• The Journal of Engineering Geology
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• v.18 no.2
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• pp.227-232
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• 2008

In this study, the pull out resistance characteristics of an anchor bar to support a spillway installed in a slope are investigated by field tests. The injection materials were a cement mortar and cement milk. Unconfined compression strengths of those materials under several conditions were measured. As the result of compression test, the unconfined compression strengths of the cement mortar and the cement milk have positive proportional relation-ship with the water-cement ratio. They also have negative proportional relationship with increasing the curing time. In the same condition of water-cement ratio and curing time, the unconfined compression strength of cement milk is larger than that of cement mortar. In order to reduce the eccentricity in anchor bar during pull-out test in the field, the installation apparatus was improved by inserting a nut type of steel fixing coupling into the anchor bar. As the result of the pull-out test, the strength modification of cement milk was increased steeply at the early curing time. However, that of cement mortar was increased gradually with passing the curing time. Therefore, the cement milk has to use as the injection material for a prompt construction of anchor bar because the strength modification of cement milk is occurred at the early curing time.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2004.05a
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• pp.1-4
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• 2004

In this paper. applicability of high early strength type AE water reducing agent(HESAEWA) developed by the authors is discussed by applying Mock-up test. For fresh concrete properties, concrete using existing AE water reducing agent(EAEWRA) and HESAEW A meets the target slump and air content at jobsite. Setting time of concrete using HESAEWA is shorter than that using EAEWRA. Remarkable variance of bleeding and settlement is not observed with type of AE water reducing agent. For hardened concrete properties, use of HESAEW A results in higher strength development compared with that of EAEWRA at standard curing and in field curing condition. Reaching time to accomplish 5MPa of compressive strength. which is possible to remove side form. is taken using HESAEWA earlier than that of EAEWRA by 1day. Therefore, it is confirmed that use of HESAEWA can meet the requirements of general quality of concrete and achieve high early strength development as well as has a desirable field applicability.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.55-56
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• 2023

Recently, large and high-rise buildings are increasing, and accordingly, concrete weight reduction is required. Lightweight aggregate concrete can provide economic feasibility and large space, but safety can be reduced due to problems such as low strength and poor durability. Since the development of such low strength of concrete is important in the early construction stage, it is necessary to evaluate the vertical formwork demolding period at the early age. The correlation was analyzed by measuring the compressive strength and ultrasonic pulse velocity. As a result, the ultrasonic pulse rates of normal and lightweight aggregate concrete at the time of 5 MPa expression, which is the time of vertical mold deformation, were 3.07 km/s and 2.77 km/s for W/B 41, and 2.89 km/s and 2.73 km/s for W/B 33.

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.137-147
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• 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 Korea institute for structural maintenance and inspection
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• v.16 no.2
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• pp.58-64
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• 2012

Due to the influence of global oil prices, industrial productivity, which oil consumption is high, was significantly reduced. AC type of high-strength PHC piles is being manufactured through twice the steam curing process and this have resulted in a significant rise for product's manufacturing costs. NAC way other types of file manufacturing process has the advantage of reducing manufacturing costs by a turn of the steam curing. Nevertheless, because the initial strength be poor than that of AC method, shipment is being after the curing period of approximately three days. In addition, the growth of the product enhance with curing period can not be avoided, as a result, cost of inventory is acting as the rise. Piles by the AC method is immediately shipped after curing, damaging problems does not occur when they are introduced to the field site (for example, pile on-site). In the case of NAC, however, at least after the curing period of three days and after expressing the strength of 80 MPa or more, they are shipped on the scene. Therefore, NAC type has problems as follows: (1) increase in moderate inventory holding costs with type and (2) breakage in the field due to lack of strength. In this study, for NAC-typed PHC files, mixing characteristics research for the strength development at 1 day equivalent to AC method were conducted and strength characteristics with changes of original materials were evaluated were also identified.

• Journal of the Korea Institute of Building Construction
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• v.16 no.1
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• pp.1-7
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• 2016

In this research, it used cement powder and reduction slag, which generates high hydration heat in hydration reaction without heat cure below $-5^{\circ}C$ degree. Purpose of final research is preventing freezing and thawing by making the compressive strength 5MPa in 3days below zero temperature due to own heat of concrete. and it is the result of physical characteristic and thermal property evaluation of reduction slag. Because reduction slag generates high hydration heat, compressive strength development is excellent. By generating highly hydration heat by $C_{12}A_7$ and $C_3A$ in reduction slag, compressive strength is developed in low temperature. In case of displacing only reduction slag without $SO_3$, it is indicated that quick-setting occurs by shortage of $SO_3$. For preventing quick-setting, gypsum is used essentially. According to this research result, in case of using reduction slag and gypsum as a ternary system, compressive strength developed 5MPa in 3 days below zero temperature. It is identified to prevent early frost damage of concrete below zero temperature.

• Journal of the Korea Institute of Building Construction
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• v.15 no.4
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• pp.367-373
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• 2015

In this study, fundamental properties of cement were reviewed to apply high fineness cement at low temperature environment. The classified high fineness cement has large proportion of particles below $10{\mu}m$ which affects early hydration: an overall reaction of cement hydration faster. As a result of using high fineness cement, setting time of concrete was reduced and compressive strength was higher than OPC at all ages. Especially, compressive strength was more than double its value compared with OPC after three days curing in low temperature. Faster reaction and higher heat of hydration was verified by calorimetry early and maximum heat of hydration was analyzed by adiabatic temperature raising test. The analysis of this study confirmed that high fineness cement can be suitable to be used in low temperature environment.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.2
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• pp.105-111
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• 2023

In this study, the mechanical properties of high-strength concrete according to the substitution rate of NSH(Non-sintered Hwangto) as an alternative material for cement were measured and evaluated. Through UPV(Ultrasonic pulse velocity) analysis, the compressive strength prediction equation was proposed, and the substitution rate of NSH was set at 15 % and 30 %. The evaluation items were compressive strength and UPV, and the curing period was set to 24 hours. In compressive strength and UPV, as the NSH substitution rate increased, lower strength and lower UPV were shown. In addition, the correlation number(R² ) between compressive strength and UPV was 0.99 for NC(Normal Concrete), 0.97 for NSHC(Non-sintered Hwangto Concrete)33-15, and 0.94 for NSHC33-30.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.379-386
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• 2020

The present study examined the effect of bottom ash aggregate contents on the compressive strength gain and mechanical properties(modulus of elasticity and rupture and splitting tensile strength) of concrete. Main test parameters were water-to-cement ratio and bottom ash aggregate contents for replacement of natural sand. Test results showed that the 28-days compressive strength of concrete and mechanical properties normalized by the compressive strength tended to decrease with the increase in bottom ash fine aggregate content. When compared with fib 2010 model equations, bottom ash aggregate concrete exhibited the following performances: lower rates of compressive strength gain at early ages but greater rates at long-term ages; slightly higher measurements for modulus of elasticity and rupture; and lower measurements for splitting tensile strength.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.4
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• pp.116-124
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• 2015

The objective of this study is to evaluate the effects of the replacement levels of grinded fly-ash on the repaired mortar based on a polymer. The main parameters are the curing temperature and replacement levels of grinded fly-ash. The curing temperature and the replacement levels of grinded fly-ash are varied at $40^{\circ}C$, $20^{\circ}C$ and $5^{\circ}C$, and between 0% and 35% of the total binder by weight, respectively. The flow in fresh mortar and compressive strengths according to ages, the relationship of stress-strain, elastic modulus and modulus rupture in hardened mortar, as well as scanning the electron microscopy and the X-ray diffraction of mortar, were measured, respectively. The test results showed that the flow, elastic modulus and modulus rupture are great in mortar specimens with 20~30% of the replacement levels of grinded fly-ash. In addition, compressive strengths according to ages were affected by the replacement levels of grinded fly-ash and the curing temperature indicated that the strength development ratio of mortar with 20% of the replacement levels of grinded fly-ash was greater than others. In the prediction of the compressive strength specified by the ACI 209 code, the strength development at an early and late age can be generalized by the functions of the replacement levels of grinded fly-ash and the curing temperature. In the analysis of scanning the electron microscopy and the X-ray diffraction, the number and intensity of peaks increased and the form of CSH gels on the surface of the particle of grinded fly-ash was observed.