• Journal of the Korean Ceramic Society
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• v.46 no.4
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• pp.365-371
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• 2009

It is well known that the properties of concrete such as the compressive strength, water permeability, water tightness and durability are affected by micro-structure in hardened cement paste. Especially, for durability of concrete, watertightness of cementitious materials is the most critical property among various properties. Recently, many types of materials as organic and/or inorganic materials are used for watertightness of concrete. In this study, The effect of Stearic Acid at $0.5\;wt%{\sim}3.0\;wt%$ adding ratios on the hydration and watertightness property of cement were investigated. And we also discussed the changing of microstructure in hardened cement paste by addition of Stearic Acid. Cement paste with Stearic Acid showed improvement of watertightness by reducing of cement total pore volume and decomposition of Stearic Acid.

• Journal of the Korea Institute of Building Construction
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• v.4 no.2
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• pp.81-88
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• 2004

The purpose of this study is to investigate the chemical shrinkage and autogenous shrinkage of high strength cement paste and silica fume and fly ash and sand to cement ratio by the method of volumetric tests, and also investigate the autogenous shrinkage of high measurement method, and compare the results of volumetric test and linear length measurement test. A series of cement paste which have W/C ratio of 25%, 35%, 45% respectively were planed to study the effect of the W/C ratio to the shrinkages, and a series of cement paste which were replaced the cement by the silica fume and fly ash with 5%, 10%, 15% as the mass of cement respectively were planed to investigate the effects of poazolana to the shrinkages. A series of mortar which have a C/S ratio of 1:1, 1:1.5, 1:2 respectively were planed to investigate the shrinkage resistant effect of aggregate.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.949-952
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• 2006

An understanding of rheological property on cement paste is one of the important factor to design concrete such as High-fluidity Concrete (HFC) for a specific application. The HFC is a specially proportioned hydraulic cement concrete that enables the fresh concrete to flow easily into the forms and around the reinforcement and prestressing steel without vibration and segregation. Use of this type of concrete for the concrete building construction, manufacture of precast, prestressed bridge elements provides the benefits of increased rate of production and safety, reduced labor needs, and lower noise levels. This paper presents the performance of rheological properties of cement paste incorporating domestic high-water-reduced-admixture (HWRA) for an Ultra-high-fluidity concrete (UHFC). Investigation was carried out on cement pastes with combinations of various dosages of HWRA and water/cement ratios.

• Journal of the Korea Institute of Building Construction
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• v.19 no.2
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• pp.113-121
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• 2019

Single walled carbon nanotube (SWCNT) has been used as a material for reinforcing various advanced materials because it has superior mechanical properties. However, pure SWCNT that does not have any functional group has a hydrophobic character, and exists as bundles due to the strong Van der Waals attraction between each SWCNT. Due to these reasons, it is very difficult to disperse SWCNTs in the water. In this work, in order to use SWCNT for production of cementitious composites, SWCNT was first dispersed in water to make an aqueous solution. Sodium deoxycholate (DOC) and Sodium dodecyl sulfate (SDS) were chosen as surfactants, and the dosage of DOC and SDS were 2wt% and 1wt%, respectively. Sonication and ultracentrifugation were applied to separate each SWCNT and impurities. Using such processed SWCNT solutions, cement paste was prepared and its shear stress vs. strain rate relationship was studied. The yield stress and plastic viscosity of cement paste were obtained using Bingham model. According to the results in this work, cement pastes made with DOC and SDS showed similar rheological behavior to that of air entrained cement paste. While cement paste made with DOC 2 wt.% SWCNT solution showed similar rheological behavior to that of plain cement paste, cement paste made with SDS 1 wt.% SWCNT solution showed different rheological behavior showing much less yield stress than plain cement paste.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.467-474
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• 2020

Carbon nanotube has excellent mechanical strength and functionality, so it has been utilized in various applications. In recent years, utilization of carbon nanotube in construction material has started to get interests from researchers in the area of construction materials. However, there is limited amount of work with respect to the rheological properties of cement paste using carbon nanotube. In this work, solution made of multi-walled carbon nanotube with dispersing agent of polyvinyl pyrrolidone was used to prepare cement paste specimens, and rheological properties and 28 day compressive strengths of cement paste using multi-walled carbon nanotube were measured. According to the experimental results, as the amounnt of multi-walled carbon nanotube increased, plastic viscosity and yield stress of cement paste specimens also increased. It was also found that such effect was higher with lower w/c cement paste specimens. With respect to the compressive strength, it was maximized at carbon nanotube content of 0.1wt.% for w/c 0.30 cement paste, whereas the maximum strength of w/c 0.40 cement paste was observed with carbon nanotube content of 0.2wt%.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10c
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• pp.191-196
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• 1998

Under concentrational paste and dilute suspension systems, we have been tested the effects in the dosage of two superplasticizers [naphtalenic(NSF) and polycarboxylic(NT-2)] which has been varied from 0 to 2.0 wt%, in both one case of cement Ⅱ-anhydrite and fly ash itself and the other case that cement has been substituted 10wt% to Ⅱ-anhydrite and fly ash. The result of tested zeta potential tells that zeta potential values increase in addition to increasing of the NSF dosage. And it's effect was high in case of fly ash. We has confirmed the 10wt% substitution of Ⅱ -anhydrite and fly ash would be more effective than the cement itself in initial fluidity and stable fluidity. And in case of NT-2 and NSF, addition of 1.0wt% NT-2 improved the fluidity of paste cement more than that for NSF.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.549-554
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• 2001

It is possible for concrete using sea sand to contain chloride ion as well as cation such as Na$^{+}$and $K^{+}$ during mixing process. It is known that some cations such as Na$^{+}$and $K^{+}$ remain in pore solution without binding In this study, therefore, we intend to inspect the behavior of cations in cement paste as well as NaCl, CaCl$_2$ and KCI through analysis of pore solution extracted from cement paste with high pressure vessel. As a result, increase of alkali ions by adding sea sand and admixtures to the fresh concrete means use of the cement contained high alkali contents. In this case, alkali ions in pore solution can decrease durability of cement products causing alkali-aggregate reaction or accelerated carbonation. So it needs to be studied.studied.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.635-638
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• 2005

In this study, the shear box tests are carried out with cement paste in order to quantify the rheological constants. The materials have four level of water-cement ratios in $0.30\~0.45$, with or without high-range water-reducing AE agent. As the results, it was clarified that the rheological constants of cement paste are dependent on the value of shear strain, and the incremental coefficient of yield value is varied with the water-cement ratio and the dosage of high-range water-reducing AE agent.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.413-416
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• 2005

The super early hardening cement is widely used for reducing construction period. But there are some problems with handling the cement because the loss of workability is so big to control. In this study, the fluidity properties of super early hardening cement paste was evaluated at early age of hydration by using gel-time determination method. 4 types of set controlling agent were selected and combinations of them were used for gel-time test. As a result, the gel-time of super early hardening cement paste was extended up to 20 minutes by using the combinations of several types set controlling agent.

• Computers and Concrete
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• v.3 no.5
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• pp.357-373
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• 2006

The concepts of four parameters of nominal water-cement ratio, equivalent water-cement ratio, average paste thickness, fly ash-binder ratio were introduced. It was verified that the four parameters and the mix proportion of mortar can be transformed each other. The behaviors (strength, workability, et al.) of mortar primarily determined by the mix proportion of mortar now depend on the four parameters. The prediction models of strength and workability of mortar were built based on artificial neural networks (ANNs). The calculation models of average paste thickness and equivalent water-cement ratio of mortar can be obtained by the reversal deduction of the two prediction models, respectively. A mortar mix proportion design algorithm was proposed. The proposed mortar mix proportion design algorithm is expected to reduce the number of trial and error, save cost, laborers and time.