Research On Testing Methods Of Rheological Properties Of Cement-based Materials

With the wide application of self-compacting concrete and the continuous emergence and development of emerging technologies such as concrete 3D printing,slip-form construction,and concrete(super)highrise pumping,accurate characterization and scientific regulation of the rheological properties of cement-based materials are becoming more and more important.The fresh cement-based material is a complex suspension system with multi-component,multi-particle size and significant timevarying phase composition.Its complexity makes the rheological test results largely depend on the test equipment and test procedures,which makes standardized There are many difficulties in testing the rheological properties of cement-based materials.In order to propose a rheological test technique with universal applicability,it is urgent to master the influence of conventional test methods on test results.In this paper,the influence of the test components and test procedures of the rotational rheometer on the test results of the rheological properties of various cement pastes,mortars and concretes was systematically studied,and the following conclusions were drawn:(1)The rheological parameters tested in cylinder geometry and parallel plate geometry are related to the rheological behavior of the slurry.The rheological parameters of the cement paste with high fluidity,low viscosity and mixed with superplasticizer are quite different between cylinder and parallel plate rheometers.However,it has little effect on the cement paste with the water-binder ratio less than 0.4 and the addition of cellulose ether.When the water-to-binder ratio is the same,the increase in viscosity improves the consistency of dynamic rheological parameters.Furthermore,for long-term rheological tests,the plasticity of the cement paste at the edges of the parallel plates intensifies,resulting in larger errors in the rheological parameters.(2)The pre-shear time has different effects on the rheological parameters measured by the step method and the linear method and is related to the material composition.The influence of pre-shearing time on the rheological parameters tested by the step method is greater than that by the linear method,especially for the mortar with low water-to-binder ratio,high sand-cement ratio,high content of cellulose ether and attapulgite,but for the mortar mixed with mineral powder and powder Mortar rheological parameters of coal ash have little effect.The effect of pre-shearing time on the test results of the rheological parameters of the cement paste is smaller than that of the mortar.When the water-binder ratio is greater than 0.45,the dynamic rheological parameters of the cement paste show a significant downward trend with the increase of the pre-shear time.The effect is less than the net paste less than 0.45.(3)The dynamic rheological parameters obtained based on the ladder method and the linear method have significant correlation.For mortar mixed with fly ash and mineral powder,the test results of the two methods are almost identical.For the mortar with low water-binder ratio,high sandcement ratio and high attapulgite content,the test results of the two methods are quite different.The correlation coefficient analysis shows that the yield stress obtained by the step method and the linear method has a good correlation,but the plastic viscosity has a poor correlation.(4)The integrated testing equipment of concrete rheometer and tribometer was developed.Compared with the traditional rheometer,the test elements,test procedures and data acquisition and analysis procedures are optimized,and a lubricating layer performance test module is introduced.The gap between the rotor and the outer wall of the selfdeveloped rheometer test element is set to 5 times the maximum particle size of the aggregate,the gap between the rotor and the outer wall of the lubricating layer test element is set to 2 times the maximum particle size of the aggregate,and 10 times the maximum particle size of the fine aggregate.It is suitable for the test of rheological parameters of concrete with common ratios.(5)The static yield stress tested by the self-developed rheometer is about 0.44-0.53 times that of the ICAR rheometer.For HWC,the dynamic yield stress and plastic viscosity measured by the self-developed rheometer are 0.63 and 0.654 times higher than those of the ICAR rheometer,respectively,while for SCC and HSC,the dynamic yield stress and plastic viscosity obtained by the self-developed rheometer are ICAR.3.2 and 0.33 times the rheometer.In addition,the dynamic yield stress and plastic viscosity measured by the self-developed rheometer have a good correlation with the slump expansion and V-funnel time,respectively.The yield stress of the lubricating layer measured by the self-developed tribometer has a good correlation with the concrete yield stress.