• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1992년도 봄 학술발표회 논문집
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• pp.41-46
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• 1992

A potential use of superplasticizing admixture is to produce structural concrete of High-strength concrete,. By using a superplasticizer, more workable mixes can be achieved while permitting a high cement content and a low water/cement ratio both of which are necessary to obtain high strength by conventional manufacturing technique. In this study, therefore, high strength concrete having a 28-day strength in excess of 650kg/$\textrm{cm}^2$ can be obtained using a superplasticzer. However, before such a high strength concrete is recommended for use, engineering properties have to be assessed. This study is aimed to analyze and investigate the engineering properties, such as strength, elasticity, ultrasonic pulse velocity, rebound value of superplasticized concrete having a various cement content.

• Computers and Concrete
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• 제24권1호
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• pp.63-71
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• 2019

Thermal energy from high temperatures can cause concrete damage, including mechanical and chemical degradation. In view of this, the residual mechanical properties of high-strength fiber reinforced concrete with a design strength of 75 MPa exposed to $400-800^{\circ}C$ were investigated in this study. The test results show that the average residual compressive strength of high-strength fiber reinforced concrete after being exposed to $400-800^{\circ}C$ was 88%, 69%, and 23% of roomtemperature strength, respectively. In addition, the benefit of steel fibers on the residual compressive strength of concrete was limited, but polypropylene fibers can help to maintain the residual compressive strength and flexural strength of concrete after exposure to $400-600^{\circ}C$. Further, the load-deflection curve of specimen containing steel fibers exposed to $400-800^{\circ}C$ had a better fracture toughness.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2011년도 추계 학술논문 발표대회
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• pp.119-120
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• 2011

Recently, the effects of high temperature and fiber content on the residual mechnical properties of high-strength concrete were experimentally investigated. In this paper, residual mechanical properties of concrete with water to cement (w/c) ratios of 55%, 42% and 32% exposed to high temperature are compared with those obtained in fiber reinforced concretes of similar characteristics with the ranging of 0,05% to 0,20% polypropylene (PP) fibers by volume of concrete, and considered factors include pre-load levels (20% and 40% of the maximum load at room temperature). Outbreak time and water contents were tested and were determined the compressive strength. In the result, it is showed that to prevent the explosive spalling of 50MPa grade concretes exposed to high temperature need more than 0.05Vol.% PP fibers. Also, the cross-sectional area of PP fiber can influence on the residual mechanical properties and the spalling tendency of fiber reinforced concrete exposed to high temperature. Especially, the external loading increases not only the residual mechanical properties of concrete but also the risk of spalling and the brittle tendency.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.191-196
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• 1999

In underground reinforced concrete structures, such as drainage structure, water and chloride ion penetrated into concrete through the cracks of concrete and its permeable property, cause the corrosion of reinforcing steel bar, which accelerates the expansive cracks and deterioration of concrete. It is necessary to control those deterioration of underground structure by improving its permeability and durability through the reasonable solutions in design, construction and materials. In the present study, fly ash concrete, which has good material properties in long-term period, is compared and studied with plain concrete using ordinary portland cement in terms of fundamental mechanical properties, permeability, drying shrinkage and durability. Also, the mix design and its properties of low permeable concrete using fly ash are reviewed. From this study, fly ash concrete can conctrol the penetration of water and chloride ion effectively by forming dense microstructure of concrete. Therefore, fly ash concrete may increase the long-term function, performance and serviceability of underground structures.

• Geomechanics and Engineering
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• 제13권5호
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• pp.881-892
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• 2017

Design and management of concrete slabs in concrete-faced rock-fill dams are crucial issues for stability and overall dam safety since cracks in the concrete face induced by stress, shrinkage, and deterioration can cause severe leakage from the reservoir into the dam. Especially, the increase of dam height to a certain level to enhance the storage capacity and to improve hydraulic stability can lead to undesirable deformation behavior and stress distribution in the existing dam body and in the concrete slabs. In such conditions, simulation of a concrete slab with a numerical method should involve the use of an interface element because the behavior of the concrete slab does not follow the behavior of the dam body when the dam body settles due to the increase of dam height. However, the interfacial properties between the dam body and the concrete slab have yet to be clearly defined. In this study, construction sequence of a 125 m high CFRD in South Korea is simulated with commercial FDM software. The proper interfacial properties of the concrete slab are estimated based on a comparison to monitored vertical displacement history obtained from the concrete slab. Possibility of shear strength failure under the critical condition is investigated based on the simplified model. Results present the significance of the interfacial properties of the concrete slab.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.455-458
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• 2005

This study compares the concrete using natural sand with the concrete using crush sand for the examination for the properties of a concrete. In the fresh concrete, the concrete using crush sand has less of the quantity of consistency, the content of air, and bleeding than the concrete using natural sand, and the concrete using crush sand has faster setting time than the concrete using natural sand. In hardening concrete, the concrete using crush sand has higher compressive strength and tensile strength than the concrete using natural sand because minute particles fill up a gap. Drying shrinkage of the concrete using natural sand is less than the concrete using crush sand.

• Advances in concrete construction
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• 제9권2호
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• pp.207-215
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• 2020

This paper describes the experimental studies carried out to determine the properties of fresh and hardened concrete with Recycled Plastic Waste (RPW) as a partial replacement material for fine aggregates. In the experimental study, RPW was used for replacing river sand and manufactured sand (M sand) aggregates in concrete. The replacement level of fine aggregates was ranging from 5% to 20% by volume with an increment of 5%. M40 grade of concrete with water cement ratio of 0.40 was used in this study. Two different types of RPW were used, and they are (i) un-activated RPW and (ii) activated RPW. The activated RPW was obtained by alkali activation of un-activated RPW using NaOH solution. The hardened properties of the concrete determined were dry density, compressive strength, split tensile strength, flexural strength and ultrasonic pulse velocity (UPV). The properties of the concrete with river sand, M sand, activated RPW and un-activated RPW were compared and inferences were drawn. The effect of activation using NaOH solution was investigated using FT-IR study. The micro structural examination of hardened concrete was carried out using Scanning Electron Microscopy (SEM). The test results show that the strength of concrete with activated RPW was more than that of un-activated RPW. From the results, it is evident that it is feasible to use 5% un-activated RPW and 15% activated RPW as fine aggregates for making concrete without affecting the strength properties.

• Coupled systems mechanics
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• 제7권2호
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• pp.197-209
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• 2018

Fiber-reinforced concrete (FRC) is a material with increasing application in civil engineering. Here it is assumed that the material consists of a great number of rather small fibers embedded into the concrete matrix. It would be advantageous to predict the mechanical properties of FRC using nondestructive testing; unfortunately, many testing methods for concrete are not applicable to FRC. In addition, design methods for FRC are either inaccurate or complicated. In three-point bending tests of FRC prisms, it has been observed that fiber reinforcement does not break but simply pulls out during specimen failure. Following that observation, this work is based on an assumption that the main components of a simple and rather accurate FRC model are mechanical properties of the concrete matrix and fiber pullout force. Properties of the concrete matrix could be determined from measurements on samples taken during concrete production, and fiber pullout force could be measured on samples with individual fibers embedded into concrete. However, there is no clear relationship between measurements on individual samples of concrete matrix with a single fiber and properties of the produced FRC. This work presents an inverse model for FRC that establishes a relation between parameters measured on individual material samples and properties of a structure made of the composite material. However, a deterministic relationship is clearly not possible since only a single beam specimen of 60 cm could easily contain over 100000 fibers. Our inverse model assumes that the probability density function of individual fiber properties is known, and that the global sample load-displacement curve is obtained from the experiment. Thus, each fiber is stochastically characterized and accordingly parameterized. A relationship between fiber parameters and global load-displacement response, the so-called forward model, is established. From the forward model, based on Levenberg-Marquardt procedure, the inverse model is formulated and successfully applied.

• Smart Structures and Systems
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• 제25권1호
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• pp.97-104
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• 2020

Due to the superior properties of nanoparticles, using them has been increased in concrete production technology. In this study, the effect of zinc oxide (ZnO) nanoparticles on the mechanical and smart properties of concrete was studied. At the first, the ZnO nanoparticles are dispersed in water using shaker, magnetic stirrer and ultrasonic devices. The nanoparticles with 3.5, 0.25, 0.75, and 1.0 volume percent are added to the concrete mixture and replaced by the appropriate amount of cement to compare with the control sample without any additives. In order to study the mechanical and smart properties of the concrete, the cubic samples for determining the compressive strength and cylindrical samples for determining tensile strength with different amounts of ZnO nanoparticles are produced and tested. The most important finding of this paper is about the smartness of the concrete due to the piezoelectric properties of the ZnO nanoparticles. In other words, the concrete in this study can produce the voltage when subjected to mechanical load and vice versa it can induce the mechanical displacement when subjected to external voltage. The experimental results show that the best volume percent for ZnO nanoparticles in 28-day samples is 0.5%. In other words, adding 0.5% ZnO nanoparticles to the concrete instead of cement leads to increases of 18.70% and 3.77% in the compressive and tensile strengths, respectively. In addition, it shows the best direct and reverse piezoelectric properties. It is also worth to mention that adding 3.5% zinc oxide nanoparticles, the setting of cement is stopped in the concrete mixture.

• Advances in concrete construction
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• 제14권5호
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• pp.355-368
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• 2022

This paper investigates the impact of length and volume fractions (VFs) of banana fibres (BFs) on the mechanical and physical properties of concrete. The mechanical properties were compressive strength, splitting tensile, flexural strength, and bond stress, while the physical properties were unit weight and absorption. The slump test was used to determine workability. The concrete's behaviour with BFs was studied using scanning electron microscopy. Experimental work of concrete mixtures with BFs of various lengths (12 mm, 25 mm, and 35 mm) and VFs (0%, 0.5%, 1.0%, and 1.5%) were carried out. The samples did not indicate any agglomeration of fibres or heterogeneity during mixing. The addition of BFs to concrete with VFs of up to 1.50% for all fibre lengths have a significant impact on mechanical properties, also the longer fibres performed better than shorter ones at all volume fractions of BFs. The mix10, which contain BFs with VFs 1.5% and length 35 mm, demonstrated the highest mechanical properties. The compressive strength, splitting tensile, flexural strength, and bond stress of the mix10 were 37.71 MPa, 4.27 Mpa, 6.12 MPa, and 6.75 MPa, an increase of 7.37%, 20.96%, 24.13%, and 11.2% over the reference concrete, which was 35.12 MPa, 3.53 MPa, 4.93 MPa, and 6.07 MP, respectively. The absorption is increased for all lengths by increasing the VFs up to 1.5%. Longer fibres have lower absorption, while shorter fibres have higher absorption. The mix8 had the highest absorption of 4.52%, compared to 3.12% for the control mix. Furthermore, the microstructure of concrete was improved through improved bonding between the fibres and the matrix, which resulted in improved mechanical properties of the composite.