【作者】 朱兆辉；

【导师】 高建明； 刘建忠；

【作者基本信息】 东南大学 ， 材料工程（专业学位）， 2021， 硕士

【摘要】 长三角地区作为我国经济和工业最发达的地区之一,用电需求一直居高不下。为保障区域用电稳定,我国“新基建”明确提出加快特高压输电线路建设。然而,由于输变电工程的施工场所复杂,施工周期长久,施工量大但可施工时间较短,输变电工程混凝土无法在规定时间内达到预期的强度值,而冬季是整个施工周期中最为复杂的施工环境,因此探明低温低湿环境下混凝土宏观性能的发展规律对保证输变电工程的建设具有重要意义。试验研究了低温早强剂与聚羧酸减水剂的合理掺量,再设置不同养护温度(-5℃、5℃及对照组20℃,60%RH(RH为空气相对湿度))、水灰比(0.37和0.41)、低温早强剂(0%和3%)的试验,确定低温低湿环境下输变电工程早强混凝土的工作性能、抗压强度、收缩、抗渗透性能、孔结构的变化规律。并利用XRD、TG、SEM-EDS等方法尝试从微观层面剖析各因素对混凝土性能的影响机理。主要的研究结论如下:在-5℃、60%RH环境下,掺入3%低温早强剂及1.2%聚羧酸减水剂不仅可以加快混凝土早期抗压强度的增长,而且可以保证混凝土后期强度持续增长。低温环境下,成型温度的提高、水灰比的降低、3%低温早强剂的掺入均会导致混凝土坍落度和扩展度的减小、初凝时间和终凝时间的缩短。温度越低,低温早强剂对混凝土工作性能的影响越大。低温环境下,混凝土养护温度的提高、水灰比的降低、3%低温早强剂的掺入均可以提高混凝土各龄期的抗压强度及收缩率。引入低温早强剂后,试件抗压强度的提升幅度会随着养护温度的降低而升高。在-5℃、5℃、20℃,60%RH的养护条件下,混凝土7d的抗压强度增长率分别为139%、46%、9%。混凝土的转运试验结果表明,混凝土运输时间的增加、转运高度差的增大,会引起混凝土的坍落度快速减小,浆体对骨料的包裹性变差,导致输变电工程混凝土各龄期的抗压强度略有降低。微观试验结果表明低温低湿养护环境下,基体内部的水泥水化速率较慢,提高养护温度、升高水灰比、掺入低温早强剂均能加快水泥早期的水化速率;当龄期至28d时,处于5℃、60%RH养护环境下的试验组表现出最高的水化程度及最致密的微观结构。在低温低湿养护环境下,混凝土氯离子扩散系数随着龄期的延长逐渐减小,随着养护温度的升高先减小后增大,随着水灰比的降低而逐渐减小,随着3%低温早强剂的掺入而快速减小。低温低湿环境下养护3d时,养护温度的升高、水灰比的降低、低温早强剂的掺入均能加快填充基体内部的中孔及有害孔,减小临界孔径及阈值孔径,降低孔隙率,优化孔结构。当养护至28d时,净浆的临界孔径、阈值孔径、孔隙率随着养护温度的提高先减小后增大,随着水灰比的降低而小幅度减小,随着3%低温早强剂的掺入而大幅度减小,但减小效果随着养护温度的提高而逐渐降低。更多还原

【Abstract】 As one of the most economically and industrially developed regions in China,the demand for electricity in the Yangtze River Delta is always high.In order to ensure the stability of regional electricity consumption,China’s "new infrastructure" clearly proposes to speed up the construction of ultra-high voltage transmission lines.However,due to the complex construction environment of power transmission and transformation project,the construction period is long,the construction amount is large but the construction time is short.Therefore,the concrete of power transmission and transformation project can not reach the expected strength value within the specified time.Winter is the most complex construction environment in the whole construction cycle,it is of great significance to clarify the developing law of concrete macroscopic performance in low-temperature and low-humidity environment to ensure the construction of power transmission and transformation project.the reasonable mixing amount of early strength agent and polycarboxylic acid water reducer was determined through the preliminary experiment.Different curing temperature(-5℃,5℃ and control group 20℃,60%RH),Water to cement(W/C,0.37 and 0.41),low temperature early strength agent(0% and 3%)were then set to determine the workability,compressive strength,volume stability,permeability resistance,pore structure of early strength concrete under low-temperature and low-humidity environment.Additionally,advanced charactering methods including XRD,TG,SEM-EDS and other methods were used to try to analyze the influence mechanism of various factors on concrete properties from the microscopic level.The main research conclusions are as follows:Under the enviroment of-5℃ and 60%RH,adding 3% of early strength agent and 1.2%of polycarboxylic acid water reducer could not only improve the growth of early compressive strength of concrete,but also ensure the continuous growth of late strength of concrete.Under low temperature,the increase in forming temperature,the decrease in W/C and the addition of3% early strength agent would lead to a decrease in slump and expansion of concrete,and the shortening of initial setting time and final setting time.The lower the temperature,the more obvious the influence of the low-temperature and early-strength agent on the workability of concrete.Under the condition of low-temperature forming and curing,the increase in concrete’s forming temperature,the decrease in W/C and the addition of 3% early strength agent could increase the compressive strength and shrinkage rate of concrete at various ages.With the addition of early strength agent,the increase in compressive strength of the specimen decreased with the increase in curing temperature.Under the curing conditions of-5℃,5℃ and 20℃-60%RH,the growth rate of compressive strength of concrete at 7d was 139%,46% and 9%,respectively.The experimental results of concrete transport indicated that the increase in transport time of concrete and difference in transport height led to a rapid decrease in concrete’s slump and deterioration of paste’s cohesion,leading to a slight decrease in the compressive strength of concrete at various ages in power transmission and transformation engineering.The microscopic testing results manifested that the hydration rate of the matrix was slow under the condition of low-temperature and low-humidity curing.The early hydration rate of cement could be accelerated by raising the curing temperature,reducing the W/C and adding low-temperature and early-strength agent.When the age reached 28 days,the specimens under the condition of 5℃ and 60%RH showed the highest degree of hydration and the densest microstructure.In the low-temperature and low-humidity curing environment,the chloride diffusion coefficient decreased gradually with the increase in age,decreased first and then increased with the increase in curing temperature,decreased gradually with the decrease in W/C,and decreased rapidly with additng 3% of early strength agent.When curing in low-temperature and low-humidity environment for 3 days,the increase in curing temperature,the increase in W/C and the addition of early strength agent could fill mesopores and harmful pores in the matrix,reduce the critical pore size and threshold pore size,reduce porosity and optimize pore structure.When curing to 28 days,the critical pore size,threshold pore size and porosity of the net paste decreased and then increased with the increase in curing temperature,slightly decreased with the decrease in W/C,and greatly decreased with adding 3% of low temperature and early strength agent.However,the reduction effect gradually decreasesd with the increase of curing temperature.更多还原