An improved constitutive model for concentrated suspensions accounting for shear-induced particle migration rate dependence on particle radius

2014

ACT

The objective of this study is to numerically investigate the effects of coarse aggregate size on the pumpability of concrete. In actual construction of super-structures, the coarse aggregate size plays a determining factor on concrete pumping. Thus, depending on the coarse aggregate sizes, the properties of lubrication layer which is the major role facilitating concrete pumping, were numerically simulated using shear-induced particle migration analysis. Moreover, the particle shape effects according to the coarse aggregate sizes were also considered in numerical simulation to precisely simulate the actual flow conditions. For verification, 1,000m long full-scale tests with three different coarse aggregate sizes (10, 20 and 25mm) were conducted and compared with numerical results. It could be found that when concrete is being pumped, the rheological properties of concrete and lubrication layer highly depend on the coarse aggregate size, which consequently influences the flow condition of pumped concrete, whereas the thickness of lubrication layer remained almost constant irrespective of the coarse aggregate sizes.

Section: Introductionmentioning

confidence: 99%

Numerical Prediction on the Effects of the Coarse Aggregate Size to the Pipe Flow of Pumped Concrete

2014

ACT

“…The second reason for the difference is that under the action of shear, the redistribution of particles occurs within a pipe, which is a common feature of particle suspensions. Initially well mixed particles in a concentrated suspension flows undergo migration from high shear rate regions to low shear rate regions (Phillips et al 1992;Ingber et al 2009;Lu et al 2008). During concrete pumping, shear concentrates in the fluid layer of material depleted of the coarsest particles of concrete.…”

Section: Introductionmentioning

confidence: 99%

Viscoelastic Properties of Fresh Cement Paste to Study the Flow Behavior

Int J Concr Struct Mater

Park

2016

During concrete pumping, the migration and redistribution of particles occur in a pipe and the lubrication layer that forms between the bulk concrete and the pipe wall is the governing factor determining the flow behavior. In order to identify flow behavior of pumping, in this study, the viscoelastic properties related to the microstructural behavior of a flocculated suspension were examined by using dynamic oscillatory measurements. Cement paste is assumed to be a constituent material of the lubrication layer and ten cases of mixing design are employed by changing the proportions of mineral admixtures. The relationship between the yield stress obtained from the steady shear test and the dynamic modulus resulted from the oscillatory shear measurement was derived and the implications of the correlation are discussed. Moreover, based on the investigation of the viscoelastic properties with oscillatory measurements, the initial behavior of pumped concrete was analyzed systematically.

“…Kwon et al (2013aKwon et al ( , 2013b deduced correlation between properties of lubrication layer measured by tribometer and flow rates in concrete pumping. A possible mechanism that explains the formation of lubrication layer is shear-induced particle migration (Choi et al 2013b;Ingber et al 2009;Phillips et al 1992). When concrete is being pumped, a redistribution of particles occurs near the wall of the pipe due to the gradient of the shear stress.…”

Section: Introductionmentioning

confidence: 99%

Effect of the Mineral Admixtures on Pipe Flow of Pumped Concrete

Park

Kang

2015

ACT

The objective of this study is to investigate the effect of the mineral admixtures on pipe flow of pumped concrete through analyzing the properties of lubrication layer playing a dominant role to facilitate concrete pumping. Concrete mixtures incorporating blast furnace slag (BFS), fly ash (FA) and silica fume (SF) were selected with three different replacement ratios for each case and pumped through 170 m circuit. The rheological properties were measured before pumping and the thickness of lubrication layer was also experimentally observed with a special sensor, ultrasonic velocity profiler (UVP). An analytical equation considering the effect of the layer was adopted to calculate the thickness of the layer and to compare with full scale pumping results. The lubrication layer of BFS and FA indicated almost constant value regardless of replacement ratios but varied with SF mixtures. The concrete incorporating BFS or 5% SF represented satisfactory improvement of pumping efficiency.