Study On Physical And Mechanical Properties Of Straw-magnesium Oxychloride Cement Composites

Straw-magnesium oxychloride cement composite material is mainly made of magnesium oxychloride cement as cementing material,straw pretreated as filling material,and admixture and admixture with appropriate proportion.This kind of composite material has the advantages of wide source of raw materials,economic and environmental protection of products,light weight and high strength,thermal insulation and so on.The material can make full use of agricultural waste straw,suitable for high strength requirements of thermal insulation building materials.However,the water resistance of straw-magnesium oxychloride cement composite is poor,and the strength of the interface between straw and cement is low,which affects its popularization and application to some extent.In view of the above problems,this paper firstly optimized the basic mix ratio of magnesium oxychloride cement and determined the appropriate ratio of magnesium oxychloride cement.Then,magnesium chloride cement was modified by phosphoric acid and polymer,and its modification mechanism was studied by means of XRD and SEM.Secondly,the effects of straw content and morphology on the properties of the modified straw-magnesium chloride cement composite were studied.Finally,based on the above research,straw pretreatment was adopted in different ways to improve the interfacial strength of straw magnesium oxychloride cement,and the influence of straw pretreatment on the properties of straw magnesium oxychloride cement composite was deeply discussed.The results show:When MgO:MgCl₂:H₂O mole ratio is equal to n:1（n-1）to n:1（n+1）,the mechanical properties and working properties of magnesium chloride cement meet the requirements,that is,the 3d flexural strength of magnesium chloride cement reaches 7.0MPa and the 3d compressive strength reaches 30MPa.Phosphoric acid,as the best modifier,can effectively improve the water resistance of magnesium oxychloride cement.When the content is 0.6%,the softening coefficient can reach 1.38.The effect of styrene-acrylic emulsion on improving the water resistance of magnesium oxychloride cement is not good.Urinary resin can effectively improve the water resistance of magnesium chloride cement,when the content of urinary resin is 25%,the softening coefficient is 1.12.When the dosage of straw quality than changes within the range of 0-2.50%,The compressive strength of the composite decreased with the increase of straw content,when 0.5% dosage of straw,28 d compressive strength is 52.6 MPa,when straw content increased to 2.5%,the 28d compressive strength is 46.8MPa,as the increase of mass ratio,dosage of straw stalks-magnesium oxychloride cement composite material mechanics performance degradation,further increase straw dosage can reduce the water resistance of the composite.The addition of powdery straw was beneficial to improve the compressive performance of the composite material.The addition of straw 3-5cm was beneficial to improve the flexural performance of the composite material.The 28d flexural strength was 16.2mpa,while the addition of straw.The functional group of the treated straw at 873.1276cm^-1 in the FTIR spectrum was aldehydes（CH）bending vibration generated by lignin hydrolysis,but there was no significant change in the composite material of MOC-straw.After soaking in 1% Ca（OH）₂ solution and curing in CO₂ for 8 hours,TG analysis showed that the total mass loss was the largest.The lost substances were water generated by 318 phase decomposition,water generated by Mg（OH）₂ decomposition,and CO₂ generated by MgCO₃ decomposition.At this point,the best water resistance of the composite was 1.21,which was 1.34 times higher than that without CO₂ curing.And after soaking by 1% Ca（OH）₂ solution by thermogravimetric analysis of CO₂ curing 12 hours minimum quality loss,the loss of the material is 318 phase decomposition of water,water decomposition of Mg（OH）₂,and MgCO₃ decomposition of CO₂,the compound material mechanics performance is the best,the compressive strength can reach 51.8 MPa,1.56 times that of without maintenance,the flexural strength is 1.07 times than that without maintenance.