Study On Water Resistance Of Coir Fiber Magnesium Phosphate Cement

Magnesium phosphate cement(MPC)is a new construction material with short setting time,high strength,dry reduction and good wear resistance,which has good application prospect in refractory materials,dental field,civil construction and military construction.However,MPC has poor toughness and low tensile strength,which leads to its application being restricted.Our research group have mixed coir fiber(referred to as CF)in MPC to prepare coir fiber magnesium phosphate cement(referred to as CF-MPC),through the general mechanical properties of the test research found that the incorporation of CF can improve the toughness of MPC.However,there are few studies on the durability of CF-MPC,among which the water resistance is an important factor affecting the application of MPC.Therefore,the experimental study of water resistance of CF-MPC will provide a good theoretical and experimental basis for further application of CF-MPC in practical engineering in the future.The main research contents of this paper are as follows:(1)The mechanical properties of CF were studied by fiber tensile tests at different immersion times and when buried inside MPC.The results showed that the tensile strength and elongation at break of CF decreased with the increase of water immersion time.When CF is embedded in MPC and the specimen is cured in air and water,the performance of CF changes little;The change of interfacial bonding between CF and MPC at different curing ages was studied by fiber pulling test.The results showed that the interfacial bonding capacity and interfacial damage energy between CF and MPC increased with the increase of maintenance time of the specimens,and the interfacial bonding capacity and interfacial damage energy of the specimens naturally maintained in air were larger than those maintained in water.(2)The dissolution degree of CF-MPC in water under different maintenance times was studied by acid-base analysis and ion concentration measurement.The results showed that the p H value,magnesium ions and potassium ions of the specimen maintenance solution gradually increased with the increase of the maintenance time,and the dissolution degree of CF-MPC in water increased;The changes of hydration composition and microstructure of CF-MPC under different maintenance environments and different maintenance ages were investigated by XRD and SEM tests.The results showed that the hydration degree of CF-MPC naturally cured in air gradually increased with the increase of curing time,and the compactness of the specimens also gradually increased.The degree of hydration of CF-MPC curing in water is lower than that in natural curing,and the number of microcracks on the surface of the specimen gradually increases,with more pores,leading to the decrease of the strength of the specimen in water.(3)The changes of the compressive mechanical properties of CF-MPC under different curing ages and different CF admixtures were studied in air curing and water curing respectively by static compression test.The results show that the addition of CF improves the deformation resistance of MPC under compression.When the specimen is cured in air,the compressive strength of CF-MPC gradually decreases with the increase of Cf incorporation,and the compressive strength of CF-MPC increases with the increase of age.The compressive strength retention rate decreases with the increase of CF admixture and decreases with the increase of maintenance time.(4)The changes of the bending mechanical properties of CF-MPC under different curing ages and different CF admixtures were studied in air and water curing by three-point bending tests respectively.The results show that when the specimen is cured in air,the incorporation of CF increases the bending strength of MPC at first and then decreases.The bending strength reaches the maximum when the content of CF is 3%,and the bending strength of the specimen gradually increases with the increase of age.The retention rate of flexural strength showed a trend of increasing and then decreasing with the increase of CF dosing,and decreased with the increase of maintenance time.