• Journal of the Korean GEO-environmental Society
• /
• v.14 no.8
• /
• pp.53-60
• /
• 2013

The compaction control method of national road substructure is using field density test to determine the relative compaction and plate bearing test to check the load bearing capacity. However, these two tests digitize a construction site manager's judgment based on his experience, so mechanical basis is weak. Resilient modulus method, which is recently being used to resolve such problem, is evaluated as a rational design method of pavement structure that can rationally reflect the stress-strain state of pavement materials that is caused by the condition of load repetition of vehicle load. However, the method of measuring the resilient modulus is difficult and lengthy, and it has many problems. To replace it, light falling weight test is recently being proposed as a simple test method. Therefore, this research uses dynamic plate loading test, which quickly and simply measures the elastic modulus of the subgrade and sub-base construction and site of maintenance, to judge the possibility of compaction control of the stratum under the road, and it proposes relation formula by analyzing the result of static load test.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.25 no.4
• /
• pp.56-64
• /
• 2021

Leakage due to deterioration and damage is one of the major causes of volume change by freezing and thawing, and it leads micro-cracking and surface scaling in concrete structures. The deterioration of damaged concrete accelerates with the chloride attack. Thus, in the detailed guidelines for facility performance evaluation (2020), the quality of cover concrete and the freeze-thaw (FT) repetition cycle were newly suggested for concrete durability assessment. The quality of cover concrete should be evaluated by the rebound hammer test and the FT repetition cycle should be also considered in the deterioration environmental assessment. This study suggested the application of fast dynamic based nonlinear ultrasound method to monitor initial micro-scale damage under freezing and thawing environment. Concrete specimens were fabricated with different water-cement ratios (40%, 60%) and air contents (1.5% and 3.0%). The compressive strength, rebound number, relative dynamic modulus, and nonlinear ultrasound were measured with different FT cycles. The scanning electron microscopy was also performed to investigate the micro-scale FT damage. As a result, both the rebound number and the relative dynamic modulus had difficulty to detect early damage but the proposed method showed a potential to detect initial micro-scale damage and predict the FT resistance performance of concrete.

• Restorative Dentistry and Endodontics
• /
• v.25 no.3
• /
• pp.359-370
• /
• 2000

The purpose of this investigation was to observe the viscoelastic properties of five commercial flowable(Aeliteflo, Flow it, Revolution, Tetric flow, Compoglass flow), three conventional hybrid(Z-100, Z-250, P-60) and two condensable(Synergy compact, SureFil) resin composites. A dynamic oscillatory shear test was done to evaluate the storage shear modulus (G'), loss shear modulus(G"), loss tangent(tan ${\delta}$) and complex viscosity(${\eta}^*$) of the resin composites as a function of frequency - dynamic frequency sweep test from 0.01 to 100 rad/s at $25^{\circ}C$ - by using Advanced Rheometric Expansion System(ARES). To investigate the effect on the viscosity of resin composites of filler volume fraction, the filler weight % and volume % were measured by means of Archimedes' principle using a pyknometer. The results were as follows 1. The complex viscosity ${\eta}^*$ of flowable resins was lower than that of hybrid resins and significant differences were observed between brands. The complex viscosity ${\eta}^*$ of condensable resins was higher than that of hybrid resins. The order of complex viscosity ${\eta}^*$ at ${\omega}$=10 rad/s was as follows, Surefil, Synergy compact, P-60, Z-250, Z-100, Aeliteflo, Tetric flow, Compoglass flow, Flow it, Revolution. The relative complex viscosity of flowable resins compared to Z-100 was 0.04~0.56 but Surefil was 30.4 times higher than that of Z-100. 2. The storage shear modulus G' and the loss shear modulus G" of flowable resins were lower than those of hybrid resins but those of condensable resins were higher. The patterns of the change of loss tangent, tan ${\delta}$, of resin composites with increasing frequency were significantly different between brands. The phase angles, ${\delta}$, ranged from $30.2{\sim}78.1^{\circ}$ at ${\omega}$=10 rad/s. 3. All composite resins represent pseudoplastic nature with increasing shear rate. 4. The complex shear modulus $G^*$ and the phase angle ${\delta}$ was represented by the frequency domain phasor form, $G^*({\omega})=G^*e^{i{\delta}}=G^*{\angle}{\delta}$. The locus of frequency domain phasor plots in a complex plane was a valuable method that represent the viscoelastic properties of composite resins. 5. There was no direct linear correlationship but a weak positive relation was observed between filler volume % or weight % and the viscosity of the resin composites.

• International Journal of Highway Engineering
• /
• v.12 no.2
• /
• pp.107-113
• /
• 2010

In this study, the relative effects of low-chloride deicier(LCD) and two other deicing agents on the scaling of concrete were conducted in a series of tests at laboratory accordance with the ASTM C 672. The solutions concentration of deicers tested included 1, 4, 10%. Tap water was used as control. The amount of scaling was evaluated gravimetrically. As test result of deicer solution types, when applied to 4% solutions, surface scaling of concrete after 56 freeze-thaw cycles was produced significantly as about 9 times on LCD solution, as about 18 times on $CaCl_2$ solution, and as about 33 times on NaCl solution comparing with tap water. As test result of deicer solution concentrations, relatively low concentrations (of the 4% by weight) of deicer were produced more surface scaling than higher concentrations (of the 10% by weight) or lower concentrations (of the 1% by weight) of deicer. It show that the damaging concentration is of the order of 3~4% for previous research result. It appears that the mechanism of surface scaling is primarily physical rather than chemical. Also, the effect of chloride deicier types, freeze-thaw cycling, and air contents on the performance of concrete was experimentally investigated. The results show that the concrete specimens subjected to freeze-thaw cycling scaled more severely in exposure to deicing salt than those in non-exposure to deicing salt, weight losses of the specimens tested in exposure to deicing salt were twice as much as those tested in non-exposure to deicing salt. Relative dynamic modulus of elasticity of concrete specimens decreased more quickly in exposure to deicing salt than in non-exposure to deicing salt. Also, relative dynamic modulus of elasticity of concrete specimens in exposure to sodium chloride deicing salt was decreased more quickly comparing with exposure to LCD salt. It is also shown that the chloride contents according to concrete specimen depths was more largely in exposure to LCD salt. When concrete specimen is exposed to chloride deicing salts and freeze-thaw cycling, performance degradation in the entrained air concrete(AE concrete) retarded more considerably comparing with non-entrained air concrete(Non-AE concrete).

• Proceedings of the Korean Geotechical Society Conference
• /
• 2006.03a
• /
• pp.846-853
• /
• 2006

In this study, quantitative sensitivity analysis on rockfill material influencing the dam crest displacement of Concrete-Faced Rockfill Dam(CFRD) was carried out. The purpose of this study is to indicate the most important input parameter and to show the quantitative variation of displacement at the crest of CFR type dam with this input parameter. The rockfill material properties for parametric study were obtained from the results of large scale triaxial tests on 34 rockfill materials in the 22 different sites. From the statistical analysis on these data, some statistical characteristics of rockfill material properties such as property range, distribution characteristics, and correlation between the properties were investigated. based on these characteristics, 27 property combinations were constituted by Latin Hypercube sampling method. Dam crest displacements after construction, impounding, and earthquake loading were evaluated by static and dynamic numerical analysis on each combination. From the sensitivity analysis, it was found that the crest displacement of CFR type dam was absolutely affected by the shear modulus of rockfill material and the effect of friction angle of it was negligible. This relative difference of sensitivity was more outstanding in case of crest settlement than in case of crest horizontal displacement. Also, it was found that the settlement and horizontal displacement of dam crest logarithmically decreased as the shear modulus increased and the difference between the maximum value and the minimum vale amounted to about 9.5 times in case of settlement and about 10 times in case of horizontal displacement.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.6 no.4
• /
• pp.319-323
• /
• 2018

Ferronickel slag is a by-product from the ferronickel smelting process and it is divided into air-cooled ferronickel slag and water granulated ferronickel slag according to cooling system. The purpose of this experimental resesrch is to investigate the mechanical properties and resistance to freezing and thawing of concrete using air-cooled ferronickel slag(ACFNS) fine aggregate. For this purpose, the concrete specimens with water-cement ratio of 50% were made with ACFNS's replacement ratios of 0%, 20%, 30%, 40%, 50%, 70%, and 100% by volume of fine aggregate. It was observed from the test results that the compressive strength and static modulus of elasticity of ACFNS fine aggregate concrete were increased with increasing replacement ratio of ACFNS and the resistance to freezing and thawing of this was similar to reference concrete which had the relative dynamic modulus of elasticity of more than 90% during the freezing and thawing of 300 cycles.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.11a
• /
• pp.765-770
• /
• 2001

Concrete curbing blocks have been widely used in construction of roadways because they are easy too manufacture and cheap. But recently stone curbs are taking away the role from concrete curbs, because the durability of concrete curbs is inferior to stone curbs. Especially freeze-thaw effect on concrete is the most important cause that damages concrete curbs. The aim of this study is to increase the durability of concrete curbs. The concrete curbs that have been manufactured are extremely damaged below 60 cycles of freeze-thaw, but the ones that was manufactured with admixtures that entrains air are maintaining over 87% of relative dynamic modulus.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2002.05a
• /
• pp.725-730
• /
• 2002

The durability of concrete involves resistance to freeze-thaw action, corrosion, permeation, carbonation, chemical attack and so on. Generally, properties of concrete have been well understood under the separate action of these deterioration mechanisms. However, in practice, the degradation of concrete usually is the result of combined action of physical and chemical attack and can be accelerated by the combined action of several deterioration mechanisms. In the present study, to evaluate the combined deterioration by freeze-thaw action and seawater attack, ground granulated blast-furnace slag or silica fume concrete with water or seawater as mixing water was exposed to 210 cycles of freeze-thaw action. Tests were conducted to determined the relative dynamic modulus of elasticity and compressive strength. Furthermore, The XRD, SEM and EDS analysis were performed on the deteriorated part of concrete due to freeze-thaw action and seawater attack.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1999.04a
• /
• pp.331-336
• /
• 1999

Permeable polymer concrete in this study is one of the environment conscious concrete that can be applied at road, side walks and river embankment, etc. The purpose of this study is to evaluate the effects of mix proportions such as resing content, filler-binder ratio and aggregate ratio on the freezing and thawing resistance of permeable polymer concrete. The permeable polymer concrete are prepared with the resin ratio of 5%, 6% and 7%, filler-binder ratio of 0, 0.5 and 1.0, and 2.5~5mm sized aggregate ratio to standard sand of 10:10, 10:20, 20:10 and 20:20. It is tested for freezing and thawing test according to ASTM C 666092, and then, weight change, length change, relative dynamic modulus, durability factor, and compressive and flexural strengths after test are measured. From the test results, the resistance to freezing and thawing of permeable polymer concrete increased with increase the resing content, filler-binder ratio and fine aggregate ratio.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.46 no.2
• /
• pp.59-66
• /
• 2004

This study was performed to evaluate the freezing and thawing properties of the high strength concrete using recycled coarse aggregate. The recycled coarse aggregate replaced natural crushed aggregate by 0%, 25%, 50%, 75% and 100%. The compressive strength of the concrete using recycled coarse aggregate showed more than 300 kgf/$cm^2$ at the curing age 28 days. The mass loss ratio by freezing and thawing was less than 1% at all mix type. The relative dynamic modulus of elasticity was decreased with increasing the freezing and thawing cycles. Also, the durability factor by the freezing and thawing was decreased with increasing the content of recycled coarse aggregate. But, the recycled concrete except 100% recycled coarse aggregate showed 60 or more durability factor in the freezing and thawing 300 cycles. Accordingly, these recycled coarse aggregate can be used for high strength concrete.