Research On Properties Of Coconut Fiber Magnesium Phosphate Cement Based On Low Temperature Environment

Magnesium Phosphate Cement（MPC）is a new type of special construction cementing material that can be set and hardened rapidly through acid-base reaction,with the advantages of high early strength,excellent bond strength,good durability and strength can still develop in low temperature environment,etc.It has a wide range of applications in the field of road and bridge and airport road crack repair and biological materials.applications.However,MPC itself has the problems of high brittleness,insufficient toughness and low tensile strength,which limit the scope of MPC application in construction engineering.The research group found that a renewable and green natural coconut fiber（Cocoanut Fiber,CF for short）is mixed into magnesium phosphate cement in appropriate amount to form Cocoanut Fiber reinforce Magnesium Phosphate Cement（CF-MPC）fiber cement matrix,which can effectively improve its easy application.The composite material can effectively improve its shortcomings of easy cracking and low toughness.However,there are few experimental studies on the performance of CF-MPC under low-temperature curing conditions,which can provide the experimental basis and theoretical basis for the practical engineering application of CF-MPC in cold regions.In this paper,the interfacial bonding performance,static compression performance and bending performance of CF-MPC under different low-temperature curing temperatures are mainly studied,and the change law of CF-MPC performance under different curing temperatures is explored by combining with micro-level testing methods.The main research contents are as follows:（1）The effects of different low-temperature treatment temperatures on the mechanical properties of CF were investigated by fiber axial tensile tests.It was found that the tensile strength and elongation at break of CF decreased with the decrease of fiber treatment temperature,and when the fiber treatment temperature was-20℃,the tensile strength and elongation at break of CF decrease by 39.31%and 64.01%.It was found that there was no significant change in the content of cellulose,lignin and hemicellulose,but the low-temperature treatment increased the moisture content of fibers after restoration to room temperature;in addition,as the temperature decreased,the water inside the fibers froze and compressed the surface and internal structure of fibers,resulting in a significant decrease in fiber strength.（2）The effect of different fiber embedding depths on the bonding performance of CF-MPC interface under different curing temperatures was studied by fiber monofilament pulling tests.It was found that when the maintenance temperature was 25℃and 0℃,the damage of CF-MPC fiber monofilament pulling test was fiber pull-out damage,at which time the CF-MPC interfacial bond bearing capacity and interfacial damage energy increased with the increase of CF embedding depth;when the temperature decreased to-10℃and-20℃,the damage mode changed to fiber fracture damage,at which time the CF-MPC interfacial bond bearing capacity and interfacial damage The energy of the CF-MPC interface bonding load capacity and interface damage is showing a trend of increasing first and then decreasing.（3）The effect of low temperature on the performance of CF-MPC was explained by microscopic tests.The piezometer analysis shows that the lower the curing temperature the more porosity increases,and the pores larger than 10 nm increase significantly.By XRD analysis of MPC hydration products found that the curing temperature decreases,MPC main hydration product Mg KPO₄·6H₂O decreases,unreacted Mg O increases,and the degree of hydration decreases with the decrease of temperature.By SEM observation of specimens,it is found that as the curing temperature decreases,the pores and microcracks increased and the MPC structure became more sparsely.（4）The effects of different CF volume doping on the static compression properties and bending mechanical properties of CF-MPC under different low temperature maintenance were investigated by static compression test and three-point bending test of CF-MPC,respectively.It was shown that the appropriate amount of CF doping could improve the plastic deformation capacity of CF-MPC;and the compressive strength and flexural strength of CF-MPC decreased to different degrees with the decrease of the curing temperature,among which the decrease was the largest when the curing temperature was-20℃compared with 25℃;when the curing temperature is-10℃and-20℃,the flexural strength decreases with the increase of the volume dose of CF.