【摘要】：超高性能混凝土(Ultra High Performance Concrete,英文縮寫為UHPC)是一種具有高強(qiáng)度、高韌性、高體積穩(wěn)定性和優(yōu)良耐久性的新型水泥基復(fù)合材料。在新型混凝土材料研究領(lǐng)域,收縮問題始終是所有研究學(xué)者關(guān)注的焦點(diǎn),也是限制UHPC在結(jié)構(gòu)工程中廣泛應(yīng)用的因素之一。收縮是導(dǎo)致混凝土開裂的主要原因,混凝土一旦開裂,則會大大降低結(jié)構(gòu)的耐久性,甚至威脅到結(jié)構(gòu)的安全。不同養(yǎng)護(hù)條件下UHPC的收縮性能是不同的,已有研究表明:UHPC經(jīng)過熱養(yǎng)護(hù)后干燥收縮值會大幅減少,其原因是熱養(yǎng)護(hù)后UHPC中孔結(jié)構(gòu)得到細(xì)化,基體變得更密實(shí)。本文研究了不同養(yǎng)護(hù)條件下UHPC試件的早期收縮和干燥收縮,并著重研究了熱養(yǎng)護(hù)過程中UHPC的收縮變形特點(diǎn)以及熱養(yǎng)護(hù)過后UHPC的收縮發(fā)展趨勢。另外,本試驗(yàn)通過壓汞試驗(yàn)、電鏡觀測、差熱分析微觀試驗(yàn)來進(jìn)行機(jī)理分析。研究結(jié)果如下:(1)標(biāo)準(zhǔn)養(yǎng)護(hù)條件下,UHPC的早期收縮值較大,約為干燥收縮值的1.5倍。當(dāng)齡期為65d時(shí),UHPC的收縮趨于穩(wěn)定,為1490με。(2)UHPC的溫度膨脹系數(shù)為11.76με/°C。在熱養(yǎng)護(hù)過程中,UHPC在50°C以內(nèi)基本不發(fā)生收縮,當(dāng)溫度接近70°C時(shí),收縮值迅速增加,最終的收縮值為450με。(3)隨著配筋率的提高,UHPC在熱養(yǎng)護(hù)過程中的收縮減小,這說明配筋能夠抑制UHPC在熱養(yǎng)護(hù)過程中的收縮。配筋UHPC在熱養(yǎng)護(hù)過程中的彈性應(yīng)變很小,約為2.4με~10.37με,所以產(chǎn)生的殘余應(yīng)力很小。(4)試件尺寸對收縮有很大的影響,小尺寸試件的收縮通常要小于大尺寸試件的收縮,這是小尺寸試件中鋼纖維定向分布造成的。(5)通過對不同齡期UHPC試件的微觀結(jié)構(gòu)的分析,經(jīng)熱養(yǎng)護(hù)后,孔結(jié)構(gòu)得到細(xì)化,生成的水化產(chǎn)物更多,并且減少了Ca(OH)_2和鈣礬石的體積。
[Abstract]:Ultra high performance concrete (Ultra High Performance Concrete,) is a new cement matrix composite with high strength, high toughness, high volume stability and excellent durability. In the research field of new concrete materials, the shrinkage problem has always been the focus of attention of all researchers, and also one of the factors limiting the wide application of UHPC in structural engineering. Shrinkage is the main cause of concrete cracking. Once the concrete cracks, the durability of the structure will be greatly reduced, and even the safety of the structure will be threatened. The shrinkage properties of UHPC are different under different curing conditions. It has been shown that the drying shrinkage value of UHPC will be greatly reduced after thermal curing. The reason is that the mesoporous structure of UHPC is refined and the matrix becomes more dense after thermal curing. In this paper, the early shrinkage and drying shrinkage of UHPC specimens under different curing conditions are studied, and the shrinkage deformation characteristics of UHPC during thermal curing and the shrinkage trend of UHPC after thermal curing are emphatically studied. In addition, the mechanism was analyzed by mercury injection test, electron microscope observation and differential thermal analysis. The results are as follows: (1) under the standard curing conditions, the early shrinkage of UHPC is larger, about 1.5 times of the dry shrinkage. When the age is 65 days, the contraction of UHPC tends to be stable, which is 1490 渭 蔚. (2) the thermal expansion coefficient of UHPC is 11.76 渭 蔚 / 擄C. During thermal curing, UHPC basically does not shrink within 50 擄C. when the temperature is close to 70 擄C, the shrinkage value increases rapidly, and the final shrinkage value is 450 渭 蔚. (3) with the increase of reinforcement ratio, the shrinkage of UHPC decreases during thermal curing. This indicates that reinforcement can inhibit the shrinkage of UHPC during thermal curing. The elastic strain of reinforced UHPC during thermal curing is very small, about 2.4 渭 蔚 ~ 10.37 渭 蔚, so the residual stress is very small. (4) the size of specimen has a great influence on shrinkage, and the shrinkage of small size specimen is usually smaller than that of large size specimen. This is caused by the directional distribution of steel fibers in small size specimens. (5) by analyzing the microstructure of UHPC specimens of different ages, the pore structure is refined after thermal curing, and more hydration products are generated. The volume of Ca (OH) _ 2 and ettringite was reduced.
【學(xué)位授予單位】：湖南大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TU528

【參考文獻(xiàn)】

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本文編號：2389932