Experimental Study On Mechanical Properties Of Steel Fiber And Nanoparticle Reinforced Magnesium Phosphate Cement Mortar

When repairing and strengthening highways,municipal roads,bridges,airport runways and industrial flooring,it is often necessary to complete them in a very short period of time in order to resume their use as soon as possible.In addition,if the repair and reinforcement work in the cold winter,this will requires the repair of reinforced materials with a strong temperature adaptability,and thus ensure that the repair and reinforcement effect at negative temperature.Magnesium phosphate cement has the advantages of fast and hard early strength,strong temperature adaptability,strong bonding and low dry shrinkage,and is an ideal material to solve the above problems.In this paper,the properties of magnesium phosphate cement matrix are enhanced and toughened by adding nanoparticles and steel fibers,and the effects of nano-particles and steel fibers on the working performance of slurry,the compressive strength and the flexural toughness are studied.In addition,the modification mechanism of nano-particles to magnesium phosphate cement and the enhanced toughening mechanism of steel fibers on the substrate were revealed by using SEM and XRD for microscopic phase test.The main research contents and conclusions are as follows:（1）The effects of nanoparticles（nano-Al₂O₃,nano-Fe₂O₃ and nano-SiO₂）,fly ash,water glass,silica ash and SAC on the condensation time of magnesium phosphate cement,the flow degree of cement slurry,the flow degree and the compressive strength of cement mortar were studied.it is found that silica ash and SAC will greatly reduce the working performance of mortar;nano-SiO₂,fly ash,water glass will slightly reduce the working performance of mortar;nano-Al₂O₃ and nano-Fe₂O₃ doesn’t reduce the working performance of mortar,suitable dosage can improve the compressive strength of the cement.At the same time,the optimum dosage of nano-Al₂O₃ and nano-Fe₂O₃was 4%and 2%,respectively.The microscopic phase test of nano-granular magnesium phosphate cement was carried out to reveal the mechanism of nanoparticle modification by SEM and XRD.It was found that the addition of nano-SiO₂ into the reaction system would lead to defects in the internal microstructure,while the content of phosphate would be reduced,while nano-Al₂O₃ and nano-Fe₂O₃ would effectively fill the internal pores,and the formation of aluminate and other substances,so as to improve the compressive/splitting strength of magnesium phosphate cement mortar.（2）The effects of nanoparticles（nano-Al₂O₃ and nano-Fe₂O₃）and steel fibers on the working performance and compressive/splitting strength of magnesium phosphate cement mortar were studied.The results showed that the changing the fiber type doesn’t make a difference to the working performance,and the mechanical strength of steel fiber magnesium phosphate cement mortar was better when mixed with short steel fiber.With the increase of fiber content,the working performance decreases gradually,but the mechanical strength will gradually increase,and the mechanical strength remains stable when the fiber content exceeds 1.5%.The addition of nanoparticles will improve the working performance and mechanical strength of cement mortar,but when the substitution of nano-Al₂O₃ and nano-Fe₂O₃ is more than4%and 2%respectively,the mechanical strength no longer increase.At the same time,the combination of nano-Fe₂O₃ and steel fiber can effectively improve the working performance of cement mortar,and the combination of nano-Al₂O₃ and steel fiber will obviously improve the mechanical strength of cement mortar.（3）The effects of nanoparticles（nano-Al₂O₃ and nano-Fe₂O₃）and steel fibers on flexural toughness of magnesium phosphate cement mortar were studied.The results show that short steel fiber will obviously improve the flexural toughness of on cement mortar,and the imitation steel fiber can ensure that the cement mortar has better capacity of deformation after exceeding 2mm.The peak load of load-deflection curve increases gradually with the increase of fiber content,and the flexural toughness Index and equivalent bending toughness ratio increase gradually;however,when the fiber dosage exceeds 1.5%,the peak load and flexural toughness index remain stable.and when the substitution of nano-Al₂O₃ and nano-Fe₂O₃ is 4%and 2%respectively,the load-deflection curve is fuller,and the Flexural toughness Index and equivalent bending toughness ratio are also better.In addition,the enhancement of nano-Al₂O₃ to the flexural toughness on cement mortar is more obvious.