【摘要】：混凝土早期開裂降低了混凝土的耐久性,開裂問題成為研究熱點問題。目前研究開裂問題的方法很多,但尚未形成一個標(biāo)準(zhǔn)方法,本文基于預(yù)裂紋水泥漿體環(huán)開裂實驗,提出了一種快速預(yù)測水泥漿體環(huán)開裂時間的方法——電阻率法。采用預(yù)裂紋水泥漿體環(huán)開裂裝置研究了水灰比、水泥等級對預(yù)裂紋水泥漿體環(huán)開裂時間的影響。結(jié)果表明:同一水泥等級的水泥漿體環(huán),不同水灰比對開裂時間的影響有相同的趨勢,即水灰比越低,水泥漿體環(huán)開裂時間越早。P?C32.5的水泥漿體環(huán)開裂時間與水灰比變化曲線位于P?O42.5的水泥的上方,即同一水灰比水泥漿體環(huán),水泥等級越高,水泥漿體環(huán)開裂時間越早。采用電阻率法研究了水灰比、水泥等級對水泥漿體1440 min(24 h)內(nèi)電阻率曲線和其變化速率曲線的影響。結(jié)果表明:在水泥等級相同的條件下,低水灰比水泥漿體的電阻率曲線始終在高水灰比水泥漿體電阻率曲線的上方,其電阻率變化速率曲線的3個極大值點出現(xiàn)的時間越早。在水灰比相同的情況下,在水化早期P?O42.5水泥漿體的電阻率小于P?C32.5的電阻率,但是在水化后期P?O42.5水泥漿體的電阻率卻高于P?C32.5的電阻率,P?O42.5水泥漿體的1440 min內(nèi)電阻率變化速率曲線的3個極大值點出現(xiàn)時間的比P?C32.5的早。在預(yù)裂紋水泥漿體環(huán)開裂實驗和電阻率實驗基礎(chǔ)上,得到了水泥漿體24 h(1440min)的電阻率越大,預(yù)裂紋水泥漿體環(huán)開裂時間越早;建立了水泥漿體環(huán)開裂時間與水泥漿體24 h電阻率的關(guān)系式;提出了用水泥漿體24 h電阻率來預(yù)測水泥漿體環(huán)開裂時間的方法。利用ANSYS熱——結(jié)構(gòu)耦合場模擬水泥漿體環(huán)濕度場變化時程進(jìn)而得到水泥漿體內(nèi)部最大拉應(yīng)力變化時程,對比實際抗拉強度得到開裂時間,為研究開裂問題提供了一種可供借鑒的方法。
[Abstract]:The early cracking of concrete reduces the durability of concrete. At present, there are many methods to study the cracking problem, but no standard method has been formed. Based on the cracking experiment of pre-cracked cement paste, a new method, resistivity method, is proposed to predict the crack time of cement paste ring quickly. The effects of water-cement ratio and cement grade on crack time of pre-cracked cement paste ring were studied by using pre-cracked cement paste ring cracking device. The results show that the influence of different water-cement ratio on the cracking time of cement paste ring with the same cement grade has the same trend, that is, the lower the water-cement ratio, the earlier the crack time of cement paste ring. The C32.5 cement paste ring crack time and water-cement ratio change curve is located in P? The higher the cement grade is, the earlier the cracking time of cement paste ring is. The effects of water-cement ratio and cement grade on the resistivity curve and the change rate curve of cement paste in 1440 min (24 h) were studied by resistivity method. The results show that under the same cement grade, the resistivity curve of low water-cement ratio cement paste is always above the resistivity curve of high water-cement ratio cement paste, and the three maximum points of the resistivity change rate curve appear earlier. In the case of the same water-cement ratio, in the early stage of hydration, P? The resistivity of O42.5 cement paste is less than that of P? The resistivity of C32.5, but at the later stage of hydration? The resistivity of O42.5 cement paste is higher than that of P? C32.5 resistivity? In 1440 min of O42.5 cement paste, the ratio of the time to appear of the three maximum points of the resistivity change rate curve is P? C32.5 early. On the basis of crack test and resistivity experiment of pre-cracked cement paste, the higher the resistivity of cement paste is 24 h (1440min), the earlier the crack time of pre-cracked cement paste ring is. The relationship between the crack time of cement paste ring and the 24 h resistivity of cement paste is established, and the method of predicting the crack time of cement paste ring with 24 h resistivity of cement paste is put forward. The ANSYS thermal-structural coupling field is used to simulate the time history of moisture field change in cement paste ring, and then the maximum tensile stress change time history of cement slurry is obtained, and the cracking time is obtained by comparing the actual tensile strength. The method can be used for reference in the study of cracking problem.
【學(xué)位授予單位】：華中科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TU528

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