• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.05b
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• pp.113-117
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• 2009

Fly ash (called FA hereafter) that results from thermal power plants is a long-term strength improving substance with reactivity to pozzolan and has been used for long. However, large amount of FA shows many advantages such as reduction of hydratio energy, long-term improvement in strength and economic feasibility and also has difficulties from reduction in initial strength and durability. In a preceding study, fine particle cement was applied to test the effects on initial strength. Therefore in this study, the effects of fine particle cement on the quality of FA concrete were reviewed. The results can be summarized as follows. Liquidity was increased by the most at FC substitution ratio of 15%. Air capacity was reduced according to increasing substitution ratio of FA and FC. Compressive strength showed high strength expression at all ages when FC was substituted at 45%. Synthesizing the above results, appropriate mixing of FC in FA concrete can improve liquidity, reduce unit quantity and show improvement in strength. In particular, mixed use of FC seems effective in improving early quality of concrete.

• International Journal of Concrete Structures and Materials
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• v.9 no.4
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• pp.487-498
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• 2015

A proper initial curing is a very simple and inexpensive alternative to improve concrete cover quality and accordingly extend the service life of reinforced concrete structures exposed to aggressive species. A current study investigates the effect of wet curing duration on chloride penetration in plain and blended cement concretes which subjected to tidal exposure condition in south of Iran for 5 years. The results show that wet curing extension preserves concrete against high rate of chloride penetration at early ages and decreases the difference between initial and long-term diffusion coefficients due to improvement of concrete cover quality. But, as the length of exposure period to marine environment increased the effects of initial wet curing became less pronounced. Furthermore, a relationship is developed between wet curing time and diffusion coefficient at early ages and the effect of curing length on time-to-corrosion initiation of concrete is addressed.

• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.560-564
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• 2001

Nowadays, according to the trend of a high performance of concrete structure, the research results have been announced for the purpose to make the high quality. With this respect, we began research to use the Ground Calcium slurry Carbonate (GCC) to a concrete admixtures which ground the limestone until about $1.5mutextrm{m}$. In this paper, we examined the quality of GCC to fine out the value in use as the concrete admixtures. And mechanical properties of concrete using cement blended with GCC, silica fume and mixed two were investigated. It was result from this study that air contents of concrete replaced with GCC were constant regardless of replacement ratio, but the more GCC it had the use of, the less slump was measured. Especially 10% GCC concrete had a good result of compressive strength. In case of mixture with GCC and silica fume, the workability and compressive strength don't seem to be any problems. In the scope of this study it was indicated that the most reasonable replacement with GCC was 10% of cement weight as concrete admixture.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2003.11a
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• pp.9-12
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• 2003

High flowing concrete has not spread whole in the normal concrete structure, because it requires special quality control technique. And recently owing to the lack of natural resources and reinforcement of environmental standard, the construction cost of cement is increased rapidly. Also rem icon industry has gone through various economical difficulty as the manufacture cost of concrete is increased. So, the purpose of this study is to evaluate the qualities of middle fluidity concrete using the fly-ash and portland blast-furnace slag cement in order to decrease the amount of cement and resolve the problem of the quality control of high flowing concrete and the manufacture cost. The results of this study show that it reduce the amount of addition of superplasticizer and develope properties of concrete to the use the fly-ash and portland blast-furnace slag cement.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2005.11a
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• pp.63-66
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• 2005

Recently, Trouble of sand supply is occurred according to exhaustion of natural sand resources. therefore, various measures are proposed for solution of trouble of sand supply also the government settled trouble of sand supply through application of crushed sand. but because both crushed sand are poor against general sand, they lead to lowering of qualify of ready-mixed concrete. Therefore, this study evaluated engineering property and durability of concrete using crushed sand and applied evaluation result to fundamental data for quality control of concrete using crushed sand. The results of this study have shown that quality of concrete using crushed sand independently is poor against general concrete. but, the workability, compressive strength and durability of concrete mixed crushed sand with genera can improve on those of concrete used general sand.

• Journal of the Korea Institute of Building Construction
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• v.3 no.3
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• pp.107-112
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• 2003

This study is to investigate the properties of concrete with crushed sand on site and to propose a quality guideline for its use as artificial sand and concrete. From our experimental result in laboratory and site, we found that demand water of concrete with crushed sand for target slump increased by 18kg/m3 compared to mixed sand and l8kg/m3 compared to sea sand respectively. The compressive strength increased by around 3∼6% when compared to concrete with sea sand. Accordingly, our study showed that the combined sand mixed with sea sand would be desirable to obtain workability and strength of concrete including dry shrinkage and bleeding test. Furthermore, the optimal replacement percentage of crushed sand was 50% with sea sand. As such, crushed sand would be sufficient as fine aggregate for concrete in terms of economic efficiency and quality. Crushed sand, on the other hand can only be used as fine aggregate when VFS(Very Fine Sand) is below 3.5 percentage of weight of sand and particle shape is above 55 percentage. Also, the particle shape and microsand passing NO.200 sieve should continually be improved to increase workability of concrete on site.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.10
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• pp.11-18
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• 2018

In this study, the cross-sectional image has been acquired to evaluate the aggregate distribution affecting quality of lightweight aggregate concrete, and through the binarization method, the study is to calculate the aggregate area of upper and lower sections to develop the method to assess the aggregate distribution of concrete. The acquisition of cross-section image of concrete for the above was available from the cross-sectional photography of cleavage tension of a normal test specimen, and an easily accessible and convenient image analysis software was used for image analysis. As a result, through such image analyses, the proportion of aggregate distribution of upper and lower sections of the test specien could be calculated, and the proportion of aggregate area U/L value of the upper and lower regions of concrete cross-section was calculated, revealing that it could be used as the comprehensive index of aggregate distribution. Moreover, through such method, relatively easy image acquisition methods and analytic methods have been proposed, and this indicated that the development of modeling to assess aggregate distribution quantitatively is available. Based on these methods, it is expected that the extraction of fundamental data to reconsider the connectivity with processes in concrete will be available through quality assessment of quantitative concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.605-608
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• 2008

We have studied statistically about quality difference of Blast furnace slag Type Ⅲ that affects carbonation of concrete. According to KS F 2563 blast furnace slag was classified 3 types. Type Ⅲ blast furnace slag(specific surface area is $4000cm^2/g$) from different providers with Type A, the B and the C. The statistical technique was applied to exclude error of engineering judgement. T test and F test were used among 3 groups to investigate statistical meaning. The effect which on the quality of blast furnace slag type Ⅲ that affects carbonation of concrete is significant.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.4
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• pp.320-327
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• 2015

This study implicates a quality evaluation technique for lining concrete using the ultra-sonic technique and proposed a classification for quality evaluation. From the comparison of test results, an improved result comparable to the results by destructive test can be obtained by using averaged transmission velocity of velocities obtained at pure space and central space between two sensors of ultrasonic tester. It is also shown that strength evaluation by ultra-sonic method is not reliable and an evaluation according to the transmission velocities can be improved method for the strength evaluation of concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.1
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• pp.125-130
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• 2010

It is necessary to re-establish the code and to control the quality of the recycled aggregate itself for ensuring the useability of the recycled aggregate using waste concrete. Generally, adhering mortar cause of the water absorption ratio increment and strength decreased at the surface of the aggregate of the recycled aggregate using waste concrete, thus removing the adhering mortar could increase the useability of the recycled aggregate in the concrete industry. In this study, as a quality control method of the recycled aggregate using waste concrete, the quality characteristic of the recycled aggregate according to the mixing proportion between the recycled and the natural aggregate is obtained Therefore, a system is established to reuse the recycled aggregate in the construction industry.