• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.490-497
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• 2020

This work has been initiated to find possibility whether recycled fine aggregate can be used as a source of aggregate for structural concrete or not. Two-stage mixing approach was chosen in order to maximize strength potential from recycled fine aggregate. Moisture content of the recycled fine aggregate was changed, and two different types of two-stage mixing approaches were applied to produce cement mortar. The strength of mortar made of 100% recycled fine aggregate by two-stage mixing approaches was compared to that of mortar made of 100% washed sea sand. According to the results, the effect of moisture content on compressive strength was observed from low water cement mortar(W/C 0.3). In case of W/C 0.5 cement mortar, no clear relationship was observed between moisture content and strength development. It was found that two-stage mixing approach has a potential to increase the strength of mortar made of 100% recycled fine aggregate. In case of modified version of two-stage mixing approach which first prepares cement paste and pours recycled fine aggregate into the cement paste, was more effective to increase the strength of mortar made of 100% recycled fine aggregate.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.741-744
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• 2008

There are two ways to reduce cement content for a given quality level(strength, workability etc.) in concrete. First, reducing the required paste volume by varying the shape or the grading of aggregates. Secondly, holding the paste volume constant while replacing cement volume with mineral admixtures or mineral fillers. And It will also be proved that the required minimum paste volume is independent of the paste composition, provided the paste composition is in a reasonable range. In this study, therefore, we have an object to determine the required minimum paste volume for a given workability level. For this purpose, we tried the following experiments: vary the paste volume for the three different grading of aggregates and determine the minimum paste volume to achieve a certain level of workability with high-range water reducing admixture.

• Journal of the Korea Concrete Institute
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• v.13 no.4
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• pp.354-361
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• 2001

In this paper, three kinds of poly(acrylate-co-methylacrylate) with different number average molecular weight(Mn) were synthesized and studied for the effects on the mechanical properties and the fluidities of the cement mortar admixtured with them. The physical properties of the cement mortar are more favorably enhanced by the poly(acrylate-co-methylacrylate) of Mn,, 5,000 than that of Mn, 2,000∼3,000. And the optimum dosage was decided to ca. 0.6 % of cement weight in cement mortar. However, the dispersion abilities of the polymers in cement mortar was not kept long time. This last result could not be explained by the theory that the fluidity of the cement mortar added with the slow releasing polycarboxylates is kept by the releasing of the carboxylic group of the copolymer in alkaline solution of cement paste.

• Journal of the Korea Concrete Institute
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• v.12 no.6
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• pp.51-56
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• 2000

Fly ash used as a cement replacement material increases the long term strength and also improves the durability of concrete and mortar. However, the use of fly ash is a little in spite of great benefit. In order to increase the consumption of fly ash, it has to be used as a cement replacement materials in the production of mortar and concrete, and the reduction of early strength development due to the use of fly ash also has to be diminished. In this study, many chemical compounds which accelerate the early strength was investigated. The $Na_2$$SO_4$, $K_2$$SO_4$, Triethanolamine were selected and applied to the production of mortar. It was found that they enhance the early strength development of mortar(1, 3day) and decrease the amount of $Ca(OH)_2$, and also increase the production of ettringite. According to the results of mercury instruction test, the pores ranged from 0.01 $\mu\textrm{m}$ to 5$\mu\textrm{m}$ were decreased and it was also found in the analysis of X ray and SEM that fly ash increases the amount of ettringite at early ages.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.281-286
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• 2001

The utilization of metakaolin as a pozzolanic material for mortar and concrete has received considerable attention in recent years. This paper estimates the fundamental properties of metakaolin as a pozzolanic material in view of fluidity and compressive strength of cement paste and mortar in comparison of silica fume, fly ash and slag. The results show that in order to obtain the same initial fluidity, metakaolin needs higher dosage of PNS superplasticizer than fly ash and slag, however, less dosage than silica fume. In view of compressive strength of mortar, metakaolin exhibits much higher compressive strength than fly ash and slag, and similar compressive strength with silica-fume when 10 % of cement is replaced with a pozzolanic material.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.501-504
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• 2006

Recycled aggregate mortar contains plenty of calcium hydroxide to improve the strength of blast furnace slag, although the surface mortar made of recycled aggregate deteriorates adhesion to cement paste and blast furnace slag has a low initial strength. Therefore, this study assumes that the combination with both recycled aggregate and blast furnace slag will produce a better performance. The results of the experiment show that dry mortar made of recycled aggregate provides with higher strength than wet mortar does at the 3-day and 7-day age, while lower at the 28-day age. It indicates that a large amount of cement mortar made of dry recycled aggregate has deteriorated adhesion strength. The mixes with 30% and 50% of blast furnace slag and 50% and 75% of recycled aggregate provide with much better strength at the 7-day age, although they usually have latent hydraulic property at the 28-day age. It indicates that calcium hydroxide($Ca(OH){_2}$) in recycled aggregate has affected ground granulated blast furnace slag.

• International Journal of Concrete Structures and Materials
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• v.4 no.2
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• pp.119-125
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• 2010

In this study, the effects of the fineness modulus of reactive aggregate on ASR expansion and ASR products have been investigated. The reactive aggregate used was metamorphic aggregate originated from Korea. ASR tests were conducted according to accelerated mortar bar test. The morphology and chemical composition of products formed in mortar bars, 5 years after the mortar bar test had been performed, were studied by scanning electron microscopy equipped with energy dispersive spectroscopy. Test results indicated that ASR expansion of mortar bars decrease in linear proportion to the fineness modulus of reactive aggregate. SEM images indicated that mortar bars showed reactive products formed in cement paste, within air voids and within cracks through particles except for the mortar bar with the fineness modulus of 3.25. The EDS analysis of the reactive products showed presence of silica, calcium and sodium, typical of ASR product composition.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.807-810
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• 2005

In this study, MMA-modified paste of coating material for protecting the concrete structures was developed. The coating material was applied to cement concrete specimens by brush, roller and spray in each of which one, two and three layers to survey, by the cold-hot iterative test, the neutralization test, the chloride ion permeation test and the ante-abrasion test, the affect of painting methods and layers influencing on the durability of coating material. Results of the cold-hot iterative test showed that, regardless of the painting methods and layers, the defects such as crack or fuzz on surface were not produced. As the number of painting layers increased, the neutralization prevention as well as the chloride ion permeation prevention effects were increased. On the other hand, no difference was found between the painting methods. Reducing weight by abrasion of polymer paste coating material was $20\%$ comparing to that of cement mortar.

• Advances in concrete construction
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• v.3 no.1
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• pp.71-90
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• 2015

In order to investigate the feasibility and advantage of tuff used as pozzolan in cement-based composite, the representative specimens of tuff were collected, and their chemical compositions, proportion of vitreous phase, mineral species, and rock structure were measured by chemical composition analysis, petrographic analysis, and XRD. Pozzolanic activity strength index of tuff was tested by the ratio of the compression strength of the tuff/cement mortar to that of a control cement mortar. Pozzolanic reaction degree, and the contents of CH and bond water in the tuff/cement paste were determined by selective hydrochloric acid dissolution, and DSC-TG, respectively. The tuffs were demonstrated to be qualified supplementary binding material in cement-based composite according to relevant standards. The tuffs possessed abundant $SiO_2+Al_2O_3$ on chemical composition and plentiful content of amorphous phase on rock texture. The pozzolanic reaction degrees of the tuffs in the tuff/cement pastes were gradually increased with prolongation of curing time. The consistency of CH consumption and pozzolanic reaction degree was revealed. Variation of the pozzolanic reaction degree was enhanced with the bond water content and relationship between them appeared to satisfy an approximating linear law. The fitting linear regression equation can be applied to mutual conversion between pozzolanic reaction degree and bond water content.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10c
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• pp.93-98
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• 1998

Fluidity retention of concrete used high range water reducing AE agent(HWAE) is varied according to type, dosage amount and dosing method of HWAE. The type and substitution ratio of mineral admixture also have influence on the fluidity retention of concrete using HWAE. For the purpose of improving the fluidity retention in concrete used HWAE, 3 types of HWAE and ground granulated blast furnace slag(SG) are applied in cement-based composites such as cement paste, mortar and concrete respectively. According to using the HWAE of naphthalene sulfonates and SG, the fluidity retention of mortar and concerete is improving the fluidity retention and strength of concrete regardless of type of HWAE.