• Proceedings of the Korea Concrete Institute Conference
• /
• 1999.04a
• /
• pp.638-644
• /
• 1999

Workability time of superplasticized concrete is maintained generally for 30-60 minutes only. Therefore it is of great advantage for the concrete producer to use a high range water reducer which provides an extended slump life. Recently slump retentive srperplasticizer has been developed. Concrete mixing tests were done to know slump, setting, air content, bleeding and hardening characteristics of concrete using slump retentive superplasticizer. With slump retentive superplasticizer, high quality concrete was produced and slump loss of concrete was reduced in big way, making long transportation time possible as a practical alternative to on-site addition.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.10a
• /
• pp.451-454
• /
• 2000

Recently, the antiwashout underwater concrete has been increasingly used for underwater structure such as high strength massive concrete structures. However, Concrete has poor quality ad durability due to dilution with separating cementitious material. In this study, specimens were made with antiwashout underwater concrete replaced with mineral admixtures to improve their properties and were placed in air, water, and salt water. To estimation the chloride ion permeation in concrete, ASTM C 1202 Test was performed. The experimental results demonstrate that the increase of the admixtures improved the properties of antiwashout underwater concrete.

• Journal of the Korea Institute of Building Construction
• /
• v.7 no.2 s.24
• /
• pp.85-92
• /
• 2007

In the past, recycled aggregate was used very limitedly in low value-added areas such as the base layer of roads. However, in response to the shortage of natural aggregate, high consciousness of resource saving and changed idea on environment, the quality of recycled aggregate has been improved considerably, and the percentage of recycled construction waste is increasing every year compared to simple landfill or incineration. Recently the Act on the Promotion of Construction Waste Recycling was enacted on December 2003 for the efficient use of recycled aggregate, and the Standards for the Quality of Recycled Aggregate for Concrete (Proposal) were announced in order to use and manage recycled aggregate according to quality. According to the Standards for the Quality of Recycled Aggregate for Concrete (Proposal), it is recommended to substitute recycled coarse aggregate and fine aggregate below 30% each. However, compared to the trend of recycling, the recycling rate of aggregate is still quite low. It is because of low performance of recycled aggregate, users' lack of understanding, etc. These problems basically come from the decrease of strength of recycled concrete resulting from the use of recycled aggregate, and recycled aggregate is still considered not reliable because there have been not many cases of actual application. If the basic problem of strength decrease is solved and data on recycled aggregate is provided through actual field placing, we may maximize the use of recycled aggregate. Thus, in order to maximize the use of recycled aggregate that satisfy the recycled aggregate quality standards, the present study made a mock-up similar to real structures, evaluated its performance and examined the field applicability of recycled aggregate concrete.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.11a
• /
• pp.351-354
• /
• 2005

Quality of concrete required to achieve the desired levels of strength and durability depend on the effectiveness of the curing method. During cold weather, the concrete at the time of placement should be taken to prevent damage to concrete due to freezing. Since the cement-water reaction is exothermic by nature, the temperature within mass concrete can be quite high. The temperature control for massive sections should be taken more careful than for shallow sections. However, in the constructing hydraulic structures, the curing temperature control for concrete had been very difficult to be taken in a proper way because the conditions constructing them are poor and contractors are small enterprises. For several. reasons including above, Rural Research Institute has developed a device and program for recording curing temperature history in cold weather concrete and mass. As there are two major advantages of the device, namely cheapness and availability, this program and device has been recommended to the use of curing temperature control in cold weather concrete and mass.

• Journal of the Korean Society of Industry Convergence
• /
• v.4 no.4
• /
• pp.419-426
• /
• 2001

Concrete mix proportioning is a process of selecting the right combination of many materials such as cement, fine aggregates, coarse aggregates, water, and admixtures to make concrete satisfying for specification and cost. In determining proportioning of concrete mixes, code information, specification, and the experience of experts are needed. However, all factors regarding mix proportioning factor cannot be considered. Therefore, the final acceptance depends on concrete quality control test results. The proportioning of concrete mixes and the adjustments are somewhat complicated, time-consuming, and uncertain tasks. In this paper, as a tool to predict the factor of the proportioning of concrete mixes, an artificial neural network is used. To consider the varieties of material properties, the standard mixed table of two companies of ready mixed concrete are used. The results show that neural net works is successfully applied to the prediction of concrete mix proportioning factor.

• Korean Journal of Construction Engineering and Management
• /
• v.7 no.2 s.30
• /
• pp.71-80
• /
• 2006

It is required to study systematical on the concrete quality management to extend structure life because rebuilding effect is reducing under present condition of large sized and high stories structure. Concrete, which shows its intensity by hydrating action and a big change in quality according to hot weather and temperature, produces a lot of quality problem under hot and cold weather. Because of each specification and construction plan which does not have basic standard on site, concrete's quality is irregular and makes some defect. As a result, Dae-gu is fumed out to be the longest area after investigating application period and days focused on 8 cities weather information about t relationship between hot weather circumstance and construction environment. Therefore, we first surveyed the curing construction processing in the region and found out the problem of quality management. Then figure out the way of solution. Moreover, we integrated curing quality management, which is applied differently to each site, to have equal quality and to reduce defect from construction site. And then, based on various test of construction condition and analysis of quality management item, we suggest effective concrete quality management to make curing construction standard guide and plan under hot weather.

• Proceedings of the Korean Society of Agricultural Engineers Conference
• /
• 2002.10a
• /
• pp.157-160
• /
• 2002

This study was developed high-quality a large size precast channel structure using polymer concrete to improve quality of the product as well as to enhance construction quality. Practical precast channel structure design and manufacture procedure for the high polymer concrete were described in this paper. Precast PC represent the fastest growing segment of the polymer concrete industry. The fast curing, high strength, and low impermeability permit thin section and rapid reuse of moulds. Precast channel structure will carry out structural experiment and analysis.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.05b
• /
• pp.145-148
• /
• 2005

Recently, because of the increase of management system about waste concrete and the policy of recycling promotion of government, the use of recycled aggregate is rapidly increasing nowadays. But, due to the poverty of quality and the lack of KS standard, the use of recycled fine aggregate is not active. Therefore, it was intended to compare and investigate effects which types of sand and replacement ratio of recycled fine aggregate. As the result of this study, in the case of the recycled replacement ratio of 25$\%$, fresh and engineering properties were higher than those of natural fing aggregates with the exception of durability. Also, because quality according to types of fine aggregate shows the difference between various properties, it was considered that the profound study for this result would be necessary.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2015.05a
• /
• pp.204-205
• /
• 2015

Exterior insulation board in cast-in-place concrete form system could reduce construction period and improve quality in apartment construction. However, the method is progressed with insulation and concrete frame works at the same time, then risk is increased in duration control and quality management. Therefore, this paper analyzed risk factors through FMEA method. We found that the key risk factors delaying schedule was insulation material that soaked in the rain and quality defects on the insulation material joint. Based on this research, the risk management approach should be developed for improvement of method activation.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.401-404
• /
• 2008

This study exploited the design of mixture proportion for the high strength concrete to establish the method of the quality control and high strength ready-mixed concrete for the application to the construction filed systematically how to output the estimated formula which could forecast mixture proportion for the high strength concrete classed 40${\sim}$60MPa through a experiment. It might contribute for systematic establishment of the method of the quality control and high strength ready-mixed concrete because it was possessed of the function of common data though a server, preservation and output of data, and estimation for the design of mixture proportion for the high strength concrete due to the experimental result, and Visual Basic, MS-SQL were used. Simply, it was produced corresponding to the condition of a laboratory, so it could be fundamental data for the design of mixture proportion for the high strength concrete. If upgrade is enforced with mixture proportion data of the each factory after then, it may contribute to the stability on quality and manufacture of high strength ready-mixed concrete to agree with the properties of each factory.