Young Il Jang

An experimental study on the hazard assessment and mechanical properties of porous concrete utilizing coal bottom ash coarse aggregate in Korea

This study evaluates quality properties and toxicity of coal bottom ash coarse aggregate and analyzes mechanical properties of porous concrete depending on mixing rates of coal bottom ash. As a result, soundness and resistance to abrasion of coal bottom ash coarse aggregate were satisfied according to the standard of coarse aggregate for concrete. To satisfy the standard pertaining to chloride content, the coarse aggregates have to be washed more than twice. In regards to the result of leaching test for coal bottom ash coarse aggregate and porous concrete produced with these coarse aggregates, it was satisfied with the environment criteria. As the mixing rate of coal bottom ash increased, influence of void ratio and permeability coefficient was very little, but compressive and flexural strength decreased. When coal bottom ash was mixed over 40%, strength decreased sharply (compressive strength: by 11.7-27.1%, flexural strength: by maximum 26.4%). Also, as the mixing rate of coal bottom ash increased, it was confirmed that test specimens were destroyed by aggregate fracture more than binder fracture and interface fracture. To utilize coal bottom ash in large quantities, it is thought that an improvement method in regards to strength has to be discussed such as incorporation of reinforcing materials and improvement of aggregate hardness.

Chloride Resistance of Concrete with Marine Blended Cement Using Corrosion Resistant Mineral Admixture

In this study, the chloride resistant properties of concrete with MBC (marine blended cement) were evaluated by an accelerated corrosion test of reinforced concrete. The half-cell potential measurements indicated that the chloride resistance of MBC concrete is approximately 32% larger than that of TBC (ternary blended cement) concrete. As for the reinforcement corrosion area, while the TBC specimens exhibited 5.32-6.11% corrosion at the final 40th cycle, the MBC specimens did not show any sign of steel corrosion. The chloride penetration depth of the MBC specimens was approximately 41-79% smaller than that of the MBC specimens.

Performance Evaluation of Semiplastic Recycled Cold Asphalt Using Noncement Binders

The optimal mixing conditions for semiplastic recycled cold asphalt, which recycled waste asphalt and used noncement binders (NCB), were assessed through verification of the performance. The NCB of 6% desulfurization gypsum mixing was found to have the most outstanding properties. For the Marshall stability, 4% (NCB) filler mixing brought about a 1.92-time strength increase effect compared to OPC (2%) and was improved when using modified asphalt and SBR. The flow test results showed that although an increase dosage of filler and SBR decreased the flow value of the semiplastic recycled cold asphalt, an increase dosage of asphalt emulsion improved the flow value. The indirect tensile strength and liquid immersion residual stability for the condition with greatest Marshall stability were most outstanding with 0.95 MPa and 83.6%, respectively. Evaluation of the recycled cold asphalt abrasion durability revealed that for the case of mixing more than 4% NCB the mass loss rate was lower than 20%. The abrasion durability was found to improve when using modified emulsified asphalt and SBR substitution. From the test results, it was found that the optimal mixing proportion of semiplastic recycled cold asphalt satisfied mechanical properties and durability is NCB with 4%, emulsified asphalt with 3%, and SBR substitution with 20%.

Influence of Cold Weather on Compressive Strength in High Performance with Silica Fume

This paper addresses the influence of cold weather on the compressive strength of high performance concrete with silica fume under different curing days. Test variables of this study are weather condition (5°C, -5°C and-15°C) and different curing days (7days and 28 days). In this work, the specimen was designed a water-binder ratio of 0.34. One batches of concrete were prepared for each mixing hour, and the compressive strength of cylindrical concrete specimens was measured after 7 and 28 days. Test results for concrete compressive strength show that the concrete’s best mechanical performance occurred when there was the least difference between ambient temperature and concrete temperature, that is, during the later hours of the day in hot weather conditions.

The Behavior of Pseudo Strain-Hardening Cementitious Composite (PSH2C) Using Synthetic Fibers under Uniaxial Tensile Loading

The application of pseudo strain-hardening cement composites (PSH2C) to structural systems depends primarily on the tensile response of the materials, which is a direct function of fiber and matrix characteristics, the fiber content or volume fraction. In general, improved response of material is observed with an increase in the fiber volume fraction, as long as the fiber content does not impede mixing. This paper addresses the direct tensile response of pseudo strain hardening cement composites (PSH2C) reinforced with PET fibers, which belongs to a class of discontinuous short fiber reinforced cement based composites characterized by a strain hardening and multiple cracking responses under direct tensile loading. The variables are different types of fibers (PET, PET+PE, PET+PVA).

The Seismic Behavior of Pseudo Strain-Hardening Cemetitious Composites Coupling Beams with Polyvinyl Alcohol Fiber

This paper addresses the seismic behavior of pseudo strain hardening cementitious composite (PSH2C) coupling beams with different failure modes in hybrid coupled shear wall. Test variables included the ratio of steel coupling beam strength to beam-wall connection strength. The results show that Specimen PSH2C-SCF exhibits a better stable behavior in comparison with Specimens PSH2C-SBVRT and PSH2C-FCF.

Physical Properties of Waste Concrete Recycled Aggregates According to Coating Factor

The physical properties of waste concrete recycled aggregate according to the mixing ratio of the coating agent and the number of coatings investigated in this study. As the result, the Density of recycled aggregate increased, as the mixing ratio of the coating agent and the number of coatings increased. The percent of water absorption decreased rapidly for all coating conditions, and potential contamination test showed that among 21 items of concern, five were detected. The compressive strength of the water-permeable concrete increased by approximately 16.2% as produced with coated recycled aggregate.

Stiffness and Energy Dissipation of Steel Coupling Beam Embedded in the PSH2C and Normal Concrete Shear Wall

Hybrid coupled shear wall with steel coupling beams has often been used as load-resisting system of high-rise buildings under lateral loads. However, joint between steel beam and shear wall is under combined and high stress. Reinforcement details of the joint are very heavy. This study addresses the effect of shear wall cement composites type in hybrid wall system on the seismic performance of steel coupling beams embedded in shear wall. The main test variables were the failure mode of steel coupling beam and types of cement composites, such as PSH2C and concrete, for shear wall.

Mechanical Properties of Water-Permeable Concrete Using Coated Recycled Aggregates and Material for Performance Improvement

The mechanical properties of water-permeable concrete after mixing with coated recycled aggregates, silica fume, and PVA fiber were investigated in this study. Recycled aggregate was coated double-layer and then mixed as the coarse aggregate of water-permeable concrete. As a result, the void ratio, water-permeability coefficient and strength decreased, as compared to concrete with mixed crushed aggregates. When both silica fume and PVA fiber was added, the strength of the water-permeable concrete increased (compressive strength : by 4.3%, flexural strength : by 2.1 times). Also, the freeze and thaw resistance of the water-permeable concrete increased by approximately 44.15% compared to the plain concrete with no added reinforcing element.

The Effects of Expansive Additive on Rapid Hardening Cement Grout for Semi-Rigid Pavement

Semi-rigid pavement, which mitigates the drawbacks of cement concrete and asphalt concrete pavements, is being widely used, but the body of research on enhancing the performance of cement grout remains limited. This paper discusses basic research on the development of a rapid hardening cement grout for semi-rigid pavement that meets chloride resistance, rheological property, and strength requirements. Evaluation results indicate that with up to 10% addition of expansive additive, in terms of the weight fraction of cement particles, the rheological property and strength requirements were satisfied. Examination of the chlorine ion penetration resistance revealed that an increase of expansive additive content yielded lower numbers of charged chlorine ions, resulting in 75.5 times higher resistance over a plain mix designed without expansive additive. In contrast, it was found that excessive addition of expansive additive, that is, beyond 10% in terms of the weight fraction of cement particles, was detrimental to achieving the desired rheological property.