- 學位論文
以成熟度法預測混凝土早期水化行為與巨積混凝土早期溫度場之有限元分析
Prediction of Early Hydration Behavior of Concrete by Maturity Method and Finite Element Analysis of Early Thermal Field for Mass Concrete
摘要
混凝土的強度、勁度來自水泥、卜作嵐材料與拌合水進行水化反應後產生的C-S-H膠體，而水化反應為放熱的化學反應，混凝土澆置後的1至3天為水化反應最劇烈的時期，此時期也是混凝土溫升最快的階段。巨積混凝土因其尺寸龐大加上混凝土為導熱性較差之材料，因此於早齡期在混凝土中心處有蓄熱之情形，再加上高溫環境會再刺激水化反應的速率，使混凝土中心、表面之溫差會快速增大而形成較大的熱張應力，造成混凝土早期開裂，因此巨積混凝土的早期溫度預測、控制為本研究要探討的課題。 本研究使用ANSYS以有限元素法模擬巨積混凝土早齡期的溫度場。透過混凝土絕熱溫升試驗結果來預測早期水化反應，並以成熟度法推導出可同時考慮齡期及溫度效應之混凝土單位體積生熱率，希望進行有限元分析時給予模型之熱源荷載能隨時間、溫度調整其生熱的速率以符合較真實之水化行為；另外，會再給予模型僅能隨時間調整水化速率之熱源荷載來分析溫度場。本研究分別採用以上兩種熱源荷載，進行現地巨積混凝土試體早期溫度場之有限元素分析，比較兩種分析方法之差異。 除了混凝土水化行為的發展，混凝土初始溫度、環境溫度、混凝土熱傳導係數及保溫措施也會影響巨積混凝土早期溫度場之發展，本研究透過有限元素法分析探討以上各變因影響心溫、表溫及心表溫差之情形。建議巨積混凝土盡量避免高溫澆置、避免澆置於氣溫較低之環境及盡量在表面佈設保溫措施。 另外，透過蒐集國內外近15年之絕熱溫升試驗資料，以建置水化參數資料庫來探討影響混凝土早齡期水化行為之變因，以提供日後建立水化度預測公式之參考及建議。
並列摘要
The strength and stiffness of concrete come from the C-S-H gel produced by hydration reaction of cement, pozzolanic material and mixing water. Hydration reaction is exothermic chemical reaction. 1 to 3 days after concrete placement is the most severe stage of hydration reaction, and this period is also the fastest stage of concrete temperature rise. Because of its large size and poor thermal conductivity of concrete, mass concrete has heat storage at the center at the early age. Moreover, the high temperature environment stimulates the rate of hydration reaction, so that the temperature difference between the center and surface of the concrete will increase rapidly to form larger thermal stress, resulting in the early cracks of concrete. Therefore, early temperature prediction and control of mass concrete is the topic to be discussed in this study. In this study, the finite element method were used to simulate the temperature field of the early age of mass concrete in ANSYS. The early hydration reaction was predicted through the experimental results of concrete adiabatic temperature rise test, and the unit volume heat generation rate of concrete, which could simultaneously consider the age and temperature effects, was derived by the maturity method. It was hoped that the heat load given to the model during the finite element analysis could adjust the heat generation rate with time and temperature to conform to the actual hydration behavior. Moreover, this study gave another heat load of the model which could only be adjusted the hydration rate with time to analyze the temperature field. In this study, the above two kinds of heat loads were respectively used to do the finite element analysis of the early temperature field of the mass concrete specimen in the field, and this study also compared the difference between the two methods. In addition to the development of concrete hydration, initial temperature, ambient temperature, thermal conductivity and heat preservation measures of concrete will also affect the development of the early temperature field of the mass concrete. In this study, the effects of above variables on center temperature, side temperature and center-side temperature difference were analyzed by finite element analysis. It is recommended that mass concrete should be avoid high temperature pouring, be avoid pouring in a low temperature environment and be arranged insulation measures on the surface. Moreover, by collecting the data of adiabatic temperature rise test at home and abroad for nearly 15 years, the variation of hydration behavior of concrete at the early age was discussed with the establishment of the database of hydration parameters to provide reference and suggestions for establishing the prediction formula of the degree of hydration in the future.