Study On High Temperature Resistance Of Coconut Fiber Magnesium Phosphate Cement

Magnesium potassium phosphate cement(MPC)is a kind of early strength and quick setting cementing material with the advantages of high early strength,fast setting and hardening,small drying shrinkage deformation,strong bonding ability and good high temperature resistance,which can be used for quick repair of viaducts,airport runways and municipal main roads.However,MPC has the disadvantages of insufficient toughness and poor crack resistance,which seriously limits the application of MPC in practical repair engineering.Through the preliminary study of our team,we found that adding proper amount of green natural fiber--coconut fiber(CF)into MPC can greatly improve the toughness of magnesium phosphate cement.In order to adapt to the performance evaluation of MPC in high temperature environment such as airport runway and nuclear waste treatment and after engineering fire,this paper investigated the effects of temperature on static compressive properties,bending properties and interfacial bonding properties of Cocoanut Fiber reinforce Magnesium Phosphate Cement(CF-MPC).The morphology,composition and thermal stability of CF-MPC were studied by scanning electron microscopy,X-ray diffraction and thermogravimetric differential scanning thermal analysis.The main research contents are as follows:(1)The effects of temperature on mechanical properties of CF were studied by axial drawing test.The results show that the tensile strength and elongation at break of CF decrease with the increase of temperature.When the temperature rises to 400℃,CF is completely carbonized and loses its basic mechanical properties.When the temperature rises to 600℃,CF is completely thermally decomposed into gaseous products.In addition,the changes of chemical composition and microstructure of CF at different temperatures were analyzed by microscopic testing.It was found that at20-200℃,the main structure of CF did not change significantly,but the surface roughness increased.The water content of CF decreased from 7.12% to 0,while the content of cellulose,hemicellulose,lignin and other main structural components of CF did not change significantly.(2)The effect of temperature on the interfacial bonding properties of CF-MPC buried at different depths was studied by fiber pull-out test.It is found that temperature has a great influence on the interface bond performance of CF-MPC,and the decrease is most significant in the temperature range of 200-400℃.At 20℃,the failure mode of each buried depth is pult-out failure.The interface bond bearing capacity and interface failure energy increase with the increase of buried depth,and reach the maximum when buried depth is 15 mm.When the temperature was 100℃and 200℃,the specimens with different buried depths were all broken by pulling out.The interface bond bearing capacity increased with the increase of buried depth,and reached the maximum value when buried depth was 15 mm,while the interface failure energy increased first and then decreased with the increase of buried depth,and reached the maximum value when buried depth was 12.5mm.(3)The static compression and bending mechanical properties of MPC with different CF content were investigated by static compression test and three-point bending test.The results show that in the temperature range of 20-200℃,the incorporation of CF can significantly improve the anti-deformation ability and anti-bending strength of MPC,and the anti-deformation ability becomes stronger with the increase of CF content,but the enhancement effect of CF on the anti-deformation ability of MPC decreases with the increase of temperature.At 20℃ to 200℃,the bending strength of MPC increases first and then decreases with the increase of CF content.The bending strength is the maximum when CF content is 3% at 20-100℃,and the maximum when CF content is 2% at 200℃.When the temperature was higher than 400℃,the failure mode of the specimen was brittle failure.The compressive strength and flexural strength of CF-MPC continued to decrease with the increase of temperature,and the decrease was most significant in the temperature range of100-200℃,mainly because the main hydration product of MPC,Potassium magnesium phosphate hexahydrate(Mg KPO4·6H2O,MKP for short)continued dehydration reaction at 100-200℃,but with the temperature continued to rise,the reduction of CF-MPC strength was basically unchanged.