Study On The Power Characteristics Of Vibration And Multi-Step Mixing Concrete And Its Change Rules

Mixing influences the formation process of concrete structure and determines the properties of fresh and hardened concrete.But the dynamic complexity of the concrete mixing process makes it difficult to accurately describe the changes in mixture state and forces.The mixing power-time curve can reflect the interaction process and mechanism between the mixing device and the mixture during the mixing process.And its variation is not only related to the concrete material,but also to the mixing device and the mixing approach.It is a new technique to identify the concrete state and mixing process quantitatively that study the power-time relationship during the mixing process,and further study the relationship between the resistance and mixing time,and the meso-structural state of the mixture and the mixing time.Therefore,the research on the power characteristics of vibration and multi-step concrete mixing and its change rules is of theoretical and practical value to improve the mixing quality and efficiency of concrete,improve the reliability of mixer power and transmission system and reduce the installed power.This paper uses the power-time curve method to study the influence of vibration parameters and multi-step mixing approaches on the power characteristics during the mixing process and change rules.Systematically analyze the meso-structural state and interaction force of the mixture in the process by establishing the mathematical relationship between mixing power and resistance coefficient and combining with the influence of solid-liquid ratio on power consumption in the wet granulation process.The change process of mixing resistance is revealed and the measures to improve the mixing process are proposed.The quantitative indexes of mixing process are proposed by analyzing the change law of mixing power and the meso-structural state of the mixture,which are the power at the cohesion point and flow point,the arrival time and the mixing energy during the process.By studying the effects of ordinary mixing and vibratory mixing on the meso-structure state of the mixture during the mixing process of concrete with different proportions,it is proposed that the meso-structure change during the mixing process can be divided into four stages: aggregate coating,wetting granular,particle suspension formation,and agglomerate destruction stage,the corresponding mesoscopic state of the mixture is dry particles,wet particles,"raspberry-like",particle suspension,and part of cement aggregates.Vibratory mixing can reduce the mixing resistance caused by the internal friction,cohesion and viscous force of the mixture,reduce the power consumption of the cohesion point and the fluidity point,advance the arrival time,and reduce the mixing energy during the mixing.According to the analysis of the power-time curve in the multi--step mixing process,five kinds of multi-step mixing processes are determined based on the mesoscopic structure of the mixture,which are mainly divided into two categories: coating process and pre-mixing process.The mixing stage of the multi-step mixing process is mainly divided into 3-5 stages.The sequence and the position of the feature points are used to divide the mixing stage.The combination of vibratory mixing and multi-step mixing process can further reduce the power and arrival time of feature point,and mixing energy during process.The fresh properties and hardened properties of concrete were studied,the calculation method of the rheological parameters of fresh concrete was determined,and the effects of vibratory mixing and vibratory multi-step mixing technology on the properties of concrete were analyzed.Vibratory mixing increased the slump of fresh concrete by 13 mm to 48.5 mm,and the higher the cement content,the greater the vibration acceleration was needed to destroy the cement flocs to release the liquid and increase the slump.At the same time,vibratory mixing reduced the rheological parameters values of fresh concrete and improved the fluidity of concrete.The multi-step mixing process has different effects on the rheological parameters.The multi-step mixing process combined with vibration can further reduce the rheological parameters values both by dispersing the cement particles and by strengthening the adhesion between the cement particles and the aggregates to reduce concrete segregation.Vibratory mixing can increase the compressive strength and improve the homogeneity of concrete with different mix proportions,and the reasonable vibration parameters vary depending on the ratio.The multi-step mixing process combined with vibration has a better effect on the improvement of compressive strength and uniformity of concrete at a vibration acceleration of 8g.The load of the mixing power and transmission system is studied from the perspective of machine reliability.The power curve is converted into a torque load time course.And more reliable load data is obtained after preprocessing the mixing resistance load data.Then the rainflow counting method is used to count the cyclic frequency of the load mean-amplitude value.The load mean-frequency and amplitude-frequency are fitted to obtain the probability density distribution function.The mean value conforms to the Gaussian normal distribution and the amplitude value conforms to the Weibull distribution.The measures to reduce the load of power and transmission system in the mixing process are proposed.Vibratory mixing can reduce the load caused by cohesive force and viscous resistance;vibration and multi-step mixing approach can reduce the peak load and make the peak resistance distribution more dispersed.Combined with the influence of vibratory mixing and vibratory multi-step mixing process on the power consumption,the performance of fresh concrete and hardened concrete,and the load amplitude and mean value,the reasonable vibration parameters and mixing approach of concrete are determined,which can decrease the power consumption and the load of transmission system,improve the fluidity,compressive strength and uniformity.For the mixture of M1 and M2 ratio,the amplitude of 0.82 mm and the vibration acceleration of 2g are suggested;for M3,the amplitude of 0.82 mm and the vibration acceleration of 4g are suggested;for the M4 ratio,the amplitude of 1.36 mm and the vibration acceleration of 8g are suggested.For the same proportion of concrete,the aggregate enveloped cement approach(AECA)under the vibration acceleration of 8g is suggested.