| High ductility magnesium phosphate cement-based composites(HDMPCC)are a kind of magnesium phosphate cement(MPC)matrix composites reinforced by polyvinyl alcohol(PVA)fiber.It can not only give full play to the advantages of MPC such as fast setting speed,high early strength and good bonding performance,but also solve the problem of brittleness.At present,the research and application of HDMPCC mainly focus on ordinary pouring construction technology.In this thesis,firstly,the sprayability and rheological properties of HDMPCC under different mixing ratios were explored,and the relationship between them was established.Secondly,the mechanical properties of HDMPCC under better sprayability were studied.Finally,the pore structure analysis was used to explain the related mechanism.The main results are as follows:(1)With the increase of the content of starch ether,the spray thickness increases first and then decreases,and the rebound rate decreases gradually.The yield stress is sensitive to the change of starch ether.The compressive strength of the casting block decreases gradually,and the tensile property increases first and then decreases.The pore size<50 nm shows a decreasing rule.(2)With the increase of water-solid ratio,the plastic viscosity and yield stress decreased significantly,the compressive strength of the casting block and the spray specimen decreased gradually,and the tensile performance index increased first and then decreased.The pore sizes of the casting sample and the spray sample<50 nm decreased gradually with the increase of water-solid ratio.(3)With the change of sand-binder ratio,the primary injection thickness and rebound rate fluctuate greatly,and the rheological index increases with the increase of sand-binder ratio.The compressive strength of casting block and injection block decreases,and the tensile performance index increases first and then decreases.When the sand-cement ratio is 0.2,the pore size of<50 nm is the most.The proportion of pore size<50nm decreased with the increase of sand-binder ratio.(4)With the increase of borax content,the thickness of the first injection increases first and then decreases,and the rebound rate increases gradually.The plastic viscosity and yield stress increase first and then decrease,and the compressive strength and tensile performance index of the casting block decrease gradually.The compressive strength and tensile performance index of the injection block increase first and then decrease.The pore diameter of the casting sample<50 nm decreases first and then increases with the increase of borax content.The proportion of the injection sample<50 nm shows a gradual increase with the increase of borax content.(5)With the increase of FA substitution amount,the thickness of primary jet increases gradually,and the springback rate fluctuates greatly with the change of FA substitution amount.The rheological parameters decrease first and then increase with the increase of FA substitution amount.The compressive strength and tensile performance index of pouring test block increase first and then decrease.The compressive strength of jet test block increases gradually,and the tensile performance index increases first and then decreases.The porosity increases gradually,and the proportion of harmless pores increases first and then decreases.(6)With the increase of fiber content,the thickness of the first injection increases first and then decreases,while the rebound rate decreases first and then increases,and the rheological parameters will increase.The compressive strength and tensile performance index of the casting block increase first and then decrease,and the compressive strength and tensile performance index of the injection specimen increase gradually.The pore sizes of the casting sample and the injection sample<100 nm show a gradual increase with the increase of PVA fiber content.(7)The rebound rate is inversely proportional to the spray thickness,the spray thickness is mainly concentrated between 20mm and 40mm,and the rebound rate is mainly between 8%and 22%.The rheological parameters are mainly positively correlated with the spray thickness and negatively correlated with the rebound rate. |
