不同干燥条件对预湿轻细骨料内养护混凝土性能的影响

发布时间：2018-01-08 10:02

本文关键词：不同干燥条件对预湿轻细骨料内养护混凝土性能的影响　出处：《清华大学》2015年硕士论文　论文类型：学位论文

【摘要】：收缩开裂是混凝土结构常见的问题,严重危害结构物的安全性和耐久性。在传统外部水养护效果不佳、减缩剂和膨胀剂使用条件较复杂的背景下,内养护技术作为一种新兴的技术,引起学者的普遍关注。其主要思想是通过掺入预湿轻骨料以减少混凝土的收缩变形。尽管在过去几十年内,内养护技术研究已经取得阶段性成果,但是内养护技术在不同养生方式(实际工程结构物往往最终会暴露于干燥条件)下对混凝土的收缩、强度和开裂风险等方面影响仍有待深入研究。本文对掺入烧结粉煤灰陶砂的内养护混凝土收缩、强度和开裂风险等性能进行较为全面的研究。结果表明,烧结粉煤灰陶砂具有多孔性质,1um-10um的孔隙占总孔隙体积的比例较大,其吸水性能较优,且具有显著的释水性,是一种高效的内养护材料;但多孔性质导致其强度仅有9.8MPa,低于普通骨料。粒径主要介于2mm-7mm之间,有利于在混凝土中均匀分布,从而有效促进混凝土的水化;在密闭养生方式下,内养护技术能减缓甚至消除自收缩现象,且使混凝土在密闭过程中始终处于膨胀状态;但内养护技术对减少干燥收缩的效果并不明显,干燥状态下,内养护技术总体减缩效果降低,且延长养生时间并不能提高内养护的减缩效果;混凝土质量损失速率由快到慢分为两阶段发展,且与收缩、湿度有内在联系。标准养生方式下内养护混凝土的强度发展不仅取决于水灰比,还与粉煤灰陶砂的强度有关,总体而言,内养护混凝土的28d抗压强度和弯拉强度普遍低于普通混凝土;此外内养护混凝土和普通混凝土的抗压强度和弯拉强度均对养生方式比较敏感,且养生方式对混凝土强度的影响主要体现在后期,越迟暴露于干燥条件,则混凝土的抗压强度和弯拉强度越大;相比于标准养生方式,密闭养生方式会降低内养护混凝土和普通混凝土28d的抗压强度和弯拉强度,越迟暴露于干燥条件,则强度损失越小;混凝土的弯拉强度对养生方式更为敏感,为了防止混凝土早期开裂,须避免过早在干燥环境下对混凝土进行养生。在密闭养生方式下,普通混凝土仍会开裂,延长密闭养生能够改善混凝土开裂风险,但是效果不明显;内养护技术在密闭养生下能降低混凝土的开裂风险,然而一旦内养护混凝土暴露于干燥环境,其干燥收缩增长迅速,可导致混凝土开裂。
[Abstract]:Shrinkage cracking is a common problem in concrete structures, which seriously endangers the safety and durability of structures. Internal curing technology, as an emerging technology, has attracted widespread attention of scholars. Its main idea is to reduce the shrinkage and deformation of concrete by adding pre-wet lightweight aggregate, although in the past few decades. Although the research on internal curing technology has made progress, the internal curing technology can shrink concrete in different ways (actual engineering structures will eventually be exposed to drying conditions). The effects of strength and cracking risk still need to be deeply studied. In this paper, the shrinkage, strength and cracking risk of internal curing concrete with sintered fly ash ceramic sand are studied comprehensively. The results show that. The sintered fly ash ceramic sand has a large proportion of pore volume to the total pore volume with porous property of 1um-10um, and its water absorption property is better, and it has remarkable water release, so it is a kind of high efficiency internal curing material. But its strength is only 9.8 MPA, which is lower than that of ordinary aggregate. The particle size is mainly between 2 mm and 7 mm, which is favorable to uniform distribution in concrete, thus effectively promoting the hydration of concrete. In the closed health mode, internal curing technology can slow down or even eliminate the phenomenon of self-shrinkage, and make the concrete always in the expansion state in the process of sealing. However, the effect of internal curing technology on reducing drying shrinkage is not obvious. Under dry condition, the overall shrinkage reduction effect of internal curing technology is reduced, and prolonging the curing time can not improve the shrinkage reduction effect of internal curing. The mass loss rate of concrete is divided into two stages from fast to slow, and has internal relation with shrinkage and humidity. The strength development of curing concrete under standard health is not only determined by water-cement ratio. Generally speaking, the 28d compressive strength and flexural tensile strength of inner cured concrete are lower than that of ordinary concrete. In addition, the compressive strength and flexural tensile strength of inner curing concrete and ordinary concrete are both sensitive to the health maintenance mode, and the effect of the health care mode on the concrete strength is mainly reflected in the later stage, the later exposed to the dry condition. The compressive strength and flexural tensile strength of concrete are greater. Compared with the standard way of keeping in good health, the closed health way will reduce the compressive strength and flexural strength of the inner curing concrete and the ordinary concrete for 28 days, the later the exposure to the drying condition, the smaller the strength loss. The flexural tensile strength of concrete is more sensitive to the way of health preservation. In order to prevent early cracking of concrete, it is necessary to avoid premature preservation of concrete in dry environment. Prolonging the closed health can improve the cracking risk of concrete, but the effect is not obvious. Internal curing technology can reduce the cracking risk of concrete under closed health. However, once the inner curing concrete is exposed to dry environment, its drying shrinkage increases rapidly, which can lead to concrete cracking.
【学位授予单位】：清华大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU755.7

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