Experimental Study On Compression,Bending Properties,and Microscope Mechanism Analysis Of OSP-MPC

Magnesium phosphate cement(MPC)is a new type of inorganic cementitious material,which has the characteristics of fast hardening,early strength,high bond strength,etc.However,compared with the common cement-based materials,the main raw material of MPC,magnesium oxide,requires high technology,is expensive,and the hydration heat is too large,which limits the engineering application of MPC.Shell powder is a kind of green and environmental protection natural mineral material.At present,some scholars have applied the waste shell powder instead of the natural filler to the concrete and cement mortar,which has a certain improvement effect.Therefore,in this paper,oyster shell powder(OSP)was used as the admixture to replace part of Mg O to prepare MPC.Firstly,the static mechanical properties of osp-mpc were studied to provide the basis for further research on the durability of the material.The main research contents are as follows:(1)The static uniaxial compression test was carried out to study the influence of OSP content on the static mechanical properties of MPC under different curing ages,such as compressive strength,failure mode,stress-strain curve,elastic modulus,etc.The results show that when OSP content is 3% ? 6%,the early strength of MPC can be improved,which can not only improve the spalling damage degree of MPC side,but also improve the pressure resistance of MPC to a certain extent Learning performance.With the increase of OSP content,the elastic modulus of each group of specimens decreased,which was not conducive to the increase of elastic modulus,but the deformation performance was improved.(2)Three point bending test was carried out to study the influence of OSP content on the static mechanical properties of MPC under different curing ages,such as flexural strength,failure mode,load displacement curve,stiffness and flexural compression ratio.The results showed that the MPC with 3% OSP content in each curing age had high flexural strength and small brittle failure degree,which could significantly improve the brittleness of MPC and enhance the bearing capacity of the specimen.With the increase of OSP content,the deflection of the specimen increases and the stiffness decreases.(3)The changes of microstructure and hydration composition of MPC at different ages were analyzed by SEM and XRD,and the mechanism of their influence on the mechanical properties of MPC was revealed.The results showed that with the increase of OSP content,3% OSP could accelerate the nucleation and crystallization of MKP,increase the content and crystallinity of MKP,and increase the compactness of matrix;OSP had physical properties The filling effect also involves in chemical reaction.A certain amount of OSP particles which are not involved in the reaction are filled in the gap cracks,which improves the density of the matrix,while the OSP particles which are involved in the reaction improve the mechanical properties of MPC by reducing the content of soluble phosphate in the matrix and optimizing the pore structure.