Research On Rheological Performances And Formwork Pressure Of Self-Compacting Concrete

Self-consolidating concrete(SCC) is a new type of high-performance and compacting concrete under its own weight, which is characterized by construction fast and can be placed without vibration. Formwork lateral pressure of SCC is significantly larger than normal concrete. It needs to use more ribs of formwork and support system. However, Formwork lateral pressure of self-compacting concrete is not simply equal to the normal hydrostatic pressure generated by concrete, while it is a variable that depends on the rheological properties of mixture and pouring height. Research on formwork lateral pressure and rheological properties of SCC and their relations has important theoretical and practical significance on reducing cost of mould and ensuring safety of construction.In this research, the author develops a device which can simulate different pouring heights and measure formwork lateral pressure of self-compacting concrete. The influence of two strength grades of SCC formwork lateral pressure on different mixing quantity of fly ash, ground slag and limestone powder is mainly discussed. The results indicate that the formwork lateral pressure of control concrete is lower than theoretical hydrostatic pressure about 69kPa. The results indicate that the formwork lateral pressure of SCC is lower than theoretical hydrostatic pressure about 75kPa when the mass percent of fly ash was 10-30%. The formwork lateral pressure of SCC is lower than theoretical hydrostatic pressure about 84kPa when the mass percent of ground slag was 20-40%. The formwork lateral pressure of SCC is obviously lower than theoretical hydrostatic pressure 131-174kPa, when the mass percent of limestone powder was 5-15%.Therefore, The influence of reducing formwork lateral pressure of SCC is little when ground slag and fly ash were mixed comparing to the reference concrete. While SCC mixed with limestone powder can significantly reduce the formwork lateral pressure. And the effect is best when the mass percent of limestone powder were 5% and 10%. The effect of reducing the formwork lateral pressure is not obvious when complex mineral admixtures were mixed.This paper studies rheological properties of the SCC mortar matrix of different mixes by using a latest concrete rheometer. The results show that fly ash reduces the yield shear stress and plastic viscosity of self-compacting concrete. As the increase of slag content, thixotropy of SCC decreases significantly, yield shear stress first decreases and then increases and the plastic viscosity decreases. Limestone powder increases yield shear stress and plastic viscosity of self-compacting concrete. As the extension of static stop time, the thixotropy of SCC decreases slowly, the yield shear stress increases and the plastic viscosity decreases. The yield shear stress and the slump loss of SCC have linear descending correlation with formwork lateral pressure.