Study On Mechanical And Rheological Properties Of Cement-based Materials Under Ultrasonic Action

The composite treatment of cement-based materials is an effective way to achieve its high performance,and the good particle dispersion of the paste itself is the basic premise.At present,in the production and use of cement-based materials,mixing is the only way to achieve particle dispersion.However,the existing mixing technology is difficult to achieve the uniform dispersion of cement particles,resulting in the performance of cement-based materials after composite far from people’s expectations.Therefore,this thesis intends to use ultrasonic technology to treat the cement paste,and discusses the influence of ultrasonic parameters,ultrasonic action mode,water cement ratio,water reducer and other factors on its mechanical strength and rheological properties,hoping to achieve the improvement of cement paste performance.Therefore,this thesis has done exploratory and innovative work in the following aspects:(1)Characterization and quantification of particle dispersion behavior of fresh cement pasteThe distribution state of hardened unhydrated cement particles is used to characterize the dispersion state of the particles in the fresh paste.A quantitative analysis method based on the relative position of the particles is established by the adjacent distance statistical method.The microscopic observation results show that the ultrasonic action is helpful to the dispersion of cement particles in the paste,and the dispersion degree of cement particles varies with the ultrasonic time;it is feasible to quantify the dispersion state of cement particles with the dispersion coefficient X.(2)Study on mechanical properties of cement-based materials under ultrasonic actionBy changing the ultrasonic parameters,water cement ratio,ultrasonic action mode,adding water reducer and other factors,the influence of ultrasonic action on the compressive strength of mortar specimens was measured,and the mechanism of paste performance change was studied by means of hydration heat test,XRD and SEM.The results showed that the ultrasonic power has little effect on the compressive strength of the paste,and the ultrasonic time has great effect on the strength of the paste.Short time of ultrasonic(30s)is not conducive to the establishment of hardened paste strength,but increasing water cement ratio and adding superplasticizer can weaken this effect.When the paste was treated by direct ultrasound,indirect ultrasound and intermittent ultrasound,the hardened paste strength was improved,and the effect of direct ultrasound was the best.Under reasonable ultrasonic parameters,the particles in the paste are dispersed evenly,the hydration rate is accelerated at the early stage,the CS-H gel distribution is uniform,and the pore structure is optimized.(3)Study on rheological properties of fresh paste under ultrasonic actionBy changing the ultrasonic power and action time,the fluidity,bleeding rate and rheological parameters such as shear stress,apparent viscosity,yield stress and plastic viscosity of paste under different ultrasonic parameters were measured,and the action mechanism of particle dispersion under ultrasonic action was studied.The results show that the fluidity and bleeding rate of paste are greatly affected by ultrasound.With the increase of ultrasonic power and action time,the fluidity and bleeding rate of paste first increased and then decreased,and there was a positive correlation between fluidity and bleeding rate.When the ultrasonic time is longer,the paste is heated seriously,the fluidity is decreased greatly,and the bleeding performance is improved.The rheological curve of the paste under the action of ultrasound accords with Bingham model.Under the action of ultrasonic,the yield stress of the paste changes little,and the plastic viscosity decreases significantly.Under small parameters,the rheological properties of paste are improved by reducing the plastic viscosity;under large parameters,the increase of yield stress is the main reason for the change of working properties.the dispersion of particles in paste is time-dependent by ultrasound.(4)Effect of ultrasonic and superplasticizer on rheological properties of fresh cement pasteBy changing the ultrasonic time,the rheological properties of the paste with superplasticizer were studied.The results show that the ultrasonic action time has a great influence on the dispersion effect of superplasticizer.The addition of superplasticizer greatly increases the fluidity and bleeding rate of the paste,while the fluidity and bleeding rate of the paste decrease with the increase of ultrasonic time.Through the change of rheological properties,it can be found that the failure of superplasticizer under ultrasonic action is mainly caused by the increase of yield stress of paste.After that,the yield stress and plastic viscosity of the paste decrease greatly with the addition of superplasticizer,which is more conducive to the dispersion of cement particles in the paste.There are 35 figures,20 tables and 83 references in the thesis.