Experimental Study On The Mechanical Properties Of Ductile Hybrid Fiber Magnesium-phosphate-cement-based Composite

Magnesium phosphate cement(MPC)is a new type of binde,which has the advantages of fast setting,high early strength,strong temperature adaptability and good volume stability.However,like ordinary Portland cement,MPC is a highly brittle material.MPC is susceptible to cracks and fractures when subjected to external force.The mechanical properties of MPC can be improved by adding fibers to MPC to form a ductile cement-based composite.At present,research on fiber-reinforced MPC is mainly focused on single fiber.Single fiber often improves the performance of one aspect of MPC.In order to break through the limitations of single-fiber reinforced MPC,this paper studies the effect of hybrid-fibers on the mechanical properties of MPC.In this paper,three kinds of fibers are selected: polyvinyl alcohol(PVA)fiber,micro steel(MS)fiber and polypropylene(PP)fiber.Among them,two kinds of fiber are mixed into MPC in each test to study the effects of types of hybrid fibers,mixing methods and mixing amounts on the mechanical properties of MPC.The main conclusions obtained are as follows:(1)PVA-MS hybrid with a total volume fraction of 1.6%: MS mainly enhances the cracking strength and bending strength of the composite;PVA fiber mainly improves the deformability and toughness of the composite.When the MPC-based composite with hybrid fiber of 1.2% PVA + 0.4% MS,the PVA fiber cooperates with the steel fiber to better play the bridging effect,which makes the specimen not only have higher strength,but also has better ductility and toughness;(2)PP-MS hybrid with a total volume fraction of 1.6%: PP fiber has a weaker strengthening and toughening effect on magnesium phosphate cement.MS fiber plays a major role in improving the mechanical properties of magnesium phosphate cement.The strength of MPC-based composite materials is improved,but the bending performance is generally poor.When the MPC-based composite with hybrid fiber of 0.8%PP+0.8%MS,PP fiber and MS fiber show weak synergy,and MPC-based composites show deflection hardening characteristics.(3)PVA-PP hybrid with a total volume fraction of 1.6%: There is no synergy between PVA fiber and PP fiber.PVA fibers play a major role in strengthening and toughening for MPC-based composite.When the MPC-based composite with fiber of 1.6% PVA,specimen have the best ductility and toughness.(4)PP-MS hybrid with PP fiber volume fraction of 1.6%: The synergy between PP fiber and MS fiber is poor due to the hydrophobicity of PP fiber.With the increase of MS fiber content,the strength of MPC-based composites increases slightly,but the bending performance is still weak.(5)PVA-MS fiber hybrid with PVA fiber volume fraction of 1.6%: A large number of PVA fibers can well bear the stress during the development of micro-cracks,and improve the ductility and toughness of MPC;a small amount of MS fibers can effectively enhance the strength of magnesium phosphate cement;with the increase of the amount of MS fiber,the ductility of the MPC-based composites is slightly reduced,but the strength and toughness are further improved,and the synergy between PVA fibers and MS fiber is excellent.When the MPC-based composite with hybrid fiber of 1.6%PVA+0.6%MS,specimen not only have higher compressive strength and flexural strength,but also have excellent ductility and toughness.