• Title/Summary/Keyword: Rebound test

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Countermeasure of rebound reducing for wet-mixed steel fiber reinforced shotcrete (강섬유보강 습식 숏크리트의 리바운드 저감대책)

  • Lim Joo-Young;Park Hae-Geun;Lee Myeong-Sub;Cho Nam-Sup
    • Proceedings of the KSR Conference
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    • 2004.10a
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    • pp.1162-1167
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    • 2004
  • From the early 1980's, the New Austrian Tunnelling Method (NATM) has been developed as a one of the standard tunneling method in Korea. Owing to the results of many researches, the practical problems of shotcrete has been improved for a last decade. However, the excess amount of rebound still remains one of the critical problems in shotcrete technology. In order to improve for this rebound problem, recently developed cement mineral accelerator has been successfully applied to several NATM tunnels in Korea. An experimental investigation was carried out in order to verify the rebound characteristics of wet-mix Steel Fiber Reinforced Shotcrete (SFRS) with powder types cement mineral accelerator. Mortar setting test, SEM analysis, bonding test under spring water condition and rebound test were conducted. From the result, wet-mix SFRS with cement mineral acelerator exhibited excellent bonding characteristics even spring water condition and less rebound ratio compared to the conventional liquid accelerator.

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A Study on the Effect of Carbonation on the Rebound Numbers (콘크리트의 탄산화가 반발도에 미치는 영향에 관한 연구)

  • 유성현;전명훈;윤상천;지남용
    • Proceedings of the Korea Concrete Institute Conference
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    • 1999.10a
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    • pp.783-786
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    • 1999
  • The compressive strength of concrete is one of the most important properties in concrete structures. There are, two methods for the testing of concrete compressive strength in structure ; coring and nondestructive testing. The latter is more often used than the former in a view of time and expenses. The Nondestructive test methods used nowadays include Rebound Hammer test and Ultrasonic Pulse Velocity test. Carbonation through aging makes changes of the interior structure and the properties of concrete. It is well-known fact that the surface hardness of concrete is increased by its carbonation. This fact makes it difficult in estimating the compressive strength of concrete using Rebound Hammer test. This study aimed to quantitatively analyzed the effects of carbonation on results of the Rebound Hammer test.

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Prediction of rebound in shotcrete using deep bi-directional LSTM

  • Suzen, Ahmet A.;Cakiroglu, Melda A.
    • Computers and Concrete
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    • v.24 no.6
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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.

A Study on the Proposal of Strength Presumption Equation of Concrete Using Rebound Test and Aging Effects of Underground Structures (지하구조물 공용년수를 고려한 반발경도법에 의한 강도추정식의 제안)

  • Na, Sung Oak;Yoon, Tae Gook;Rhee, Jong Woo
    • Journal of Korean Society of societal Security
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    • v.2 no.4
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    • pp.59-65
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    • 2009
  • The rebound test using Schmidt hammer is most popular method to estimate strength of concrete. However, this method is inappropriate for Seoul Metro underground structures due to unsuitable aging effects. Consequently, the strength presumption equation of underground structures is proposed according to the correlation of uniaxial compressive strength, rebound test results and age of concrete. To achieve this, the results of in-depth inspection of Seoul Metro underground structures performed annually for last 8 years was anlayed.

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An Experimental Study on the Rebound Degree Tendency of Linear Hitting Test Hammer (선 타격 반발도 시험기의 반발도 경향에 관한 실험적 연구)

  • Ahn Hyo-Soo;Seo Chee-Ho
    • Journal of the Korea Concrete Institute
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    • v.17 no.3 s.87
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    • pp.313-322
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    • 2005
  • Recently, as the remodeling market gradually substitute for new construction market and safety diagnosis for reconstruction apartment become a matter of principal Interest, it is demanded that scientific diagnosis and evaluation for existing concrete structure state. And it is increasing that the significance for reliability of data which is used for estimating the concrete compressive strength by nondestructive test. As a result, it is found that different proposal to material age and hitting angle is good to improving the reliability of presumption of concrete compressive strength in the linear hitting rebound test hammer. And for the reason that mutual relation between the compressive strength and rebound degree is highest in linear hitting rebound test hammer 25mm in all portion according to early md middle material age and hitting angle except the early material age $-45^{\circ}$, analysis showed that linear hitting rebound test hammer is more reliable than existing schmidt hammer in presumption of concrete compressive strength.

An Experimental Study on the Mechanical Properties and Rebound Ratios of SFRS with Silica Fume

  • Son, Young-Hyun;Chai, Won-Kyu
    • International Journal of Safety
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    • v.8 no.2
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    • pp.20-25
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    • 2009
  • In this study, an experiment in the field was performed to analyze the mechanical properties and the influence of steel fiber and silica fume on the rebound ratios of shotcrete. The experimental parameters which are the reinforcing methods (steel fiber, wire mesh), steel fiber contents (0.0%, 0.5%, 0.75%, 1.0%), silica fume contents (0.0%, 10.0%), layer thickness (60 mm, 80 mm, 100 mm), and the placing parts (sidewall, shoulder, crown) were chosen. From the mechanical test, it was found that the flexural strength and toughness is significantly improved by the steel fiber and/or silica fume. According to the results for the side wall in this test, the larger the fiber contents are in case of steel fiber reinforced shotcrete, the less the rebound ratios are within the range of 20-35%, compared to the wire mesh reinforced shotcrte. And also, the reduced rebound ratios were very larger in using steel fiber reinforced shotcrete with silica fume content of 10%, and these results are true of the shoulder and the crown. respectively.

A Study on the Minimum Number of Rebound Number Test and Pulse Velocity Method for Estimating Compressive Strength of Concrete (콘크리트 압축강도 추정을 위한 반발도법과 초음파속도법의 최소시험횟수에 관한 연구)

  • Lee Mun-Hwan;Choi Chang-Woo
    • Journal of the Korea Concrete Institute
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    • v.16 no.6 s.84
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    • pp.833-840
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    • 2004
  • Among non-destructive tests for compressive strength, rebound number test and pulse velocity test are the most widely used methods. However, the non-destructive tests mostly used in Korea was developed by foreign country. Therefore, it is unreasonable to directly apply them to concrete structures in Korea. In accordance with the suggestion of Institute of Architecture in Japan for rebound number test, a compressive strength is calculated by the mean value of 20 hit points without being considered standard deviation. Furthermore, there is no regulation on the number of measurements required for measuring compressive strength by pulse velocity test. This study, therefore, reviewed the rebound number test and pulse velocity test by chi-square, and suggested the minimum number of each test. As a result, the minimum number that falls within range of reliability for rebound number test and pulse velocity test are 11 and 7, respectively. If abnormal values are processed as missing and test groups are assumed to be arrayed in cross by considering changes in quality of actual concrete structures, 20 times and 9 times are appropriate for rebound number test and pulse velocity test, respectively.

Estimation of Compressive Strength of Reinforced Concrete Structure Using Impact Testing Method and Rebound Hardness Method

  • Hong, Seonguk;Kim, Seunghun;Lee, Yongtaeg;Jeong, Jaewon;Lee, Changyong;Park, Chanwoo
    • Architectural research
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    • v.20 no.4
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    • pp.137-145
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    • 2018
  • The nondestructive test is widely used in the field of diagnosis and maintenance to evaluate the degree of damaging of structures caused by aging, and the demand for this test method is expected to continue increasing. However, there is a lack of standards related to the nondestructive test, and South Korea is relying heavily on developed nations for original technologies related to diagnosis. It is an urgent task to establish a nondestructive test method appropriate for the circumstance of South Korea. The purpose of this study is to compare and analyze estimated error of compressive strength in single-story structures comprised of vertical and horizontal reinforced concrete members using the impact testing method and rebound hardness method, which are nondestructive test methods, and to review on-site applicability of these methods. Based on compressive strength of the structures estimated, overall mean error was 21.2% for the impact testing method and 15.6% for the rebound hardness method. The necessity of a reliable diagnostic method based on compound nondestructive test methods to increase accuracy of estimation was confirmed.

A Study on the Statistical Distribution of Rebound Number and Ultrasonic Pulse Velocity in RC and PSC Concrete Structures (RC 및 PSC 콘크리트에서 반발도 및 초음파 속도의 변화에 대한 연구)

  • Sa, Min-Hyung;Yoon, Young-Geun;Lee, In-Bok;Woo, In-Sung;Oh, Tae Keun
    • Journal of the Korean Society of Safety
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    • v.32 no.4
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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.

A Study Using Rebound Method and Impact Echo Method for the Comparison of the Compressive Strength of Concrete Slab (반발 경도법 및 충격반향기법을 이용한 콘크리트 슬래브의 압축강도 비교에 관한 연구)

  • Hong, Seong-Uk;Cho, Young-Sang
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.12 no.3
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    • pp.199-207
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    • 2008
  • As infrastructures are being deteriorated, nondestructive evaluation of existing structures and construction quality control are increasingly demanded. The importance of predicting compressive strength of concrete structure is also gradually increasing in construction industry. The estimation of concrete compressive strength is a critical factor of the construction management and quality control. This study has been conducted using Schmidt hammer test and Impact echo method, which are nondestructive test methods for the comparison of the concrete compressive strength. It is focusing to examine the relationship between compressive strength of concrete and rebound number by Schmidt hammer test result by Impact echo method. It was found that concrete compressive strength and rebound number have a close correlation.