本文選題：干寒 + 預(yù)制混凝土箱梁　； 參考：《蘭州交通大學(xué)》2017年碩士論文

【摘要】：隨著我國西北地區(qū)基礎(chǔ)交通建設(shè)的迅速發(fā)展,預(yù)制混凝土箱梁在公路建設(shè)中被大量使用。西北地區(qū)具有大溫差、干寒等氣候特點,在這種環(huán)境中澆筑的混凝土極易產(chǎn)生裂縫,影響混凝土結(jié)構(gòu)質(zhì)量及安全,而且既有預(yù)制混凝土箱梁的一些養(yǎng)護方式不能完全適用于這種特殊氣候環(huán)境。因此,研究大溫差、干寒地區(qū)不同養(yǎng)護方式下預(yù)制混凝土箱梁開裂規(guī)律及開裂機理有其必要性。本文以白明高速公路為依托項目,通過對現(xiàn)場氣候環(huán)境的監(jiān)測、原材料的檢測和養(yǎng)護方式的調(diào)研,選擇了部分養(yǎng)護方式進行試驗,對不同養(yǎng)護方式下試驗預(yù)制混凝土箱梁的強度、抗裂性、抗?jié)B性、微觀孔結(jié)構(gòu)、早期應(yīng)變和水化溫度場等進行了分析和研究。具體研究內(nèi)容如下:(1)通過測試和分析不同養(yǎng)護方式下混凝土箱梁在不同齡期時的抗拉強度,得出以下結(jié)論:28d齡期時,按照蒸汽養(yǎng)護、標(biāo)準(zhǔn)養(yǎng)護、橡塑板包裹養(yǎng)護、土工布包裹養(yǎng)護、薄膜包裹養(yǎng)護、灑水養(yǎng)護、自然養(yǎng)護順序混凝土抗拉強度逐漸減小;在混凝土28d齡期時,不同養(yǎng)護方式下混凝土抗拉強度與抗壓強度的比值在1/18-1/14之間,且按上述的順序28d齡期時混凝土拉壓比值逐漸降低。(2)通過測試和分析不同養(yǎng)護方式下預(yù)制混凝土箱梁不同齡期時的抗拉及抗壓強度,得出以下結(jié)論:在齡期28d時蒸汽養(yǎng)護與標(biāo)準(zhǔn)養(yǎng)護下混凝土抗壓強度最高,且強度均大于50MPa,而其他養(yǎng)護方式下則小于50MPa;試驗箱梁的回彈強度與同條件試塊強度的比值在0.96-0.98之間,而蒸汽養(yǎng)護為1.1倍,同時箱梁外側(cè)強度是內(nèi)側(cè)強度的1.2-1.4倍;蒸汽養(yǎng)護天數(shù)大于4d時,在齡期28d時強度可達到50MPa;當(dāng)蒸汽養(yǎng)護天數(shù)為7d時,在齡期7d時強度可達到50MPa;本文得出了蒸汽養(yǎng)護、標(biāo)準(zhǔn)養(yǎng)護、橡塑板包裹養(yǎng)護及不同蒸汽養(yǎng)護天數(shù)下混凝土在不同齡期時的強度計算公式。(3)通過分析和研究不同養(yǎng)護方式下混凝土抗裂環(huán)及試驗預(yù)制混凝土箱梁裂縫寬度、開裂時間、裂縫長度、裂縫條數(shù),得出以下結(jié)論:標(biāo)準(zhǔn)養(yǎng)護下混凝土抗裂性最好,蒸汽養(yǎng)護、橡塑板包裹養(yǎng)護次之,土工布養(yǎng)護與薄膜養(yǎng)護較差,灑水養(yǎng)護與自然養(yǎng)護最差;試驗箱梁的裂縫寬度分布主要在0-0.02mm和0.03-0.06mm兩個區(qū)間,說明早期混凝土開裂主要是各類收縮變形所致;不同養(yǎng)護方式下水化反應(yīng)所產(chǎn)生的溫差遠小于規(guī)范要求;在澆筑20h后,混凝土應(yīng)變基本不再變化,后期受到大溫差及太陽輻射的影響呈小范圍的正弦變化。(4)通過研究大溫差、干寒、強風(fēng)地區(qū)日照對混凝土箱梁的影響,得出以下結(jié)論:日照可促進水泥水化反應(yīng)速度,提高強度,但是會加速混凝土開裂;存放在梁場的預(yù)制混凝土試驗箱梁日照溫度場梯度變化在規(guī)范要求內(nèi),但是底板處的溫度變化與規(guī)范稍有不同。(5)通過測試和研究不同養(yǎng)護方式下混凝土微觀孔結(jié)構(gòu)及抗?jié)B性,得出以下結(jié)論:按照標(biāo)準(zhǔn)養(yǎng)護、蒸汽養(yǎng)護、橡塑板包裹養(yǎng)護、薄膜包裹養(yǎng)護、土工布包裹養(yǎng)護、灑水養(yǎng)護、自然養(yǎng)護的順序混凝土抗?jié)B性和強度逐漸減弱,而孔間距系數(shù)、平均孔徑、孔的數(shù)目及含氣量逐漸增加;不同養(yǎng)護方式下混凝土孔間距系數(shù)均小于0.300mm,因此混凝土抗凍等級可達到F300;綜合所有因素,在干寒大溫差地區(qū)蒸汽養(yǎng)護為最佳的養(yǎng)護方式。
[Abstract]:With the rapid development of basic traffic construction in the northwest of China, the precast concrete box girder is widely used in highway construction. The northwest area has the characteristics of large temperature difference, dry cold and so on. The concrete poured in this environment will easily produce cracks, affect the quality and safety of concrete structure, and have some prefabricated concrete box beams. Therefore, it is necessary to study the cracking rules and cracking mechanism of precast concrete box beams under different maintenance methods of large temperature difference and dry cold areas. The strength, crack resistance, impermeability, micropore structure, early strain and hydration temperature field of the prefabricated concrete box beams under different curing methods were analyzed and studied. The specific contents are as follows: (1) the concrete box beams under different curing modes are tested and analyzed in different ages. At the age of 28d, the tensile strength of concrete decreased gradually in accordance with steam curing, standard curing, rubber and plastic package maintenance, geotextile package maintenance, film wrap maintenance, sprinkler maintenance, natural curing order, and the ratio of tensile strength to compressive strength of concrete under different curing modes at the age of 28d. The value is between 1/18-1/14, and the ratio of tensile and compression of concrete gradually decreases at 28d age. (2) through testing and analyzing the tensile and compressive strength of prefabricated concrete box beams under different curing modes, the following conclusion is drawn: the compressive strength of concrete under steam curing and standard curing is the highest and the strength is all under the age of 28d. It is more than 50MPa and less than 50MPa in other curing methods; the ratio of the rebound strength to the test block strength of the test box beam is between 0.96-0.98, and the steam curing is 1.1 times, at the same time, the strength of the box beam is 1.2-1.4 times of the inside strength; the strength of the steam curing days is greater than 4D, and the strength can reach 50MPa when the age is 28d; and the number of steam curing days is 7. At D, the strength of 7D can reach 50MPa at the age of age. The formula of strength calculation for concrete under different ages of steam curing, standard curing, rubber and plastic sheet maintenance and different steam curing days is obtained. (3) through analyzing and studying the crack width and cracking time of concrete crack resistance ring and prefabricated concrete box beam under different curing methods The crack length and the number of cracks draw the following conclusions: under the standard curing, the crack resistance of concrete is the best, the steam curing, the rubber plastic sheet parcel maintenance, the poor maintenance of the geotextile and the thin film maintenance, the worst sprinkler maintenance and the natural maintenance, the crack width distribution of the test box girder is mainly in the two intervals of 0-0.02mm and 0.03-0.06mm, indicating the early concrete opening. The crack is mainly caused by various types of shrinkage and deformation; the temperature difference produced by the hydration reaction of different curing methods is far less than the standard requirement; after the 20h, the concrete strain is no longer changed, and the later is affected by the great temperature difference and the influence of the solar radiation in a small sine change. (4) through the study of the large temperature difference, dry cold, and strong wind area, the concrete box is on the concrete box. The effect of beam is concluded as follows: sunshine can promote the speed of hydration reaction and increase the strength of cement, but it will accelerate the cracking of concrete. The gradient of the temperature field of the prefabricated concrete test box beam stored in the beam field is within the standard requirement, but the temperature change at the floor is slightly different from that of the standard. (5) through testing and studying different maintenance parties. The micro pore structure and permeability resistance of concrete are obtained. The following conclusions are drawn: according to standard curing, steam curing, rubber and plastic package maintenance, film wrapping maintenance, geotextile package maintenance, sprinkler maintenance and natural curing, the permeability and strength of concrete are gradually weakened, and the pore space coefficient, average pore size, number of holes and gas content increase gradually. The distance coefficient of concrete hole is less than 0.300mm under different curing methods, so the frost resistance of concrete can reach F300, and the best curing method is steam curing in dry cold and large temperature difference area.
【學(xué)位授予單位】：蘭州交通大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：U445.57

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