藉由貯鹽試驗及鹽霧加速劣化試驗探討高強度混凝土添加鋼纖維之耐久性

Study of the Durability of High Strength Concrete with Steel Fiber by Ponding Test and Salt Spray Test

何郁姍(Yu-Shan Ho)

指導教授 ： 廖文正

國立臺灣大學/工學院/土木工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201602404

摘要

使用高強度材料能縮減梁柱斷面的尺寸，使結構物輕量化，並增加建築物的使用空間，亦可減少材料用量，但高強度混凝土極為脆性，韌性甚差，所以藉由添加鋼纖維改善脆性破壞行為。相關研究已顯示添加鋼纖維能增加高強度混凝土的韌性，抑制早期保護層的剝落及紓解橫向鋼筋密集配置的問題。
鋼纖維對高強度混凝土的力學行為有顯著幫助，但台灣處於高溫高濕的環境，且大氣中帶有鹽分，鋼纖維和水泥漿體的界面層(interfacial transition zone, ITZ)恐形成外界污染物侵入的通道，降低建物的耐久性，尤其當鋼纖維因為外界氯離子侵入而鏽蝕時，會加速結構的劣化。
本研究透過添加不同體積取代率的鋼纖維，來探討高強度混凝土添加鋼纖維的耐久性影響。其中試驗分成兩大部分，一為鹽霧加速劣化試驗，一為貯鹽試驗。鹽霧加速劣化試驗模擬外界環境經過多年鹽害乾濕交替曝曬行為後，進行抗壓、抗彎、直拉、劈裂等力學試驗來評估劣化處理後試體的力學行為；由試驗結果顯示，在水膠比較低之高強度混凝土中，劣化處理後僅有表面鋼纖維產生嚴重鏽蝕，故鋼纖維的添加對劣化處理前後的整體力學性質無顯著影響。另外，由貯鹽試驗結果發現，擴散係數沒有顯著差異，所以ITZ 的存在不會影響整體孔隙結構的連通性。綜上所述，於高強度混凝土中添加鋼纖維不會影響結構的耐久性。

關鍵字

鋼纖維高強度混凝土 ； 貯鹽試驗 ； 鹽霧加速劣化試驗 ； 氯離子 ； 擴散係數

並列摘要

High strength materials have been widely used because using high strength concrete and reinforcement can further reduce the member section, which lights the weight of the elements and increases the available space of buildings, and save materials. To solve the brittleness of high strength concrete, the addition of the steel fibers can provide more confinement and shear capacity to enhance the ductility and toughness. It also prevents the early cover spalling and solves the congestion of the transverse reinforcements in the plastic hinge region of buildings.
Although the addition of the steel fibers provides good benefit on mechanical behavior of high strength concrete, Taiwan is an island surrounded by sea with the subtropical climate, made the structures easily deteriorated by salt damage. Worried about the chloride ion may penetrate into the concrete from the interfacial transition zone (ITZ) between the steel fibers and cement paste, and therefore reduce the durability of the structures. The other hesitation is the steel fibers may easily corrode so that the steel fibers lose its advantage, inducing the steel-fiber concrete structures become weaker.
This study investigates the addition of the steel fibers influencing the durability of the high strength concrete. The experiment divides into two parts. One is using the ponding test to discuss the ITZ of the materials. According to the result, the diffusion coefficient doesn’t change between the content of steel fibers. The other is using salt spray test to simulate the structures exposing outside several years. Finally, doing mechanical experiments, such as compressive test and flexural test to evaluate the mechanical behavior after the deterioration process. According the result of the mechanical test, the strength doesn’t worsen after the deterioration by the salt spray test.
In summary, the addition of the steel fibers doesn’t reduce the durability of high strength concrete.

並列關鍵字

Steel-fiber concrete ； Ponding test ； Salt spray test ； Chloride ion ； diffusion coefficient

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