• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2013.11a
• /
• pp.68-71
• /
• 2013

Reactive Powder Concrete (RPC) is an ultra high strength and high ductility cement-based composite material and has shown some promise as a new generation concrete in construction field. It is characterized by a silica fume-cement mixture with very low water-binder (w/b) ratio and very dense microstructure, which is formed using various powders such as cement, silica fume and very fine quartz sand (0.15~0.4mm) instead of ordinary coarse aggregate. However, the unit weight of cement in RPC is as high as 900~1,000 kg/㎥ due to the use of very fine sand instead of coarse aggregate, and a large volume of relatively expensive silica fume as a high reactivity pozzolan is also used, which is not produced in Korea and thus must be imported. Since the density of RPC has a heavy weight at 2.5~3.0 g/㎤. In this study, the modified RPC was made by the combination of ternary pozzolanic materials such as blast furnace slag and fly ash, silica fume in order to economically and practically feasible for Korea's situation. The fire resistance and structural behavior of the modified RPC exposed to high temperature were investigated.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.2 no.2
• /
• pp.100-106
• /
• 2014

High strength concrete has a structural advantage as well as superior usability and durability, so that its application in building is being steadily augmented. However, in the high temperature like in a fire, the high strength concrete has extreme danger named explosive spalling. It is known that the major cause of explosive spalling is water vapour pressure inside concrete. General solution for preventing concrete from spalling include applying fire protection coats to concrete in order to control the rising temperature of members in case of fire. The purpose of this study is to investigate the high temperature properties of fireproof mortar using organic fiber and various types of fine aggregate for fire protection covering material. The results showed that addition of perlite and polypropylene fiber to mortar modifies its pore structure and reduces its density. This causes the internal temperature to rise. As a results, it is found that a new fireproof mortar can be used in the fire protection covering material in high strength concrete.

• International Journal of Highway Engineering
• /
• v.17 no.3
• /
• pp.49-58
• /
• 2015

PURPOSES : The use of environmentally friendly construction methods has been recently encouraged to reduce fuel consumption and the effects of global warming. For this purpose, the roller compacted concrete pavement (RCCP) construction method has been developed. RCCP is more environmentally friendly and economically efficient than general concrete by reducing the amount of CO2 generated through the application of a smaller amount of cement. RCCP has a number of advantages such as an easy construction method, low cost, high structural hydration performance, and aggregate interlocking. However, mix design standards and construction guidelines of RCCP are required for domestic application. In addition, a study on aggregate selection, which has an effect on the characteristics of RCCP, is necessary owing to a limited number of researches. Thus, the aggregate effect on the performance of RCCP in securing the required strength and workability was evaluated in consideration of domestic construction. METHODS : Sand and coarse aggregates of both 19mm and 13mm in maximum size were used in this study. Four types of aggregate gradations (s/a = 30%, 58%, and 70% for the sand and coarse aggregate of 19mm in maximum size, and s/a = 50% for a combination of the three types of aggregates) were set up to investigate the effects of the PCA band on the RCC characteristics. The conditions of s/a = 30% and 70% were evaluated to check the gradation effect outside of the recommended band. The conditions of s/a = 58% and 50% were used because they are the optimum combination of the two and three types of aggregates, respectively. RCCP gradation band was suggested gradation with a proper construction method of RCCP by synthetically comparing and analyzing the correlation of optimum water content, maximum dry density, and strength of requirements through its consistency and compaction test. RESULTS : The lower and upper limit lines are insufficient to secure a relatively strong development and workability compared to an aggregate gradation in the RCCP gradation band region. On the other hand, the line in the RCCP gradation band and the 0.45 power curve in the RCCP gradation band region were satisfactory, ensuring the required strength and workability. CONCLUSIONS : The suitable aggregate gradation on RCCP process should meet the RCCP gradation band area; however, fine particles passing through a #60 sieve do not need to be within the recommended gradation band because the influence of this region on such fine particles is small.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.15 no.5
• /
• pp.75-81
• /
• 2011

Recently prestressed concrete bridges are generally used instead of reinforced concrete. PSC is more durable than RC because it can reduce crack problems, reinforcement corrosion, leakage and carbonation etc. And also PSC is more effective because there is no crack in tension area, and the entire concrete section is considered in section analysis. And it can reduce section size because vertical component by prestressing force can reduce the shear force. However, using high strength concrete can increase the self weight of bridge because of it's higher density. So the hollowed PPC girder with light weight aggregate can be a alternative. In this study the hollowed PPC girder with light weight aggregate is designed and the performance of hollowed PPC girder is evaluated by experimental tests as well as numerical analysis. As a result, The hollowed PPC girder of light aggregate behaved fully elastically under service load of 110kN, and the plastic behavior was showed after elastic behavior through experimental test, and it can be also estimated by numerical analysis.

• Economic and Environmental Geology
• /
• v.54 no.5
• /
• pp.515-533
• /
• 2021

Based on the supply location, demand location, and transportation network, aggregate supply-demand characteristics and aggregate distribution status were analyzed from the results of the closest distance, service areas, and location-allocation scenarios using GIS network analysis. As a result, it was found that the average transport distance of aggregates from the supplier was 6 km on average, the average range of 7 km for sand, and 10 km for gravel was found to reach the destination. In particular, the simulated service area covers about 92% in Seoul-Gyeonggi Province, 85% in Busan-Ulsan-Gyeongnam Province, and more than 90% in Daejeon-Sejong-Chungnam Province. These results have a significant implication in quantitatively interpreting primary data on aggregate supply-demand. Furthermore, these results suggest the possibility of a wide-area quantitative analysis of aggregate supply regions necessary for establishing a basic aggregate plan. The results also evaluated by the site-allocation scenario show that aggregate supply may be possible through companies less than 200 with large-amounts quarries, which is the 700 companies currently supplying small amounts of aggregates on the country. Therefore, in terms of distribution of aggregates, a policy approach is needed to form an appropriate market for regions with high and low density of aggregate supply services, and the necessity of regional distribution and re-evaluation is suggested through an aggregate supply analysis demand across the country. Furthermore, in analyzing the supply-demand network for the aggregate market, additional research is needed to establish long-term policies for the aggregate industry and related industries.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.561-564
• /
• 2008

Concrete is considered to be one of the excellent and versatile shielding material and is widely used for the radiation shielding material. Specially, heavyweight(or high density) concrete is used in counter weights of bascule and lift bridges, but it is generally used in radiation shielding structures and differ from normal weight concrete by having a higher density and special compositions to improve its attenuation properties. Thorough examination and evaluation of heavyweight aggregate sources are necessary to obtain material suitable for the type of shielding required. Therefore, this paper aims to study mechanical properties of heavyweight concrete by using normal cement, natural and heavyweight aggregate.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.3 no.2
• /
• pp.132-139
• /
• 2015

In this study, the different unit cement content by the ratio of water absorption and water-cement ratio are applied to examine the properties of the concrete used the aggregate recycled by the crushing treatment. According to the experimental results, in the mix of low strength and high water-cement ratio, both of the compressive strength is almost equal in the concrete using the recycled aggregate by the crushing treatment and the concrete using broken stones. It means that the recycled aggregate has the low effect of the amount of bonded mortar. But, in the mix of high strength and low water-cement ratio, the concrete using the recycled aggregate by the crushing treatment has 40% less of the compressive strength than that using broken stones by the effect of the amount of bonded mortar. On the other hand, after 8 weeks, the dry shrinkage of the recycled aggregate with 7% of the ratio of water absorption doubles that of the broken stones with 1% ($-350{\times}10^{-6}$), in other words $-700{\times}10^{-6}$. Thus, the dry shrinkage should be prior to any other conditions in recycling waste concrete for the aggregate for concrete. When the recycled aggregate with 3% of the ratio of water absorption is used, the compressive strength of the rich mix concrete ($450kg/m^3$ of the unit cement content) is equivalent to that of the concrete using broken stones, while in using the recycled aggregate with 7% of the ratio of water absorption, the rich mix concrete has 7% lower compressive strength than the concrete using broken stones. But, the compressive strength of the ordinary mix concrete ($350kg/m^3$ of the unit cement content) is far lower than that using broken stones.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1993.04a
• /
• pp.34-39
• /
• 1993

Recently inappropriate aggregates are used as a raw material for ready-mixed concretes, due to the shortage of natural aggregate resources and the prohibition of their extraction for the environmental protection. We, therefore, have conducted experiments to obtain some knowledge of properties of domestic aggregates and to investigate subsequent changes in the properties of the fresh and hardened concretes. To this end, aggregates currently used in 13 domestic ready-mixed concrete plants were collected. Most of aggregate used in this experiment satisfied the KS in density and unit weight. But some of the aggregates have the particle size distribution that can effect bad influence on concrete. In this experiment the aggregates are found to have a bad particle size distribution, resulting in high amount of a unit water content and a unit cement content in concrete.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.11a
• /
• pp.443-446
• /
• 2005

Recently, according to increase use of concrete which is the main material of construction, the natural aggregate of good quality is more and more decreased. Most of all, among the concrete materials, the development of alternation materials of sand is urgently needed. In this study, investigating the production equipment and the sample of crushed sand company and analyzing properties of sand, manufactured mortar by the KS to use crushed sand as the fine aggregate of concrete material. The experiment result is as follows. 1. The density, an absorptivity, and the amount of 0.08mm passage ratio of crushed sand, and the mortar used crushed sand satisfied KS. The mechanical results is similar to sea sand. 2. The crushed sand which used impact crusher instead of cone crusher for 3rd or 4th crusher was similar properties to sea sand, so it is judged that impact crusher has high effect of particle shape improvement of crushed sand.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.23 no.1
• /
• pp.163-170
• /
• 2019

In recent years, various types of industrial wastes are rapidly increasing with the development of high-tech industries. Specially, high-density waste glass of CRT TV containing heavy metals are buried or disposed of due to reprocessing costs and environmental pollution problems. Thus, more basic research is needed to recycle waste such as CRT waste glass such. In this study, the fundamental properties and radiation shielding performance of mortar specimens substituted CRT waste glass as a fine aggregate were analyzed and their application to shielding materials was evaluated. According to the results, the bulk density of mortar specimen replaced with CRT waste glass was increased and the compressive strength and flexural strength were decreased. Meanwhile, the CRT waste glass substitute specimen containing a large amount of lead component showed a higher shielding performance than the general mortar specimen. Especially, the linear attenuation coefficient of CRT waste glass in $122KeV{\cdot}^{57}Co$ of the low energy field was 2.5 times higher than that of normal specimen.