• Journal of the Korea Concrete Institute
• /
• v.22 no.4
• /
• pp.559-566
• /
• 2010

Fifteen lightweight concrete mixes were tested to evaluate the effect of maximum size of coarse aggregate and the replacement level of natural sand on the various properties of fresh lightweight concrete. The different properties, such as water absorption against the elapsed time, pore size distribution and micro-structure of lightweight aggregates used, influencing on the workability of fresh concrete were also measured. Test results showed that the initial slump of lightweight concrete decreased with the increase of the replacement level of natural sand. The slump of all-lightweight concrete sharply decreased by around 80% of the initial slump after 30~60 minutes. The air content and bleeding rate of lightweight concrete were significantly affected by the replacement level of natural sand as well as the maximum size of coarse aggregates. Empirical equations recommended in ACI 211 and Korea concrete standard specifications underestimated the air content of the lightweight concrete, indicating that the underestimation increases with the decrease of the replacement level of natural sand. In addition, equations to predict the air content and bleeding rate of lightweight concrete were proposed based on the test results.

• Journal of the Korea Concrete Institute
• /
• v.23 no.5
• /
• pp.551-558
• /
• 2011

The effect of the maximum aggregate size and substitution rate of natural sand on the mechanical properties of concrete is evaluated using 15 lightweight aggregate concrete mixes. For mechanical properties of concrete, compressive strength increase with respect to age, tensile resistance, elastic modulus, rupture modulus, and stress-strain relationship were measured. The experimental data were compared with the design equations specified in ACI 318-08, EC2, and/or CEB-FIP code provisions and empirical equations proposed by Slate et al., Yang et al., and Wang et al. The test results showed that compressive strength of lightweight concrete decreased with increase in maximum aggregate size and amount of lightweight fine aggregates. The parameters to predict the compressive strength development could be empirically formulated as a function of specific gravity of coarse aggregates and substitution rate of natural sand. The measured rupture modulus and tensile strength of concrete were commonly less than the prediction values obtained from code provisions or empirical equations, which can be attributed to the tensile resistance of lightweight aggregate concrete being significantly affected by its density as well as compressive strength.

• Journal of the Korea Concrete Institute
• /
• v.27 no.3
• /
• pp.229-236
• /
• 2015

This paper describes the effect of aggregate size on compressive behavior of high-strength steel fiber reinforced concrete. The Specified compression strength is 60 MPa and the range of fiber volume fraction is 0~2%. The main variable is the aggregate size, which was used for the aggregate size of 8 and 20 mm. So, ten concrete mixtures were prepared and tested to evaluate the fresh and hardened properties of SFRC at curing ages (7, 14, 28, 56 and 91 days), respectively. Items estimated in this study are the fresh properties (air contents, slump), hardened properties (compressive strength, modulus of elasticity, post-peak response and compressive toughness). As a result, the aggregate size has little effect on the compressive strength and modulus of elasticity. On the other hand, the ductile behavior was shown after post peak and the compressive toughness was increasing as decreasing the aggregate size. These effects are clearly represented in the fiber volume fraction 2%, which are the point appeared fiber ball. It is considered that the decreasing the aggregate size has effect on the fiber dispersibility.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.18 no.6
• /
• pp.1-10
• /
• 2014

In this study, thirteen reinforced concrete beams, ground granulated blast furnace slag, replacing recycled coarse aggregate with PVA fiber (BSPG series) and recycled coarse aggregate with hybrid fiber ($BSPGR_1$, $BSPGR_2$ series), and standard specimen (BSS) were constructed and tested under monotonic loading. Experimental programs were carried out to improve and evaluate the Structural performance of such test specimens, such as the load-displacement, the failure mode, and the maximum load carrying capacity. All the specimens were modeled in 1/2 scale-down size. Test results showed that test specimens ($BSPGR_1$, $BSPGR_2$ series) was increased the compressive strength by 13%, the maximum load carrying capacity by 4~21% and the ductility capacity by 4~28% in comparison with the standard specimen (BSS). And the specimens ($BSPGR_1$, $BSPGR_2$ series) showed enough ductile behavior and stable flexural failure.

• Journal of the Korea Concrete Institute
• /
• v.23 no.4
• /
• pp.431-440
• /
• 2011

Concrete structures exposed to fire produce changes in their internal structure, resulting in their service life reduction due to the deterioration of its strength and performance capacity. The deterioration level are dependent on the temperature, exposure time, concrete mix proportions, aggregate property, and material properties. This study was performed to evaluate the thermal behavior of ultra-high strength concrete for the parameters of water to cement ratio (compressive strength), fine to total aggregate ratio, and maximum coarse aggregate size. At room temperature and $500^{\circ}C$, tests of ultrasonic pulse velocity, resonance frequency, static modulus of elasticity, and compressive strength are performed using ${\varnothing}100{\times}200\;mm$ cylindrical concrete specimens. The results showed that the residual mechanical properties of ultra-high strength concrete heated to $500^{\circ}C$ is influenced by variation of a water to binder ratio, fine to total aggregate ratio, and maximum coarse aggregate size.

• Journal of the Korea Concrete Institute
• /
• v.17 no.3 s.87
• /
• pp.329-334
• /
• 2005

The use of Polymer Concrete (PC) is growing very rapidly in many structural and construction applications such as box culverts, hazardous waste containers, trench lines, floor drains and the repair and overlay of damaged cement concrete surfaces in pavements, bridges, etc. However, PC has a defect economically because resin which be used for binder is expensive. Therefore the latest research is being progressed to replace existing resin with new resin which can reduce the high cost. Here, Polymer concrete using the recycled PET(polyethylene terephthalate) has some merits such as decrease of environmental destruction, decrease of environmental pollution and development of new construction materials. The variables of this study are amount of resin, curing condition and maximum size of coarse aggregate to find out mechanic properties of this. Stress-strain curve was obtained using MTS equipment by strain control. The results indicated that modulus of elasticity was increased gradually in an ascending branch of curve, as an increase of resin content. Compressive strength was the highest for resin content of $13\%$. And Compressive strength was increased as maximum size of coarse aggregate increases. The strain at maximum stress increases with an increase of resin content and size of coarse aggregate. For the descending branch of stress-strain curve the brittle fracture was decreased when it was cured at the room temperature compared to high temperature.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.10 no.3
• /
• pp.185-196
• /
• 2006

Fracture toughness is a material property for crack initiation and propagation in fracture mechanics. For mode I fracture toughness measurement in concrete, RILEM committees 89-FMT proposed three-point bend tests based on the two-parameter fracture model. But, there is no proposed test method as a standard for mixed mode test for now. And RILEM three-point bend test procedure is complicate. Therefore, in this study, brazilian disks of various size were designed as the concrete with a similar specified concrete strength and maximum size of coarse aggregate($G_{max}$) were respectively 20mm and 40mm. And mode I fracture toughness of brazilian disks was compared with that of RILEM three-point bend test. As a result, it was suggested appropriate size(thickness, diameter) and notch length ratio of brazilan disk on the $G_{max}$. And it was verified that stress intensity factors for mixed mode can be easily calculated with the disk specimen. Stress intensity factors of a concrete brazilian disk were evaluated with finite element analysis and five terms approximation for comparison.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.24 no.5
• /
• pp.95-102
• /
• 2020

For the purpose of developing a PE fiber-reinforced highly ductile cementitious composite having high tensile strain capacity more than 2% under the condition of containing aggregates with large particle size, this study investigated the tensile behavior of composites according to the particle size and distribution of aggregates in the composite. Compared with the mixture containing silica sand of which particle size is less than 0.6 mm, mixtures containing river sand and/or gravel with the maximum particle size of 2.36 mm, 4.75 mm, 5.6 mm, 6.7 mm were considered in the experimental design. The particle size distributions of aggregates were adjusted for the optimized distribution curves obtained from modified A&A model by blending different sizes of aggregates. All the mixtures presented clear strain-hardening behavior in the direct tensile tests. The mixtures with the blended aggregates to meet the optimum curves of aggregate size distributions showed higher tensile strain capacity than the mixture with silica sand. It was also found that the tensile strain capacity was improved as the maximum size of aggregate increased which resulted in wider particle size distribution. The mixtures with the maximum size of 5.6 mm and 6.7 mm presented very high tensile strain capacities of 4.83% and 5.89%, respectively. This study demonstrated that it was possible to use coarse aggregates in manufacturing highly ductile fiber-reinforced cementitous composite by adjusting the particle size distribution.

• 한국방재학회:학술대회논문집
• /
• 2011.02a
• /
• pp.178-178
• /
• 2011

도로소음은 다양한 소음원에 의해 발생하며, 도로를 이용하는 사람과 도로 주변사람에게 큰 불편을 초래한다. 보다 쾌적한 환경을 원하는 현대인에게 있어 도로 소음의 경감은 중요한 환경 공해로 작용한다. 도로 소음을 줄이기 위해서는 여러 가지 방법이 있을 수 있으며, 이 중 도로 포장의 개선을 통해 도로 소음을 경감할 수 있으며, 이와 같은 포장을 저소음 포장이라고 한다. 저소음 포장은 주행하는 차량의 타이어와 노면이 마찰하면서 발생하는 소음을 최소화하기 위한 것으로 소음 발생의 메커니즘을 바탕으로 하고 있다. 저소음 포장중 가장 널리 사용되고 있는 방법은 공극을 늘리는 것이다. 약 20%의 공극은 타이어와 노면 사이의 에어펌핑음을 최소화 하며, 소리를 흡수하는 역할로 약 3dB의 소음 가소 효과가 있는 것으로 알려져 있다. 소음을 감소시키는 또 하나의 방법은 노면의 표면 조직을 매끈하게 하여 타이어와 노면의 충격음을 줄이는 방법이다. 노면의 평탄성을 개선하기 위해 포장에 사용되는 골재의 최대크기를 줄이는 소입경 포장을 소음 가소의 목적으로 유럽 등지에서 많이 사용되고 있다. 본 연구에서는 이와 같은 저소음 기능을 위해 공극률을 크게 하고 소입경 골재를 사용하는 소입경 저소음 포장의 현장 적용을 위한 배합 설계를 수행하였다. 소입경 저소음 포장의 최대 골재 크기는 현장 적용성과 경제성을 고려하여 10mm 골재를 사용하였으며, 수도권에서 입수한 4곳의 산지 골재를 분석하여 골재 합성 입도를 산정하였다. 10mm 저소음 포장의 골재 입도 범위는 공극률 15~18%를 목표로 하며, 이를 만족하기 위하여 배합 설계를 수행한 결과 5mm 통과 중량 백분율이 약 30%로 하는 개립도가 적당한 것으로 나타났다. 공극이 증가함에 따라 포장의 내구성 향상을 위해 사용된 고점도 바인더는 아스팔트 혼합물의 생산 및 시공온도를 증가시키게 된다. 또한 굵은골재의 비율이 높은 개립도 아스팔트 혼합물의 경우 운반과정과 포설 과정에서 온도가 빨리 떨어지는 단점이 있다. 이를 극복하기 위하여 중온 첨가제의 사용을 통해 생산 및 다짐온도를 낮추고자 하였다. 소입경 저소음 포장의 배합설계 과정은 배수성 포장의 배합설계 과정과 유사하나, 칸타브로 손실률과 흐름실험의 변곡점을 기준으로 할 경우, 칸타브로 손실률과 흐름 손실률이 매우 작아 변곡점을 판단하기 어렵기 때문에 칸타브로 손실률과 흐름 손실률의 기준 만족 여부로 판별하고, 최적 아스팔트 함량은 공극률을 기준으로 산정하는 것이 바람직할 것으로 판단된다. 중온 첨가제를 사용할 경우는 중온 첨가제로 인한 점도의 변화를 감안하여 혼합 및 다짐 온도를 결정하고 배합 설계를 수행하며, 중온 첨가제의 특성과 양에 따라 최적 아스팔트 함량이 변화하게 된다.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.14 no.4
• /
• pp.357-365
• /
• 2016

We observed the ${\gamma}-ray$ shielding characteristics and compressive strength of five types of concrete using general aggregates and high-weight aggregates. The aggregates were classified into fine aggregate and coarse aggregate according to the average size. The experimental results obtained an attenuation coefficient of $0.371cm^{-1}$ from a concrete with the oxidizing slag sand (OSS) and oxidizing slag gravel (OSG) for a ${\gamma}-ray$ of $^{137}Cs$, which is improved by 2% compared with a concrete with typical aggregates of sand and gravel. In the unit weight measurement, a concrete prepared by iron ore sand (IOS) and OSG had the highest value of $3,175kg{\cdot}m^{-3}$. Although the unit weight of the concrete with OSS and OSG was $3,052kg{\cdot}m^{-3}$, which was lower than the maximum unit weight condition by $123kg{\cdot}m^{-3}$, its attenuation coefficient was improved by $0.012cm^{-1}$. The results of chemical analysis of aggregates revealed that the magnesium content in oxidizing slag was lower than that in iron ore, while the calcium content was higher. The concrete with oxidizing slag aggregates demonstrated enhanced ${\gamma}-ray$ shielding performance due to a relatively high calcium content compared with the concrete with OSS and OSG in spite of a low unit weight. All sample concretes mixed with high-weight aggregates had higher compressive strength than the concrete with typical sand and gravel. When OSS and IOS were used, the highest compressive strength was 50.2 MPa, which was an improvement by 45% over general concrete, which was achieved after four weeks of curing.