• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.4
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• pp.349-355
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• 2016

This study is about the reuse of bottom ash, which is released as a necessity in thermal power plant. In general, coal-ash are classified as fly-ash, bottom-ash, cinder-ash. Of these, a large amount of fly ash is being recycled as cement substitutes. While, recycling rates of bottom ash are the lowest due to its porosity and high absorption. In this study, the durability of the concrete using bottom ash as a concrete fine aggregate was evaluated. The using level of the bottom ash ranges to step-by-step from 0% to 30%. According to the result of the durability test, regardless of the presence of the bottom ash, freeze-thaw durability could be secured by air entrainment. In case of the resistance to chloride ions penetration, the length change, and the effects on heavy metals, the replacement of bottom ash as fine aggregate was not critical. Although carbonation penetration was higher as the replacement level of bottom ash increased, the experiment showed that it could be possible to use bottom ash as concrete fine aggregate with proper mix design.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.1
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• pp.21-25
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• 2009

The results of a recent case study for material characterizations and structural evaluation to design asphalt overlay thickness of William P Hobby airport in Houston, Texas are presented herein. The existing runway 12R-30L of Hobby airport consisted of thick asphalt overlay over Portland Cement Concrete (PCC) and the localized surface shoving as evident in the closure of surface groove has been observed recently. Using the field cored asphalt concrete mixtures, measurements of percent air voids, asphalt content and aggregate gradation were conducted to find out the causations of surface shoving and groove closure. The FAA layered elastic program, LEDFAA was utilized to evaluate pavement structural conditions for new asphalt overlay. Two different composition assumptions for existing pavement were made to evaluate the pavement as followings: 1) APC, Asphalt Concrete Overlay over PCC pavement and 2) AC, Asphalt Concrete pavement. Based on laboratory testing results, a ratio of percent passing #200 to asphalt content ranged 1.1 to 2.2, which is considered a high ratio and a tendency of tender mix design was observed. Thus, the localized surface shoving and groove closure of the runway 12R-30L could be attributed to the use of excessive fine contents and tender mix design. Based on the structural evaluation results, it was ascertained that the analysis assuming the pavement structure as AC pavement gives more realistic structural life when the asphalt overlay is thicker enough compared to PCC layer because the existing PCC pavement under asphalt overlay acts more like a high quality base material.

• Journal of the Korea Institute of Building Construction
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• v.13 no.3
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• pp.282-290
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• 2013

In this study, the adjustment range of mixture factor with replacement mineral admixture was reviewed to secure the mixture change data of high volume concrete compared to general concrete. When changing the concrete mix to high volume concrete within the universal concrete mixing, the adjustment range of mixture to ensure optimum quality is as follows. Unit-water content is $20{\sim}30kg/m^3$ downward. Fine aggregate ratio dropped by approximately 1% when W/B was reduced by 5%, and it is reduced by approximately 0.12% when there is a 5% increase in the total replacement rate. When the FA replacement rate was increased by 5%, the AE agent was approximately 20% to 30% higher compared with the conventional one. When the FA and BS replacement rate rose by 5%, W/B was reduced by about 1 to 4%.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.977-980
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• 2008

Recently, the study on the application of SCC(Self-Compacting Concrete) is actively underway, in order to solve the lack of flowability and the poor compacting which is one of the chronic problems of tunnel lining concrete. The aim of this study is that to verify the validity of the application of SCLC(Self-Compacting Lining Concrete) for tunnel lining concrete and to examine the characteristic of flowing and mechanics of SCLC in term of comparing before and after casting SCLC was developed by Packing Factor mix method and casted in field mix-design according to the condition of site and the characteristic of aggregate. Before casting, the tests of the capability of flowability and durability was performed by slump flow, air void and so on. Additionally, the slump flow loss is measured to evaluated the possibility of cast-in-place. Furthermore, considering on the first time SCLC casting applied to the tunnel lining in Korea, it is provided that the careful items and the correct way for construction when applied the SCLC on site.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3D
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• pp.425-433
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• 2006

The presented work provided a predictive equation for dynamic modulus of hot mix asphalt, which showed higher reliability and more simplicity. Lots of test result by UTM at laboratory has been used to develop the precise predictive equation. Evaluation of dynamic modulus for 13mm and 19mm surface course and 25mm of base course of hot mix asphalt with granite aggregate and two asphalt binders (AP-3 and AP-5) were carried out. Superpave Level 1 Mix Design with gyrator compactor was adopted to determine the optimum asphalt binder content (OAC) and the measured ranges of OAC were between 5.1% and 5.4% for surface HMA, and around 4.2% for base HMA. The dynamic modulus and phase angle were determined by testing on UTM, with 5 different testing temperature (-10, 5, 20, 40, & $55^{\circ}C$) and 5 different loading frequencies (0.05, 0.1, 1, 10, 25 Hz). Using the measured dynamic modulus and phase angle, the input parameters of Sigmoidal function equation to represent the master curve were determined and these will be adopted in FEM analysis for asphalt pavements. The effect of each parameter for equation has been compared. Due to the limitation of laboratory tests, the reliability of predictive equation for dynamic modulus is around 80%.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.821-828
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• 2005

To investigate the role of RH and temperature on the transport of chloride in the concrete, two groups of specimens were configured. For both groups, mix design was based on w/c=0.45, $400kg/m^3$ cement, $794kg/m^3$ fine aggregate and $858kg/m^3$ coarse aggregate. After specimen fabrication these were exposed to four different RH (35, 55, 75 and $95\%$ RH) and temperature (0, 20, 30 and $40^{\circ}C$) conditions. After 3 and 6 months $15\%$ NaCl exposure 5mm cores were taken. These cores were sliced and individual cores were ground to powder. In addition, to evaluate the effect of temperature on the chloride binding some powder samples were leached in the each of four temperature chambers. Chloride titration fur these was performed using FDOT acid titration method. Based upon the resultant data conclusions were reached regarding that 1) effective diffusion coefficient, $D_e$, increased with increasing exposure RH, suggesting that the size and number of water paths increased with elevated moisture content in the specimens, 2) $D_e$ increased with increasing temperature in the range of 0 to $40^{\circ}C$ possibly by elevated thermal activation of chloride ions and reduced chloride binding at higher temperature, 3) water soluble chloride concentration, $[Cl^-]_s$, increased with increasing temperature, and 4) chloride concentration profile for initially dry concrete specimens was higher than for the initially wet ones indicating pronounced capillary suction (sorption) occurred for the dry concrete specimens.

• Computers and Concrete
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• v.21 no.5
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• pp.525-530
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• 2018

As a nondestructive testing method, the Schmidt rebound hammer is widely used for structural health monitoring. During application, a Schmidt hammer hits the surface of a concrete mass. According to the principle of rebound, concrete strength depends on the hardness of the concrete energy surface. Study aims to identify the main variables affecting the results of Schmidt rebound hammer reading and consequently the results of structural health monitoring of concrete structures using adaptive neuro-fuzzy inference system (ANFIS). The ANFIS process for variable selection was applied for this purpose. This procedure comprises some methods that determine a subsection of the entire set of detailed factors, which present analytical capability. ANFIS was applied to complete a flexible search. Afterward, this method was applied to conclude how the five main factors (namely, age, silica fume, fine aggregate, coarse aggregate, and water) used in designing concrete mixture influence the Schmidt rebound hammer reading and consequently the structural health monitoring accuracy. Results show that water is considered the most significant parameter of the Schmidt rebound hammer reading. The details of this study are discussed thoroughly.

• International Journal of Highway Engineering
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• v.19 no.6
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• pp.129-137
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• 2017

PURPOSES : The purpose of this study is to develop bridge deck concrete materials based on ordinary Portland cement concrete, and to evaluate the applicability of the developed materials through material properties tests. METHODS : For field implementation, raw material (cement, fine aggregate, and coarse aggregate) properties, fresh concrete properties (slump and air content), strength (compressive, flexural and bond strength) gain, and durability (freeze-thaw resistance, scaling resistance, and rapid chloride penetrating resistance) performance were evaluated in the laboratory. RESULTS : For the selected binder content of $410kg/m^3$, W/B = 0.42, and S/a = 0.48, the following material performance results were obtained. Considering the capacity of the deck finisher, a minimum slump of 150 mm was required. At least 6 % of air content was obtained to resist freeze-thaw damage. In terms of strength, 51.28 MPa of compressive strength, 7.41 MPa of flexural strength, and 2.56 MPa of bond strength at 28 days after construction were obtained. A total of 94.9 % of the relative dynamic modulus of elasticity after 300 cycles of freeze-thaw resistance testing and $0.0056kg/m^2$ of weight loss in a scaling resistance test were measured. However, in a chloride ion penetration resistance test, the result of 3,356 Coulomb, which exceeds the threshold value of the standard specification (1000 Coulomb at 56 days) was observed. CONCLUSIONS : Instead of using high-performance modified bridge deck materials such as latex or silica fume, we developed an optimum mix design based on ordinary Portland cement concrete. A test construction was carried out at ramp bridge B (bridge length = 111 m) in Gim Jai City. Immediately after the concrete was poured, the curing compound was applied, and then wet mat curing was applied for 28 days. Considering the fact that cracks did not occur during the monitoring period, the applicability of the developed material is considered to be high.

• Journal of the Korea Concrete Institute
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• v.20 no.4
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• pp.469-475
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• 2008

It is obvious that chloride penetration through cracks can threaten the durability of concrete substantially, according to the previous studies of author. It was proposed that crack depth corrseponded with critical crack width from the surface is a crucial factor in view of durability design of concrete structures. It is now necessary to deal with chloride penetration through microcracks characterized with the mixing features of concrete. The purpose of this study is examining the effect of mix proportional features of concrete such as coarse aggregate, high strengtherize of concrete and reinforcement of steel fiber on chloride penetration through cracks. Although small size of coarse aggregate can lead to many microcracks in concrete, the cracks should not impact on chloride penetration directly. On the contrary, chloride should penetrate through cracks easily in concrete with a large size of coarse aggregate because mixrocracks are connected to each other. Second, high strength concrete has an excellent performance to resist with chloride penetration. However, for cracked high strength concrete, its performance is reduced upto the level of ordinary concrete. Finally, steel fiber reinforcement is effective to reduce chloride penetration through cracks because steel fiber reinforcement can lead to reduce crack depth significantly.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.83-91
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• 2015

Porous concrete consists of cement, water and coarse aggregate and has been used for the purpose of decreasing the earth environmental load such as air and water permeability, sound absorption, etc. However, the physical and mechanical properties of porous concrete changes due to compaction load during construction. For such a reason, the purpose of this study is to investigate the physical and mechanical properties of porous concrete according to the kinds of binder, the ratio of water to binder and target void ratio. In particular, this study has been carried out to investigate the influence of compaction load on the void ratio, strength and coefficient of permeability. Aggregate used in this study are by-products generated during production of crushed gravel with a maximum size of 13mm. The results of this study showed that the target void ratio, the coefficient of permeability and compressive strength of porous concrete had a close relationship with the void ratio, and it will be possible that the void ratio is suggested by the mix design of porous concrete. The compressive strength of porous concrete was the highest at the content of the expansive admixture of 5% and compared to non-mixture, 10% mixture of silica fume improved compressive strength about 32%. And in the result of the study to change the compaction load, the compressive strength increased from the load of 15kN, the void ratio decreased from the load of 0.8kN, the coefficient of permeability decreased from the load 35kN, respectively.