Seung-Bum Park

Experimental study on the engineering properties of carbon fiber reinforced cement composites

Abstract In order to reinforce ordinary cement matrix, carbon fibers (CF) derived from two different precursors are added to the cement mix containing two different silica aggregates. The main experimental variables applied in forming the carbon fiber reinforced cement composites (CFRC) are PAN-based CF vs. pitch-based CF, different fiber lengths and the aspect ratios, silica powder vs. silica fume, water to cement ratios, fiber volume loadings, and air or water curing vs. autoclave curing. Based on the test results, a fabrication procedure for lightweight CFRC, has been developed and the optimum proportions of the ingredients are successfully identified. It is concluded that the reinforcement of carbon fiber is very effective in improving the tensile strength, flexural strength, fracture toughness, and the reduction in drying shrinkage of CFRC compared with conventional mortar.

Effects of processing and materials variations on mechanical properties of lightweight cement composites

Low-density/low-cost cement composites were fabricated. Carbon and alkali-resistant glass fibers were used to reinforce the matrix of industrial by-products; fly ash with silica fume, Portland cement, and calcium silicates were mixed in different proportions. The additional low density was obtained by adding perlite and foaming agents followed by hot water curing. The composites also were prepared by autoclave curing for comparison. The mechanical properties were improved by increasing the amount of silica fume, fly ash, and fibers. Both carbon fibers and alkali-resistant glass fibers were effective in reinforcing the matrices, but carbon fibers were superior to glass fibers. Fabrication techniques for producing lightweight cement composites that can substitute for autoclaved lightweight concrete was developed.

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.

Mechanical properties of carbon-fiber-reinforced polymer-impregnated cement composites

A Portland cement was reinforced by incorporating carbon fibers (CF), silica powder, and impregnating the pores with styrene monomers which were polymerized in situ. The effects of type, length, and volume loading of CF, mixing conditions, curing time, and curing conditions on mechanical behavior as well as freeze-thaw resistance and longer-term stability of the carbon-fiber-reinforced cement composites (CFRC) were investigated. The composite paste exhibited a decrease in flow values linearly as the CF volume loading increased. Tensile, compressive, and flexural strengths all generally increased as the CF loadings in the composite increased. Compressive strength decreased at CF loadings above approx. 3% in CFRC having no impregnated polymers due to the increase in porosity caused by the fibers. However, the polymer impregnation of CFRC improved all the strength values as compared with CFRC having no polymer impregnation. Tensile stress-strain curves showed that polymer impregnation decreased the fracture energy of CFRC. Polymer impregnation clearly showed improvements in freeze-thaw resistance, creep resistance, and drying shrinkage when compared with CFRC having no impregnated polymers.

Expansion Properties of Mortar Using Waste Glass and Industrial By-Products

Waste glass has been increasingly used in industrial applications. One shortcoming in the utilization of waste glass for concrete production is that it can cause the concrete to be weakened and cracked due to its expansion by alkali-silica reaction(ASR). This study analyzed the ASR expansion and strength properties of concrete in terms of waste glass color(amber and emerald-green), and industrial by-products(ground granulated blast-furnace slag, fly ash). Specifically, the role of industrial by-products content in reducing the ASR expansion caused by waste glass was analyzed in detail. In addition, the feasibility of using ground glass for its pozzolanic property was also analyzed. The research result revealed that the pessimum size for waste glass was regardless of the color of waste glass. Moreover, it was found that the smaller the waste glass is than the size of , the less expansion of ASR was. Additionally, the use of waste glass in combination with industrial by-products had an effect of reducing the expansion and strength loss caused by ASR between the alkali in the cement paste and the silica in the waste glass. Finally, ground glass less than 0.075 mm was deemed to be applicable as a pozzolanic material.

Rheology Control of Cement Paste for Applying ECC Produced with Slag Particles to Self-Consolidating and Shotcreting Process

An engineered cementitious composite produced with slag particles (Slag-ECC) had been developed based on micromechanical principle. Base grain ingredients were properly selected, and then the mixture proportion was optimized to be capable of achieving robust tensile ductility in the hardened state. The rheological design is performed in the present study by opti- mizing the amount of admixtures suitable for self-consolidating casting and shotcreting process in the fresh state. A special focus is placed on the rheological control which is directly applicable to the construction in field, using prepackaged product with all pulverized ingredients. To control the rheological properties of the composite, which possesses different fluid properties to facilitate two types of processing (i.e., self-consolidating and shotcreting processing), the viscosity change of the cement paste suspensions over time was initially investigated, and then the proper dosage of the admixtures in the cement paste was selected. The two types of mixture proportion were then optimized by self-consolidating & shotcreting tests. A series of self-consolidating and shotcreting tests demonstrated excellent self-consolidation property and sprayability of the Slag-ECC. The rheological properties altered through this approach were revealed to be effective in obtaining Slag-ECC hardened properties, represented by pseudo strain-hard- ening behavior in uniaxial tension, allowing the readily achievement of the desired function of the fresh Slag-ECC. These ductile composites with self-consolidating and shotcreting processing can be broadly utilized for a variety of applications, e.g., in strength- ening seismic resistant structures with congested reinforcements, or in repairing deteriorated infrastructures by shotcreting process.

Mechanical Properties of Porous Concrete For Pavement Using Recycled Aggregate and Polymer

The purpose of this study is to utilize recycled concrete aggregates as permeable pavement materials. This study evaluates mechanical properties and durability of porous concrete depending on mixing rates of recycled aggregates and polyme. As a result, void ratio and permeability coefficient of porous concrete for pavement increased a little as mixing rate of recycled aggregates increased. Void ratio and permeability coefficient increased a lot as mixing rate of polymer increased. As polymer was mixed , national regulation of permeable concrete for pavement( and 0.01cm/sec) was met. Compressive strength and flexural strength decreased as mixing rate of recycled aggregates increased but they increased a lot as mixing rate of polymer increased. Even when recycled aggregates were mixed polymer mixed, national regulation of pavement concrete(18MPa and 4.5MPa) was met. In addition, regarding sliding resistance, BPN increased as mixing rate of recycled aggregates increased. But BPN decreased as polymer was mixed. Compared to crushed stone aggregates, abrasion resistance and freeze-thaw resistance decreased as mixing rate of recycled aggregates Increased. When polymer was mixed, abrasion resistance and freeze-thaw resistance improved remarkably. Compared to non-mixture, mixture of polymer improved abrasion resistance and freeze-thaw resistance about and 3.8times respectively.

A Study on the Sound Absolution Properties of Porous Concrete by Recycled Aggregate Contents and Target Void Ratio

This study peformed an evaluation of the physical and mechanical properties and sound absorption characteristics of porous concrete according to the target void ratio and content of the recycled aggregate in order to reduce the noise generated in roads, railroads, residential areas and downtown areas and effectively utilize the recycled waste concrete aggregate generated as a byproduct of construction. The test results demonstrated that the difference between the target void ratio and the actual measured void ratio was less than and that the tendency of the compression strength was to reduce rapidly when the target void ratio and the content of the recycled aggregate exceeded and , respectively. In addition, the sound absorption characteristics of the porous concrete using recycled waste concrete aggregate showed that the NRC was the highest at the target void ratio of and the content of the recycled aggregate had very little influence on the NRC. Therefore, when considering the compression strength and the sound absorption characteristics of porous concrete, the proper target void ratio and the content of the recycled waste concrete aggregate are thought to be and , respectively

Physical and mechanical properties of carbon fiber reinforced smart porous concrete for planting

The reinforcement strength of porous concrete and its applicability as a recycled aggregate was measured. Changes in physical and mechanical properties, subsequent to the mixing of carbon fiber and silica fume, were examined, and the effect of recycled aggregate depending on their mixing rate was evaluated. The applicability of planting to concrete material was also assessed. The results showed that there were not any remarkable change in the porosity and strength characteristics although its proportion of recycled aggregate increased. Also, the mixture of 10% of silica was found to be most effective for strength enforcement. In case of carbon fiber, the highest flexural strength was obtained with its mixing rate being 3%. It was also noticed that PAN-derived carbon fiber was superior to Pitch-derived ones in view of strength. The evaluation of its use for vegetation proved that the growth of plants was directly affected by the existence of covering soil, in case of having the similar size of aggregate and void.

DURABILITY AND ENGINEERING PROPERTIES OF SUPERPLASTICIZED CONCRETE

This study investigated the effects of superplasticizers on fresh and hardened concrete. The experimental program included tests on the slump and slump loss, bleeding, setting time, air content, compacting factor, Vee Bee, compressive strength, tensile and flexural strength, permeability, shrinkage, creep and freeze-thaw durability. Properties of superplasticized concrete were compared to those of conventional and base concretes. Superplasticizers were observed to have an appreciable fludifying action in fresh concrete. The compressive, tensile and flexural strengths of superplasticized concrete were significantly higher than those of the conventional concrete. The permeability and drying shrinkage of superplasticized concrete was significantly less than those of the conventional concrete, but there were no significant differences between the base and superplasticized concrete. Compared to the base concrete, non-air entrained superplasticized concrete had slightly higher freeze-thaw durability, and superplasticized concrete with an appropriate amount of entrained air gave even better resistance to freezing and thawing. And superplasticized concrete was found to exhibit slightly lower creep in 0.4% dosage of superplasticizer than the conventional concrete, but slightly higher creep in 1.0% dosage of superplasticizer.