• International Journal of Concrete Structures and Materials
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• v.8 no.4
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• pp.327-333
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• 2014

The objective of this work was to examine the influence of carbonation on the microstructure of cement materials. Different materials, which were CEM I mortar and paste, CEM II mortar and paste, were carbonated at $20^{\circ}C$, 65 % relative humidity and 20 % of $CO_2$ concentration. The specific surface area and pore size distribution were determined from two methods: nitrogen adsorption and water adsorption. The results showed that: (1) nitrogen adsorption and water adsorption do not cover the same porous domains and thus, we observed conflicts in the results obtained by these two techniques; (2) the CEM II based materials seemed to be more sensible to a creation of mesoporosity after carbonation than the CEM I based materials. The results of this study also helped to explain why observations in the literature diverge greatly on the influence of carbonation on specific surface area.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2005.05a
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• pp.69-72
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• 2005

Recently, there have been many studies seeking towards the utilization of cementitious powder from concrete waste as recycle cement. However, most of the studies actually have been researches about the reuse of mortar or paste, not concrete waste. In fact, either mortar or paste is quite different from a real concrete waste in terms of age and mixture. Thus the purpose of this study is to examine basic physical properties of recycle cement, manufactured with cementitious powder from concrete waste, and analyze differences in chemical and hydraulic properties of the cement and its tested model. As a result of the chemicai analysis, recycle cement is composed mainly of CaO and SiO2, and that it is even lower in the content of CaO than Portland cement, which is also supported by previous studies. But, Differently from previous studies, plastic working at the temperature of 650 was found an optimal condition under which cementitious powder from concrete waste could restore its hydraulic properties.

• Journal of the Korea Institute of Building Construction
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• v.5 no.3 s.17
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• pp.109-116
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• 2005

Recently, there have been many studies seeking towards the utilization of cementitious powder from concrete waste as recycled cement. However, most of the studies actually have been researches about the reuse of mortar or paste, not concrete waste. In fact, either mortar or paste is quite different from a real concrete waste in terms of age and mixture. Thus the purpose of this study is to examine basic physical properties of recycled cement, manufactured with cementitious powder from concrete waste, and analyze differences in chemical and hydraulic properties of the cement and its tested model. As a result of the chemical analysis, recycle cement is composed mainly of CaO and $SiO_2$, and that it is even lower in the content of CaO than Portland cement, which is also supported by previous studies. But, Differently from previous studies, calcining temperature of 650 was found an optimal condition under which cementitious powder from concrete waste could restore its hydraulic properties.

• Computers and Concrete
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• v.8 no.2
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• pp.163-176
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• 2011

By virtue of chord-length density function from the field of statistical physics, this paper introduced a quantitative approach to estimate the distribution of cement paste thickness between aggregates in concrete. Dynamics mixing method based on molecular dynamics was employed to generate one model structure, then image analysis algorithm was used to obtain the distribution of thickness of cement paste in model structure for the purpose of verification. By comparison of probability density curves and cumulative probability curves of the cement paste thickness among neighboring aggregates, it is found that the theoretical results are consistent with the simulation. Furthermore, for the model mortar and concrete mixtures with practical volume fraction of Fuller-type aggregate, this analytical formula was employed to predict the influence of aggregate volume fraction and aggregate fineness. And evolution of its mean values were also investigated with the variation of volume fraction of aggregate as well as the fineness of aggregates in model mortars and concretes.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.1
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• pp.95-102
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• 2011

Vicker's hardness and pore size distribution of mortar adhered to the recycled coarse aggregate were tested according to the strength level of original concrete of recycled coarse aggregate to find the change of mortar adhered to the recycled coarse aggregate in cement paste. The strength levels of original concrete of recycled coarse aggregate were 25.5MPa, 41.7MPa and 60.1MPa and the aggregates were used at the state of saturated surface dry condition and oven dry condition. The results of this experimentation indicated that the mean value of Vicker's hardness was increased according to age and strength of original concrete of recycled aggregate. Porosity of $100nm{\sim}10{\mu}m$ size was reduced and porosity of 6nm~100nm size was increased in cement paste.

• Journal of the Korean Ceramic Society
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• v.27 no.3
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• pp.437-443
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• 1990

The resistivity of cement paste and mortar for freezing and thawing was investigated for densifying the structure of cement paste and mortor, slag, diatomaceous earth and fly ash as blending materials and superplasticizer were used, and air entraining agent was added to absorb the volume expansion by freezing and thawing reaction. And then the specimens were subjected to freeze-thaw in water. When both of air entraining agent and superplasticizer as additives were mixed to specimens, their freeze-thaw resistance was enhanced by the air entraining effect and the water reduction effect. When 4% of slag were added to cement, freeze-thaw resistance was especially excellent. In addition, it was found that the specimens with blending materials were more influenced by curing periods than those without admixture. It is assumed that the curing periods contribute to exibit the potential hydraulicity and pozzolanic reactivity of blending materials and to densify their texture.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.365-368
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• 2005

Waste concrete powder(WCP) has been estimated with a great value-added material as by-product of waste concrete manufactured to fine and coarse aggregate for concrete, because it is able to utilized for cement clinker and concrete admixture. Experimental tests were performed as such plastic viscosity of paste, flow and compressive strength of mortar by surface area of WCP. As a result, flow and 28days compressive strength of mortar was decreased according to increased replacement ratio of WCP as compared to control mortar. Also, plastic viscosity of paste used WCP1 and WCP2 was decreased with increasing replacement ratio, but WCP3 was increased with increasing replacement ratio.

• Earthquakes and Structures
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• v.5 no.4
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• pp.477-497
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• 2013

This paper reports extensive experimental study done to compare workability and bond strength of five different types of polymer-based bonding agents for reinforcing bars in pinning retrofit. In pinning retrofit, steel pins of 6 to 10 mm diameters are inserted into holes drilled diagonally from mortar joints. This technique is superior to other techniques especially in retrofitting historic masonry constructions because it does not change the appearance of constructions. With an ordinary cement paste as bonding agent, it is very difficult to insert reinforcing bars at larger open times due to poor workability and very thin clearance available. Here, open time represents the time interval between the injection of bonding agent and the insertion of reinforcing bars. Use of polymer-cement paste (PCP), as bonding agent, is proposed in this study, with investigation on workability and bond strengths of various PCPs in brick masonry, at open times up to 10 minutes, which is unavoidable in practice. Corresponding nonlinear finite element models are developed to simulate the experimental observations. From the experimental and analytical study, the Styrene-Butadiene Rubber polymer-cement paste (SBR-PCP) with prior pretreatments of drilled holes showed strong bond with minimum strength variation at larger open times.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.888-893
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• 1998

Calcium sulfoaluminate, $C_4$A$_3$$\bar{S}$, was prepared for reutilizing industrial by-products, such as II-CaSO$_4$, Al(OH), CaF$_2$ and cement sludge wastes. Mixed powder was fired at 1,15$0^{\circ}C$. $C_4$A$_3$$\bar{S}$ clinkers fired at 1,15$0^{\circ}C$ were analyzed by SEM and XRD. Also were added in cement paste and mortar and characterized as setting time, flow values and compressive strength. $C_4$A$_3$$\bar{S}$ could be found in the X-ray diffraction pattern. The setting time of cement pastes added clinkers fired at 1,15$0^{\circ}C$ was shorter than that of ordinary portland cement. Also the compressive strengths of the cement mortar added clinkers was higher than those of ordinary portland cement.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2005.05a
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• pp.211-214
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• 2005

Recently, Deterioration of the concrete sewer concrete structures by biochemical corrosion has been issued and a development of the inhibition system of corrosion that has been demanded. The sulfuric acid may react with the hardened cement paste and originate expansive products which can induce swelling and breakless of concrete. Also, a sulphuric acid reacts with calcium hydroxide to from $CaSO_4\;\cdot\;2H_2O$. This reaction accounts for consumption of the calcium hydroxide present in hardened cement paste. In this study, To present from biochemical corrosion of the sewer repair mortar that was spread with liquefied antibiotic and then its experimental properties were experimentally investigated and to estimate the effect of absorbed condition of restorative mortar, the number of coating times and coating contents with antibiotic on the durability properties of restorative mortar spread with antibiotics. Also, testing items such as carbonation depth, choloride ion penetration depth and chemical resistance was tested to estimate the durability properties in third study. In results, the novellus bacillus inhabiting in sewer concrete structures was restrained by antibiotics developed in this study. And carbonation depth, choloride ion penetration depth and chemical resistance of restorative mortar spread with antibiotics was superior to that of plain mortar.