• Journal of the Korea Institute of Building Construction
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• v.16 no.1
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• pp.67-76
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• 2016

Concrete exposed to severely low temperature below $-20^{\circ}C$ should be provided with proper heat supplying curing to protect the concrete from early frost damage at the time of pouring.meanwhile, so far, effective heat curingmethods of the concrete under severely low temperature are not well established in Korea. For this reason, the objective of this paper is to provide effective heat curingmethod of concrete exposed to severely low temperature to protect early frost damage by varying the combination of heat curingmaterial combinations. Temperature history,maturity development and core strength results are investigated. Fourmock-up specimens simulating slab, wall and column were prepared and heat insulation, heat supplying and both were applied. Test results indicate that the combination of quadruple layer bubble sheet(4BS) and embedding of heating cable has desirable performance for a slab, and heat supplying curing inside heat enclosure and heat generationmat also shows desirable performance for a wall, and for a column, use of EPS heat insulation has proper performance against early frost damage, which reaches $45^{\circ}D{\cdot}D$ and helps the concretemaintain above $0^{\circ}C$ within 3 days. Themethodsmentioned above are believed to be optimum protection from early frost damage of the concrete under $-20^{\circ}C$.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.2
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• pp.1-8
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• 2022

The corrosion of reinforcement is the main reason for the performance degradation of concrete structures. The pre-rusted parts of rebar in concrete structures are vulnerable to the corrosion, especially if the structure is exposed to wet or chlorinated environments. In this study, effects of different curing solution on corrosion behavior of the pre-rusted rebars in the cement composites were investigated. HCl(3%) and CaCl₂(10%) solution were utilized to accelerate the pre-rust of the rebar, and each pre-rust condition rebar including reference (RE) were placed in mortar cylinder. Three kinds of samples then were cured in CaCl₂ (3%) solution and tap water respectively for 120 days. Electrochemical polarization and half-cell potential measurement were used to monitor the influence of curing water on the corrosion behavior of pre-rusted steel bar in cement composite. The surface morphology and composition of corroded steel bar were analyzed by scanning electron microscope and energy dispersive X-ray diffraction. The results show that the corrosion rates of pre-rusted samples in both curing water are higher than that of non-pre-rusted samples. The corrosion rates of RE, CaCl₂ and HCl pre-rusted samples in salt water were 8.14, 4.48, 13.81 times higher than those in tap water respectively, on the 120th day.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.1
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• pp.62-69
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• 2023

For the nuclear power concrete plant structures in the UAE, it is necessary to consider the deterioration from high sulfate ions in the atmosphere and high chloride ions from the coast. In this study, two strength grade concrete mixture (40 MPa and 27 MPa) and two curing/diffusion temperatures (20 ℃ and 50 ℃) were considered for evaluating the temperature effects on diffusion and strength due to high average temperature above 38 ℃ a year in UAE. When the initial curing temperature was high, the compressive strength increased in high-temperature curing to 7 days, but the strength slightly increased in the 20 ℃ curing condition at 28 days. Regarding diffusion test, unlike the compressive test results, reduced chloride diffusion coefficients were evaluated both in 40 MPa and 27 MPa grade at 28 days. In the case of 91 days of curing, an increase in diffusivity due to high temperature and a decrease in diffusivity due to age effect occur simultaneously. Compared to the results of the curing and diffusion tests at 20 ℃ and 28 days, when the curing and diffusion tests were conducted at 50 ℃ in 91 days, the diffusion coefficients decreased to 76.2 % in 40 MPa grade and 85.4 % in 37 MPa grade with increasing curing period, respectively.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.303-311
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• 2009

In this study, weakly cemented sand was cured at air dry condition with different periods (3, 7, 14, 21, 28 days) and its unconfined compressive strength was evaluated. As a result, the strength of specimens with low cement ratios such as 4 and 8% increases until 7 days curing but, after 7 days, their strength continuously decreases. The strength of specimens with relatively high cement ratios such as 12 and 16% increases up to 7 days curing and then stays almost constant until 21 days. After 21 days curing, their strength suddenly dropped down, which is much lower than the strength of 3 days curing specimen. A cemented sand and gravel called CSG, which is highly permeable, could be exposed to repetitive drying and wetting conditions due to rainfall or groundwater table change during curing. In this study, the weakly cemented sand is exposed to repetitive drying and wetting and then its unconfined compressive strength was evaluated. As a result, the strength of a specimen with 27 days drying condition following 1 day wetting was at maximum 35% lower than the one cured under 28 days drying. The strength degradation due to wetting decreases as a cement ratio increases. However, the strength of a specimen with repetitive drying and wetting increases as the number of wetting increases until 3 cycles. After 3 cycles of drying and wetting, the rate of strength increase decreases due to an insufficient water for hydration or stays constant. If the sufficient water supply is provided to cemented sand during curing, the target or design strength increase can be achieved. Otherwise, the strength degradation due to wetting should be considered at the design stage.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.4
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• pp.307-315
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• 2023

In this study, mortar test specimens were produced by varying the mixing ratio of CO₂ reaction hardening cement (CSC) and general cement (OPC), and the mechanical and carbonation characteristics were evaluated by controlling the primary curing temperature and secondary curing CO₂ pressure. Under all curing conditions, it was observed that the higher the CSC ratio in the binder, the lower the mechanical properties. Specifically, a first curing temperature of 60 ℃ yielded higher mechanical properties compared to the case of 20 ℃, and a greater carbonation penetration depth was also observed. At a first curing temperature of 60 ℃, it was noted that the curing pressure and bending strength during the second CO₂ curing were inversely proportional, while the compressive strength showed a proportional relationship. This phenomenon is believed to be due to excessive carbonation, which reduces mechanical properties, and the fact that flexural strength is more sensitive to these properties compared to compressive strength. However, based on the evaluation of the limited curing conditions, it is evident that future test conditions need to be expanded and reviewed more thoroughly.

• Journal of the Korean Geotechnical Society
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• v.40 no.3
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• pp.85-91
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• 2024

To realize stable use of ground treated with cementitious materials, the curing process must be evaluated. In this study, a time domain reflectometry (TDR) measurement system was employed to evaluate the curing process of cementitious grout based on the electromagnetic property. A coated probe was manufactured to prevent electrical connection between the electrodes by the electrically conductive cementitious grout, and a calibration process was performed to estimate the actual relative permittivity using the coated probe. To assess the curing process of cementitious grout using the TDR measurement system, cementitious grout with added retarder was prepared with a water-to-cement ratio of 45%. A preliminary measurement was conducted immediately after pouring the cementitious grout into the mold to test the applicability of the coated probe, and TDR signals and relative permittivity were measured at 3~288 hours of curing time. The experimental results demonstrate that the relative permittivity of the cementitious grout immediately after pouring was greater than 100, decreased rapidly over time, and converged to approximately 13.8 at 144 hours, which is considered the fully cured time. This findings of this study demonstrate that the TDR measurement system with a coated probe is applicable to electrically conductive materials. In addition, the TDR measurement system can be used effectively to monitor the curing process of cementitious grout based on electromagnetic properties.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.1
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• pp.139-146
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• 2015

The amount of by-product from sulphur increases in domestic industrial facilities. However, the amount of its consumption is limited so that the amount of unused sulphur continues to increase. Therefore, in this study, the use sulfur polymer as the concrete surface protecting material was conducted. The compressive strength showed that as the substitution ratio of filler increased up to 40%, the compressive strength also increased. A high compressive strength was shown at the curing temperature of $40^{\circ}C$ (SS, FA) and $60^{\circ}C$ (OPC) according to the type of filler. The difference of compressive strength between air dry curing and water curing was insignificant so that there was no significant influence of moisture during curing process. The evaluation result of bond strength showed that the highest bond strength was shown at the air-dry condition of $40^{\circ}C$ regardless of type of filler. Bonding didn't occur properly during water curing in comparison to air dry curing. Also, in case of the specimen cured at $60^{\circ}C$, discoloration and hair cracks appeared due to the influence of temperature, and the highest bond strength was shown at the substitution ratio of 20% (SS, FA) and 30% (OPC) according to the type of filler. The releasing test result of harmful substance showed that no harmful substance was released, so there is no harmfulness in the surface protecting material using sulfur polymer. As a conclusion drawn in this study, it is most appropriate to substitute silica by approximately 20%, mix and cure at the air-dry condition of $40^{\circ}C$ in order to use sulfur polymer as the surface protecting material.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 1994.03a
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• pp.75-80
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• 1994

지반의 진동은 크게 지진과 같은 자연적인 진동과 발파, 항타(piling) 및 중장비의 가동 등에 따른 건설진동 등 인공진동으로 나눌 수 있는데 이들 지반진동은 지상 구조물의 안전도에 큰 영향을 미친다. 특히 양생(養生)중인 모르타르 및 콘크리트의 강도 및 물리적 성질에 큰 영향을 미치기 때문에 선진국에서는 엄격히 제한하고 있다. (중략)

• The Journal of the Korea Contents Association
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• v.14 no.4
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• pp.389-396
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• 2014

This study was conducted as the basic research for the replacement of Blast Furnace Slag, Red Mud, Silica Fume, etc., with cement as a solution to the problems arising from the global warming caused by the generation of $CO_2$, and conducted the experimental review to examine the feasibility of matrix having properties identical to those of cement by using the Blast Furnace slag, Red mud, Silica fume, and alkali-activator. For this, by using the the inorganic binder, such as Blast Furnace Slag, Red Mud, Silica Fume, etc., and NaOH, $Na_2SiO_3$ and others as the cement substitute material, the strength characteristic according to the mixture time variation was performed in the tentative experiment. Based on the preceding experiment, this study performed the experiment to analyze the strength properties of hardener through the curing by air-dry temperature, curing by temperature in water, coating curing, and Korean paper curing. For the water curing at $80^{\circ}C$, the compressive strength and flexural strength were found to be the most excellent at the age of the 28th day, and furthermore, it was found that the non-cement hardener could be made, which is considered to affect the production of eco-friendly concrete.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.693-700
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• 2007

The maturity method is used to estimate the effects of time and temperature on the strength development of concrete. The purpose of this paper is to show how variable curing temperatures affect strength development for both normal and high-strength concrete using the maturity concept. The experimental results for normal-strength concrete show clearly the cross-over effect of strength development as the time of the peak temperature varied. However, this cross-over effect does not exist after the actual ages are converted to the temperature dependent equivalent age. In other words, the existing maturity method does not include the effect of varying the time to peak temperatures but instead includes the effect of the magnitude of peak temperatures. For high-strength concrete, the results were inconclusive. This fact for normal-strength concrete coincides with the ASTM stated limitation that the existing maturity method doesn't take into account the effect of early age temperature on long-term ultimate strength. The results of this 3-year study are used as a basis for an improved concrete maturity function.