• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.11a
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• pp.100-101
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• 2020

In this study, the temperature history and compressive strength of the concretes according to the type of cement were measured and analyzed in comparison as part of the experiment on the material mixing side to reduce the hydration heat crack of the mat foundation constructed with mass concrete. As a result, the peak temperature and maximum temperature reach time of concrete using high rapid cement were shown to be similar to that of semi rapid cement. In particular, in compressive strength after three days, semi rapid cement was measured higher than that of concrete using high rapid cement. Therefore, if semi rapid cement is used in accordance with the site conditions, it is deemed possible to shorten the air due to reduction of temperature cracks and improvement of initial strength.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.44-50
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• 2016

A study to apply phase change material(PCM) to rapid hardening cement paste forming semi-rigid pavement was carried out. The characteristics fresh and hardened paste were evaluated through the experiment for a total of 6 mixtures according to the cement type and the substitution of phase change material for acrylate. The fluidity by substituting phase change material for acrylate satisfied the target flow time of 10 to 13 seconds. In case of setting time, it was possible to secure the performance of rapid hardening cement by substituting phase change material, and if the substitution ratio over 60%, the initial set occurred 1 to 2 minutes faster than other mixtures. In case of compressive strength and bond strength, it showed similar strength characteristics with the plain mixture, and it satisfied both the target compressive and bonding strength of 36MPa and 2MPa. The mixture substituting phase change material showed higher resistance to chloride ion penetration than the mixture only using acrylate and the OPC level was insufficient. From the results of physical and mechanical performances of semi-rigid pavement cement paste, the phase change material substitution rate of 20% was effective in the range of this study.

• Journal of the Korean Ceramic Society
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• v.12 no.4
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• pp.3-8
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• 1975

Hydration processes of the rapid hardening cement clinkers, which were synthesized from domestic alunite for major alumina source, limestone, kaolin and fluorite, were investigated by means of x-ray diffraction analysis, thermal analysis and microscopic observation etc. The clinkers were composed mainly of alite, calcium fluroaluminate (C11A7.CaF2) minerals. While the hydratio processes of the clinkers are altered by concentration of SO3 in the paste, calcium aluminate hydrates such as C4AH13, CAH10 and calcium monosulfate hydrate (C3A.CaSO4.12H2O) are formed at first and then some of them are transformed into ettringite(C3A.3CaSO4.32H2O) within 30~60 min. when the concentration of SO3 in the paste are enough. However the formed ettringite are changed slowly into calcium monosulfate hydrate as the concentration of SO3 become lowered, and the paste is hardened with these close-packed minerals. When the content of SO3 in clinker is so enough, calcium sulfoaluminate hydrates are found without any addition of anhydrite or hemi-hydrite.

• International Journal of Highway Engineering
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• v.17 no.3
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• pp.85-95
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• 2015

PURPOSES : Recently, bonded concrete overlay has been used as an alternative solution in concrete pavement rehabilitation since its material properties are similar to those of the existing concrete pavements. Deteriorated concrete pavements need rapid rehabilitation in order to prevent traffic jams on Korean expressways. Moreover, speedy and effective repair methods are required. Therefore, the use of bonded concrete overlay with ultra-rapid hardening cement has increased in an effort to reopen promptly the expressways in Korea. However, mobile mixer is required for ultra-rapid hardening cement concrete mixing in the construction site. The use of mobile mixer causes various disadvantages aforementioned such as limitation of the construction supply, open-air storage of mixing materials, increase in construction cost, and etc. In this study, therefore, hydration accelerator in-situ mixing on polymer modified concrete produced in concrete plant is attempted in order to avoid the disadvantages of existing bonded concrete overlay method using ultra-rapid hardening cement. METHODS : Bonded concrete overlay materials using ultra-rapid hardening cement should be meet all the requirements including structural characteristics, compatibility, durability for field application. Therefore, This study aimed to evaluate the application of hydration accelerator in-situ mixing on polymer modified concrete by evaluating structural characteristics, compatibility, durability and economic efficiency for bonded concrete overlay. RESULTS : Test results of structural characteristics showed that the compressive, flexural strength and bond strength were exceed 21MPa, 3.15MPa and 1.4MPa, respectively, which are the target strengths of four hours age for the purpose of prompt traffic reopening. In addition, tests of compatibility, such as drying shrinkage, coefficient of thermal expansion and modulus of elasticity, and durability (chloride ions penetration resistance, freezing-thawing resistance, scaling resistance, abrasion resistance and crack resistance), showed that the hydration accelerator in-situ mixing on polymer modified concrete were satisfied the required criteria. CONCLUSIONS : It was known that the hydration accelerator in-situ mixing on polymer modified concrete overlay method was applicable for bonded concrete overlay and was a good alternative method to substitute the existing bonded concrete overlay method since structural characteristics, compatibility, durability were satisfied the criteria and its economic efficiency was excellent compare to the existing bonded concrete overlay methods.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.507-512
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• 2002

In road pavements, it is known that cement concrete pavement has superior durability. But in repairing pavement, cement concrete pavement is not usually applied because of the length of time while the road is interrupted when using Ordinary and Rapid-hardening Portland Cement. And Super High Early Strength Cement and Ultra Super High Early Strength Cement are not favorable for ready mixed concrete because of rapid setting time, high slump loss and other restrictions. We developed special cement developing 1 day strength of over 30.0N/$mm^2$ to open the road within 1 day and workable time is maintained over 1 hour so that it can be used as ready mixed concrete. We performed experimental overlay construction with concrete and evaluated the properties of the fresh and hardened concrete. The flexural strength was over 5.0N/$mm^2$ and the compressive strength was over 30N/$mm^2$ at 1 day. So it is thought that the road can be open to traffic within 1 day after placement.

• Advances in concrete construction
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• v.5 no.2
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• pp.155-171
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• 2017

The phenomenon of concrete column shortening has been widely acknowledged since it first became apparent in the 1960s. Axial column shortening is due to the combined effect of elastic and inelastic deformations, shrinkage and creep. This study aims to investigate the effects of ambient temperature, relative humidity, cement hardening speed and aggregate type on concrete column shortening. The investigation was conducted using a column shortening prediction model which is underpinned by the Eurocode 2. Critical analysis and evaluation of the results showed that the concrete aggregate types used in the concrete have significant impact on column shortening. Generally, aggregates with higher moduli of elasticity hold the best results in terms of shortening. Cement type used is another significant factor, as using slow hardening cement gives better results compared to rapid hardening cement. This study also showed that environmental factors, namely, ambient temperature and relative humidity have less impact on column shortening.

• Journal of the Korea Institute of Building Construction
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• v.11 no.6
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• pp.587-596
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• 2011

Ultra rapid-hardening cement is widely used for latex-modified mortar and concrete as repair and finishing material during urgent work. The purpose of this study is to evaluate the improvements in strength made to SBR cement mortars by the adding of various admixtures and by the use of different curing methods. SBR cement mortar was prepared with various polymer-cement ratios, curing conditions and admixture contents, and tested for flow, flexural and compressive strengths. From the test results, it was determined that the flow of SBR cement mortar increased with an increase in the polymer-cement ratio, and the water reducing ratio also increased. The strength of cement mortar is improved by using SBR emulsion, and is strengthened by adding metakaoline. The strength of SBR cement mortar cured in standard conditions was increased with an increase in the polymer-cement ratio, and attained the maximum strengths at polymer-cement ratios of 15 % and 10 %, respectively. The maximum strengths of SBR cement mortar are about 1.8 and 1.3 times the strengths of plain mortar, respectively. In this study, it is confirmed that the polymer-cement ratio and curing method are important factors for improving the strengths of rapid-hardening SBR cement mortar.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.4
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• pp.95-103
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• 2012

Precast concrete method is known to have advantages of minimizing works in the construction, controlling concrete quality easily and saving construction period due to only fabrication work in the construction field, but it needs to apply steam curing to accelerate early concrete strength. In the meanwhile, the oil cost for steam curing has been continuously increased because of political instability in the middle East and international economic shaky. Thus, this study addresses the development of precast/ prestressed concrete which has over 14MPa at 1 day age and specified concrete strength of 40MPa at low temperature, not applying steam curing. Tests were carried out in terms of material characteristics in fresh concrete and compressive strength using 3 types of cement such as Type I, Type III and rapid hardening compound cement. As results of tests, it is found that cements for rapid hardening had disadvantages with respect to slump, slump loss, and air content, but showed higher compressive strength than specified one, especially the highest value when using rapid hardening compound.

• Magazine of the Korea Concrete Institute
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• v.2 no.4
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• pp.83-90
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• 1990

Ultra Rapid Hardening Cement (LJRHC) makes immediate response, cracks and finally collapses in the 5 % acid solution. Such physical and chemical reaction is assumed to occur beCaUSE) it contains calcium aluminate( 11 Cao . 7AI,O, . CaF,) and the hydrate. This experimental study aims to improve URHC by making up for its weakness, which appears when its pro¬perties are compared with other cements properties, in the Polymer Cement Mortar(PCM) The result are : PCM using URHC proved to be inferior to PCM using other cements in the resistance to the acid in that the former cracked and collapsed after 10 days, and 22 days, in P/C=O%, and 5% respectively. And in P/C=15% and 20 % the PCM using URHC proved to be more resistant to the acid.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.421-428
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• 2020

Recently, excellent thermal and electrical performance of cementitious composites by mixing nano materials are being studied. The purpose of this study is to research the heat generation and power consumption of rapid hardening nano-cementitious composites. The experiment was carried out after setting the rapid hardening cementitious material, curing day, and supply voltage as parameters. Rapid hardening nano-cementitious materials were classified into cement paste, mortar, and concrete The heat performance of all rapid hardening nano-cementitious composites in curing 1 day has increased over 10℃. The rapid hardening nano-cementitious composites can exhibit heat performance within 1 day. The heat performance of the rapid hardening nano-cementitious composites is maintained after 28 days.