Kyu-Seok Yeon

Tensile reinforcement of asphalt concrete using polymer coating

Abstract This study investigates the possibility of utilizing a polyester resin for reinforcing flexible pavements. The application of a thin-layer coating with a polymer, unsaturated polyester resin (UPR) on the surface of a laboratory-prepared unmodified asphalt concrete mixture was studied as a tensile reinforcement method for such a material. Selected laboratory performance tests were conducted and the results are compared with those of a normal (uncoated) asphalt concrete mixture and a modified asphalt mixture, both mixtures being widely used in Korea. The polymer coating was found to be effective in improving Marshall stability, tensile strength and flexural strength of asphalt concrete. These improvements can be explained as the effect of reinforcement by a thin polymer layer which is fully bonded to the specimen faces. The reinforcement was also effective in reducing the stiffness of the mixture whilst improving load-carrying capacity. This improvement in strength and reduction in stiffness resulted in a retardation of crack initiation resulting from cyclic load application and a significantly improved resistance to crack propagation. The study has shown that there is a possibility of using the polymer coating as a method of tensile reinforcement with flexible pavements.

Setting Shrinkage, Coefficient of Thermal Expansion, and Elastic Modulus of UP-MMA Based Polymer Concrete

This study examines setting shrinkage, coefficient of thermal expansion, and elastic modulus of unsaturated poly- ester(UP)-methyl methacrylate(MMA) polymer concrete, which is generally used for repair of portland cement concrete pavement and manufacturing of precast products. In this study, a series of laboratory test were conducted with variables such as UP-MMA ratio, shrinkage reducing agent (SRA) content, and test temperature. The results showed that the setting shrinkage ranged from 29.2 to 82.6×10 -4 , which was significantly affected by test temperature. Moreover, the findings revealed that the coefficient of thermal expansion, elastic modulus and ultimate strain of UP-MMA based polymer concrete ranged from 21.6 to 31.2×10 -6 / o C, 2.8 to 3.3×10 4 MPa, and 0.00381 to 0.00418, respectively. The results of this study will be used as important data for design and appli-

Compressive Strength Properties and Freezing and Thawing Resistance of CSG Materials

The cemented sand and gravel (CSG) method is a construction technique that adds cement and water to rock-like materials, such as rivered gravel or excavation muck which that can be obtained easily at areas adjacent to dam sites. This study was performed to evaluate the unconfined compressive strength properties and freezing and thawing resistance of CSG materials with unit cement content. The three types of CSG-80, CSG-100 and CSG-120 with cement content were designed to evaluate the optimum water content, dry density, strength, stress-strain, micro structure and durability factor. As the results, the optimum water content ratio with cement content showed almost similar tendency, and the unconfined compressive strength and dry density increased as cement content increases. The strength ratio of 7 days for 28 days were in the range of 55~61 % and the strain ratio in stress-strain curve were in the range of 0.8~1.6 % nearby maximum strength in 28 days. It is expected that this study will contribute to increasing application of CSG method as well as to increasing the utilizing of CSG materials as a environmentally friendly CSG method.

A Study on the Water-Purification Characteristics of Bio-Composite Planting Blocks

This study was performed to evaluate the water purification properties of bio-composites planting blocks using oyster shell and effective microorganism that have high absorption ability of heavy metals and organics to develop environmentally friendly river embankment technique contained various factors such as oyster shells, effective microorganism, porous concrete and planting embankment block. To maximize greening effect, the seeds were arbitrarily sown. In addition, in order to analyze the effect of water quality purification after the planting, the samples were collected from each designated zone 1, 7 and 30 days after steeping in water. Then, the samples were analyzed in terms of seven test items such as SS, BOD, COD, T-N, T-P, pH, etc. on the basis of the test method for water pollution. The following conclusions were reached from the test result. As a result of analysis for water quality purification for the concrete block containing the effective microorganism, it was found that the values for SS, BOD, T-N and T-P for the sample taken after 30 days were lower than the initial values, which indicated that the water purification effect had been created. The result of the water quality purification analysis for the concrete block containing oyster shell showed that the values for SS, BOD, COD and T-P for the sample taken after 30 days were lower than the initial values which also indicated that it had been effective in water quality purification.

The Compaction and Compressive Strength Properties of CSG Material Reinforced Polypropylene Fiber

The cemented sand and gravel (CSG) method is a construction technique that adds cement and water to rock-like materials, such as rivered gravel or excavation muck which can be obtained easily at areas adjacent to dam sites. This study was performed to evaluate the compaction and compressive strength properties of stress-strain, elastic modulus and fracture mode CSG materials reinforced polypropylene fiber. Polypropylene fiber widely used for concrete reinforcement is randomly distributed into cemented sand. The two types of polypropylene fiber (monofillament and fibrillated fiber) were used and fiber fraction ratio was 0, 0.2 %, 0.4 %, 0.6 % and 0.8 % by the weight of total dry soil. The effect of fiber fraction ratio and fiber shape on compaction and compressive strength were investigated. The optimum moisture contents (OMC) of CSG material increased as fiber fraction increased and the dry density of CSG material decreased as fiber fraction. Also, the maximum increase in compressive strength was obtained at 0.4 % content of monofillament and fibrillated fiber. CSG material behaviour was controlled not only by fiber fraction but also fiber distribution, fiber shape and fiber type.

Performance improvement of local Korean natural hydraulic lime-based mortar using inorganic by-products

Our goal was to verify the manufacturing availability of local Korean natural hydraulic lime (K-NHL) using local Korean low-grade limestone and to test the basic physical properties on the basis of EU standards (BS EN 459-1:2015). We also sought to improve the physical properties of natural hydraulic lime by adding inorganic by-products such as blast furnace slag and silica fume. Where the inorganic by-products were not incorporated, properties such as soundness, air content, particle size, and water absorption (excluding compressive strength and setting time) did not show significant differences with the physical properties evaluated based on EU standards. Also, in terms of the composition of hydraulic phase, local Korean NHL A5 and A8 were similar to NHL 2 of EU standards, whereas local Korean NHL HL correlated with NHL 3.5 or NHL 5. When inorganic by-products were added, the compressive strength and setting time were improved.

Engineering Properties of Volcanic Ash-Cement Soil Mixtures and Zeolite-Cement Soil Mixtures

In this study, the engineering characteristics of volcanic ash-cement soil mixtures and zeolite-cement soil mixtures are investigated by using unconfined compression test, freezing-thawing test, SEM and XRD analysis. The samples were mixed with volcanic ash from Mt. Baekdusan or porous zeolite, and cement as the ratios of 3.5:1, 4.0:1, 4.5:1, 5.0:1 with and without metakaolin. It is confirmed that compressive strength degraded with increasing of the amount of volcanic ash or zeolite, and increased with addition of metakaolin as a binder. Moreover, test results suggested that the mixtures provided sufficient freezing-thawing resistance. In addition, ettringite as a product of cement hydration was detected by SEM and XRD, and that possibly contributes to the strength of the mixtures.

An Experimental Study of Reservoir Failure Phenomena According to Transitional Zone: Spillway Scour During Overflow

This study is a preliminary investigation into the development of a construction method that will protect a reservoir even during over flows caused by severe flooding. Through hydraulic modeling tests, the destructive phenomena caused by spillway-junction scour during reservoir overflow were modeled, and the effects on the embankment during such an overflow and the spillway-junction movements are discussed. The reservoir destruction model used the Tanbu reservoir, located in Gangwondo Chuncheon-si Namsanmyeon (H＝22 m, L＝115 m), as the model reservoir and created an embankment with a 1/60 ratio. We review the spillway-junction safety factor during overflow and embankment movement following reinforcement measures for three different cases: no reinforcement, cemented sand and gravel (CSG) reinforcement and water-blocking sheet reinforcement. The results of this study confirmed that when the spillway-junction is exposed to soil, it is very vulnerable to overflow and that a water-blocking sheet or CSG reinforcement are very effective measures in preventing embankment destruction in the long-term period.

A Study on the Engineering and Environmental Characteristics of Phosphogypsum-Cement-Soil Mixtures

This study aimed to investigate the engineering and environmental characteristics of phosphogypsum-cement-soil mixtures composed of phosphogypsum, soil, and a small amount of cement was analysed on the basis of the unconfined compression test, the tensile strength test, the freezing and thawing test, the wetting and drying test, SEM and EDS analysis, XRD analysis and Leaching test. The specimens were manufactured with soil, cement and phosphogypsum. The cement contents was 10 %, and the phosphogypsum contents was 10, 20, 30, and 40 % by the weight of total dry soil. Each specimen was manufactured after curing at constant temperature and humidity room for 3, 7 and 28 days, after which the engineering characteristics of phosphogypsum-cement-soil mixtures were investigated using the unconfined compression test, the tensile strength test, the freezing and thawing test, the wetting and drying test. The basic data were presented for the application of phosphogypsum-cement-soil mixtures as construction materials. To investigate the environmental characteristics, leaching test was performed and the leaching test results were far below than of regulatory requirement of Waste Management Act in Korea. Therefore the results show that phosphogypsum is environmentally safe and can be used as construction materials in environmental aspect.

Effects of Aggregate and Curing Temperature on Strength Development of UP-MMA based Polymer Mortar under Sub-Zero Temperature

In this paper, the effects of aggregate and curing temperature on strength development characteristics of UP (Unsaturated Polyester)-MMA (Methyl Methacrylate) based polymer mortar under sub-zero temperature are experimentally investigated to provide a criterion for repair and production of precast products. The result showed that the setting time of the binder was 4 minutes at whereas 35 minutes at . The result also revealed that the compressive, flexural, and splitting tensile strengths of UP-MMA based polymer mortar significantly decreased as the aggregate and curing temperatures decreased. However, sufficient strengths which can be implemented in actual practices -36.6 MPa of compressive strength, 6.11 MPa of flexural strength, and 5.81 MPa of splitting tensile strength - were obtained even though both aggregate and curing temperatures were . Strength development of polymer mortar is largely affected by curing temperature rather than aggregate temperature. It was found that the effects of aggregate temperature on strength development become smaller as the curing temperature becomes lower. Also, toughness, a ratio of compressive strength to flexural strength, increased from 3.5 to 5.9 as both aggregate and curing temperatures decreased from to .