Seungwon Kim

Fundamental Study on Pervious Concrete Materials for Airport Pavement Cement Treated Base Course

PURPOSES : As a research to develop a cement treated base course for an airport pavement which can enhance its drainage, this paper investigated the strength, infiltration performance and durability of the pervious concrete with respect to maximum coarse aggregate sizes and compaction methods. METHODS : This study measured compressive strength, infiltration rate, continuous porosity and freeze-thaw resistance of pervious concrete specimens, which were fabricated with five different compaction methods and different maximum aggregate sizes. In addition, in order to reduce the usage of Portland cement content and to enhance environment-friendliness, a portion of the cement was replaced with Ground Granulated Blast Furnace Slag (GGBS). RESULTS: Compressive strength requirement, 5 MPa at 7 days, was met for all applied compaction methods and aggregate sizes, except for the case of self-compaction. Infiltration rate became increased as the size of aggregate increased. The measured continuous porosities varied with the different compaction methods but the variation was not significant. When GGBS was incorporated, the strength requirement was successfully satisfied and the resistance to freezing-thawing was also superior to the required limit. CONCLUSIONS: The infiltration rate increased as the maximum size of aggregate increased but considering construct ability and supply of course aggregate, its size is recommended to be 25mm. With the suggested mix proportions, the developed pervious concrete is expected to successfully meet requirements for strength, drainage and durability for cement treated base or subbase course of an airport pavement.

Fundamental properties and mechanical characteristics of high performance cement composite with steel fibres under high temperature

Abstract High-performance fibre-reinforced cementitious composite (HPFRCC) is characterized by multiple functioning composite materials comprising fibre and cement matrix. HPFRCC is able to withstand tensile stress forming distributed micro-cracks since embedded fibres in concrete are to improve energy-absorption capacity and apparent ductility. This characteristic can be applied to protect structures under an extreme state of loading, such as blast or impact. In order to determine a mix proportion, this study considered various variables in the mix. Following experimental results, this study suggests an optimum mix proportion of HPFRCC and investigated fundamental properties of the considered mixes. Flexural performance is one of the representing characteristics of the high-fracture energy-absorbing materials. This study investigated the flexural performance of HPFRCC, which used high-strength steel fibres with volume fraction 8%. Under ASTM 1609, load–deflection curves were obtained. The major test variables include silica fume replacement ratio 0 and 15% and exposure temperature, ambient and 400 °C. The flexural strength was similar to the compressive strength and the absorbed fracture energy was relatively greater than other typical HPFRCC. This may be a composite reaction of the strong bonding between fibre and matrix and high-compressive strength of the matrix itself.

Optimum Mix Proportions of In-fill Slurry for High Performance Steel Fiber Reinforced Cementitious Composite

Seung-Won Kim･Cheol-Woo Park*･ Seong-Wook Kim･ Hyun-Myung Cho･ Sang-Pyo Jeon･Min-Kwan Ju(Received August 5, 2014 / Revised September 23, 2014 / Accepted September 25, 2014)As political circumstances in oversea countries and Korea varies, the risk of vulnerability from unexpected extreme loading con ditions,such as explosions or extreme impacts, also increased. In additi on, construction companies in Korea recently have taken chances of overseas expansion to countries where their domestic situations are not in rest. Therefore, the resistance of construction mate rials forblast or impact loading become taking more consideration from engineering field. This study is a part of the research to develo p a highperformance fiber reinforced cementitious composite materials with high volume steel fibers and primary purpose of this study i s to find an optimum mix proportions of in-fill slurry. In order to accomplish the tasks this study performed experimental investiga tions onthe slurry for consistency, compressive strength, flowability, J-penetration, bleeding and rheology properties as well as mecha nical properties, compressive and flexural strength, with respect to different mix proportions.키워드 : 강섬유보강 시멘트 복합체, 폭발 및 충격하중, 최적배합, 충전슬러리Keywords : Steel fiber reinforced cementitious composite, Blast and Impact loading, Optimum mix proportions, In-fill slurry* Corresponding author E-mail: tigerpark@kangwon.ac.kr

Experimental Study on Mechanical Properties of Carbon-Capturing Concrete Composed of Blast Furnace Slag with Changes in Cement Content and Exposure

PURPOSES: This study investigates the mechanical performance of carbon-capturing concrete that mainly contains blast furnace slag. METHODS: The mixture variables were considered; these included Portland cement content, which was varied from 10% to 40% of the blast furnace slag by weight. The specimens were exposed to different conditions such as high and concentrations, laboratory conditions and high conditions. Mechanical performances, including compressive and flexural strengths and carbon-capturing depth, were evaluated. RESULTS : The slump, air content and unit weight were not affected significantly by the variation in cement content. The strength development when the specimens were exposed to high purity air was slightly greater than that when exposed to high . As the cement content increased the compressive and flexural strength increased but not considerably. The carbon-capturing capacity decreased as the cement content increased. The specimens exposed in the field for 70 days had flexural strength greater than 3 MPa. CONCLUSIONS : The results indicate that cement content is not an important parameter in the development of compressive and flexural strengths. However, the carbon-capturing depth was higher for less cement content. Even after field exposure for 70 days, neither any significant damage on the surface nor any decrease in strength was observed.

Fundamental Characteristics of Carbon-Capturing and Sequestering Activated Blast-Furnace Slag Mortar

PURPOSES : To investigate the fundamental characteristics of blast-furnace slag mortar that was hardened with activating chemicals to capture and sequester carbon dioxide. METHODS : Various mix proportions were considered to find an appropriate stregnth development in regards with various dosages of activating chemicals, calcium hydroxides and sodium silicates, and curing conditions, air-dried, wet and underwater conditions. Flow characteristics was investigated and setting time of the mortar was measured. At different ages of 3, 7 and 28days, strength development was investigated for all the mix variables. At each age, samples were analyzed with XRD. RESULTS : The measured flow values showed the mortar lost its flowability as the activating chemicals amount increased in the scale of mole concentration. The setting time of the mortar was relatively shorter than OPC mortar but the initial curing condition was important, such as temperature. The amount of activating chemicals was found not to be critical in the sense of setting time. The strength increased with the increased amount of chemicals. The XRD analysis results showed that portlandite peaks reduced and clacite increased as the age increased. This may mean the keeps absorbing in the air during curing period. CONCLUSIONS : The carbon capturing and sequestering activated blast-furnace slag mortar showed successful strength gain to be used for road system materials and its carbon absorbing property was verified though XRD analysis.

Investigation of Potential Fire Hazard Resources of Bridges on National Routes by Field and Web-based Satellite

PURPOSES : The occurrence of unexpected disasters, including fire events, increases as the road network becomes complicated and traffic volume increases. When a fire event occurs on and under bridges, the damage extensively influences direct damage to structures, vehicles, and human life and secondary socioeconomic issues owing to traffic blockage. This study investigated potential fire-hazard risks on bridges of the Korean national route road. METHODS : The investigation was conducted using field investigation and analysis with satellite pictures and road views from commercial websites and the Bridge Management System (BMS). From the filed investigation, various potential fire resources were identified. The satellite pictures and road views were helpful in measuring and recognizing conditions underneath bridges, stowage areas, etc. RESULTS : There are various potential fire resources underneath bridges such as piled agricultural products, parked petroleum tanks, construction equipment, and attached high-voltage cables. A total of 94.6% of bridges have underneath clearances of less than 15 m. A bridge underneath volume that can stow a potential fire hazard resource was 7,332 m on average, and most bridges have about 4,000 m of space. Based on the BMS data, the amounts of PSC and steel girders were 29% and 25%, respectively. CONCLUSIONS : It was found that the amount of stowed potential fire hazard resources was proportional to the underneath space of bridges. Most bridges have less than 15 m of vertical clearance that can be considered as a critical value for a bridge fire. The fire risk investigation results should be helpful for developing bridge fire-protection tools.

Flexural Behavior of High-Volume Steel Fiber Cementitious Composite Externally Reinforced with Basalt FRP Sheet

High-performance fiber-reinforced cementitious composites (HPFRCCs) are characterized by unique tensile strain hardening and multiple microcracking behaviors. The HPFRCC, which demonstrates remarkable properties such as strength, ductility, toughness, durability, stiffness, and thermal resistance, is a class of fiber cement composite with fine aggregates. It can withstand tensile stresses by forming distributed microcracks owing to the embedded fibers in the concrete, which improve the energy absorption capacity and apparent ductility. This high energy absorbing capacity can be enhanced further by an external stiff fiber-reinforced polymer (FRP). Basalt fabric is externally bonded as a sheet on concrete materials to enhance the durability and resistance to fire and other environmental attacks. This study investigates the flexural performance of an HPFRCC that is externally reinforced with multiple layers of basalt FRP. The HPFRCC considered in the study contains steel fibers at a volume fraction of 8%.

Mix Proportions of High Flowable Early Strength Mortar for Emergency Repair of Damaged Road Base in Rural Area

Recently, due to the climate changes, the frequency and severity of natural disasters such as torrential rain have become more significant worldwide. In South Korea, there are number of summer typhoons and localized torrential downpour every year and these cause severe damages onto a residential area and road networks. More than 70% of the land of Korean peninsula is a mountainous area and thus damages onto road networks result in serious harm to daily lives especially in a rural area by isolating residents from networks. Therefore, there is a strong demand on the immediate and emergency repair technology for the collapsed road networks. This study develops an emergency repair technique for damaged road base where the damaged road base can be packed with gravels and then the pores or open-gaps of the packed gravels can be filled with high flowable mortar that develops strength in an early age. The aim of this research study was to find the suitable mix proportions of high flowable early strength mortar. Throughout the experimental work, study was done on two stage mix variables, where in the 1st stage, W/C ratio and high range water reducer was considered whereas in the 2nd stage cost effective early strength cement was used for the mix-design. With various variables in mix proportions, compressive strength and flow capacity were investigated. Finally from those experimental study, optimum mix proportions of the high flowable early strength mortar was found. The hardened materials composited with gravels and mortars can be used as a permanent road base with no need for compaction thereafter.

Compressive Strength Properties of Concrete Using High Early Strength Cement and Recycled Aggregate with Steam Curing Conditions

Recycled aggregate is a valuable resource in Korea in lack of natural aggregate. Government recognizes the importance and suggests various policies enhancing its use for higher value-added application. Most of recycled aggregate produced currently in Korea, however, is applied for low value-added uses such as embankment, reclamation, etc. Its higher valued application such as for structural concrete is very limited. Although domestic manufacturing technology of recycled aggregate is at the world level, recycled aggregate is not applied for structural concrete. Primary reasons for the limited use of the recycled aggregate include bonded mortar and cracks occurred during crushing and hence it is very difficult to predict and control the quality of recycled aggregate concrete. This research intended to grasp combined characteristics of recycled aggregate, high early strength cement, maximum temperature and time duration of steam curing and then, analyze the effects of factors. Also, it suggested the method to improve field applicability of recycled aggregate concrete.

Fundamental Study of Mix Proportions of High-Flow Cement-Based Mortar for Gravel-Fill Used in Restoration of Collapsed Roads

PURPOSES: As a part of our research into repair techniques for roads that have collapsed as a result of a natural disaster, this study set out to find the optimum mix proportion for gravels to be used to restore a damaged area. METHODS: This study considered flow and strength-development characteristics. The experimental variables were the W/C ratio, the usage of the admixture, the types of cement, and the quantity of fine aggregate over three different experimental stages. The compressive strength was measured at 12 hours, one day, three days, and seven days. RESULTS : The flow varied with the amount of fine aggregate and the use of a high-range water-reducing (HRWR) admixture. The compressive strength also varied with respect to the type of cement and the W/C ratios. The strength satisfied the expected requirement of 21 MPa after one day, provided the mix proportion was appropriate. CONCLUSIONS: A gravel-filling high-flow cement-based mortar exhibited strength and consistency with a W/C ratio in the range of 0.40 to 0.45, assuming the use of HRWR at 0.5 to 0.7% and a fine aggregate/cement ratio of 1.0 to 1.5.