격반향기법을 이용하여 수행되었다. 콘크리트 압축강도와 슈미트해머에 의한 반발경도 값과 충격반향기법 실험결과와의 관계를 알아내는데 초점을 두었으며, 콘크리트의 압축강도와 반발경도 값은 밀접한 관계가 있음을 알 수 있었다.

• Computers and Concrete
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• 제24권6호
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• pp.555-560
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• 2019

During the application of shotcrete, a part of the concrete bounces back after hitting to the surface, the reinforcement or previously sprayed concrete. This rebound material is definitely not added to the mixture and considered as waste. In this study, a deep neural network model was developed to predict the rebound material during shotcrete application. The factors affecting rebound and the datasets of these parameters were obtained from previous experiments. The Long Short-Term Memory (LSTM) architecture of the proposed deep neural network model was used in accordance with this data set. In the development of the proposed four-tier prediction model, the dataset was divided into 90% training and 10% test. The deep neural network was modeled with 11 dependents 1 independent data by determining the most appropriate hyper parameter values for prediction. Accuracy and error performance in success performance of LSTM model were evaluated over MSE and RMSE. A success of 93.2% was achieved at the end of training of the model and a success of 85.6% in the test. There was a difference of 7.6% between training and test. In the following stage, it is aimed to increase the success rate of the model by increasing the number of data in the data set with synthetic and experimental data. In addition, it is thought that prediction of the amount of rebound during dry-mix shotcrete application will provide economic gain as well as contributing to environmental protection.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2013년도 춘계 학술논문 발표대회
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• pp.69-70
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• 2013

This is an foundational study to adequacy the non-destruction testing for the estimation of compressive strength of high strength concrete The results are as follows, In high strength concrete, H type is NR type rebound number rather than higher. The relation between rebound number and compressive strength of high strength concrete have lower coefficient. when compressive strength estimation of high strength concrete, it consider that rebound hardness test is not applied and should be consider to combined method or addition method.

• 한국건축시공학회지
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• 제2권3호
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• pp.123-130
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• 2002

Recently, it is being studied on the high strength concrete in many laboratories and being applied to the construction field actually. But non-destruction testing equation that to be proposed about normal strength concrete in Japan has been using because the systematic study results for the estimation of compressive strength of high strength concrete do nit exist. So it is essential to suggest the non-destruction testing equation for the estimation of compressive strength of high strength concrete. This is an experimental study to analyze and investigate the non-destruction testing equation for the estimation of compressive strength of high strength concrete. The results are as follows; The relation between rebound number, pulse velocity and compressive strength of high strength concrete have lower coefficient than combined method of rebound number and pulse velocity. Also new non-destructive testing equation for the estimation on the compressive strength of high strength concrete was suggested in this study, and it is considered that these equations have possibility to be applied in domestic construction field.

• 한국산학기술학회논문지
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• 제21권9호
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• pp.604-609
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• 2020

콘크리트 표면 마감에는 다양한 방법이 있으며, 시공성을 고려할 때 스프레이 방법이 효과적이나 리바운드 발생 현상이 발생한다. 통상 숏크리트의 손실률은 30-45%가량 보고되고 있으며, 이로 인하여 작업 효율 저하 및 공사비 상승 등의 문제를 발생시킨다. 이를 해결하고자 다양한 선행 연구가 진행되었으며 리바운드량을 저감하기 위해서는 사용재료에 따라 리바운드 발생 억제를 위해 배합을 조정하여야 하며 본 연구에서는 광촉매가 포함된 표면 마감재료에 적합한 리바운드 발생량 저감 목적의 배합 기술에 대한 기초 연구를 진행하였다. 본 연구의 선행연구로는 광촉매 성능에 대해 저감효과 및 최적 혼합 비율을 도출하였고, 선행연구를 바탕으로 규사 함량에 따른 리바운드 저감 및 혼화 재료 별 역학적 내구 특성 검증을 진행하였다. 시험 방법으로는 리바운드, 압축강도, 휨강도, 테이블 플로 시험으로 진행하였고, 모르타르 스프레이 장비의 작업성을 고려하였을 때 Flow 170±10mm로 고정하였다. 실험 변수로는 시멘트 중량 대비 규사 변수로 맞추어 리바운드량 측정을 하였고 규사는 5호, 7호 규사를 사용하였다. 실험 결과 최종 S-1 변수에서 가장 높은 압축강도를 나타냈고 리바운드 양을 최소화할 수 있었다. 이러한 결과는 규사 공극의 결합재가 충분히 충진하게 되어 골재 사이의 결합력이 증가되므로 낮은 리바운드 양을 확보할 수 있었다.