Effect Of Fiber Dispersion Method On Mechanical Properties Of Magnesium Phosphate Cement

Magnesium phosphate cement(MPC)is mainly used in structural repair,road emergency repair and construction,and solidification of nuclear waste due to its advantages of early high-strength,fast hardening,good volume stability and high bonding strength.However,MPC has obvious brittleness,which limits its application in structural reinforcement and repair.In this paper,according to the toughness strengthening theory,the fibers were added to improve the toughness of MPC.And the effect of mineral admixtures and dispersant dispersion methods on the mechanical properties of FRMPC was studied.The influence of fiber dispersion on the mechanical properties of FRMPC was studied,and the influence of dispersion methods on the dispersion of synthetic fibers and steel fibers was analyzed.The digital microscopic and scanning electron microscopic images of FRMPC specimens were collected,and the distribution coefficient and orientation coefficient of fibers were calculated by image processing method.The variation law of fiber dispersion in FRMPC was quantitatively analyzed,and the empirical equation of fiber dispersion coefficient and flexural strength enhancement ratio was established.The main research results are as follows:(1)Mineral admixture dispersion method can effectively improve the mechanical properties of FRMPC by reducing the viscosity of cement matrix and improving the fiber dispersion,metakaolin(MK)dispersion can significantly enhance the early strength,when MK is 20%,the compressive strength of SF reinforced MPC cement can reach 45 MPa and the flexural strength is 7.5 MPa;fly ash(FA)and FA-MK dispersion can greatly enhance the later strength;when FA is 20%,the compressive strength of PVA-reinforced MPC is 93 MPa and the flexural strength is 17 MPa;the replacement rate of mineral admixture should not be too large,FA should be controlled within 20%,MK is 10%.(2)Dispersant dispersion method can improve the dispersibility of fibers by wetting the fibers,but it has little effect on the compressive strength of FRMPC,and slightly improves the flexural strength of FRMPC.Among this,EG 360 dispersion has better effect on PE fiber reinforced MPC than ASM dispersion on PVA fiber reinforced MPC,when the content of EG 360 is 1%,the 28 day flexural strength of PE reinforced MPC is 14.5 MPa,the increase is 50%;the dosage of dispersant should not be too large,and both should be controlled within 1.5%.(3)The dispersion of FRMPC was effectively improved by dispersing methods,in which mineral admixtures significantly increased the dispersion of steel fibers,and dispersants further improved the distribution of synthetic fibers;FA significantly increased the dispersion of fibers at the same substitution rate of mineral admixtures;EG 360 significantly increased the dispersion of PE fiber at the same dosage of dispersants.(4)Image processing analysis shows that increasing fiber dispersion can improve the mechanical properties of FRMPC,and the increase of flexural strength is more significant,when FA was 20%,the SF dispersion increased by 18%,the flexural strength of hardened body increased by 30%,and the 28-day strength increased by 21.3 MPa.the ratio of fiber dispersion to the increase of flexural strength of FRMPC is linear,and the increase of fiber dispersion has a limit on the increase of flexural strength.