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標題: 高強度水工混凝土掺加飛灰之耐磨性及裂縫防制
Influence of Fly Ash on the Abrasion-Erosion Resistance and Cracking Controlled of High-Strength Concrete
作者: 徐造華
Hsu, Tsao-Hua
關鍵字: high-strength concrete;高強度混凝土;abrasion-erosion;cracking;fly ash;silica fume;水中磨損;裂縫;飛灰;矽灰
出版社: 土木工程學系
本文以ASTM C1138水中磨損試驗法,探討不同飛灰取代率對高強度混凝土耐磨性的影響。第一組試驗以水膠比0.28~0.54及飛灰取代率15%、20%、25%及30%,進行飛灰對一般混凝土水中耐磨性影響研究,試驗結果顯示,混凝土耐磨性隨抗壓強度增加或水膠比降低而增加,對飛灰取代率在15%以內者,其28天與91天齡期的耐磨性與一般混凝土者相近;當飛灰取代水泥量超過15%後,飛灰掺量越多耐磨性越差。飛灰對混凝土耐磨性的影響,可介入「飛灰耐磨影響因子」作修正;修正後的有效抗壓強度及有效水膠比,都可利用線性模式更準確地評估混凝土的耐磨能力。

The high-strength concrete (HSC) with superior resistance to abrasion-erosion is more frequently applied as abrasion-resistant coatings of hydraulic structure. However, HSC mixtures have high cement content, particularly when it contains silica fume (SF), which enhances the heat of hydration and may cause increased shrinkage that results in a potential of cracking and low durability. Therefore, in most mixtures, cement is replaced partly with supplementary cementitious materials such as fly ash (FA) to reduce the hydration heat and increase the durability. But using FA as cement replacement in concrete may reduces the abrasion resistance of concrete.
This study investigates the abrasion-erosion resistance of HSC by ASTM C1138. In series I concrete mixes, the water-to-cementitious materials (w/cm) ratios varied from 0.28 to 0.54. For every w/cm ratio, cement was partially replaced with four kinds of replacements (15%, 20%, 25% and 30%) of FA by weight. Experimental results show that the abrasion-erosion resistance of FA concrete mixtures was improved by increasing compressive strength and decreasing the ratio of w/cm. The abrasion-erosion resistance of concrete with cement replacement up to 15% was comparable to that of control concrete without FA. Beyond 15% cement replacement, FA concrete showed lower resistance to abrasion-erosion compared to non-fly ash concrete. Equations were established based on effective compressive strengths and effective w/cm ratios, which were modified by cement replacement and developed to predict the 28- and 91-day abrasion-erosion resistance of concretes with compressive strengths ranging from approximately 300-1000 kgf/cm2. The calculation results are compared favorably with the experimental results.
Whereas in series II concrete mixes, the w/cm ratios varied from 0.24 to 0.33, the levels of cement replacement by FA were same to series I and a further 10% SF replacement was made. Experimental results also show that the abrasion-erosion resistance of concrete mixtures was improved by increasing compressive strength and decreasing the ratio of w/cm and the 10% SF provided improvement in the abrasion-erosion resistance of the concrete. The FA replacement level can be more than 25% was comparable to that of control concrete without FA.
According to in situ cases studied, the marked cracking may occur in HSC made with SF, and the race against cracking of HSC can be won if using 15% FA as cementitious materials replacement with well curing practices.
Replace cementitious materials by proper proportion of FA in HSC. It can take into account both abrasion-erosion resistance and cracking controlled which suit with abrasion-resistant coatings of hydraulic structure.
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