Role of matrix structure and flaw size distribution modification on deflection hardening behavior of polyvinyl alcohol fiber reinforced engineered cementitious composites (PVA-ECC)
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The multiple cracking and deflection hardening performance of polyvinyl alcohol fiber reinforced engineered cementitious composites (PVA-ECC) under four-point flexural loading have been investigated. Matrices with different binder combinations and W/B ratios (from 0.44 to 0.78) providing satisfactory PVA fiber dispersion were specially designed. Effect of pre-existing flaw size distribution modification on deflection hardening behavior was comparatively studied by adding 3 mm diameter polyethylene beads into the mixtures (6% by total volume). Natural flaw size distributions of composites without beads were determined by cross sectional analysis. The crack number and crack width distributions of specimens after flexural loading were characterized and the possible causes of changes in multiple cracking and deflection hardening behavior by flaw size distribution modification were discussed. Promising results from the view point of deflection hardening behavior were obtained from metakaolin incorporated and flaw size distribution modified PVA-ECCs prepared with W/B=0.53. The dual roles of W/B ratio and superplasticizer content on flaw size distribution, cracking potential and fiber-matrix bond behavior were evaluated. Flaw size distribution modification is found beneficial in terms of ductility improvement at an optimized W/B ratio.
Key wordsfiber reinforced cementitious composites metakaolin deflection hardening multiple cracking flaw size distribution
研究了聚乙烯醇纤维增强工程水泥基复合材料(PVA-ECC)在四点弯曲载荷作用下的多重开裂 和挠度硬化性能, 设计了不同粘结剂组合和水胶比(W/B)(0.44~0.78)的矩阵,使PVA 纤维得到了较 好的分散。通过在混合物中加入直径为3 mm 的聚乙烯微球(总体积为6%),比较研究了预先存在的 缺陷尺寸分布修正对挠度硬化行为的影响。通过横断面分析,确定了无珠复合材料的自然缺陷尺寸分 布。对弯曲加载后试件的裂纹数和裂纹宽度分布进行了表征,并讨论了缺陷尺寸分布改性引起多次裂 纹和挠度硬化行为变化的可能原因。在W/B=0.53 的条件下制备了含偏高岭土和缺陷尺寸分布改性的 PVA-ECC, 得到了较好的挠度硬化行为。分析了W/B 比和超增塑剂含量对缺陷尺寸分布、潜在开裂、 和纤维-基体粘结行为的双重作用。在优化的W/B 比下,发现了有利于改善延展性的尺寸分布修正。
关键词纤维增强胶凝复合材料 偏高岭土 挠度硬化 多重开裂 缺陷尺寸分布
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The authors would like to gratefully acknowledge the cooperation of Civil Engineers; Emin Demirkaya, Gülizar Sönmez, Selim Aykal Akıl and Sabri Kökmen for specimen preparation and testing are greatly appreciated. The authors are also thankful to Çimentas Group (Cementir Holding), Powerpozz-USA and Kuraray Co. Ltd. for supplying the materials used in this research.
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