• Journal of the Korea Concrete Institute
• /
• v.24 no.5
• /
• pp.597-604
• /
• 2012

The present study assessed the $CO_2$ emissions of concrete according to the type and replacement ratio of supplementary cementitious materials (SCM) and concrete compressive strength using a comprehensive database including 2464 cement concrete specimens and 776 cement concrete mixes with different SCMs. The system studied in $CO_2$ assessment of concrete based on Korean lifecycle inventory was from cradle to pre-construction, which includes consistent materials, transportation and production phases. As the performance efficiency indicators, binder and $CO_2$ intensities were analyzed, and simple equations to evaluate the amount of $CO_2$ emission of concrete were then formulated as a function of concrete compressive strength and the replacement ratio of each SCM. Hence, the proposed equations are expected to be practical and useful as a guideline to determine the type and replacement ratio of SCM and unit content of binder in concrete mix design that can satisfy the target compressive strength and $CO_2$ reduction percentage relative to cement concrete.

• Journal of the Korea Concrete Institute
• /
• v.14 no.1
• /
• pp.24-32
• /
• 2002

The modified compression field theory is already applied in shear problem at some code(AASHTO-1998) partly. Nominal shear strength of concrete beam is sum of the concrete shcar strength and the steel shear strength in the current design code. But Torsional moment strength of concrete is neglected in the calculation of the nominal torsional moment strength of concrete beam In the current revised code. Tensile stress of concrete strut between cracks is still in effect due to tension stiffening effect. But The tensile stresses of concrete after cracking are neglected in bending and torsion In design. The torsional behavior is similar to the shear behavior in mechanics. Therefore the torsional moment strength of concrete should be concluded in the nominal torsional moment strength of reinforced concrete beam. This paper shows that the torsional moment strength of concrete is caused by the average principal tensile stress of concrete. To verify the validity of the proposed model, the nominal torsional moment strengths according to two ACI codes (89, 99) and proposed model are compared to experimental torsional moment strengths of 55 test specimens found in literature. The nominal torsional moment strengths by the proposed model show the best results.

• Journal of the Korea Concrete Institute
• /
• v.13 no.6
• /
• pp.536-543
• /
• 2001

Nowadays, with high-stoned and large-sized of structures, high-strength concrete is applicable to various methods. When high-strength concrete is used jointly with system form, seizing on the development of compressive strength at early age is very important in aspect of construction process. Because system form is stripped more faster than ordinary form. But, we have little data of compressive strength before system-form is stripped, and it isn't yet established that decision criterion of the time when system-form is stripped. So this paper deals with the development of compressive strength at early age before system-form is stripped. In this study, the experimental results indicate the boundary of curing temperature and mixing factor that is able to get needful early-strength in the application of slip-form method, and curing temperature must be kept over 15 degrees in winter season.

• Journal of the Korea Concrete Institute
• /
• v.14 no.2
• /
• pp.137-147
• /
• 2002

Maturity models involving curing temperature and curing ages have been widely used to predict concrete strength, which can accurately estimate concrete strength. However, they may not consider physical quantities such as the characteristics of hydrates and the capillary porosity of microstructures associated with strength development. In order to find out the effects of both factors on a strength increment, the hydration model and the estimation method of the amount of capillary porosity were established, and the compressive strength test of concrete nth various water/cement ratios was carried out considering two test parameters, curing temperature and curing age. In this study, by analyzing the experimental results, a strength estimation model for early-age concrete that can consider the microstructural characteristics such as hydrates and capillary porosity was proposed. Measured compressive strengths were compared with estimated strengths and good agreements were obtained. Consequently, the proposed strength model can estimate compressive strength of concrete with curing age and curing temperature within an acceptable error.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.8 no.1
• /
• pp.1-10
• /
• 2013

In this study utilize industry product for OPC(ordinary portland cement) and BFS(blast furnace slag) mixing concrete early age compressive strength elevation and executed study for high strength binder. Association ratio of industry product for high strength binder manufacture is Titanogypsum (4) : Limestone (3) : Waterworks Sludge by ratio of (3) as it is proper move. high strength binder mixing rate appeared that (7~9) % are proper via preliminary test. Could confirm that display high compressive strength incidence rate in early age than plain harmony according as mix high strength binder mixing concrete compressive strength high strength binder. Also, high strength binder generality that give function than high strength binder used in existing displayed more excellent intensity, and compressive strength displayed result that multiply single breadth according as high strength binder substitute that give function increases.

• Journal of the Korea Concrete Institute
• /
• v.14 no.2
• /
• pp.249-256
• /
• 2002

High performance concrete is prone to large autogenous shrinkage due to its low water to binder ratio (W/B). The autogenous shrinkage of concrete is caused by self-desiccation as a result of water consumption by the hydration of cement. In this study, the autogenous shrinkage of high performance concrete with and without fly ash was Investigated. The properties of fresh concrete, slump loss, air content, and flowability as well as the mechanical properties, compressive strength and modulus of elasticity, were also measured. Test results was shown that the autogenous shrinkage of concrete increased as the W/B decreased. For the same W/B, the autogenous shrinkage of high strength concrete with fly ash was considerably reduced although the development of its compressive strength was delayed at early ages. Furthermore, the autogenous shrinkage and compressive strength of high strength concrete were more rapidly developed than those of normal strength concrete. It was concluded that fly ash could improve the quality of high strength concrete with respect to the workability and autogenous shrinkage.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.4 no.3
• /
• pp.284-291
• /
• 2016

To evaluate the properties of inorganic composites using a great quantity of high-calcium fly ash generated in combined heat and power plants, high-calcium fly ash and F-class fly ash commonly used as concrete admixtures were substituted with binding materials to examine changes of fluidity and compressive strength depending on the substitution ratio for each curing temperature. According to the experimental result, CFA-mixed mortar showed a tendency to reduce its flow unlike FFA-mixed mortar as the substitution ratio was increased, but its flow loss showed smaller than FFA as time passed. As a result of examining compressive strength depending on mixing FA, FFA-mixed mortar had an optimum range within 50% when curing at ambient temperature, but it was found that the compressive strength is reduced when mixing CFA. When curing at high temperature, FFA did not relatively have a great effect on the substitution ratio, but CFA could expect a strength enhancement effect compared with 100% of OPC when using within 25% of binding materials.

• Magazine of the Korea Concrete Institute
• /
• v.9 no.1
• /
• pp.195-206
• /
• 1997

비선형 layered 유한요소법과 비선형 프로그래밍 기법에 의하여 주어진 기존의 철근콘크리트 보의 휨강도 및 연성을 근사하게 나타낼 수 있는 강섬유고강 철근콘크리트 보(Reinforced Steel Fibrous Concrete Beam : RSFC Beam)의 인장 및 압축철근량, 강섬유의 혼입률 등을 산정하였다. 개발된 모델을 이용하여 콘트리트의 압축강도 및 철근비가 서로 다른 일반 철근콘크리트 보에 있어서 강섬유보강 콘크리트를 사용할 경우, 기존 철근을대체하는 강섬유의 량과 또한 이로 인한 인장 \ulcorner 압축 철근량의 변화량을 조사하였다. 기존 문헌에 나타난 강섬유보강 콘크리트보의 전간강도식을 이용하여 일반 철근콘크리트보와 비교하여 강섬유보강 철근콘크리트 보에서 증가될 수 있는 스터럽의 간격을 산정하였다.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2010.05a
• /
• pp.361-362
• /
• 2010

Six alkali-activated(AA) concrete mixes were tested to ascertain the effect of unit binder content on the slump and compressive strength of concrete. Test results showed that the compressive strength of AA-concrete increased with the increase of the unit binder content, while the increasing rate was lower that recorded in ordinary portland cement concrete.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2010.05a
• /
• pp.227-228
• /
• 2010

Five lightweight concrete mixes were prepared to examine the effect of the replacement level of lightweight fine aggregates on the slump loss and compressive strength of lightweight concrete. Test results showed that the increase of the replacement level of lightweight fine aggregate accelerated the slump loss of the lightweight concrete, while had marginal influence on the compressive strength development of the concrete.