【作者】 周富荣；

【导师】 钱晓倩； 詹树林；

【作者基本信息】 浙江大学 ， 结构工程， 2006， 硕士

【摘要】 混凝土的早期收缩裂缝是一个亟待解决的问题。本文紧紧围绕养护对混凝土早期收缩和开裂的影响展开试验研究和理论分析。尽管科研人员已经认识到养护能减小混凝土的早期收缩,但迄今为止的试验研究都还停留在定性研究的层面上。本文从研究掺减水剂混凝土的早期收缩的特点入手,定量地研究了采用养护措施控制混凝土早期收缩时,起始养护龄期、养护时间和养护方式等对混凝土早期收缩的影响。本文在此基础上提出了比较合理的养护制度,并通过平板开裂试验进行了验证。研究表明: 现浇混凝土工程中更易出现早期收缩裂缝,一个重要的原因就是减水剂的使用。在不同相对湿度条件下,掺减水剂混凝土的早期收缩都远大于不掺减水剂的混凝土,且相对湿度越小两者的差值越大。虽然不同的减水剂对混凝土早期收缩的影响不一样,但都增大了混凝土的收缩。因此对于掺减水剂的混凝土必须重视其早期收缩的控制。 及时采取养护措施可有效地减小掺减水剂混凝土的收缩,随着起始养护龄期的推迟,养护的减缩效果下降,在初凝后8h再开始养护已经收效甚微。随着水灰比的减小,混凝土的早期收缩量增加,其中温度变形和自收缩的比重增大,养护的减缩作用也有所减弱,因此对混凝土起始养护龄期的要求也更高。密封养护和喷雾养护均能减小混凝土的早期收缩,但必须要强调养护的“及时性”。为获得良好的减缩效果,养护宜从混凝土初凝甚至浇筑后就开始。 如果起始养护龄期一定,则混凝土的早期收缩将取决于养护时间。随着混凝土水灰比的减小,养护的减缩作用有所减弱。无论是采用密封养护还是喷雾养护来抑制混凝土的早期收缩,都应保证足够的养护的时间。对于水灰比大于0.32的混凝土,如果能在初凝后养护8h,则早期收缩将显著减小。 平板试验的结果表明:无论是采用密封养护还是喷雾养护,只要在初凝后持续养护8h就可以使混凝土的早期收缩裂缝得到有效地控制。但通过养护措施来减缩抗裂的方法以及相关的养护制度还需在实际工程中检验和改进。更多还原

【Abstract】 The problem of early age shrinkage cracking of concrete requires urgently to be solved. The effects of curing on early age shrinkage and cracking were studied in this paper by experimental research and theoretical analysis. As is known, early age shrinkage of concrete can be reduced by curing, but only qualitative studies have been carried out in this field so far. Started with discussing the characteristics of early age shrinkage of concrete with superplasticizer (SP), this paper quantificationally studied the influences of the initial curing age, the curing time and the curing methods on early age shrinkage of concrete under curing. As a result, an appropriate curing system is proposed, after being validated by the slab test. The research results can be concluded as follows:Early age shrinkage cracking is apt to appear in cast-in-situ concrete, and its main reason is the SP application. On condition of different values of relative humidity, early age shrinkage of concrete with SP application is larger than that without it, and the differences are larger if the relative humidity is lower. The influences of different SP on early age shrinkage are not always the same;however, the SP usage increases early age shrinkage. Therefore, it is important to control early age shrinkage in the concrete with SP.The shrinkage of concrete with SP can be reduced effectively by timely curing measures. The shrinkage-reducing effect of cuing is decreased as the initial curing age delays;It is too late if the curing starts 8 hours after the initial setting of concrete. Early age shrinkage is increasing with the reducing water to cement ratio, and the proportions of thermal deformation and autogenous shrinkage are enlarged;the shrinkage-reducing effects of curing decrease, and thus it is more important to choose the right initial curing age. Both the sealed curing and the fog curing can reduce early age shrinkage of concrete, but the initial curing age must be emphasized. To obtain the good shrinkage-reducing effect, it is suggested that the curing should be started from the initial setting or even from the casting.If the initial curing age is appointed, the early age shrinkage of concrete will depend on the curing time. The curing effect will be lowered if the water to cement ratio of concrete reduces. Adequate curing time must be ensured whether the sealedcuring or the fog curing is applied to control early age shrinkage of concrete. As to the concrete of water to cement ratio above 0.32, its early age shrinkage could be controlled effectively if cured for 8 hours after the initial setting.The results of the slab test indicate that early age shrinkage cracking of concrete will be soundly controlled if the concrete is cured, whether by sealed curing or by fog curing, for 8 hours immediately after the initial setting. But the methods and the systems of curing for reducing shrinkage cracking should be tested and improved in the practical projects yet.更多还原