飛灰對水中自充填混凝土的影響

Abstract

本研究在探討飛灰對水中自充填混凝土的影響，其取代方式為重量取代，在使用相同增黏劑(趙教授研究室所研發之增黏劑)以及對水中不分散能力(通過L型流度測試之pH與濁度值)影響最小的情況下，測試飛灰可取代的最高比例，將測試完成後之最佳配比與過去配比來做比較，比較內容包括抗壓強度、體積穩定性、混凝土耐久性等，其中體積穩定性又分做塑性收縮、自體收縮、乾燥收縮、潛變，耐久性測試為快速氯離子滲透試驗(RCPT)。 將抗壓強度、乾燥收縮、抗氯離子滲透試驗分做不同澆置方式(空氣澆置、淡水澆置、海水澆置)以及不同養護方式(飽和石灰水、淡水、海水、空氣)來討論並且與過去做比較；而塑性收縮試驗分做氣養(相對溼度40%)與濕養(相對溼度95%以上)兩種養護方式做比較；自體收縮試驗分做空氣澆置、淡水澆置、海水澆置；而將潛變又分做空氣中潛變試驗與水中潛變試驗，深入討論各種混凝土可能會遇到的各種情況。 由實驗結果得知水中不分散能力能保持過去之品質，而抗壓強度也有上升的趨勢，平均抗壓強度約為過去的1.26倍；對於體積穩定性試驗來看，配比改良後自體收縮量約降為過去平均的0.87倍、乾燥收縮應變量可降至0.76倍、空氣中潛變應變量為為過去之0.95倍、水中潛變應變量為0.96倍，皆可看出抑制的效果，而耐久性測試(RCPT)之累積電量為過去之0.63倍也有下降的趨勢。

This study focus on the effect of fly ash on the properties on underwater self-compacting concrete. The fly ash was added on weight basis, while all the other ingredients remain the same. The optimum amount of fly ash was determined based on the minimized effect of fly ash on performances on L-flow test, pH value, and turbidity. The specimens with and without fly ash were compared on compressive strength, volume stability, and durability. The volume stability includes plastic shrinkage, autogenous shrinkage, drying shrinkage, and creep. RCPT was used as durability index. The tests were designed to simulate various structures under different environmental conditions. The specimens were cast in air, tap water, and sea water and cured in air(RH=40%) and wet cure(RH=95%). The creep test was performed in air and in water. The results were analyzed and compared to determine the quality and durability of structures. It is found that the underwater self-consolidating concrete with or without fly ash has better performance than conventional concrete.The concrete with fly ash showed that 1. Due to the better workability of fly ash, the water cementitious can be reduced and thus an26% increase in compressive strength is achieved. 2. The autogenous shrinkage for specimens with fly ash was reduced by 13%, 3. Drying shrinkage was reduced by 24%, 4. The creep tested in air or water showed a decrease of 4-5%. As to RCPT, due to a long term pozzolanic reaction of fly ash, the cumulated current was reduced by 37% compared to control specimens.