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Performance of concrete with vacuum dewatering process
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摘要: 为提高混凝土保护层的抗渗透性能并避免表面裂缝的产生，从而提升钢筋混凝土的耐久性，采用真空脱水工艺，通过宏观性能试验结合微观孔结构分析，研究了真空脱水混凝土的性能及其性能改善机理。试验结果表明：（1）真空脱水混凝土的配合比在试验设计范围内取较低的初始水胶比、较少的单位用水量和比非真空混凝土增加约20 %以上的适宜砂率，可以提高真空混凝土的真空脱水率和混凝土性能；（2）采用真空脱水工艺后，混凝土28 d抗压强度的提高值随着水胶比的增大而增加；混凝土72 h抗冲磨强度的提高值随着水胶比的增大而减小，低水胶比混凝土的抗冲磨性能的提高效果尤为显著；（3）与非真空混凝土相比，真空混凝土的干缩变形减小，抗渗透性能显著提高。孔结构分析结果表明：真空脱水主要增加了混凝土中20~50 nm这一孔级的体积含量，混凝土总孔隙率明显降低、最可几孔径减小、临界孔径和平均孔径均明显减小，从而优化和细化了混凝土孔结构。真空脱水工艺可以作为提高钢筋混凝土保护层性能的有效措施，供设计和施工参考。Abstract: In order to improve the permeability resistance of concrete protective layer and avoid surface cracks, and then improve the durability of reinforced concrete, vacuum dewatering process was adopted in this research. The performance of vacuum dewatered concrete and its improvement mechanism were studied by macroscopic performance test and micro pore structure analysis. The test results show that: (1) The vacuum dewatering rate and performance of vacuum dewatered concrete can be improved by using lower initial water-binder ratio, less water consumption per unit and more than about 20% suitable sand ratio compared with non-vacuum dewatered concrete. (2) After vacuum dewatering, the increamental value of compressive strength of concrete after 28 d increases with the water-binder ratio; and the improvement value of concrete abrasion resistance strength after 72 h decreases with the increase of water-binder ratio. And the improvement effect of low water-binder ratio on abrasion resistance strength is particularly significant. (3) Compared with non-vacuum dewatered concrete, the dry shrinkage deformation of vacuum dewatered concrete decreases and the permeability resistance of vacuum dewatered concrete improves significantly. The results of pore structure analysis show that vacuum dewatering process mainly increases the volume content of pore size of 20~50 nm in concrete, and the total porosity, maximum pore size, critical pore size and average pore size of concrete decrease obviously. Vacuum dewatering process optimizes and refines concrete pore structure. Vacuum dewatering process can be used as an effective measure to improve the performance of reinforced concrete protective layer.
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Key words:
- vacuum dewatering process /
- strength /
- dry shrinkage /
- permeability resistance /
- concrete pore structure
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图 1 不同水胶比下真空脱水混凝土的强度性能
Figure 1. Strength properties of vacuum dewatered concrete with different water-binder ratios
图 2 使用真空脱水工艺后混凝土的表观效果
Figure 2. Apparent effect of concrete with vacuum dehydration process
图 3 不同强度真空脱水混凝土的干缩变形性能
Figure 3. Shrinkage deformation properties of vacuum dewatered concrete with different strengths
图 4 真空与非真空条件下混凝土的微分孔径分布曲线
Figure 4. Differential pore size distribution curves of vacuum and non-vacuum dewatered concretes
图 5 真空与非真空条件下混凝土的孔级分布
Figure 5. Pore size distribution of vacuum and non-vacuum dewatered concretes
表 1 水泥的化学成分
Table 1. Chemical compositions of cement
单位：% SiO2 Al2O3 CaO MgO Fe2O3 K2O SO3 烧失量 25.63 8.27 53.36 2.73 3.22 0.62 1.69 3.62 
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表 2 真空脱水混凝土配合比正交试验设计与试验结果
Table 2. Orthogonal test design and results of vacuum dewaterd concrete mix
试验号 因子 真空脱水率/% 28 d抗压强度/MPa A
水胶比B
砂率C
用水量/(kg·m−3)D
外加剂非真空 真空 1 0.40 0.38 150 聚羧酸系 11.0 45.1 49.1 2 0.40 0.44 160 氨基系 11.2 43.5 48.8 3 0.40 0.50 170 萘系 9.1 43.1 47.6 4 0.44 0.38 160 萘系 12.2 42.1 45.0 5 0.44 0.44 170 聚羧酸系 13.5 40.8 46.3 6 0.44 0.50 150 氨基系 13.0 40.2 45.2 7 0.48 0.38 170 氨基系 13.8 39.2 43.2 8 0.48 0.44 150 萘系 16.7 38.4 44.1 9 0.48 0.50 160 聚羧酸系 15.4 37.9 41.9
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表 3 各因子对真空脱水混凝土性能影响的极差分析
Table 3. Range analysis in influence of each factor on the performance of vacuum dehydrated concrete
状态 性能参数 各因子的极差 水胶比 砂率 单位用水量 外加剂 极差R（脱水前） 28 d抗压强度 5.40 1.73 0.20 0.30 极差R（脱水后） 真空脱水率 4.87 1.47 1.43 0.63 28 d抗压强度 5.37 1.50 1.07 0.53
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表 4 不同水胶比下真空脱水混凝土配合比及拌合物性能
Table 4. Mix ratio and properties of vacuum dewatered concrete with different water-binder ratios
试件编号 水胶比 砂率 用水量/ (kg·m−3) 外加剂掺量/% 水泥品种 坍落度/mm 真空脱水率/% PC-1 0.32 0.42 150 1.2 P·O 42.5 55 9.6 PC-2 0.40 0.46 150 1.2 P·O 42.5 65 14.4 PC-3 0.48 0.50 150 1.2 P·O 42.5 70 16.2
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表 5 真空与非真空脱水混凝土抗渗性能试验结果
Table 5. Permeability resistance results of vacuum and non-vacuum dewatered concretes
工艺条件 试件平均渗水高度/mm 水压0.6 MPa 水压0.9 MPa 水压1.2 MPa 非真空脱水 3 8 16 真空脱水 5 8 10
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表 6 真空与非真空脱水混凝土的孔结构参数
Table 6. Pore structure parameters of vacuum and non-vacuum dewatered concretes
试件及其部位 最可几孔径/nm 临界孔径/
nm平均孔径/nm 总孔隙率/
%非真空试件 PC-1 56.7 85.7 61.0 5.932 真空试件 表层 ZPC-1S 46.5 73.2 50.2 3.946 中间层 ZPC-1M 53.5 78.1 61.0 5.203 底层 ZPC-1B 56.7 81.0 62.4 5.466 非真空试件 PC-2 59.2 99.2 73.4 6.495 真空试件 表层 ZPC-2S 48.9 81.2 56.1 4.328 中间层 ZPC-2M 56.8 90.3 73.2 5.619 底层 ZPC-2B 57.6 96.2 76.2 5.609
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