Showing papers by "Byung-Wan Jo published in 2007"

Characteristics of cement mortar with nano-SiO2 particles

Abstract: The amorphous or glassy silica, which is the major component of a pozzolan, reacts with calcium hydroxide formed from calcium silicate hydration. The rate of the pozzolanic reaction is proportional to the amount of surface area available for reaction. Therefore, it is plausible to add nano-SiO 2 particles (NS) to make high-performance concrete. The compressive strengths of cement mortar were evaluated at various water-cementitious material ratios (w/cm). Five different w/cm were used, including 0.23, 0.25, 0.32, 0.35, and 0.48 and four contents of NS, 3, 6, 9, and 12% by weight of cement. The compressive strengths of cement mortar with the addition of silica fume were also evaluated at a w/cm of 0.35 to compare with mortar containing nano-SiO 2 particles and three contents of silica fume were: 5, 10, and 15% by weight of cement. The experimental results show that the compressive strengths of mortars with NS were all higher than those of mortars containing silica fume at 7 and 28 days. It was demonstrated that the nano-particles were more valuable in enhancing strength than silica fume. This paper also analyzes some available examinations to monitor the hydration progress continuously, such as SEM observation, residual quantity test for Ca(OH) 2 , and the rate of heat evolution. The results of the examinations indicate that the SiO 2 in nano scale behave not only as a filler to improve the microstructure, but also as an activator to promote pozzolanic reactions.

Investigations on the development of powder concrete with nano-SiO2 particles

Abstract: The nano scale of particles can result in dramatically improved or different properties from conventional grain-size materials of the same chemical composition. Therefore, it is practical to add nano-silica in particle form with 99.9% of SiO2 in nano scale to improve the characteristics of cement mortar. The compressive strengths of cement mortar were evaluated at various water-cementitious ratio. Five different water-cementitious ratios were used including, 0.23, 0.25, 0.32, 0.35, and 0.48 and four contents of nano-SiO2 particles, 3%, 6%, 9%, and 12% by weight of cement. The compressive strength of cement mortar with the addition of silica fume were also evaluated at w/cm ratio of 0.48 to compare with mortar containing nano-SiO2 particles and three contents of silica fume were: 5%, 10% and 15% by weight of cement. The experimental results show that the compressive strengths of mortars with nano-SiO2 particles were all higher than those of mortars containing silica fume at 7 and 28 days. It was demonstrated that the nano-particles were more valuable in enhancing strength than silica fume. This paper also analyzed some available examinations to monitor the hydration progress continuously, such as SEM observation, residual quantity test for Ca(OH)2 and the rate of heat evolution. The results of the examinations indicate that the SiO2 in nano scale behave not only as a filler to improve the microstructure, but also as an activator to promote pozzolanic reactions.

Properties of concrete made with alkali-activated fly ash lightweight aggregate (AFLA)

Abstract: An experiment was performed to investigate the properties of the hardened paste of fly ash by alkali activation and to determine the possible use of the paste in the production of lightweight aggregates. The highest compressive strength was 33.9 MPa, for paste with 10% NaOH, 15% sodium silicate, and 5% MnO 2 , cured at room temperature after 24 h of moisture curing at 50 °C. The hardened paste of fly ash was granulated to produce AFLA (alkali-activated fly ash lightweight aggregate). AFLA exhibited specific gravity (SSD, OD), water absorption, unit weight, and solid volume percentages of 1.85 (SSD), 1.66 (OD), 11.8%, 972 kg/m 3 , and 58.6%, respectively. The results of the heavy metals leaching test met US EPA regulations. The concrete using AFLA exhibited a compressive strength of 26.47 MPa and good freeze–thaw resistance at 6.0% entrained air content.

Properties of Eco-Construction Material Using Recycled Sewage Sludge Ash

Abstract: As the 21st century began, cement and concrete that are representatives of modem building materials became a major factor in global warming, air pollution and environmental pollution Also, the problems that are generated while pursuing high performance and high strength became social issues Therefore, it has become urgent to prepare counter plans This study has aimed at the recycling of sewage sludge ash and developing it as a new concept in building material which serves the environmental considerations for long-lasting developmental purpose Also, the study aimed to find a substitute for scarce natural resources and to secure high techniques for waste recycling The purpose of this study was also to solve fundamentally secondary environmental pollution The results revealed that the chemical components of sewage sludge ash are mainly which are similar to the components of pozzolan Also, it was identified that sewage sludge ash can be utilized as a hardened specimen with an alkali activated pozzolan reaction Considering the possibility of appropriate strength development and the advantage of drying shrinkage, compared with that of cement, it was believed that sewage sludge ash can demonstrate a function as a substitute for cement given

Bridge Health Mornitoring using Wireless Sensor Networks

Abstract: Wireless sensor networks bring new challenges to Bridge monitoring. To monitor a bridge, behavior, including vibration and displacement, must be measured to analyze the health of the structure based on measured and collected data. The collected data can be used to compute modal properties of the bridge. A bridge is moved by external forces, including wind, seismic activity, and traffic. So it is very hard reliance of safety through a preexistence method which uses Data Logger. Dynamic behavior of a bridge is difficult to measure because of costs and installation methods. In this paper, a new method, using a U-Smart Sensor and Sensor Networking to measure the dynamic behavior of the bridge, is suggested. A new wireless MEMS accelerometer sensor (U-Smart Sensor) board is designed to meet the specific hardware and software requirements of structural engineering applications.

Dynamic Characteristics of Seohae Cable-stayed Bridge Based on Results from Long-term Structural Health Monitoring

Abstract: This paper presents the long-term dynamic characteristics of a cable-stayed bridge where installed the SHM (Structural Health Monitoring) system. Modal parameters such as natural frequencies and mode shapes were identified from the modal analysis using the three-dimensional finite element model. The modal parameters of the developed baseline model have a good correlation with those identified from field ambient vibrations. By the analysis of correlations between the measured natural frequencies and temperatures, it was found the natural frequency was in linearly inverse proportion to the temperature. Mode shapes were extracted from the TDD (Time Domain Decomposition) technique for ambient vibration measurements. Finally, these results demonstrate that the TDD technique can apply to identify modal parameters of large-scaled bridges.