Study On The Performance Of Slag Powder Concrete With Large Dosage

In this paper,the mechanical properties of concrete prepared with a large proportion of slag fine powder to replace P·O 42.5 cement are studied.Based on the results of mechanical tests,a fixed amount of 70% slag fine powder is selected.Several kinds of activators are used for single and multiple admixtures.,Select the ones with better excitation effect and determine the optimal amount,and then remix the concrete with the selected activator for durability test.Test results show that,with the increase of the content of slag powder,the strength of concrete shows a nonlinear decreasing trend,and the influence on the split tensile strength lags behind the compressive strength;The activator Na₂SO₄ and Ca（OH）₂ can promote the growth of concrete strength in the later period,and the addition of Na OH causes the strength of concrete to collapse,Mixed with Na₂SO₄ + Ca（OH）₂ is most beneficial to increase the concrete strength;Compared with ordinary silicate concrete,The impermeability of the concrete with a large amount of slag powder has been improved by one grade,the resistance to sulfate corrosion has been enhanced,but the resistance to freezing has not been improved;The activator Na₂SO₄ can degrade the impermeability,frost resistance and sul AFte resistance of concrete.Adding Ca（OH）₂ alone and Na₂SO₄+Ca（OH）₂ together improved the impermeability and frost resistance of concrete,but not the sul AFte resistance.When mixed with Na₂SO₄+Ca（OH）₂+Na OH,the later strength development of concrete was inhibited by the ‘concentration effect’ of OH-,which made the strength and durability of concrete lower than other groups.It was found by the microscopic test and analysis（XRD,SEM）of the slag-cement composite cementing material and its preparation of concrete and P·O 42.5 grade cement paste and its preparation of concrete,because of secondary hydration of slag powder,increased the amount of C-S-H gel,and AFt crystals appear embedded in the gel,the pore size is smaller,the pore structure is improved,the cement becomes denser,the gap between aggregate and slurry is reduced and the bond is closer,The addition of Na₂SO₄ + Ca（OH）₂ effectively stimulated the slag fine powder activity and promoted the production of AFt.