Physical And Mechanical Properties Of Straw Fibre Reinforced Basic Magnesium Sulfate Cement-based Material

The new energy saving lightweight cement-based composites has been prepared when straw fibers are used as reinforced materials and basic magnesium sulfate cement are used as matrix materials in this paper.The effect of straw pretreatment,molar ratio of cement,length of straw,dosage of straw and slag on physical and mechanical properties of straw fiber reinforced basic magnesium sulfate cement materials were studied.On this basis,according to the importance of the properties of the composite material,the important order of the influence degree of several factors on the properties of the composite material is distinguished,and the optimum mix ratio design of the composite material is determined by orthogonal test.The results show that the pretreatment of straw with NaOH solution can effectively extract the water-solubles present in straw fibers.After pretreatment,the shape of straw changed from hollow to flat,the surface of straw became rough,the retarding effect of basic magnesium sulfate cement decreased,the porosity of composites reduced,and the interface adhesion between matrix materials and straw fibers is enhanced.By analyzing the influence of raw materials component on physical and mechanical properties of composites,it can be found that composites has the highest toughness index and good bending strength when the molar ratio of cement is 8/1/20 and the length of straw fibers are 15 mm,but the other properties slightly lower.With the increase of straw content,the bending strength of the composites decreased gradually.The toughness index increased by 10%²0%when the content of straw fiber was 5%¹0%.Slag instead of light-burned magnesia powder makes the composites pores larger,the structural strength decreasing,the composites toughness decreased,but the frost resistance slightly improved when the amount of slag is15%.According to the results of orthogonal test,the optimal design of the composites was determined,which were after pretreatment of straw with 2%NaOH solution,the MgO/MgSO₄/H₂O molar ratio of cement is 8/1/20,the replacement of slag is 0%,the contents of straw are 10%,the length of straw is 15 mm.Based on the optimum design,the volume density of composites is 1.5 g/cm³,the water absorption is 8.47%,the bending strength is 21.28 Mpa,and the toughness index is 9.64,after 25 times freeze-thaw cycling under-20?,the surface of composites was intact and the strength was retained at about 85%.It is now clear that the feasibility and practical value of using abandoned resources of straw to enhance basic magnesium sulfate cement-based material as light-weight composites were demonstrated.