振动搅拌对超高性能混凝土施工及力学性能影响

Effect of Vibratory Mixing on the Construction and Mechanical Properties of Ultra-High Performance Concrete

搅拌过程是超高性能混凝土(UHPC)获得良好施工性能及实现优异力学性能的重要环节。为此,设计两个UHPC配合比,分别采用传统单、双卧轴强制搅拌及振动搅拌,通过对比试验研究振动搅拌对UHPC施工及力学性能影响。通过扩展度、抗压强度和四点弯曲试验,得到了各组UHPC随不同湿拌时间的扩展度、充分湿拌时间、静停一段时间扩展度损失量、抗压、抗折强度、能量吸收、断裂能及弯曲应力-挠度曲线及四点弯曲出现可视裂纹时下缘等效拉应力;对抗压、抗折强度进行了变异性分析;利用应力-挠度曲线,基于规范及其改进法、Nemkumar法计算了弯曲韧性指标。结果表明:湿拌时间相同时,振动搅拌相较强制搅拌可显著提升UHPC的扩展度;UHPC达最大扩展度时,单、双卧轴强制搅拌和振动搅拌的充分湿拌时间分别为6 min、6 min、5 min;振动搅拌3 min时,UHPC扩展度即可达到或超过充分湿拌(6 min)时的强制搅拌;静停时间为4 h时,振动搅拌下UHPC的扩展度损失量均较大幅度低于强制搅拌;振动搅拌相较强制搅拌可显著提升UHPC的抗压强度,提升幅度最大可达33.1%(平均值)和41.46%(标准值),同时变异系数大幅降低;不同搅拌方式时,UHPC抗折强度平均值和标准值基本持平,但振动搅拌可显著降低抗折强度变异系数,降低幅度在19.61%~80.85%之间;采用振动搅拌时UHPC弯曲韧性指数、能量吸收及断裂能均显著优于强制搅拌。

Mixing process is an important segment for ultra-high performance concrete(UHPC)to obtain good construction performance and achieve its excellent mechanical properties.Therefore,two mix ratios of UHPC were designed,and the traditional single horizontal-shaft forced mixing,twin horizontal-shaft forced mixing and twin horizontal-shaft vibratory mixing were used respectively.The effects of vibratory mixing on construction and mechanical properties of UHPC were studied through comparative experiments.The expansion of each group of UHPC with different wet mixing time,full wet mixing time,loss of expansion of UHPC for a standing time after full wet mixing,compressive strength,flexural strength,energy absorption,fracture energy,four-point flexural stress-deflection curves,and the equivalent tensile stress at the lower edge of the test piece when the visible first crack occured were obtained through expansion,compressive strength and four-point flexural test.Subsequently,the variability of compressive strength and flexural strength test results were analyzed.The flexural toughness index of UHPC were calculated based on the stress-deflection curves,the standard and its improvement method,and the Nemkumar method.The results show that the expansion of UHPC can be significantly improved by vibration stirring compared with forced stirring when the wet mixing time is the same.The full wet mixing time of forced stirring with single and twin horizontal-shaft and vibratory stirring is 6 min,6 min and 5 min when UHPC get its maximun expansion.When the vibratory mixing time is 3 min,the expansion of UHPC can reach or exceed the forced mixing with the full wet mixing time(6 min).The loss of expansion of UHPC under vibratory mixing is much lower than that under traditional forced mixing when the total standing time is 4 h.Compared with forced mixing,vibratory mixing can significantly improve the compressive strength of UHPC,and the maximum increase can be 33.1%(average value)and 41.46%(standard value),while the coefficient of variation is significantly reduced.The flexural strength average and standard value of UHPC are basically same under different mixing modes,but vibratory mixing can significantly reduce the coefficient of variation of flexural strength,and the reduction range is between 19.61%and 80.85%.The flexural toughness index,energy absorption and fracture energy of UHPC with vibratory mixing are significantly better than those with forced mixing.