Experimental Study On Compression,bending Properties,and Microscope Mechanism Analysis Of Coir-MPC

Magnesium phosphate cement(MPC)is a new type of inorganic cementitious material,which has the advantages of short setting time,high early strength,high volume stability and good wear resistance.It is commonly used in road,bridge,airport runway,military engineering reinforcement and rapid repair.However,like ordinary portland cement,MPC has the problems of poor toughness and easy cracking,which limits its application.Coir fiber is a kind of renewable green plant fiber,which has the characteristics of environmental protection,low price and good mechanical properties.In view of this,this paper will use Coir fiber to improve the above problems.And through the combination of macro test and micro test,this paper will study the influence of coir fiber on the static compression performance,bending performance and micro structure of MPC to provide the basis for further study on the durability and engineering application of Coir-MPC.The main research contents are as follows:First,the effects of treatment methods on chemical composition and surface morphology of coir fiber are studied.The results show that boiling treatment can increase the content of cellulose in coir fiber,increase the crystallinity of cellulose,and easily form a large number of hydrogen bonds;at the same time,it can improve the surface cleanliness of coir fiber,and form the surface morphology with high roughness,which is helpful to enhance the interface bonding between coconut fiber and MPC,and play the role of coconut fiber bridging.Second,through static compression test,the effects of different volume and length of coir fiber on MPC failure mode,compressive strength,stress-strain curve,secant modulus and plasticity are studied.The results show that the MPC matrix changes from brittle failure mode to plastic failure mode with the incorporation of coir fiber.With the increase of volume and length of coir fiber,the compressive strength of MPC decreases slowly,but the influence is weak.At the same time,the rising section of stress-strain curve is gentle,secant modulus is gradually smaller,and the falling section is also gentle and plastic strengthens.Third,through three-point bending test,the effects of different volume and length of coir fiber on MPC failure mode,flexural strength,load-displacement curve,secant stiffness,toughness and plasticity are studied.The results show that the MPC matrix changes from brittle failure mode to low toughness and high toughness failure mode with the incorporation of coir fiber.The influence of coir fiber on the flexural strength of MPC is significant,which shows that with the increase of the volume and length of coir fiber,the overall flexural strength of MPC increases first and then decreases,reaching the maximum flexural strength when the volume and length of coir fiber are respectively 3% and 20 mm At the same time,the approximate linear elastic section of the load-displacement curve gradually flattens,secant stiffness decreases slowly,the descending section also tends to flatten,and the toughness and plasticity gradually increase.Finally,the effects of coir fiber on the hydration composition and microstructure of MPC are studied by means of XRD and SEM.The results show that coir fiber hinders the hydration process of MPC,the content of MPC hydrate decreases slowly,and then the density of MPC decreases slowly.