A study on prediction method of quality change for fresh concrete under pressure of pumping

为了建立泵送压力下新拌混凝土质量变化的预测方法，有必要对其质量变化机理进行评价。1.受压流动性机理研究为了评价受压下流动性变化的机理，进行了水泥净浆和石灰粉净浆在统计压力下的时变试验。对于不是活性粉末的石灰粉，粘度保持稳定。普通硅酸盐水泥的粘度增大，颗粒尺寸增大。静压和动压下粘度预测方法的研究本研究假设水泥颗粒之间的相互作用通过水泥水化作用减弱，建立了静压下粘度的预测方法。3.预测模型在现场实际泵送中的应用研究为评价现场压力下粘度预测方法的应用，进行了现场研究。结果表明，泵送不改变混凝土配合比的单位含量，但缩短了混凝土在V型漏斗中的流动时间，降低了砂浆的粘度。所提出的模型可以预测混凝土生产时间和到达现场时间之间的粘度随时间的变化。但该模型可能不能正确预测泵送时的降粘效果。

In order to develop a prediction method of quality change for fresh concrete under pressure of pumping, it is necessary that the mechanism of quality change have been evaluated. In this study, three experimental series were carried out following ;1.A study on mechanism of flowability under pressureIn this study, in order to evaluating mechanism of flowability change under pressure, time-depending-change tests of cement paste and lime powder paste under statistic pressure were carried out. For lime powder, which is not active powder, viscosity kept steady. On the other hand, viscosity increased and grain size of particles grew for ordinary portland cement. It was considered that hydration was accelerated under pressure for cement paste.2.A study on prediction method of viscosity under static and dynamic pressureIn this study, a prediction method of viscosity under static pressure was established assuming that interaction between cement particles was decreased by hydration of cement. Under dynamic pressure on real site, it was considered that we might predict viscosity by evaluating pressure with mean value.3.A study on application of prediction model to real pumping on siteIn order to evaluating the application of prediction method of viscosity under pressure, a site research was carried out. It was appeared that unit contents of mix proportion were not change by pumping, but, flow time in V funnel was decreased for concrete and viscosity of mortar was decrease too. A presented model may predict time-dependent-change of viscosity between time of producing concrete and time of arriving to site. But this model may not predict correctly decreasing viscosity under pumping.