自充填摻料混凝土收縮潛變行為之實驗研究

Experimental study on shrinkage and creep behavior of Self-Compacting Concrete with fly ash and slag

吳丞駿(Cheng-Jun Wu)

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(2022年)

https://doi.org/10.6342/NTU202202581

摘要

自充填混凝土(Self-Compacting Concrete, SCC)具有高品質、人工成本低、工作性佳等優點，是實際工程中應用最廣泛的混凝土之一，而自充填混凝土在體積穩定性之行為(收縮、潛變)與搗實混凝土有所差異，若沒辦法準確預測其收縮潛變值，其長期變形將降低建築物之使用年限和安全性，而雖然國外已有許多預測模型，但其多數為設計給搗實混凝土使用，且由於各國配比特性，粒料強度皆有不同之處，故直接使用國外之預測模型可能會導致預測結果失真。
為發展適用於台灣之自充填混凝土收縮潛變預測模型，廖文正團隊透過收集大量自充填混凝土之文獻建立NTU 自充填混凝土收縮潛變資料庫，以Model B4、Model B4TW-2020 為基礎，透過資料庫進行回歸、參數修正，發展出Model B4TW-SCC。
本研究將以實驗輔助修正 Model B4TW-SCC 收縮、潛變預測模型中有關飛灰之參數，透過對NTU 資料庫之分析，得出最具代表性之配比、常見之飛灰取代率來進行配比設計，配比以水膠比0.36、骨膠比3.44、砂率0.5 進行設計，皆是資料庫之平均值，而飛灰取代率分別為20%及40%。
自體收縮於水膠比下降時，有收縮量上升之趨勢，且此現象在水膠比低於某個門檻時更為明顯，本研究為確認此水膠比門檻，以水膠比作為實驗變數來設計實驗，水膠比從0.30 至0.48，以0.06 為間距，透過比較不同水膠比之自充填混凝土自體收縮量，得出自體收縮量於每一間距之成長幅度，以此來確認水膠比門檻。
從實驗結果顯示，飛灰對於自充填混凝土之總收縮、總潛變及基本潛變皆有抑制的效果，其中，總收縮、總潛變因為試體處於乾燥環境，內部水分大量流失，導致試體內無法形成有利卜作嵐反應之環境，部分飛灰無法反應而形成充當細粒料的效果，而基本潛變則因試體內水化反應與卜作嵐反應形成良好循環，令添加飛灰試體之長期強度發展高於未添加飛灰組，在荷載不變的前提下，更高的強度意味著更小的潛變量，導致添加飛灰後基本潛變量下降，而在添加飛灰後自體收縮上升之原因同樣是因試體內水化反應與卜作嵐反應形成良好循環，導致自乾現象加劇。
觀察自體收縮量隨水膠比變動之趨勢，發現當水膠比從0.42 降至0.36 時，自體收縮量平均提升約25μ，但當水膠比從0.36 降至0.30 時，自體收縮量平均提升約160μ，同樣下降0.06 的水膠比，但自體收縮之成長卻增加了6 倍，確認令自充填混凝土自體收縮量急遽提升之水膠比門檻介於0.36~0.30 之間。
關鍵字： 潛變、收縮、自充填混凝土、飛灰、爐石、水膠比、預測模型

關鍵字

潛變 ； 收縮 ； 自充填混凝土 ； 飛灰 ； 爐石 ； 水膠比 ； 預測模型

並列摘要

Self-Compacting Concrete (SCC) has the advantages of high quality, reducing
labor cost and improving constructibility, and it has been widely utilized in practical engineering. Since the behavior of self-compacting concrete in volume stability is different from that of vibration concrete, there are safety concerns for its long-term deformation will reduce the service life of the building. Thus, developing accurate prediction of shrinkage and creep value of self-compacting concrete is necessary.
Although there are existed prediction models in foreign countries, most of them are designed for vibration concrete. Moreover, different mix proportion of concrete and strength of aggregates between Taiwan and foreign countries can lead to wrong predicted values when directly using foreign prediction models.
In order to develop a self-compacting concrete shrinkage and creep prediction model designed for Taiwan, a NTU self-compacting concrete shrinkage and creep
database has been established by collecting a large number of self-compacting concrete literatures. Based on Model B4 and Model B4TW-2020, the model B4TW-SCC is developed through regression and parameter correction through the database. In this study, the parameters related to fly ash in the Model B4TW-SCC shrinkage and creep prediction model will be corrected through experiments. The most representative mixproportion and the most common fly ash replacement rate is obtained through the analysis of the NTU self-compacting concrete shrinkage and creep database, which are carried out with to conduct design of experiments. The experimental results are compared with the predicted results for further discussion. Furthermore, watercementitious material ratio is considered to be influential on the self-shrinkage of self-compacting concrete, and therefore is used as the experimental variable to design the experiments. The water-cementitious material ratio is from 0.48 to 0.3, and the interval is 0.06. By comparing the self-shrinkage of self-compacting concrete with different water-cementitious material ratios, the growth of self-shrinkage by each interval is obtained, which helps confirming the water-cementitious material ratios threshold.
Keywords：creep, shrinkage, self-compacting concrete, fly ash, slag, water-cementitious material ratio, prediction model

並列關鍵字

creep ； shrinkage ； self-compacting concrete ； fly ash ； slag ； watercementitious material ratio ； prediction model

參考文獻

1 參考文獻

[1] A. M. Poppe, G. D. Schutter, Creep and shrinkage of self-compacting concrete, in First International Symposium on Design, Performance and Use of Self-Consolidating Concrete, (2005) 329-336.

[2] AASHTO, AASHTO LRFD bridge design specifications, 8th ed. Washington: American Association of State Highway and Transportation Officials, 2017.

[3] AASHTO, AASHTO LRFD bridge design specifications, 8th ed. Washington: American Association of State Highway and Transportation Officials, 2017.

[4] ACI Committee 209, "Prediction of Creep, Shrinkage, and Temperature Effects in Concrete Structures," American Concrete Institute, ACI 209R-92, 1992 (Reapproved 1997).