风积沙掺量对冻融-碳化耦合作用下混凝土耐久性的影响
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国家自然科学基金资助项目(51569021,51769025)


Effect of aeolian sand content on durability of concrete under freezing-thawing-carbonization coupling
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    摘要:

    针对寒区农业水利工程中混凝土的实际服役环境,利用风积沙等质量替代部分天然河砂制备不同风积沙替代率的混凝土为研究对象进行冻融循环-碳化耦合试验。分析冻融循环-碳化耦合作用下风积沙混凝土的损伤过程,借助核磁共振仪探讨了混凝土的孔隙结构演变与其耐久性之间的联系。试验结果表明,每个试验周期中,经历相同冻融循环次数和碳化时间,但作用顺序不同的情况下,冻融循环-碳化作用对混凝土造成的损伤大于碳化-冻融循环作用;当风积沙替代率由0增加至40%时,混凝土的初始孔隙度降低,同时试验中的质量损失率和相对动弹性模量变化减小;混凝土内部凝胶孔和少害孔占比对其孔隙度和相对动弹性模量具有主导作用,当凝胶孔和少害孔占比之比在5~25之间时相对动弹性模量和孔隙度变化不超过1%,在0~5之间减小时相对动弹性模量和孔隙度变化明显;风积沙的加入改善了混凝土的孔隙分布,风积沙替代率为40%的风积沙混凝土表现出良好的抗冻融、抗碳化能力。该研究可为风积沙混凝土在寒区农业水利工程中的研究与应用提供依据。

    Abstract:

    China is one of the countries with abundant reserves of aeolian sand in the world. Aeolian sand is widely distributed in North China. If the material can be taken locally in the construction of the project, that is, the aeolian sand can be used to replace natural river sand as fine aggregate to prepare concrete, which can not only promote the development of the construction industry, but also slow down the sand damage and benefit the environment. According to the actual service environment of concrete in the agricultural water conservancy projects of cold regions, the river sand was replaced by aeolian sand, and the concrete samples with different aeolian sand substitution rates were prepared. And they were used as the research objects for the freeze-thaw cycle-carbonization coupling test. An analysis was conducted on the damage process of aeolian sand concrete under the influence of freezing-thaw cycle-carbonization coupling. The relationship between the pore structure evolution of concrete and its durability was discussed by nuclear magnetic resonance instrument. The internal damage of different treatments concrete were analyzed by measuring the mass loss and dynamic elastic modulus of different periods of concrete. The test results showed that under the condition of the same number of freeze-thaw cycles and carbonization time in each test cycle, the damage caused by freeze-thaw cycle-carbonization was greater than that of carbonization-freeze-thaw cycle. With the increase in the number of freeze-thaw cycles and carbonization time, the concrete mass loss rate significantly increased while the relative dynamic elastic modulus greatly decreased; when the replacement rate of aeolian sand increased from 0 to 40%, the initial porosity of the concrete decreased, and the mass loss rate and relative dynamic modulus change in the test decreased. So the porosity of the concrete could not be used as an indicator in this test to accurately evaluate concrete durability; the pore distribution of concrete at different time was measured by nuclear magnetic resonance technology. The internal pores of concrete were divided to gel pores (0-0.05 μm), capillary pores (>0.05-1 μm), less harmful pores (>1-10 μm) and more harmful pores (>10 μm). Through the correlation analysis between the evolution of four kinds of pore proportions and the porosity and the relative dynamic elastic modulus of concrete, it was found the proportion of gel pores and less harmful pores in concrete had a dominant effect on its porosity and relative dynamic elastic modulus. When the ratio of gel pores to less harmful pores was 5 - 25, the change of the relative dynamic elastic modulus and porosity were not more than 1%; and the change of the relative dynamic elastic modulus and porosity of the concrete were change obviously when the ratio of gel pores to less harmful pores was 0-5; The addition of aeolian sand improved the pore distribution of concrete, and the aeolian sand concrete with an aeolian sand replacement rate of 40% showed a good resistance to freeze-thaw and carbonization. This study can provide a basis for the research and application of aeolian sand concrete in agricultural water conservancy projects of cold regions.

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申向东,邹欲晓,薛慧君,李根峰.风积沙掺量对冻融-碳化耦合作用下混凝土耐久性的影响[J].农业工程学报,2019,35(2):161-167. DOI:10.11975/j. issn.1002-6819.2019.02.021

Shen Xiangdong, Zou Yuxiao, Xue Huijun, Li Genfeng. Effect of aeolian sand content on durability of concrete under freezing-thawing-carbonization coupling[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE),2019,35(2):161-167. DOI:10.11975/j. issn.1002-6819.2019.02.021

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  • 收稿日期:2018-09-07
  • 最后修改日期:2019-01-04
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  • 在线发布日期: 2019-01-21
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