Study On Durability Of MOS Mortar

MOS（Magnesium Oxysulfate,Magnesium oxysulfide）cement is a green cementitious material composed of a mixture of lightly burned magnesium oxide and a certain concentration of magnesium sulfate solution.It has excellent properties such as lightweight,wear resistance,high temperature resistance,and green environmental protection.It can be used as a building material.Cement mortar is a building slurry composed of cementitious materials and fine aggregates,which is widely used in construction.This article studies the changes in basic performance and durability of MOS cement mortar from two aspects:molar ratio and fineness modulus,providing a theoretical basis for the application of MOS cement mortar in construction.Determine its basic properties by testing slump,impermeability,bulk density,water absorption,moisture content,and mechanical properties.Analyze the phase composition,microstructure,and pore size distribution of MOS cement mortar using detection equipment such as XRD and SEM.The water resistance,weather resistance,and frost resistance were tested by soaking in distilled water,wet heat cycling,and freeze-thaw cycling.The test results showed that:（1）Among the samples with MgO:MgSO₄:H₂O molar ratios of 8:1:20,9:1:20,and 10:1:20,MOS cement mortar with molar ratios of 9:1:20 has the best physical properties.After 28 days of curing,its compressive strength can reach 100.1 MPa and flexural strength can reach 8.55 MPa.At the same time,it performs well in terms of impermeability,bulk density,water absorption,and moisture content.（2）The molar ratio of 9:1:20 performs better in water resistance,weather resistance,and frost resistance.After soaking in water for 28 days,its compressive strength reached as high as 50 MPa,flexural strength reached as high as 4.8 MPa,and the total porosity and ITZ porosity were only 7.22%and 15.48%,respectively.After 30cycles of humid heat,its compressive strength reaches 33.7 MPa,flexural strength reaches 4.8 MPa,and strength loss rate is only 66.33%.After 30 freeze-thaw cycles,its compressive strength reaches up to 57.7 MPa,with a strength loss rate of only 42.36%and a flexural strength of up to 5.1 MPa.（3）When the molar ratio is 9:1:20 and the ratio of medium sand to fine sand is 7:3,the physical properties of MOS cement mortar are the best among samples with different fineness modulus.After 28 days of curing,its compressive strength can reach110.1 MPa and flexural strength can reach 9.27 MPa.It performs well in terms of impermeability,bulk density,water absorption,and moisture content.（4）When the ratio of medium sand to fine sand is 7:3,MOS cement mortar exhibits good water resistance,weather resistance,and frost resistance.The MOS cement mortar with this ratio has a compressive strength of 65.34 MPa,a softening coefficient of 0.59,a strength loss rate of 40.7%,and a flexural strength of 6.22 MPa after soaking for 28days.After 30 cycles of humid heat,its compressive strength reaches 44.7 MPa,softening coefficient is 0.4,strength loss rate is 59.4%,and flexural strength is 5.71MPa;After 30 freeze-thaw cycles,the compressive strength and flexural strength were71.6 MPa and 5.99 MPa,respectively,with a strength loss rate of 34.9%.