Research On The Influence Of Mineral Admixture On The Performance Of Manufactured Sand Self-Compacting Concrete

Self-compacting concrete is widely used in engineering practice.But its cement consumption is relatively large.The cost is relatively high.Its strength and durability have certain defects.In view of the above problems,this study selects slag,fly ash and limestone powder as the mineral admixtures of self-compacting concrete,and manufactured sand is the fine aggregate to prepare a self-compacting concrete with excellent strength and durability,and can effectively reduce the cost.By studying the influence of mineral admixtures on the workability,mechanical properties,freeze-thaw resistance and sulfate corrosion resistance of manufactured sand self-compacting concrete under different mineral admixtures and admixing methods.Using hydration heat test and AC impedance test and SEM experiment to explore the influence of mineral admixtures on the hydration degree and micro morphology of manufactured sand self-compacting concrete,laying a foundation for the application and promotion of manufactured sand self-compacting concrete.The main contents and conclusions are as follows:(1)The mineral admixtures were used to replace cement alone with a mixing amount of 10% to 40% for the workability test.The results show that when the slag content is 20%,the fly ash content is 30%,and the limestone powder content is 20%,the self-compacting concrete has the best workability.(2)The mineral admixtures were partially replaced with cement in the form of compound admixture and single admixture to carry out workability test comparisons.The study found that the slag-limestone powder mixed with 20%-10%,fly ash 30%,and limestone powder-fly ash mixed with 20%-20% have the best working performance.(3)Slag,fly ash and limestone powder reduces the early strength of self-compacting concrete,and compounding can alleviate the decrease in early strength.Mineral admixtures increase the mid-and late-stage strength of self-compacting concrete,and the amount of fly ash has the greatest impact on the mid-and late-stage strength of self-compacting concrete.(4)This study choose a mix ratio with excellent workability and strength for freeze-thaw cycle and sulfate corrosion resistance tests.The test results show that slag and fly ash improve the freeze-thaw resistance and sulfate corrosion resistance of self-compacting concrete,limestone powder is the opposite.The freeze-thaw resistance and sulfuric acid corrosion resistance are the best when the slag-fly ash is mixed with 20%-20% respectively.(5)The research results of the effect of different mineral admixtures on the heat of hydration of cement show that slag has little effect on the total heat and rate of cement hydration.The heat of hydration is basically released within the first 50 hours,and then it enters a stable period.(6)The AC impedance test results show that the AC impedance curve of each group of specimens is non-Randles shape at the initial stage of hydration,and the hydration reaction is mainly affected by ion diffusion.As the age increases,the AC impedance curve gradually shifts to the right.The chemical reaction is gradually controlled by the reaction kinetics.(7)The SEM test results of self-compacting concrete specimens with different mineral admixtures show that with the increase of age,the hydration degree of slag and fly ash deepens,the pore diameter of each group of specimens gradually decreases.The internal density of self-compacting concrete improve the strength and durability in the later stage.Limestone powder mainly plays a filling role.Its hydration degree is very low.