Mixing of high performance concrete: effect of concrete composition and mixing intensity on mixing time
Mixing of high performance concrete: effect of concrete composition and mixing intensity on mixing time
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DOI：
10.1617/s11527-009-9494-y
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发表时间：
2010-04-01
影响因子：
3.8
通讯作者：
Schiessl, P.
中科院分区：
文献类型：
--
作者：
Mazanec, O.;Lowke, D.;Schiessl, P.
目前，超高性能混凝土（UHPC）的使用仅限于少数特殊应用。这主要是由于混合UHPC混合料所需的时间比普通混凝土所需的时间要长得多。本研究旨在确定导致UHPC混合时间延长的成分特征。系统地改变混凝土混合料的各个组成部分（硅粉、石英粉、水、高效减水剂和粗骨料），以研究它们对达到最佳流动性能所需的搅拌时间的影响。除混凝土成分外，还考虑了搅拌工具转速的影响。所需的最短混合时间（稳定时间）是根据混合过程中施加在工具上的功率的变化来计算的。经证实，高w/c值导致稳定时间短。此外，硅灰和石英粉的含量以及水泥和高效减水剂的种类对稳定时间有显著影响。可以用相对固体浓度I中心点/I中心点（max）来描述单个变量的影响，这取决于混凝土成分。这是混凝土混合料I中心点中固体的实际体积浓度与根据颗粒体积（粒径分布）计算的固体I中心点的最大可能浓度（max）之比。相对固体浓度是计算特定成分和工具速度下UHPC混合时间模型的基础。较高的刀具速度和较低的固体实际浓度缩短了稳定时间。
At present the use of ultra high performance concrete (UHPC) is limited to a small number of special applications. This is essentially due to the time needed to blend the UHPC mix which is considerably longer than required for ordinary concrete. The present investigations aimed at the determination of the composition features which result in the longer mixing time of UHPC. The individual components of the concrete mix (silica fume, quartz flour, water, superplasticizer and coarse aggregate) were systematically varied in order to investigate their effect on the mixing time needed to achieve optimal flow properties. Besides concrete composition, the effect of mixing tool speed was considered. The shortest necessary mixing time (stabilisation time) was calculated from the evolution of the power applied to the tool during mixing. It was confirmed that high w/c values resulted in short stabilisation times. In addition, the contents of silica fume and quartz flour as well as the type of cement and superplasticizer affected the stabilisation time significantly. It was possible to describe the effect of the individual variables in terms of the relative solid concentration I center dot/I center dot(max) which depends on concrete composition. This is the ratio of the actual volumetric concentration of solids in the concrete mix I center dot to the maximum possible concentration of solids I center dot(max) calculated from the volumes of particles (particle size distribution). The relative solid concentration is the basis of a model for the calculation of the mixing time of UHPC of a given composition and for given tool speed. High tool speeds and low actual concentrations of solids shorten the stabilisation time.