• Journal of the Korea Concrete Institute
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• v.13 no.5
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• pp.438-446
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• 2001

Recently, porous concrete has been used for the purpose of decreasing the load of earth environment. It consists solely of cement, water and uniform-sized coarse aggregate. And its fundamental properties will be considerably affected by the physical properties of aggregate because the aggregate occupies for the most part in its mix proportion. For such a reason, this study was carried out to investigate the influence of the sizes and kinds of aggregate for the fundamental properties of porous concrete. It showed that the fundamental properties of porous concrete were the similar value in all sizes of aggregate except in the case of using the 2.5∼5㎜ aggregate and were varied according to the kinds of aggregate. In particular, compressive strength of porous concrete using 2.5∼5㎜ aggregate was more higher than that using other aggregate, and its void ratio and coefficient of permeability was lower. And the maintenance capacity of permeability of porous concrete was varied by the sizes and the kinds of aggregate. In particular, it was greatly decreased in case of using the 2.5∼5㎜ aggregate. And unlike dynamic modulus of elasticity of ordinary concrete, that of porous concrete was very high value in early ages and was slowly increased after that time.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.605-608
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• 2008

This study investigated fundamental properties corresponding to mixtures for the high strength, and their properties of spalling prevention after a fire test. The results were summarized as following. For the flowability of using mixtures for the high strength, the target flow was satisfied with a small quantity of high performance reducing water agent to compare with silica fume. For the compressive strength in the case of using mixtures for the high strength, it was higher to compare with silica fume at 7 days, so it was proved that using mixtures for the high strength was profitable to prevent early frost damage. The compressive strength at the 28 days of silica fume and mixtures for the high strength were similar. There was no reduced tendency at the compressive strength according fiber contents, so it found out that the bonding strength between the fiber and concrete was hardly effective. For the spalling properties, the specimens without fibers were destroyed, however using over 0.05% of NY and PP fibers was effective to prevent spalling on the high strength concrete.

• Polymer(Korea)
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• v.35 no.4
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• pp.342-349
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• 2011

The effect of the amount of vinyltriethoxysilane (VTEOS) in precipitated silica filled silicone rubbers was extensively investigated in terms of the change of mechanical properties, heat resistance, oil resistance, compression set, resilience, and curing characteristics. As the content of VTEOS increased from 0 to 2.0 phr, the hardness of the silicone rubber increased, however, tensile strength, elongation at break, and tear strength decreased. From heat resistance test, the change of mechanical properties was pronounced for silicone rubber treated with more VTOES. The best heat resistance was achieved at 2.0 phr VTOES. In addition, oil resistance was proportionally improved with VTEOS content. From oil resistance test. it was found that the decrease in hardness and maximum elongation was reduced for VTEOS-added systems. Finally, resilience, compression set, degree of cure and crosslink density were significantly enhanced with the amount of VTEOS.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.1
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• pp.50-57
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• 2015

Portland cement production is under critical review due to high amount of $CO_2$ gas released to the atmosphere. Attempts to increase the utilization of a by-products such as fly ash and ground granulated blast-furnace slag to partially replace the cement in concrete are gathering momentum. Many researchs on alkali-activated concrete that does not need the presence of cement as a binder have been carried out recently. Instead, the sources of material such as fly ash, that are rich in Silicon(Si) and Aluminium(Al), are activated by alkaline liquids to produce the binder. Hence concrete with no cement is effect reduction of $CO_2$ gas. In this study, we investigated the influence of the fluidity, air content and compressive strength of mortar on alkaline activator in order to develop cementless fly ash and ground granulated blast-furnace slag based alkali-activated mortar with superplasticizer. In view of the results, we found out that Pn of fluidity and compressive strength is the best in four type of superplasticizer, and PNS of powder type of fluidity is better than that of liquid type in the case of AA.

• Resources Recycling
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• v.33 no.3
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• pp.12-20
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• 2024

The global cement industry emits approximately 2.9 billion tons of greenhouse gases, of which 1.74-1.89 billion tons are emitted from limestone, which is the main raw material for clinkers. Therefore, the feasibility of using slag, a non-carbonated CaO-based raw material, must be investigated, and the physical properties of cement must be considered. In this study, the mixing ratios of the raw mix and properties of cement were analyzed. The CaCO₃ replacement ratio was limited when one type of slag was used; however, when the mixed slag was utilized, the CaCO₃ replacement ratio increased by more than 12 %. The compressive strength of the slag-incorporated cement was lower than that of Ordinary Portland Cement (OPC). Therefore, the lime saturation factor (LSF) of the raw mix and fineness of the cement were increased to improve the compressive strength. The compressive strength of cement with improved fineness was similar to that of OPC for a CaCO₃ replacement ratio of up to 6 %, and it decreased as the CaCO₃ replacement ratio was increased to 9 %. When both fineness and LSF were increased, the compressive strength and flow value of the cement with a CaCO₃ replacement ratio of 12 % were similar to that of OPC.

• Explosives and Blasting
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• v.21 no.2
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• pp.21-30
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• 2003

Currently, the shotcrete used as basic support in the tunnel excavation, has the advantages of maintaining high-level strength in condition of early shooting with thin thickness based on the excavation characteristics of rock mass. Therefore supreme equipment and materials were developed and the great strides have continued. Also, the development of measurement technology and the rocks behaviors of undergound are evaluated in detail and the designs of strength and thickness are made. The reinforcement materials development of new material is carried on. Most of the coal fly ash produced in Korea fire power plant is fly ash and bottom mash. Fly ash has been producing to be applied in many fields such as cement, aggregate, construction, civil, agriculture and fisheries. Also a lot of experiments are actively on the way. Therefore in this experiment, in order to use the fly ash mixed with concrete as a material of shotcrete, the experiment was performed in the best content to reduce the compression strength and the shooting rebound ratio of the excavated surface to use fly ash as a substitute material of concrete. As a result, when 15%.wt substitution was made to the fly ash, about 10% of compression strength and 6% of rebound ratio was reduced.

• The Journal of Engineering Geology
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• v.34 no.1
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• pp.25-38
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• 2024

Laboratory tests of accelerated artificial weathering compared the effects of seawater and acidified distilled water on rock weathering. The experiments simulated chemical and physical weathering of five different types of volcanic rock by applying 45 freeze-thaw cycles using seawater and acidified distilled water (pH 3), both at 70℃. The physical properties and uniaxial compressive strength (UCS) of the rocks were measured after 15 and 45 cycles of artificial weathering. Most of degradation of physical properties appeared within the first 15 cycles, and acidified distilled water had a greater effect than seawater. Analysis of variance (ANOVA) statistically evaluated the differences in UCS of the different rock types during the tests. The rate of UCS reduction after 45 cycles was similar across the samples, being independent of the rock type and the trend of changes in physical properties. In contrast to the changes in the physical properties, the UCS was more affected by seawater than by acidified distilled water.

• Magazine of the Korea Concrete Institute
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• v.8 no.6
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• pp.173-182
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• 1996

An experimental research was carried out to investigate the effect of thc compressive strength of concrete on the stirrup effectiveness in shear behavior of concrete beams. For this purpose. total 24 beams of section dimension of $300{\times}600mm$ were tested: 4 specimens without web reinforcement and 20 specimens with web reinforcement in the form of vertical stirrups. Main variables were two levels(norma1 and high strength) of the compressive strength of concrete and six types of t h e shear rcinfor.cement ratios. Prior to experiment, for given sections and assumed material constants, the reference shear reinforcement ratio(${\rho}_vACI$) which leads to the flexure failure using the provisions of the ACI Building Code(AC1 318-95) was calculated. and the shear reinforcement ratios were relatively selected from the value of ${\rho}_vACI$. From test results, it was shown that thc safety factor of ACI eyuation for p1,ediction of shear strength was decreased with increasing the compressive strength of concrete in beams without stirrups. However. it was observed that as the amount of' stirrup is increased, the safety factor for high strength conci,ete beams with high stirrup ratio is ensured more than that for normal strength concrete beams. Therefore i t appears that the stirrup effectiveness of high strength concrete beams is greater than that of normal strength concrete beams.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.51-58
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• 2018

This study was a basic research for actual production of recycled aggregate concrete, and experiments were carried out on the change of water cement ratio and physical properties of recycled aggregate concrete with fixed slump. Results were as follows. Concrete using recycled aggregate were required increased water to maintain the target slump, and the recycled fine aggregate are necessary more increased water more than the recycled coarse aggregate. The replacement ratio of recycled fine aggregate be less than 60%, would be possible to obtain the air content volume that did not deviate from the concrete quality specification. The compressive strength of concrete using recycled aggregate decreased with increasing the replacement of recycled aggregate, and compressive strength decreased by 25% when 100% recycled fine aggregate were replaced. As a result of analyzing the correlation of compressive strength according to the mixing factors of concrete, it was found that replacement of recycled fine aggregate> water cement ratio> air content volume were influenced in order.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.547-553
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• 2006

To know the effect of pigments on the material properties of color concrete, mortar and concrete tests were carried out by the using 5 kinds of pigment. The major component of red, yellow and black pigments was iron oxide and coloring component of blue and green pigments was copper phthalocyanine. Properties of mortar and concrete were some of difference according to adding ratio and kind of pigments. In case of using red, yellow and black pigments, setting time of concrete speeded a little and compressive strength was tendency to increase and slump or air content of concrete was same or decreased. On the other hand, in case of using green and blue pigments, compressive strength of concrete decreased largely because of the excessive air entrainment of surfactant and sump or air content of concrete increased highly. When the antifoaming agent was added to the color concrete mixed with green and blue pigments, compressive strength of concrete was improved and similar to that of concrete without pigment.