改良式水中自充填混凝土

Abstract

土木工程在施工過程常需要於水中澆置混凝土，諸如橋墩、基樁等，在過去多使用坍度較低、富配比之混凝土，使混凝土具有較好的工作度及黏滯性，此時工程人員最關心的是混凝土離開特密管後，水泥砂漿是否隨著水流失，或者混凝土與水混合而增加水灰比導致強度因而減少。而構造物因配置鋼筋量的增加，較高的鋼筋用量導致間隙更密，除了增加施工的困難性，結構物的品質更是難以控制。若能將水中混凝土達到自行充填的性能且在水中不分散，便能大幅改善水中結構物的品質。 所以本研究以自充填特性和水中不分散、減少凝結時間以及增加抗壓強度為實驗目標，嘗試用不同種類之添加試劑改善初凝、終凝時間，而實驗結果對初凝時間有所提升3~4小時，終凝時間甚至提升了4~5小時；除了基本的工作性測試需符合自充填混凝土規範之外，並經過抗沖蝕試驗對新拌混凝土之相關性質，達到水中不分散的要求，並在混凝土硬固後測試力學性質，在水中澆置時最高達到6000psi以上；亦測試耐久性與體積穩定性之試驗以確保混凝土之品質，使得施工過程達到快速、環保，降低生態破壞，而水中結構物的品質達到安全、耐久、實用等目的，對我國在混凝土方面上的研究、創新與開發新的技術有所貢獻。

關鍵字：水中自充填混凝土、抗沖蝕、特密管

There are many concrete structures are constructed under water, such as footings, piers, and slurry walls. In the past, rich mix design concrete were used to obtain a low slump, and high viscosity. The engineers are concerned about the mortar dispersion after the concrete is placed in water or the water was mixed with concrete which yields a higher w/c. If the concrete used in underwater condition can have the self-compacting ability, a much better quality of concrete can be expected.

This study focused on the non-dispersion, less setting time, higher strength, and self-compacting concrete. Various admixtures were tried and the test results showed that the initial setting time can be 3-4 hours less and final setting time 4-5 hours less. The anti-washout tests were also performed. The concrete placed in water showed a compressive strength at 28 days of 6000 psi. The shrinkage was also measured. Thus a new underwater self-compacting concrete was developed to guarantee the quality, safety, and economy.

Key words: underwater self-compacting concrete, anti-washout, tremie