• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.1 s.53
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• pp.97-105
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• 2009

Development and use of blended cement concrete is gaining more importance in the construction industry with reference to durability mainly due to the pore refinement and reduction in permeability. Cracks play a major role on important parameters like permeability, rate of chloride ingress, compressive strength and thus affect the reinforcement corrosion protection. Furthermore, when a crack occurs in the cover concrete, the corrosion of the steel reinforcement may be accelerated because the deterioration causing factors can pass through the crack. In recent years the effect of cracking on the penetration of concrete has been the subject of numerous investigations. Therefore assessing the service life using blended concrete becomes obviously in considering the durability. In the present study, the corrosion assessment of composite concrete beams with and without crack with of 0.3mm using OPC, 30% PFA, 60% GGBS, 10% SF was performed using half cell potential measurement, galvanic potential measurement, mass loss of steel over a period of 60days under marine environmental conditions and the results were discussed in detail.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6A
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• pp.419-426
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• 2012

Fresh concrete has 10~20% extra water in it. As those water remain entrapped air in the concrete, life span of structures is reduced. For that reason, if extra water is eliminated, it will be useful to improve the durability of the structures. Though there were many reports about permeable formwork, the study on the properties of permeable liner itself has been insufficient. In addition, making holes on the form causes lowering of workability. Therefore, this study reviewed the properties of woven and non-woven permeable liner and formwork which has no holes on the form. For the woven and non-woven permeable liner, they showed great application with W/C decrease, lowering roughness, increased compressive strength of surface area and slight loss of cement paste, when the were applied to concrete. In addition, they showed different performance according to the density of woven liner or thickness of non-woven liner. Furthermore, when using the draining non-woven permeable liner which has drainage path inside, concrete surface showed required performance with high workability, without drilling the holes on the form.

• Journal of the Korean GEO-environmental Society
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• v.21 no.11
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• pp.11-20
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• 2020

For water barrier and reinforcing grout in soft ground, the verification of durability was conducted over the initial and long-term ages under various curing conditions. The grout was made of water glass system, fast-hardening mineral (FHM) system, and acrylic polymer system. There were three types of curing conditions that were tab water curing, artificial seawater curing, and atmospheric curing. And the various tests were performed for each sample by age, uniaxial compressive strength, length change, and weight change. As artificial seawater, MgCl₂ and MgSO₄ aqueous solutions were prepared and used, respectively. As the test results, the fast-hardening mineral system and acrylic polymer system were cured stably without significant change in durability in tap water and artificial sea water, whereas water glass system showed a very rapid drop in durability under artificial sea water conditions compared to tap water. In atmospheric curing conditions, durability is lowered compared to water curing in all cases, and in particular, the weight loss in the FHM system and water glass system is about 62% and 60%, respectively, resulting in a significant decrease in durability.

• Resources Recycling
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• v.27 no.3
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• pp.39-47
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• 2018

According to Vietnam government establishes additional coal-fired power plants to secure generation capacity, emission of ashes is accelerating and processing them is urgent issue. This study targeted utilize fly ashes that occurred in circulating fluidized bed combusion (CFBC) power plant to use ground solidification materials. CFBC fly ashes are used to make solidification with ground granulated blast furnace slag (GGBFS), gypsum and cement. Then produced specimens by mixing with soft ground soil to confirm mixing effect of fly ash in solidification. As a result it was possible to find mixture design that is satisfied 3 MPa compressive strength in age 28 days and reduce weight loss rate over 50% in acid immersion test than plain specimens that using only ordinary portland cement.

• Restorative Dentistry and Endodontics
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• v.43 no.3
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• pp.32.1-32.11
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• 2018

Objectives: This study evaluated the effects of a bleaching agent on the composition, mechanical properties, and surface topography of 6 conventional glass-ionomer cements (GICs) and one resin-modified GIC. Materials and Methods: For 3 days, the specimens were subjected to three 20-minute applications of a 37% $H_2O_2$-based bleaching agent and evaluated for water uptake (WTK), weight loss (WL), compressive strength (CS), and Knoop hardness number (KHN). Changes in surface topography and chemical element distribution were also analyzed by energy-dispersive X-ray spectroscopy and scanning electron microscopy. For statistical evaluation, the Kruskal-Wallis and Wilcoxon paired tests (${\alpha}=0.05$) were used to evaluate WTK and WL. CS specimens were subjected to 2-way analysis of variance (ANOVA) and the Tukey post hoc test (${\alpha}=0.05$), and KH was evaluated by one-way ANOVA, the Holm-Sidak post hoc test (${\alpha}=0.05$), and the t-test for independent samples (${\alpha}=0.05$). Results: The bleaching agent increased the WTK of Maxxion R, but did not affect the WL of any GICs. It had various effects on the CS, KHN, surface topography, and the chemical element distribution of the GICs. Conclusions: The bleaching agent with 37% $H_2O_2$ affected the mechanical and surface properties of GICs. The extent of the changes seemed to be dependent on exposure time and cement composition.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.3
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• pp.389-396
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• 2021

In this paper, it was evaluated that the effect of self-healing microcapsules on the quality and healing properties of cement composites. In the mixing of microcapsules, the plastic viscosity and yield stress of the cement composites decreased due to the particle properties of the microcapsules, and decreased in proportion to the mixing ratio. The table flow showed a tendency to decrease as the core material acted as a stimulant due to the loss of microcapsules, and the compressive strength could be supplemented through unit quantity correction. As a result of evaluating the effect of microcapsule mixing on the healing properties of cement composites, it was found that the unit water flow rate decreased by the healing reaction immediately after crack initiation. When more than 3% of microcapsules were mixed, it was found that there was a healing rate of more than 95% at 7 days of healing age.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1A
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• pp.15-24
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• 2008

This paper presents the analytical method for the long-term behavior of simply supported composite beams with precast decks prestressed in the longitudinal direction. The objectives of time-dependent analysis are to estimate losses of prestress on the concrete slab and long-term deflection due to creep and shrinkage of concrete, relaxation of prestressing steel. Also, the time-dependent analysis was carried out using the presented analytical method to evaluate the effects of several parameters on the long-term behavior of composite bridge with precast deck, including geometrical shapes of composite beams, compressive strength of concrete and magnitude of initial prestress. The results of the analysis indicated that, in the effects of geometrical shapes of composite beams, the main parameters affecting the losses of prestress and the long-term deflection were the cross sectional area and the moment of inertia of steel beam, respectively. Finally, the determination method for the required initial prestress was proposed by evaluation of the loss characteristics due to shrinkage and creep of concrete.

• Journal of Conservation Science
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• v.32 no.4
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• pp.471-490
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• 2016

This study investigated provenance of raw materials and making technique of lime-based materials used in the tomb barriers of the Yesan Mokri tombs from Joseon dynasty on the basis of analysis to material characteristics and physical properties. In the barrier materials, dry density and porosity are the highest value ($1.82g/cm^3$) and the lowest value (25.20%) in the south wall of No. 1 tomb, respectively. Dry density and porosity are inversely proportional in all barrier materials, but unconfined compressive strength, which is the highest value of $182.36kg/cm^2$ in the No. 2 tomb, does not show an interrelation with porosity and density. Mineral components in the lime-soil mixtures of the tomb barrier are mainly quartz, feldspar, mica and calcite about 200 to $600{\mu}m$ size with yellowish brown matrix. Hydrotalcite and portlandite are detected in the lime mixture, and kaolinite in the soils. The lime materials of the tomb barrier occurred in large quantities weight loss and variable endothermic peaks caused by decarbonization reaction of $CaCO_3$ in the range from 600 to $800^{\circ}C$ in thermal analysis. Making temperature of lime for the tomb barrier is presumed approximately about $800^{\circ}C$ based on the occurrences, compositions and thermal analysis. The tomb barriers are revealed to very wide composition ranges of major elements and loss-on-ignition (22.5 to 33.6 wt.%) owing to mixture of the three materials (lime, sand and clay). It is interpreted that low quality construction technique was applied as the limes are very heterogeneous mixture with aggregates, and curing of the lime was poorly processed in the tomb barriers. Possible limestone sources are distributed in many areas around the Mokri site where limestone conformation and quarries for commercial production are found within Yesan and Hongseong areas. Therefore, we estimated that raw materials were possibly supplied from the local mines near the Mokri site.

• Journal of the Korea Concrete Institute
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• v.24 no.5
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• pp.605-612
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• 2012

Spalling of concrete occurs due to vapor pressure ignited explosion, temperature difference across a section, and combination of these factors. Factors affecting spalling can be classified into internal and external factors such as material property and environmental condition, respectively, have to be considered to precisely understand spalling behavior. An external environmental factor such as differences in heating rate cause internal humidity cohesion and different vapor pressure behavior. Therefore, spalling property, vapor pressure and thermal strain property were measured from concrete with compressive strengths of 30 MPa, 50 MPa, 70 MPa, 90 MPa, and 110 MPa, applied with ISO-834 standard heating curve of $1^{\circ}C/min$ heating rate. The experimental results showed that spalling occurred when rapid heating condition was applied. Also, when concrete strength was higher, the more cross section loss from spalling occurred. Also, spalling property is influenced by first pressure cancellation effect of thermal expansion caused by vapor pressure and heating rates.

• Journal of the Korean Geotechnical Society
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• v.29 no.5
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• pp.29-38
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• 2013

The G-class cement is commonly used in practice for geothermal well cementing in order to protect a steel casing that is designed to transport hot water/steam from deep subsurface to ground surface during operating a geothermal power plant. In order to maintain optimal performance of geothermal wells, physical properties of the cementing material should be satisfactory. In this paper, relevant factors (i.e., groutability, uniaxial compression strength, thermal conductivity and free fluid content) of the G-class cement were experimentally examined with consideration of various water-cement (w/c) ratios. Important findings through the experiments herein are as follows. (1) Groutability of the G-class cement increases by adding a small dose of retarder. (2) There would be a structural defect caused when the w/c ratio is kept higher in order to secure groutability. (3) Thermal conductivity of the G-class cement is small enough to prevent heat loss from hot steam or water to the outer ground formation during generating electricity. (4) The G-class cement does not form free water channel in cementing a geothermal well. (5) The Phenolphthalein indicator is applicable to the distinction of the G-class cement from the drilling mud.