• Journal of the Korea Concrete Institute
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• v.20 no.5
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• pp.661-668
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• 2008

It is necessary to develop a new technology for effectively reducing hydration heat and controlling thermal cracking caused increasing construction of large size massive concrete structures such as mat foundation of high-rise building, grandiose bridge, and LNG tank. Therefor, to develop a new technology for reducing hydration heat of large size massive concrete in this study, after developing the latent heat binder for controling hydration heat of concrete by application of latent heat material, it was investigated basic properties and durability such as slump, air content and compressive strength, shrinkage properties, permeability, freezing and thawing resistance, corrosion, and hydration heat generation properties of concrete using latent heat binder. As a test result, it was confirmed that latent heat binder was not affected adversely the basic property and durability of concrete, and was advanced on the reduction of hydration heat and control of thermal crack. It is expected to be applied as the excellent technology on the management of hydration heat and thermal crack in large size mass concrete structures.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.689-696
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• 2017

The practical applications of ordinary high-fluidity concrete have been limited due to several drawbacks, such as high hydration heat, high amount of shrinkage, and non-economic strength development. On the other hand, due to its advantages, such as improvement of construction quality, reduction of construction cost and period, the development of high-fluidity concrete is a pressing need. This study examined the properties of high-fluidity concrete, which can be manufactured on the low binders using a viscosity agent to prevent the segregation of materials. The optimal viscosity agent was selected by an evaluation of the mechanical properties of high-fluidity concrete among six viscosity agents. The acrylic type and urethane type viscosity agents showed the best performance within the range where no material separation occurred. The mechanical properties were evaluated to examine the optimal amount of AC and UT viscosity agent added by mixing two viscosity agents according to the adding ratio and blending them together with high performance water reducing agent. When the ratio of the AC : UT viscosity agents was 5:5, it was most suited for high-fluidity concrete with low binders by increasing the workability and effect of the reducing viscosity.

• Journal of the Korea Concrete Institute
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• v.20 no.3
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• pp.405-412
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• 2008

Six alkali-activated (AA) concrete mixes were tested to explore the significance and limitations of developing an environmental friendly concrete. Ground granulated blast-furnace slag and powder typed sodium silicate were selected as source material and an alkaline activator, respectively. The main parameter investigated was the replacement level of lightweight fine aggregate to the natural sand. Workability and mechanical properties of lightweight AA concrete were measured: the variation of slump with time, the rate of compressive strength development, the splitting tensile strength, the moduli of rupture and elasticity, the stress-strain relationship, the bond resistance and shrinkage strain. Test results showed that the compressive strength of lightweight AA concrete sharply decreased when the replacement level of lightweight fine aggregate exceeded 30%. In particular, the increase in the discontinuous grading of lightweight aggregate resulted in the deterioration of the mechanical properties of concrete tested. The measured properties of lightweight AA concrete were also compared, wherever possible, with the results obtained from the design equations specified in ACI 318-05 or EC 2, depending on the relevance, and the results predicted from the empirical equations proposed by Slate et al. for lightweight ordinary Portland cement concrete. The stress-strain curves of different concrete were compared with predictions obtained from the mathematical model proposed by Tasnimi. The measured mechanical properties of lightweight AA concrete generally showed little agreement with the predictions obtained from these equations.

• Journal of the Korean Ceramic Society
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• v.41 no.3
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• pp.221-228
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• 2004

Basic properties of artificial lightweight aggregate by using waste dusts and strength properties of LWA concrete were studied. Bulk specific gravity and water absorption of artificial lightweight aggregates varied from 1.4 to 1.7 and 13 to 16%, respectively. Crushing ratio of artificial lightweight aggregate was above 10% higher than that of crushed stone or gravel. As a result of TCLP leaching test, the leaching amount of tested heavy metal element was below the leaching standard of hazardous material. Slump, compressive strength and stress-strain properties of LWA concrete made of artificial lightweight aggregate were tested. Concrete samples derived from LWA substitution ratio of 30 vol% and W/C ratio of 45 wt% showed the best properties overall. Thermal insulation and sound insulation characteristics of light weight concrete panel with the optimum concrete proportion were tested. Average overall heat transmission of 3.293W/㎡$^{\circ}C$ was observed. It was higher by about 15% than those of normal concrete made by crushed stone. Sound transmission loss of 50.9 ㏈ in frequency of 500 ㎐ was observed. It was higher by about 13% than standard transmission loss.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.2
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• pp.536-544
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• 2016

Recently, with the increase in the number of high rise and huge scaled buildings, ultra-high strength concrete with 80~100 MPa has been used increasingly to withstand excessive loads. Among the components of concrete, the effects of the kinds and properties of fine aggregates on the performance and economic advantages of ultra-high strength concrete need to be evaluated carefully. Therefore, this study examined the effects of the type of fine aggregates and mixing methods on the engineering properties of ultra-high strength concrete by varying the fine aggregates including limestone fine aggregate (LFA), electrical arc slag fine aggregate (EFA), washed sea sand (SFA), and granite fine aggregate (GFA) and their mixtures. Ultra-high strength concrete was fabricated with a 20 % water to binder ratio (W/B) and incorporated with 70 % of Ordinary Portland cement: 20 % of fly ash:10 % silica fume. The test results indicate that for a given superplasticizer dose, the use of LFA resulted in increases in slump flow and L-flow compared to the mixtures using other aggregates due to the improved particle shape and grading of LFA. In addition, the use of LFA and EFA led to enhanced compressive strength and a decrease in autogenous shrinkage due to the improved elastic properties of LFA and the presence of free-CaO in EFA, which resulted in the formation of C-S-H.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.8
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• pp.5636-5645
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• 2015

Physical characteristics of aggregates affect the workability and strength of mortar and concrete, which include their fineness ratio, particle size distribution and water absorption. The workability of construction materials decreases if the incorporated fine aggregates show improper size distribution of their particles. This study shows the particle size effect on the rheological behavior of mortar and provides basic information for evaluating its workability. A mini-slump flow test was adopted to evaluate the workability of mortar. In addition, its plastic viscosity and yield stress were measured using a rheometer for building materials. The sand samples were prepared by sieving river sand and sorting out with their particle sizes. As a result, it was observed that the fines less than 0.7 mm increases the yield stress and plastic viscosity of the mortar samples. If the fines are less than 0.34 mm, the water absorption of the fines dominates change on the workability.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.74-82
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• 2017

This research presents the results of the strength and drying shrinkage properties to study the effect of ground granulated blast furnace slag(GGBFS), fly ash(FA) and calcium sulfoaluminate(CSA) for activated ternary blended slag cement. The activated ternary blended cement(ATBC) mortar were prepared having a constant water-cementitious materials ratios of 0.4. The GGBFS contents ratios of 100%, 80%, 70% and 60%, FA replacement ratios of 10%, 20%, 30% and 40%, CSA ratios of 0%, 10%, 20% and 30% were designed. The superplasticizer of polycarboxylate type were used. The activator was used of 10% sodium hydroxide(NaOH) + 10% sodium silicate($Na_2SiO_3$) by weight of binder. Test were conducted for mini slump, setting time, V-funnel, water absorption, compressive strength and drying shrinkage. According to the experimental results, the contents of superplasticizer, V-funnel and compressive strength increases with an increase in CSA contents for all mixtures. Moreover, the setting time, water absorption ratios and drying shrinkage ratio decrease with and increase in CSA. One of the major reason for the increase of strength and decrease of drying shrinkage is the accelerated reactivity of GGBFS with alkali activator and CSA. The CSA contents is the main parameter to explain the strength development and decreased drying shrinkage in the ATBC.

• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.311-320
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• 2011

Fly ash (FA), byproduct from power plant has been actively used as mineral admixture for concrete. However, since bottom ash (BA) is usually used for land reclaim or subbase material, more active reuse plan is needed. Pond ash (PA) obtained from reclaimed land is mixed with both FA and BA. In this study, 6 PA from different domestic power plant are prepared and 5 different replacement ratios (10%, 20%, 30%, 50%, and 70%) for fine aggregate substitutes are considered to evaluate engineering properties of PA as fine aggregate and durability performance of PA concrete. Tests for fine aggregate of PA for fineness modulus, density and absorption, soundness, chloride and toxicity content, and alkali aggregate reaction are performed. For PA concrete, durability tests for compressive strength, drying shrinkage, chloride penetration/diffusion, accelerated carbonation, and freezing/thawing are performed. Also, basic tests for fresh concrete like slump and air content are performed. Although PA has lower density and higher absorption, its potential as a replacement material for fine aggregate is promising. PA concrete shows a reasonable durability performance with higher strength with higher replacement ratio. Finally, best PA among 6 samples is selected through quantitative classification, and limitation of PA concrete application is understood based on the test results. Various tests for engineering properties of PA and PA concrete are discussed in this paper to evaluate its application to concrete structure.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.793-796
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• 2008

Recently early strength concrete has been required for economical assurance and the prevention of frost damage in winter through air reduction in construction of concrete structures. This study presented the optimum condition revealing compressive strength 5MPa which has the possibility of removal of form in 24 hours, and researched the changes of unit weight of cement types of high early strength AE water reducing agents, characteristic of compressive strength expression as cure temperature conditions and slump or airspace. Test results showed at $15^{\circ}C$ with compressive strength of 5MPa that premature removal of form was possible in case of using highly early strength PC water reducing agent with unit weight of cement 360 ; 22hours faster than 10, unit weight 360 ; 20hours faster than 7, unit weight 390 ; 18 hours faster than 4 comparing with OP water reducing agent. And at $5^{\circ}C$ in case of using highly early strength PC water reducing agent with unit weight of cement 330 ; 32hours faster than 10, unit weight 360 ; 30hours faster than 7, unit weight390 ; 27hours faster than 4 comparing with OP water reducing agent. Therefore as the temperature rises $10^{\circ}C$, compressive strength of 5MPa reaching hour shortens 10 hours.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.769-772
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• 2008

The problem of disposing construction waste materials has become a national and social problem. Recycled powder generated in the process of making aggregate, and the recycled powder is land-filled in its entirety. Results of toxicity testing of recycled power show that it contains base-pair substituent mutagenicity. As recycled powder is disposed of as landfill, it can cause secondary contamination such as soil and underground water contamination. There has been very little research made on recycled powder. This study has examined the utilization of concrete mixture by using recycled powder in a mixture instead of cement and compared and analyzed the characteristics of dynamics and workability. This study has examined the application of recycled powder in concrete. Depending on the replacement rate and workability, test piece was manufactured using different mixing rate by CP, WCP, PCP. The CP was used to examine the physical property of concrete and characteristics its dynamics. The letters W of WCP and P of PCP are the initials of water and mixture. They were made using the standard mixing ratiosemphasizing the workability to determine the characteristic of dynamics of concrete based on the mixing ratio of recycled powder. With the increase in the replacement rate, CP had very little change in the strength. But with the decline of slump, the workability was not good. The result of manufacturing WCP and PCP using the standard mixing ratio showed that WCP had a drop in strength compared to the plain. PCP had almost the same value as the plain only when the replacement rate was 10%. When it was higher than that, a reduction in strength was observed.