Research On Performance Optimization Of Heavy-weight Concrete Based On Wet Packing Density Theory

Against the backdrop of the proposed goals of peak carbon emissions and carbon neutrality,clean,low-emission and efficient nuclear technology has undergone rapid development.However,the development of nuclear technology is accompanied by the occurrence of nuclear radiation leaks,which pose risks of cancer and genetic mutations to individuals who have been exposed to a certain dosage of nuclear radiation,and can also affect the health of several generations.In order to cope with the risk of nuclear leakage and protect the health safety of worldwide people,heavy-weight concrete is commonly used as shielding materials to filter the harmful radiation.Heavy-weight concrete refers to the concrete with unit weight≥2600 kg/m~3,which is produced using high-density(apparent density≥3.0 kg/m~3)aggregates.It is commonly adopted as the construction material in nuclear power stations and nuclear medicine facilities due to its superior radiation shielding performance.Iron sand(IS)and steel slag coarse aggregate(SSCA)are newly developed high-density aggregates which used as fine aggregate and coarse aggregate respectively in this study making high-radiation shielding performance heavy-weight concrete.However,the mechanical properties,especially segregation resistance of heavy-weight concrete reduced significantly and then prone to reduce the passing ability since the cement paste is not able to hold the high-density aggregates firmly lead to the low workability which restrict the application in construction.To solve this problem,cementitious fillers,such as silica fume(SF)and fly ash(FA)was adopted,which was well-known to be effective in increasing the flowability by improving the wet packing density(WPD)such that more excess water could be produced to lubricate the solid particles.Moreover,the fillers could enhance the segregation resistance by increasing the fine powders content to make the paste more viscous.Based on the research approach above,this paper is divided into two parts,with a total of103 specimens prepared to study the properties of heavy-weight concrete.The first part focuses on the performance optimization of normal heavy-weight concrete.75 specimens were designed using IS as the high-density aggregate,with the variables of IS substitution rate,SF substitution rate,FA substitution rate and dosage of superplasticizer(SP).The second part focuses on the performance optimization of ultra-heavy-weight concrete.Using IS and SSCA to completely replace natural aggregates,28 specimens were designed with the variables of SF substitution rate and dosage of SP.The 103 specimens were tested for flowability,segregation resistance,passing ability,compressive strength,apparent density and WPD.Results demonstrated that IS could effectively increase the flowability,compressive strength and apparent density,SSCA could increase the segregation resistance and apparent density,the addition of SF in heavy-weight concrete could increase the wet packing density(WPD),passing ability and compressive strength simultaneously whereas FA could only improve passing ability slightly.Finally,guided by the WPD theory,the optimal substitution rates of IS,SSCA,cementitious fillers,and dosage of SP were obtained through performance optimization tests on 103 groups of specimens.Based on this,the optimized mix proportion with the best overall performance was determined,and heavy-weight-concrete with high WPD,high workability,high strength,high apparent density and superior radiation shielding performance was ultimately prepared.