Long-term Autogenous Volume Deformation Of Externally Mixed MgO Concrete At Room Temperature

This paper studies the effects and mechanism of autogenous volume deformation of MgO concrete related to MgO content,water-cement ratio,fly ash and aggregate gradation in long age(five years)by micro and macro measures.The results show that:(1)No matter what aggregate gradation is,the autogenous volume deformation and its increasing width of MgO concrete increase with the increasing of MgO content.MgO has more obvioue effects on the autogenous volume deformation in short age than that in long age(2)No matter what aggregate gradation is,water-cement ratio has an obvious effect on the autogenous volume deformation of MgO concrete,which increases with the increasing of water-cement ratio.(3)No matter what aggregate gradation is,fly ash does not change the delay mcro-expansive of MgO concrete.The autogenous volume deformation of MgO concrete mixed with fly ash becomes large in short age,while small in long age.Fly ash has inhibition on the autogenous volume deformation of MgO concrete in long age.And the inhibition enhances with the extension of age and the increasing of fly ash.(4)Aggregate gradation has an obvious effect on the autogenous volume deformation of MgO concrete in long age.when the MgO content is 5% and 6%,the autogenous volume deformation of MgO concrete order is: one-grade MgO concrete > two-grade MgO concrete > three-grade MgO concrete.When the MgO content is 7%,the order is: one-grade MgO concrete > three-grade MgO concrete > two-grade MgO concrete.(5)MgO content and ages have an obvious effect on the microstructure MgO concrete.When the age is two and four years,the microstructure of MgO(5%,6%)concrete is dense,when mixed with 7% MgO,the microstructure of MgO concrete is from dense(two years)to loose(four years).(6)With the extension of age,fly ash makes the microstructure of MgO concrete more dense.Aggregate gradation does not change the microstructure of MgO concrete obviously,which shows dense.(7)With the extension of age,the porosity,average pore size and pore size distribution of concrete are related to MgO content,fly ash and aggregate gradation.