• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.973-981
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• 2002

Recently, the use of high strength concrete (HSC) has increased dramatically md however, few studies have been conducted on the early-age properties of HSC such as setting. The penetration resistance test (specified by KS F 2436) that is the standard test method for determining initial and final setting times of concrete, may not be appropriate for HSC because of the high viscosity of the mortar mixture. To address this issue, an ultrasonic pulse velocity (UPV) monitoring system was used to investigate the setting behavior of mortar and concrete. The experimental study was carried out to measure the UPV's of mortars and concretes having various water/binder ratios (W/B) and various fly ash replacement levels, during the first 24 hours of testing. Test results showed that the UPV in concrete was developed faster than that of mortar with the same W/B, and that of ordinary concrete was greater than that of fly ash concrete. Typical values of UPV were suggested that correspond to the initial and final setting times, based on following criteria: (1) the penetration resistance method; (2) the instant when the UPV begins to develop; and (3) the instant when the UPV development rate is maximum. The method and UPV monitoring device used in this study is promising for the setting assessment of concrete, particularly for HSC.

• Advances in concrete construction
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• v.11 no.4
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• pp.307-314
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• 2021

Activated hwangtoh (ACT) is a natural resource abundant in South Korea, approximately 15.0% of soil. It is an efficient mineral admixture that has activated pozzolanic properties through high-temperature heating and rapid cooling. The purpose of this study is to improve a curb mixture that can reduce NOx outside and investigate durability performance. To this end, mortar curb specimens were manufactured by replacing OPC with ACT. The ACT substitution ratios of 0.0, 10.0, and 25.0% were considered, and mechanical and durability tests on the curb specimens were conducted at 28 and 91 days of age. Steam curing was carried out for three days for the production of curbs, which was very effective to strength development at early ages. The reduction in strength at early ages could be compensated through this process, and no significant performance degradation was evaluated in the tests on chloride attack, carbonation, and freezing and thawing. The mortar curb with an ACT of 10.0~25.0% replacement ratio exhibited clear NOx reduction through photocatalytic (TiO2) treatment. This is due to the increase in physical absorption through surface absorption and the photocatalyst-containing TiO2 coating. In this study, the reasonable range of the ACT replacement ratio for NOx reduction was quantitatively evaluated through a comprehensive analysis of each test.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.2
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• pp.185-194
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• 2004

In recent years, construction company makes inroads into the world construction market, and receives the order of extra-large concrete structure under marine environment in south-east asia specially. At this point of time, to enhance the quality of concrete, we research the High Strength Concrete (HSC) containing mineral admixtures. In this study, therefore, HSC with various combination of ordinary portland cement(OPC), blast-furnace slag(SG), silica fume(SF), and expansion admixture(SS) are cured 23 and $35^{\circ}C$ considering the site weather, and are cured in water for 3, 7 or 56 days respectively. Test results show that the HSC cured at $35^{\circ}C$ gains higher early-age strength but eventually gains lower later-age strength compare with the HSC cured at $23^{\circ}C$. Especially, HSC with combination of OPC+SG+SF+SS or OPC+SG+SF show very excellent resistance of chloride penetration. The permeability of HSC was therefore enhanced as because of containing the proper content of SG, SF, and SS and making dense micro-structure of HSC.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.95-104
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• 2005

The research conducted to study the potential practicability of recycled aggregate concrete by analyzing the characteristics of concretes made of recycled quality aggregates produced by wet and dry process has found the following results. The air content of recycled aggregate concrete increased with increase of the substitut on rate due to mortar included while producing recycled aggregates. However, the concretes with aggregate produced by dry process had relatively low rate of increase in air content. The slump showed generally decreasing trend as the substitution rate of recycled aggregate increased regardless of the wet or dry process. It was assumed that the mortar particles remained in recycled aggregate absorbed the surplus hydration in concrete and decreased fluidity The compressive strength generally decreased as the substitution rate of recycled aggregate increased, however there was an increasing trend as well due to decreasing effect of water-cement ratio when the substitution rate of recycled aggregate reached 25, 50% after mix. This phenomena also appeared in early age, which meant that recycled aggregate concrete should not be retarded in setting when applied in the field. The tensile strength also reached the maximum when wet or dry recycled aggregate replaced with 25%. To conclude, recycled aggregates for concrete produced by wet or dry process are expected to demonstrate essential characteristics of concrete without significant decline in physical or dynamic quality when the substitution rate is below 25% although there are variations subject to water-cement ratio. However, slight differences are expected due to types of recycled aggregate and physical quality.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.3
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• pp.78-83
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• 2010

This paper presents the feasibility of incorporating ultrafine particles collected in the separator bag filter (separator bag filter cement, SBFC) during the cement manufacturing process as an substitution material for cement. SBFC does not require additional processes needed in the existing processes to manufacture high early strength cement such as modifying mineral components and adjusting the firing temperature. Moreover, it can also solve the issue of efficiency decrease resulted from the increase of the grinding time applied in the existing process of manufacturing microcement. Therefore, this research has examined the characteristics of SBFC and fresh properties and mechanical properties after making paste and mortar using SBFC in order to use SBFC as a material to gain early strength of concrete. For results, analyzing the chemical composition and physical properties of SBFC, its blaine value was $6,953cm^3/g$, about double than that of OPC, but its chemical composition showed no significant difference. According to the result of the paste and mortar examination, the paste and mortar mixed with SBFC showed a lower flowability, earlier setting time, and higher compressive strength than that with OPC. The result of microstructure analysis of paste, the paste mixed with SBFC indicated about 9% lower internal porosity at an early age than that of OPC. The compressive strength and flexural strength of mortar were higher in the order of SBFC ratio of 100, 50 and 0% SBFC.

• Korean Institute of Interior Design Journal
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• v.13 no.5
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• pp.11-20
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• 2004

F. L. Wright was, from his early days, influenced by Japanese Culture and endeavored his original concept of orgonic orchitecture. In his 1st Golden Age, he devoted to establish an architectural concept of Organism which was proved by the theories of New Science and also had been universal in ancient Orient. Later, in his 2nd Golden Age, he tried to embody his unique concept in prairie houses and office buildings. The organic structure and spatial unit that actually applied to these works, were good examples of realization of the simplicity and continuity which he found out in Japanese culture. This paper is to study on the influence of Japanese culture on a course of Wright's embodying his organic architecture, and to study on a way of its realization in his works. To be concrete, main contents of the study are as follows; 1) the relationship between Wright's integrate perception and the orientalism 2) the influence of the traditional Japanese painting like woodblock prints and the aesthetic theory of the traditional Japanese pictorial art on Wright's design principles 3) the influence of Wright's experiences in Japan on his design principles 4) the influence of Wright's analysis of the traditional Japanese dwelling on his design principles 5) the course of Wright's embodying his organic architecture concept, and the way of its realization in his works.

• International Journal of Highway Engineering
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• v.13 no.2
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• pp.115-123
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• 2011

This study was conducted to investigate the early-age behavior and performance of precast pavements constructed by replacing existing asphalt pavements for an intersection in urban bus only lanes. The monitoring items included level differences between asphalt pavement and precast panels at the beginning and ending locations of the precast pavement, level differences and joint widths between precast panels, precast panel settlement, and skid resistance of the panel surface. At a certain time after the construction, the diamond grinding method was applied and its effect was also investigated. The monitoring results showed that as time went by, the panel level, joint width, settlement, and skid resistance were not much varied. That implied the stable sustaining of external loads by the precast pavements. In addition, it was verified that employing diamond grinding could reduce the level differences between precast panels.

• International Journal of Highway Engineering
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• v.13 no.1
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• pp.229-237
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• 2011

This study was conducted to investigate the early-age performance of precast pavements constructed by replacing existing asphalt pavements for a bus stop section in urban bus only lanes. The behavior monitoring items included the differences in the levels between asphalt and precast pavements at the entrance and exit of the precast pavement, joint widths and level differences between precast slabs, slab settlement, and skid resistance at the slab surface. The applicability of diamond grinding techniques was also investigated. The results of this study showed that the slab level, joint width, settlement, and skid resistance were not much changed as time passed, which implied that the precast pavements stably sustained vehicle loads. It was also found that employing diamond grinding could much improve the leveling between precast slabs and the surface skid resistance.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2012.11a
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• pp.103-105
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• 2012

With blast-furnace slag is a by-product generated when pig iron is produced. It has been used as the concrete admixture due to high reactivity. However, It causes low strength development during early age. In order to make up for this drawback, in this study, we evaluated compressive strength of mortar replaced with high volume blast-furnace slag. Experimental results, Compressive strength of mortar based on blast-furnace slag is affected by cement type, substitution rate of blast-furnace slag and pH after mixing.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2005.05a
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• pp.45-48
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• 2005

This study is basic experiment for estimating influence of strength by curing temperature of concrete's heat of hydration and estimate relationship of compressive strength development by initial curing temperature factor, and then asume temperature factor which influence compressive strength development and for showing basic document of qualify control. According to the result of cement mortar by the curing temperature factor high-curing temperature shows high strength on 3 day compare with low curing-temperature, shows higher strength than the piece of high curing temperature.