Experimental Study On The Loss Of Fluidity Of Self-compacting Barite Radioprotective Concrete With Time

Self-compacting barite radioprotective concrete not only has good radiation protection properties,but also has high fluidity.It can flow densely in a complex and reinforced formwork without pounding,relying only on its own gravity,and has good prospects for application in radiation shielding projects such as medical facilities,nuclear power plants and defense construction.In the actual project,concrete is usually mixed centrally in the mixing plant and then transported to the construction site by the mixer truck,during which there is a time difference of 1 to 2 hours,and in the large volume radiation shielding project,the concrete usually cannot be poured immediately after entering the site and needs to wait,which will definitely cause the loss of concrete through time.If we can’t make accurate prediction on the time loss of Self-compacting barite radioprotective concrete,it will cause insufficient fluidity when concrete is poured,which will not be able to complete the pouring well and form holes inside the structure,reducing the strength and radiation shielding capacity of the structure and bringing safety hazards to the subsequent use.In this paper,the effect of superplasticizer dosage,fly ash dosage and water-cement ratio on the fluidity loss of self-compacting barite radioprotective concrete with time was investigated by single-factor test method.And the effect of fluidity losses on the compressive strength,apparent density and radiation shielding performance of self-consolidated barite concrete was also investigated.Moreover,the numerical simulation of the mix slump cylinder test was carried out by FLUENT numerical simulation software.The conclusions are as follows:（1）The initial fluidity of the concrete mix can be increased by increasing the superplasticizer dose,fly ash dose or water-cement ratio.To a certain extent,increasing the superplasticizer dose can slow down the time-loss of the concrete mix within 1 h,but the higher the superplasticizer dose the greater the fluidity losses of the concrete mix after 2 h of mixing;the occurrence of fluidity losses can effectively slow down by increasing the fly ash dose;increasing or increasing or decreasing the water to ash ratio will result in more severe fluidity losses in the concrete mix.In the single-factor analysis,the best performance was achieved with 1.1%superplasticizer,30%fly ash or 0.37 water-cement ratio.（2）Increasing the amount of superplasticizer or reducing the water-cement ratio can increase the compressive strength of concrete.With the increase fly ash admixture,the early compressive strength of concrete would be reduced,but the 28d compressive strength of concrete would be improved.Resting for 1h or 2h,before concrete mix pouring,the 28d compressive strength of concrete can be increased,i.e.the fluidity losses is conducive to the development of 28d compressive strength of self-compacting barite radioprotective concrete.（3）Formulation of self-compacting barite radioprotective concrete to over 3260kg/m³.The apparent density and radiation shielding properties of concrete can be improved by increasing the superplasticizer or water-cement ratio,while it can be reduced by increasing the admixture of fly ash,and it can also be reduced by standing after mixing.The radiation shielding performance of concrete is well correlated with the apparent density,the higher the apparent density the better the radiation shielding performance.（4）Using FLUENT numerical simulation software,self-compacting barite radioprotective concrete mix slump cylinder test which based on Bingham model was simulated.To contrast the simulating results with experimental ones,it was found that the flow patterns of the concrete mix were basically the same between the simulated values and the experimental values and the T₅₀₀ simulated values had the same trend as the experimental values,and the error was basically within 15%.And the simulated changes of yield stress and viscosity are in accordance with the general rule,which confirms that the numerical simulation is feasible for predicting the flow state and fluidity losses of the concrete mix.