Papers by Author: Cheol Woo Park

Abstract: As the amount of waste concrete has been increased and recycling technique advances, this study investigates the applicability of recycled concrete aggregate for concrete structures. In addition fly ash, the industrial by-product, was considered in the concrete mix. Experimental program performed compressive strength and chloride penetration resistance tests with various replacement levels of fine recycled concrete aggregate and fly ash. In most case, the design strength, 40MPa, was obtained. It was known that the replacement of the fine aggregate with fine RCA may have greater influence on the strength development rather than the addition of fly ash. It is recommended that when complete coarse aggregate is replaced with RCA the fine RCA replacement should be less than 60%. The recycled aggregate concrete can achieve sufficient resistance to the chloride ion penetration and the resistance can be more effectively controlled by adding fly ash. It I finally conclude that the recycled concrete aggregate can be successfully used in the construction field and the recycling rate of waste concrete and flay ash should be increased without causing significant engineering problems.

Abstract: This study intends to increase the consumption of coal ash which is an industrial by-product from power plants. The coal ash used to be deposited in the ground and its recycling has been very poor comparing to the produced amount. This study aims to enhance practical application of coal ash as a shotcrete construction material. Derived were optimum mix proportions for high performance shotcrete using coal ash. In order to enhance long term performance, silica fume was also added. Experimental variables included replacement ratio of silica fume and coal ash. Compressive strength and potential hazardous contamination to soil were the primary factors in the performance evaluation. From the test results, when fly ash was replaced up to 10% of the cement, most required specifications were satisfied. Hazardous material content was shown to be well below the specifications. Therefore, when appropriate caution in handling is given in the field, it is strongly anticipated to increase the coal ash recycling as a shotcrete construction material.

Abstract: The use of steel plates has been greatly increased in bridge construction, particularly for long-span bridges, and connections between the plates are made usually using high-tension bolts. However, the specifications on the use of large-sized high-tension bolts are not adequately stated in the currently available construction manuals. In order to provide further information on the use of the large-sized high-tension bolts, this study experimentally investigated the relaxation and slip behavior of M30 bolts with varying bolt size and plate thickness. In addition, numerical evaluation using FEM was performed to investigate the compressive stress occurred on the inside of bolt hole. The analyzed results were compared with the stress distribution measured from strain gages attached on the bolts and bolt holes. From the study presented herein, it was found that the relaxation was increased as the size of bolt increased, and that the M30 high-tension bolts developed slip coefficient greater than 0.4. The thickness of plate did not significantly affect the compressive stress distribution around the bolt holes.

Abstract: Among various types of fiber reinforced polymer (FRP) materials, sheet-formed materials are commonly used for the strengthening of reinforced concrete structures. Basalt fiber sheet has shown a good durability to a harsh environmental condition comparing to other typical fiber sheets, such as glass and carbon fiber sheets [1]. This study investigates the debonding failure characteristics of the basalt fiber sheet for its application in the field. Fundamental mechanical characteristics were evaluated prior to the bond fracture test. Experimental variables include the number of fiber sheet layers, bonding length and bonding width. Debonding failure mode was typical at the bonded interface and the failure strength increased as the number of layer increased. From the results, the effective bond length and effective bond strength were calculated and compared with the literatures. It was also found that the debonding failure strength was a function of the bonding width rather than the bonding length. Based on the test data, an equation to calculate the effective bonding length and strength was suggested.

Abstract: Three RC slab specimens were designed and manufactured to investigate the fatigue behavior of RC slab retrofitted with carbon fiber mesh (CFM) and mortar. Among three slab specimens, two slabs were pre-loaded to introduce damage prior to the fatigue loading tests. Fatigue loading was applied to the top of slab maintaining 40% of the ultimate strength of specimen at 2Hz loading speed. The fatigue test was terminated when the loading cycle exceeded 1,000,000 cycles. From the test results, the effectiveness of the retrofitting using CFM was evaluated. Test result showed that the specimens retrofitted after either severe or light damages had very similar strength and stiffness to those of the specimens retrofitted without damage. It was found that the strength was even slightly improved in the specimen retrofitted with CFM.