• Computers and Concrete
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• v.16 no.3
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• pp.487-502
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• 2015

This study investigated particle expansion in basic oxygen furnace slag (BOF) and desulfurization slag (DSS) after heat curing by using the volume method. Concrete hydration was accelerated by heat curing. The compressive strength, ultrasonic pulse velocity, and resistivity of the concrete were analyzed. Maximum expansion occurred in the BOF and DSS samples containing 0.30-0.60 mm and 0.60-1.18 mm particles, respectively. Deterioration was more severe in the BOF samples. In the slag aggregates for the complete replacement of fine aggregate, severe fractures occurred in both the BOF and DSS samples. Scanning electron microscopy revealed excess CH after curing, which caused peripheral hydration products to become extruded, resulting in fracture.

• International conference on construction engineering and project management
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• 2005.10a
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• pp.672-680
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• 2005

There are a lot of reasons to use In-place tests. Construction schedules often require that operations such as form removal, post-tensioning, termination of curing, and removal of reshores be carried out as early as possible. To enable these operations to proceed safely as soon as possible requires the use of reliable in-place tests to estimate the in-place strength. In-place test results are not reliable for engineering judgment. These results should be interpreted and correlated to standard compressive strength, based on the test method. In this paper some of these test procedures and their limitations are discussed. In this study we will go on for Rebound number, Pullout, Ultrasonic pulse velocity, and Cast-in-place cylinder methods which are most useful methods in the Asia.

• Journal of the Korea Concrete Institute
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• v.24 no.6
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• pp.651-658
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• 2012

This paper concentrates on the evaluation of microcracks in thermal damaged concrete on the basis of the nonlinear ultrasonic modulation technique. Since concrete structure exposed to high temperature accompanies the development of microcracks due to the physical and chemical changes from temperature and exposed time, the adoption of nonlinear approach is required. Instead of using the conventional ultrasonic nondestructive methods which have the limitation in evaluating excessive microcracks, accordingly, a nonlinear ultrasonic modulation method which shows better sensitivity in quantifying microcracks is introduced. Upon the analysis for the modulation of ultrasonic wave and low frequency impact to measure the nonlinearity parameter, which can be used as an indicator of thermal damage, the verification processes for the introduced technique are followed: SEM investigation and permeable pore space test are performed to characterize thermally induced microcracks in concrete, and ultrasonic pulse velocity tests are performed to confirm the outstanding sensitivity of nonlinear ultrasonic modulation technique. In advance, compressive strength of thermal damaged concrete is measured to represent the effect of microcracks on performance degradation. Correlation studies between experimental data and measured data show that nonlinear ultrasonic modulation technique can effectively be used to quantify thermally induced microcracks, and to estimate the compressive strength of thermally damaged concrete.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.782-788
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• 2002

Several non-destructive test methods have been developed to estimate compressive strength of concrete in other countries. However, their applications are limited in domestic concrete due to their inaccuracies. The purpose of this study is to propose an aging coefficient of compressive strength of structural concrete in rebound number method and ultrasonic pulse velocity method for domestic concrete. The test variables include type of aggregate, curing condition, and compressive strength. Two approaches are used to estimate aging coefficient. One is evaluated by uniform linear regression equation for all ages and shows uniform strength reduction coefficient regardless of material properties and the other is evaluated by individual regression equation for each ages and shows nonuniform strength reduction and rebound increasing coefficients which decrease with increasing of rebound number and compressive strength. The latter result which can include the effect of rebound number and compressive strength is more resonable than the former.

• Computers and Concrete
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• v.10 no.6
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• pp.631-647
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• 2012

This paper focuses on the application of Fuller's ideal gradation curve to theoretically design blended ratio of all solid materials of high performance concrete (HPC), with the aid of error function, and then to study the effect of rice husk ash (RHA) on the performance of HPC. The residual RHA, generated when burning rice husk pellets at temperatures varying from 600 to $800^{\circ}C$, was collected at steam boilers in Vietnam. The properties of fresh and hardened concrete are reviewed. It is possible to obtain the RHA concrete with comparable or better properties than those of the specimen without RHA with lower cement consumption. High flowing concrete designed by the proposed method was obtained without bleeding or segregation. The application of the proposed method for HPC can save over 50% of the consumption of cement and limit the use of water. Its strength efficiency of cement in HPC is 1.4-1.9 times higher than that of the traditional method. Local standards of durability were satisfied at the age of 91 days both by concrete resistivity and ultrasonic pulse velocity.

• Structural Engineering and Mechanics
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• v.64 no.2
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• pp.243-257
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• 2017

Investigating the properties and durability of high-strength concrete exposed to sulfuric acid attack for the purpose of its application in structures exposed to this acid is of outmost importance. In this research, the resistance and durability of high-strength concrete containing macro-polymeric or steel fibers together with the pozzolans of silica fume or nano-silica against sulfuric acid attack are explored. To accomplish this goal, in total, 108 high-strength concrete specimens were made with 9 different mix designs containing macro-polymeric and steel fibers at the volume fractions of 0.5, 0.75, and 1.0%, as well as the pozzolans of silica fume and nano-silica with the replacement levels of 10 and 2%, respectively. After placing the specimens inside a 5% sulfuric acid solution in the periods of 7, 21, and 63 days of immersion, the effect of adding the fibers and pozzolans on the compressive properties, ultrasonic pulse velocity (UPV), and weight loss of high-strength concrete was investigated and the respective results were compared with those of the reference specimens. The obtained results suggest the dependency of the resistance and durability loss of high-strength concrete against sulfuric acid attack to the properties of fibers as well as their fraction in concrete volume. Moreover, compared with using nano-silica, using silica fume in the fibrous concrete mix leads to more durable specimens against sulfuric acid attack. Finally, an optimum solution for the design parameters where the crushing load of high-strength fibrous concrete is maximized was found using response surface method (RSM).

• Computers and Concrete
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• v.21 no.3
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• pp.311-319
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• 2018

This study used a volumetric method for design. The control group used waste Liquid Crystal Displayplay (LCD) glass powder to replace cement (0%, 10%, 20%, 30%), and the PZT group used Pd-Zr-Ti piezoelectric (PZT) powder to replace 5% of the fine aggregate to make cement mortar. The engineering and the mechanical and electricity properties were tested; flow, compressive strength, ultrasonic pulse velocity (UPV), water absorption and resistivity (SSD and OD electricity at 50 V and 100 V) were determined; and the correlations were determined by linear regression. The compressive strength of the control group (29.5-31.8 MPa) was higher than that of the PZT group (25.1-29 MPa) by 2.8-4.4 MPa at the curing age of 28 days. A 20% waste LCD glass powder replacement (31.8 MPa) can fill up finer pores and accelerate hydration. The control group had a higher 50 V-SSD resistivity ($1870-3244{\Omega}.cm$), and the PZT group had a lower resistivity ($1419-3013{\Omega}.cm$), meaning that the resistivity increases with the replacement of waste LCD glass powder. This is because the waste LCD glass powder contains 62% $SiO_2$, which is a low dielectric material that is an insulator. Therefore, the resistivity increases with the $SiO_2$ content.

• Computers and Concrete
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• v.15 no.4
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• pp.503-514
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• 2015

Fibre-added concretes are frequently used in large site applications such as slab and airports as well as in bearing system elements or prefabricated elements. It is very difficult to determine the mechanical properties of the fibre-added concretes by experimental methods in situ. The purpose of this study is to develop an artificial neural network (ANN) model in order to predict the compressive and bending strengths of hybrid fibre-added and non-added concretes. The strengths have been predicted by means of the data that has been obtained from destructive (DT) and non-destructive tests (NDT) on the samples. NDTs are ultrasonic pulse velocity (UPV) and Rebound Hammer Tests (RH). 105 pieces of cylinder samples with a dimension of $150{\times}300mm$, 105 pieces of bending samples with a dimension of $100{\times}100{\times}400mm$ have been manufactured. The first set has been manufactured without fibre addition, the second set with the addition of %0.5 polypropylene and %0.5 steel fibre in terms of volume, and the third set with the addition of %0.5 polypropylene, %1 steel fibre. The water/cement (w/c) ratio of samples parametrically varies between 0.3-0.9. The experimentally measured compressive and bending strengths have been compared with predicted results by use of ANN method.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.1921-1925
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• 2010

개수로의 흐름을 측정하는 유속계는 유체역학 및 수리학적 연구와 유량 측정 등의 업무에 필수적인 장비이다. 그동안 국내에서는 일부 전자파표면유속계(이상호 등, 1997)와 영상처리 기반의 LSPIV(김영근 등, 2004)와 같은 비접촉식 유속측정 장치가 개발되어 활용되고 있지만, 유속 및 유량 측정에 보다 널리 사용되고 있는 수중 투입식 유속계의 경우 거의 개발되지 않았다. 특히 유속 분포를 측정하는데 활용될 수 있는 초음파 방식 유속 프로파일러는 거의 전적으로 외국제품에 의존하고 있다. 일반 유속계가 점유속을 측정하는데 비해 유속 프로파일러는 센서가 지향하는 방향선을 따라 공간적인 유속분포를 동시에 획득할 수 있으므로 측정 효율성이 높다는 장점을 지닌다. 본 연구에서는 국내 기술로 개수로 흐름 측정에 활용할 수 있는 초음파 유속 프로파일러를 개발하였다. 이 유속 프로파일러는 초음파 펄스를 반복적으로 송수신하는 PRF 기법을 이용하여 개발하였다. 개발된 유속 프로파일러는 직사각형 수로에서 유속 분포를 측정하기 위해 적용하였으며, 기존의 2차원 유속계와 그 결과를 비교하였다. 본 연구에서 개발한 유속 프로파일러는 실제 하천에 활용하기에는 측정 가능한 유속 및 수심 범위의 한계가 있으나 PRF 기법의 한계 범위에서는 실측 유속분포를 비교적 잘 재현하는 것으로 나타났다.

• Computers and Concrete
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• v.34 no.2
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• pp.213-230
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• 2024

The use of waste tires and industrial wastes such as fly ash (FA) and ground granulated blast furnace slag (GGBS) in concrete is an important issue in terms of sustainability. In this study, the effect of parameters affecting the physical, mechanical and microstructural properties of FA/GGBS-based geopolymer concretes with waste rubber fiber was investigated. For this purpose, the effects of rubber fiber percentage (0.6%, 0.9%, 1.2%), binder (75FA25GGBS, 50FA50GGBS, 25FA75GGBS) and curing temperature (75 ℃, 90 ℃ and 105 ℃) were investigated. The Taguchi-Grey Relational Analysis (TGRA) method was used to obtain optimum parameter levels of rubber fiber geopolymer concrete (RFGC). The slump, fresh and hardened density, compressive strength, flexural strength, static and dynamic modulus of elasticity, ultrasonic pulse velocity (UPV) tests and scanning electron microscopy (SEM) analysis were performed on the produced concretes. The analysis of variance (ANOVA) method was used to statistically determine the effects of the parameters on the experimental results. A confirmation test was performed to test the accuracy of the optimum values found by the TGRA method. With the increase of GGBS percentage, the compressive strength of RFGC increased up to 196%. The increase in rubber fiber percentage and curing temperature adversely affected the mechanical properties of RFGC. As a result of TGRA, the optimum value was found to be A1B3C1. ANOVA results showed that the most effective parameter on the experimental results was the binder with 99% contribution percentage. It is understood from the SEM images that the optimum concrete had a denser microstructure and less capillary cracks and voids. For this study, the use of the TGRA method in multiple optimization has proven to provide very useful and reliable results. In cases where many factors are effective on its strength and durability, such as geopolymer concrete, using the TGRA method allows for finding the optimum value of the parameters by saving both time and cost.