本文關(guān)鍵詞： 混凝土 凍融循環(huán) 表面剝落 內(nèi)部損傷 約束　出處：《中國建筑材料科學(xué)研究總院》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：鹽凍破壞是寒冷地區(qū)混凝土結(jié)構(gòu)面臨的重要耐久性問題。形變是混凝土材料受到損傷的表現(xiàn)之一。目前常用的凍融/鹽凍試驗方法中混凝土試件是自由變形的,與實際服役混凝土受到周圍結(jié)構(gòu)的約束無法自由變形不相符合,因而試驗結(jié)果并不能反映實際結(jié)構(gòu)混凝土損傷情況。本文研究約束狀態(tài)下混凝土鹽凍破壞試驗方法、行為和機理,探索更真實的結(jié)構(gòu)混凝土鹽凍損傷過程。本文主要工作和取得的成果有:設(shè)計不銹鋼約束環(huán)和約束錨栓限制混凝土凍融循環(huán)中的受凍膨脹和收縮,建立了混凝土變形約束裝置;設(shè)計了專用應(yīng)變測試錨桿,實時采集凍融循環(huán)中混凝土試件的應(yīng)變;采用表面剝落量、相對動彈性模量損失和殘余應(yīng)變評價混凝土的表面和內(nèi)部損傷程度。研究建立了一套完整的約束狀態(tài)下混凝土鹽凍破壞試驗方法。研究獲得了約束狀態(tài)下混凝土鹽凍破壞損傷行為規(guī)律。隨著凍融循環(huán)次數(shù)增加,約束狀態(tài)混凝土的表面和內(nèi)部損傷程度逐漸加深;提高含氣量(1.3%~7.1%)、降低水灰比(0.65~0.45)能夠降低約束狀態(tài)混凝土表面和內(nèi)部損傷程度;相同條件下,約束狀態(tài)混凝土的表面損傷程度比自由狀態(tài)混凝土嚴重、內(nèi)部損傷程度比自由狀態(tài)混凝土輕微。計算了鹽凍過程中約束和自由狀態(tài)混凝土表面最大應(yīng)力,研究其表面損傷機理。降溫至-8℃時,表面最大應(yīng)力值超過表面抗拉強度,混凝土開始出現(xiàn)表面剝落;繼續(xù)降溫至混凝土內(nèi)部結(jié)冰點-12℃附近時,約束狀態(tài)混凝土表面最大應(yīng)力開始明顯超過自由狀態(tài)混凝土,因而其表面損傷更嚴重。分析和計算了鹽凍過程中約束狀態(tài)混凝土孔隙結(jié)構(gòu)參數(shù)和孔隙裂紋應(yīng)變值,研究其內(nèi)部損傷機理。約束狀態(tài)混凝土的孔隙擴展程度、裂紋萌生數(shù)量和擴展速率均小于自由試件;降溫至-15.8℃~-20℃,飽水混凝土孔隙裂紋發(fā)生不可逆應(yīng)變,產(chǎn)生內(nèi)部損傷;約束狀態(tài)混凝土的不可逆應(yīng)變小于自由狀態(tài)混凝土的不可逆應(yīng)變,因此其內(nèi)部損傷程度更小。
[Abstract]:Salt freezing failure is an important durability problem faced by concrete structures in cold regions. Deformation is one of the manifestations of concrete material damage. In the freeze-thaw / salt freezing test methods, concrete specimens are free deformed at present. This paper studies the test method of concrete salt freezing failure under the condition that concrete in service is restrained by the surrounding structure and can not deform freely, so the test results can not reflect the actual concrete damage. Behavior and mechanism to explore a more realistic process of salt freezing damage of structural concrete. The main work and achievements of this paper are as follows: design of stainless steel confined ring and anchor bolt to limit the expansion and shrinkage of concrete in freeze-thaw cycle. A concrete deformation restraint device is established, a special strain test anchor rod is designed, and the strain of concrete specimen in freeze-thaw cycle is collected in real time. The relative dynamic elastic modulus loss and residual strain are used to evaluate the surface and internal damage of concrete. A set of complete test methods of concrete salt freezing failure in confined state are established. The concrete in confined state is obtained. With the increase of freeze-thaw cycles, The surface and internal damage degree of confined state concrete is gradually deepened, and the surface and internal damage degree of confined state concrete can be reduced by increasing the gas content of concrete by 1.3and reducing the water-cement ratio by 0.65 ~ 0.45), under the same condition, the surface and internal damage degree of confined state concrete can be reduced. The surface damage of confined concrete is more serious than that of free state concrete, and the degree of internal damage is less than that of free state concrete. The maximum surface stress of confined and free state concrete during salt freezing is calculated. The surface damage mechanism is studied. When the temperature reaches -8 鈩，

本文編號：1544272