Microcrack of Cement Paste and Mortar after Fire Damage

• Main Authors: Chih-Ching Chen, 陳姿菁
• Other Authors: I-Kuang Fang
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/74536111200683811832

碩士 === 國立成功大學 === 土木工程學系碩博士班 === 94 === 　　Crackings are deleterious to the compressive strength of concrete, however, the increase of crack width decreases the thermal conductivity of concrete. The purpose of this study is to investigate the characteristics of micro-cracks, smaller than 0.11 mm, in paste, mortar and concrete after fire damage. 　　Nine test temperatures, i.e., ambient, 100℃, 200℃, 300℃, 400℃, 500℃, 600℃, 700℃, and 800℃, were adopted to investigate the paste and mortar properties after fire damaged. In addition, in paste, the effect of fire duration for 1hr, 2hr, and 3hr were tested. Four test temperatures, i.e., ambient, 400℃, 600℃, and 800℃ were used for the normal (NC) and self-consolidating concrete (SCC). The scanning electron microscope (SEM) and image analysis software (Power Image Analysis, PIA) were used to observe and analyze the properties of micro-cracks. 　　Crack-area ratio was employed to study the relations of crack-number and crack-width. Test results revealed that, in paste, the increase of crack-area ratio within 200℃-300℃ is mainly due to the increase of the amounts of cracks. When the temperature is within 400℃-500℃, it is mainly due to the increase of the crack width. As the temperature increases up to 700℃-800℃, the ratio increase is primarily due to the increase of both the amounts of cracks and the crack width. For temperatures increased over approximately 300℃, in paste, the effect of fire duration on the amounts of cracks and the crack width is more significant in the first 2 hours period. The smaller cracks in paste, less than about 0.001 mm to 0.002 mm, can be observed clearly at approximately 300℃ and the amounts begin to increase at around 500℃. In mortar, the crack-area ratio increases more significantly between 400℃ and 600℃, and the number increase within 500℃-600℃ is primarily resulted from the increase of the crack width at the aggregate interface. The smaller cracks begin to appear in paste at approximately 200℃ and the crack width increases more significantly at 600℃. The amounts of smaller cracks increase obviously at 800℃. The smaller cracks of NC can be observed clearly at approximately 400℃ and both the amounts of smaller cracks and the crack width increase significantly at 800℃. The SCC have similar crack characteristics as NC except that the amounts of smaller cracks in SCC are slightly less than those in NC.