Effects of Leaching Behavior of Calcium Ions on Compressive Property and Durability of Cement-Based Materials

• Main Authors: Hong-Ru Liou, 柳宏儒
• Other Authors: Howard Hwang
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/53674443853856030419

碩士 === 國立宜蘭大學 === 建築與永續規劃研究所碩士班 === 99 === Concrete is a solid and porous composite material. When concrete is exposed to a damp environment for a long period of time, pore water will penetrate into the concrete causing leaching of hydration products. Leaching of calcium ions increases porosity and results in harmful ions ingressing into the concrete which reduces its strength and durability. The purpose of this study was to evaluate the effect of water-binder ratio and mineral admixtures (such as fly ash, slag and silica fume) on calcium ion leaching behavior of cement-based materials. Ammonium nitrate solution was used to accelerate the leaching process. Leaching durations were 56 days, 91 days and 140 days. Scanning electron microscopy, X-ray diffraction analysis and thermal analysis were used to analyze and compare material composition after leaching. Leaching depth, initial surface absorption test (ISAT), mercury intrusion porosimetry (MIP) and ultrasonic pulse velocity were measured to analyze pore structure of cement-based materials. Through chemical analysis, pore structure analysis was conducted to investigate the effect of leaching on the strength and durability of cement-based materials. The results showed that the porosity enhancement and ultrasonic pulse velocity decrease in pastes subjected to leaching can be attributed to the dissolution of calcium hydroxide (CH) as well as decalcification of C-S-H gel. In addition crystallization on the surface of pastes may cause misleading IAST results. Leaching resistance was increased with a decrease in water/cementitious ratio and an increase in adding mineral admixtures. The mineral admixtures reduced calcium hydroxide quantity and refined pore structure through pozzolanic reaction. The leaching depth showed that leaching behavior of the specimens without mineral admixtures can be divided into two stages, leaching of calcium hydroxide followed by C-S-H gel leaching. The mineral admixtures reduced leaching depth and enhanced strength and durability.