预湿轻骨料对混合骨料混凝土技术性能的影响研究

发布时间：2018-05-25 17:21

  本文选题：轻骨料 + 预湿　； 参考：《长沙理工大学》2014年硕士论文

【摘要】：轻骨料经过预湿处理,会对新拌混凝土的工作性、硬化混凝土内部结构、力学及收缩性能等产生重要影响。本文选用三种不同种类、不同吸水率的轻骨料,制备低塑性和高流态混合骨料混凝土。设计不同轻骨料取代率、水胶比水平以及多种养护条件,在大量试验的基础上,研究经过不同时间(干燥、预湿1h、预湿24h)浸水预湿处理的轻骨料对混合骨料混凝土工作性、力学性能、内部相对湿度和收缩的影响,并探讨其作用机理。主要工作及结论如下：1、分析不同轻骨料种类及取代率条件下,干燥与预湿轻骨料分别对低塑性和高流态混合骨料混凝土工作性的影响。试验结果表明：干燥、预湿轻骨料对低塑性混凝土工作性影响较小；而高流态混凝土中,干燥轻骨料试样经时坍落度损失最大,预湿轻骨料有效抑制了混凝土的坍落度损失。三种不同吸水率的预湿轻骨料,预湿24h时高含水率的轻骨料比低含水率的轻骨料返水时间更早,对降低坍落度损失更明显。2、分别采用高效减水剂和缓凝剂,轻骨料预湿过程中预先吸附外加剂与混凝土搅拌过程中直接掺入外加剂的对比,通过坍落度损失试验和凝结时间测定,分析多孔轻骨料对外加剂的“载体”和“缓释”作用,并得出初步结论：直接掺入减水剂搅拌混凝土,液相中减水剂浓度下降快,流动性保持能力差；轻骨料吸附的减水剂能缓慢地从其“载体”中释放出来,其液相中减水剂维持一定浓度,坍落度损失减小；轻骨料吸附缓凝剂使初、终凝时间间隔变长,轻骨料吸附缓凝剂同样也能改善混凝土坍落度损失。3、系统研究干燥、预湿1h、预湿24h轻骨料对混合骨料混凝土强度发展的影响,并分析轻骨料吸水返水作用机理。随着轻骨料预湿时间的延长,混凝土后期强度增长率逐渐加大。对吸水率小的碎石型页岩陶粒,干燥与预湿1h轻骨料对混凝土后期强度影响不大；对中等、高吸水率的轻骨料,预湿时间越久,混凝土后期强度增长率相对越大,28d基本能赶上或超出干燥轻骨料试样的强度。在净水胶比、总水胶比和有效水胶比三个参数中,混合骨料混凝土的早期强度与净水胶比相关性最大,后期强度与总水胶比相关性大,但无论早期、中期还是后期,混凝土强度总是取决于其有效水胶比。4、通过对比试验,分析浸水养护、自然养护以及密封养护等不同外界养护条件下,预湿轻骨料在混凝土内部返水作用与“内养护”功能的发挥,总结不同外部温湿度环境下“内养护”混合骨料混凝土的抗压强度发展规律。浸水养护时,预湿轻骨料无“内养护”效果；密封养护条件下预湿轻骨料改善水泥水化环境,“内养护”与外养护结合,混凝土具有较高的强度；自然养护效果居中,且预湿轻骨料与干燥轻骨料试样强度的差异随轻骨料取代率的增加而减小。5、监控混合骨料混凝土内部相对湿度变化,分析轻骨料吸水返水特性、预湿轻骨料取代率等对混凝土内部相对湿度的影响,以及混合骨料混凝土早期收缩发展规律。试验研究表明,轻骨料预湿后可以在混凝土内部形成微型蓄水源,在湿度扩散作用下释放水分,改善混凝土内部湿度环境。预湿轻骨料取代率越高,预湿时间越久,可供迁移的水分越多,混凝土内部相对湿度降低越缓慢。预湿轻骨料对混凝土收缩的影响十分明显,通过提高轻骨料预湿时间可降低混凝土的收缩率。6、从轻骨料的合理选用、预湿工艺、轻骨料对外加剂的作用、养护手段等方面对工程应用中应注意的关键问题进行初步讨论和总结,为其在实际工程中的生产和应用提供了重要的参考。
[Abstract]:The effects of light aggregate on workability , mechanical property , internal relative humidity and shrinkage of mixed aggregate concrete with different kinds and different water absorption are studied . The effects of light aggregate on workability , mechanical property , internal relative humidity and shrinkage of mixed aggregate concrete have been studied . The main work and conclusion are as follows : 1 . To analyze the influence of different light aggregate types and substitution rates on workability , mechanical property , internal relative humidity and shrinkage of mixed aggregate concrete . The results show that the drying and pre - wetting lightweight aggregate have less influence on the workability of low plasticity concrete .
In the high - flow concrete , the loss of slump of the dry lightweight aggregate is the largest , and the pre - wet lightweight aggregate effectively inhibits the slump loss of the concrete . Compared with the lightweight aggregate with low water content during the pre - wet 24h , the light aggregate with high water content is more obvious than the light aggregate with low water content , and the effect of the porous light aggregate on the carrier and the slow release of the admixture is analyzed by the slump loss test and the setting time .
the water reducing agent adsorbed by the light aggregate can be slowly released from the carrier , the water reducing agent in the liquid phase is maintained at a certain concentration , and the slump loss is reduced ;
3 . The effect of drying , pre - wetting 1h and pre - wetting 24h light aggregate on the strength development of mixed aggregate concrete can be improved .
In the light aggregate with medium and high water absorption , the longer the pre - wetting time , the higher the later strength growth rate of the concrete , the 28d is basically able to catch up with or exceed the strength of the dry lightweight aggregate specimen . In the water - purifying ratio , the total water - cement ratio and the effective water - cement ratio , the concrete strength always depends on its effective water - cement ratio .
the pre - wet light aggregate under the condition of sealing and curing can improve the hydration environment of the cement , the internal curing is combined with the outer curing , and the concrete has higher strength ;
The effect of pre - wetting time of lightweight aggregate on the internal relative humidity of concrete is analyzed . The effect of pre - wetting lightweight aggregate on concrete shrinkage can be reduced . The effect of pre - wetting lightweight aggregate on shrinkage of concrete is obvious .
【学位授予单位】：长沙理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU528
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本文编号：1934040