Research And Application Of Super High-rise Pumping C70 Concrete

With the rise of the height of super high-rise buildings,the concrete strength grade of the building structure is constantly improved,the plastic viscosity is increased,and the pumping pressure is also increasing with the rise of the height.However,there is a lack of systematic research on the pumping concrete technology of super high-rise buildings at home and abroad,especially in the pumpability evaluation system of super high-rise concrete,the variation law of pressure in the pumping pipe,and the production quality stability of high flow and low viscosity concrete The waste of design cost.The rheological properties of C70 pumping concrete in super long pumping pipeline are tested by horizontal coil method.Meanwhile,the real-time pressure in the process of concrete pumping is directly measured by embedded contact pressure sensor.The pressure distribution characteristics and pressure loss law in the whole pumping process are analyzed,and the admixture combination with viscosity reduction effect and high slump retention and reduction with viscosity adjustment function are studied The research results have been successfully applied in Changsha Beichen Delta and China Zun project.The test results show that: when the pumping pressure is constant,the pipeline pressure and the viscosity of the pumping medium increase proportionally.The pressure drop per meter at the elbow of the pumping pipeline is greater than that of the horizontal pipeline,and the pressure drop at the end of the pipe is less than that at the front end.The coil test shows that the measured pressure in the pipeline is consistent with the concrete in Appendix B of technical specification for concrete pumping construction(JGJ / t-10-2011)The empirical formula s · Morinaga does not agree with the measured data of pressure gauge,which is an order of magnitude difference;as a friction instrument,the sliding tube instrument can quickly and intuitively reflect the friction properties of the concrete lubrication layer during the pumping process,and can predict the friction resistance between the large flow concrete and the pumping pipeline;the plastic viscosity,V funnel time and pumping pressure loss are found in the test The results show that there is a certain relationship between them,and the evaluation indexes of concrete "pumpability" at different heights are given.By modifying spherical microspheres with silica fume,polyacrylamide(anion),attapulgite and ordinary fly ash,the plastic viscosity of concrete can be effectively reduced by more than 60%,and the autogenous shrinkage and carbonation depth of concrete can be reduced at the same time.The engineering application shows that the lower the plastic viscosity is,the better the super high-rise pumping concrete is,but there is a reasonable range,which makes the concrete mixture a thixotropic and homogeneous viscous mixture;in this range,the concrete mixture is a thixotropic viscous mixture,and it is necessary to avoid excessively reducing the viscosity of the slurry,thus damaging the homogeneity performance of the slurry Increase the initial pumping resistance.