干寒大温差地区不同养护方式下预制混凝土箱梁开裂规律及机理研究

发布时间：2018-06-16 21:17

本文选题：干寒 + 预制混凝土箱梁　；参考：《兰州交通大学》2017年硕士论文

【摘要】：随着我国西北地区基础交通建设的迅速发展,预制混凝土箱梁在公路建设中被大量使用。西北地区具有大温差、干寒等气候特点,在这种环境中浇筑的混凝土极易产生裂缝,影响混凝土结构质量及安全,而且既有预制混凝土箱梁的一些养护方式不能完全适用于这种特殊气候环境。因此,研究大温差、干寒地区不同养护方式下预制混凝土箱梁开裂规律及开裂机理有其必要性。本文以白明高速公路为依托项目,通过对现场气候环境的监测、原材料的检测和养护方式的调研,选择了部分养护方式进行试验,对不同养护方式下试验预制混凝土箱梁的强度、抗裂性、抗渗性、微观孔结构、早期应变和水化温度场等进行了分析和研究。具体研究内容如下:(1)通过测试和分析不同养护方式下混凝土箱梁在不同龄期时的抗拉强度,得出以下结论:28d龄期时,按照蒸汽养护、标准养护、橡塑板包裹养护、土工布包裹养护、薄膜包裹养护、洒水养护、自然养护顺序混凝土抗拉强度逐渐减小;在混凝土28d龄期时,不同养护方式下混凝土抗拉强度与抗压强度的比值在1/18-1/14之间,且按上述的顺序28d龄期时混凝土拉压比值逐渐降低。(2)通过测试和分析不同养护方式下预制混凝土箱梁不同龄期时的抗拉及抗压强度,得出以下结论:在龄期28d时蒸汽养护与标准养护下混凝土抗压强度最高,且强度均大于50MPa,而其他养护方式下则小于50MPa;试验箱梁的回弹强度与同条件试块强度的比值在0.96-0.98之间,而蒸汽养护为1.1倍,同时箱梁外侧强度是内侧强度的1.2-1.4倍;蒸汽养护天数大于4d时,在龄期28d时强度可达到50MPa;当蒸汽养护天数为7d时,在龄期7d时强度可达到50MPa;本文得出了蒸汽养护、标准养护、橡塑板包裹养护及不同蒸汽养护天数下混凝土在不同龄期时的强度计算公式。(3)通过分析和研究不同养护方式下混凝土抗裂环及试验预制混凝土箱梁裂缝宽度、开裂时间、裂缝长度、裂缝条数,得出以下结论:标准养护下混凝土抗裂性最好,蒸汽养护、橡塑板包裹养护次之,土工布养护与薄膜养护较差,洒水养护与自然养护最差;试验箱梁的裂缝宽度分布主要在0-0.02mm和0.03-0.06mm两个区间,说明早期混凝土开裂主要是各类收缩变形所致;不同养护方式下水化反应所产生的温差远小于规范要求;在浇筑20h后,混凝土应变基本不再变化,后期受到大温差及太阳辐射的影响呈小范围的正弦变化。(4)通过研究大温差、干寒、强风地区日照对混凝土箱梁的影响,得出以下结论:日照可促进水泥水化反应速度,提高强度,但是会加速混凝土开裂;存放在梁场的预制混凝土试验箱梁日照温度场梯度变化在规范要求内,但是底板处的温度变化与规范稍有不同。(5)通过测试和研究不同养护方式下混凝土微观孔结构及抗渗性,得出以下结论:按照标准养护、蒸汽养护、橡塑板包裹养护、薄膜包裹养护、土工布包裹养护、洒水养护、自然养护的顺序混凝土抗渗性和强度逐渐减弱,而孔间距系数、平均孔径、孔的数目及含气量逐渐增加;不同养护方式下混凝土孔间距系数均小于0.300mm,因此混凝土抗冻等级可达到F300;综合所有因素,在干寒大温差地区蒸汽养护为最佳的养护方式。
[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.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U445.57

【参考文献】