• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.853-856
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• 2005

A low water/cement ratio leads to autogenous shrinkage of cement paste at an early age. This autogenous shrinkage is related to the change of relative humidity in the pore structure that is formed during the hydration process. The relationship between autogenous shrinkage and relative humidity change are relatively well defined today, but the effects of temperature on autogenous shrinkage, relative humidity, and pore structures have been studied less systematically. This study focused on correlating alterations of these properties of cement paste hydrated at constant temperatures of 20, 40, and $60^{\circ}C$. The test results clearly indicate that increasing curing temperature resulted in increased porosity, particularly for pores between 5 to 50 nm as measured by MIP, and increased autogenous shrinkages, as a consequence of a reduction of relative humidity at early ages.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.567-570
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• 2000

This study is designed to manufacture the continuous foamed concrete and the sound absorption characteristics investigation due to continuous voids ratio. According to the results of experiment, it was shown that continuous voids of the foamed concrete has the influence of the amount used of foaming agent, the viscosity and flowability of cement paste, and also is shaped by cohesive power of bubbles. Also the sound absorption ratio of the foamed concrete is subject to increase as the density becomes low by raising the continuous voids ratio. The cement paste with low water-cement ratio and high cement fineness are very effective to prevent weak strength of formed concrete caused by the increase of the porosity.

• Korean Journal of Materials Research
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• v.13 no.2
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• pp.94-100
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• 2003

The interface between low carbon steel and blended cement pastes containing slag was investigated using impedance spectroscopy. In addition, the pastes were characterized by several analytical methods (XRD, EDX, electrode potential, pH and ICP). The electrical behavior of the interface in the blended slag systems is correlated to its corresponding pore solution chemistry and the products present in the interface. Passivation occurred at the paste/steel interfaces, in cement pastes up to containing from 0 to 75% slag content. 100% slag paste induced corrosion of the low carbon steel, which could be explained by the influence of sulfur on the system.

• Journal of the Korean Ceramic Society
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• v.31 no.3
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• pp.330-336
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• 1994

High strength cement composites (W/C=0.1) were prepared by using various blending materials such as SiC whisker and white carbon (hydrated silica: SiO2·nH2O). The effect of various blending materials on the microstructure and strength of the hardened cement paste were investigated in the view of fracture mechanics. The plain specimen showed 101 MPa of flexural strength, 81 GPa of Young's modulus and 1.32 MPam1/2 of fracture toughness. When the blending materials were added to the composites, their values were enhanced to about 110∼138 MPa, 95∼146 GPa and 1.32∼1.87MPam1/2 respectively. The improvement of the mechanical strength for the hardened cement paste may be due to the removal of macropores, the reduction of total porosity, pozzolanic reaction and the increase of various fracture toughening effect.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.725-728
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• 2006

This research investigates the characteristics of chloride fixation in non-sintering cement(NSC) matrix. NSC was manufactured by adding phosphogypsum and slack lime to granulated blast furnace slag as sulfate and alkali activators. As a result, the concentration of chloride ion in pore solution of NSC-solidified matrix is more low than that of OPC-solidified matrix containing the same chloride content in cement paste. Also, the concentration of chloride ion in pore solution of NSC-solidified matrix is similar with that of BSC-solidified matrix containing the same chloride content in cement paste.

• 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 Korean Ceramic Society
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• v.40 no.12
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• pp.1229-1234
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• 2003

The utilization of metakaoline as a mineral admixture for cement has received considerable attention in recent years. This paper investigates the rheological properties of cement pastes containing metakaoline in view of fluidity. The rheology of the paste is assessed by using a BROOKFIELD RVDV II + viscometer (SC4-21, 29) having cylindrical spindle. The results show the fluidity of cement pastes with metakaoline is increased by increasing W/S ratio and the dosage of superplastcizer. And also cement pastes with metakaoline as a partial replacement of cement show a dilatant behavior. Dilatancy is heavily influenced by W/S ratio and by the amount of metakaoline. However the thixotropy of the pastes is increased by silica fume.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2003.11a
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• pp.77-82
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• 2003

The purpose of this study is development of technique to use cementitious powder as recycle cement produced from deteriorated Concrete waste which has a large quantity of calcium carbonate. Therefore, after having theoretical consideration based on the properties of high-heated concrete and concerning about neutralization of Concrete, we analysis chemical properties of ingredients of cementitious powder. After making origin cement paste, then processing the accelarated carbonation, we consider the properties of hydration and chemical properties of cementitious powder under various temperature conditions. As a result of the thermal analysis, the CaCo3 content of cementitious powder would affect decision of heat temperature to recover its hydrated ability because CaCo3 content is increased when neutralization is progressed. And as a result of XRD analysis, in case of origin powder of non-neutralized paste, CaO peak is found at 700℃. but, heat temperature to generate CaO would increase when the content of neutralized ingredients is increased. Finally, recycle cement heated at 700℃ shows the best compressive strength when the content of neutralized ingredients in recycle cement is less then 50%. However, it would be quite difficult to manage quality of recycle cement according to recycling points of various concrete waste.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2003.05a
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• pp.77-82
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• 2003

The purpose of this study is development of technique to use cementitious powder as recycle cement produced from deteriorated Concrete waste which has a large quantity of calcium carbonate. Therefore, after having theoretical consideration based on the properties of hish-heated concrete and concerning about neutralization of Concrete, we analysis chemical properties of ingredients of cementitious powder After making origin cement paste, then processing the accelerated carbonation, we consider the properties of hydration and chemical properties of cementitious powder under various temperature conditions As a result of the thermal analysis, the CacO3 content of cementitious powder would affect decision of heat temperature to recover its hydrated ability because CacO3 content is increased when neutraliTation is preBlessed. And as a result of XRD analysis. in case of origin powder of non-neutralized paste, CaO peak is found at $700^{\circ}C$. but, heat temperature to generate CaO would increase when the content of neutralized ingredients is increased. Finally, recycle cement heated at $700^{\circ}C$ shows the best compressive strength when the content of neutralized ingredients in recycle cement is less then 50%. However, it would be quite difficult to manage quality of recycle cement according to recycling points of various concrete waste.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.111-118
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• 2014

The present study concerns the leachability of alkali ions from hardened cement paste in terms of an increase in the pH together with the rate of alkali leaching. To evaluate the influence of mix design on the leaching capacity and rate of alkali, different water-cement ratios (W/C) and binders were used to manufacture paste specimens. The cement paste was made in the form of rectangular bucket where deionised water was subsequently supplied as solvent media. Then the specimen was wrapped in polythene film to avoid contact to atmospheric conditions, which may affect the water chemistry in the bucket. The pH of media was monitored until no further change in the pH value was observed, of which value then used to calculate the leaching capacity and rate. The influence of binder on the pH of solvent is more dominant than that of water to cement ratio: OPC paste produced the highest level of alkali leaching, whilst 30% PFA and 60% GGBS pastes imposed lower level of alkali leaching. After the monitoring of the pH, the inner bucket was ground with an increment of 1.0 mm to measure the leaching influence using the suspension consisting of paste powder and deionised water. It was found that the impact zone for OPC was about 7-8 mm, whilst 30% PFA and 60% GGBS had deeper impact depth of the alkali leaching.