Design And Preparation And Research Of Bone-mimic Self-healing Cementitious Materials

Cementitious materials is the most widely used building materials.Due to the low tensile strength and changeable external environment,the cementitious materials are easy to crack,affecting their durability and mechanical properties.Therefore,the self-healing methods of cementitious materials have attracted wide attention.As an important component of bone tissue,hydroxyapatite?HA?plays an important role in the self-healing phenomenon of bone tissue.In the study,based on the principle of bone biomimetic,Hydrogels were used as a carrier to encapsulate phosphate and added to cement paste to manufacture self-healing cementitious materials.Hydroxyapatite-type minerals were formed and healed the cracks through the reaction between phosphate released from hydrogels and Ca²⁺from the paste and its repair efficiency and mechanism were explored.The specific conclusions are as follows.?1?Three kinds of hydrogels AN1,AN2 and AN3 were successfully prepared as self-healing carriers.The basic properties of the hydrogels as self-healing carriers and their influence on the mechanical properties,durability,working performance and hydration of the samples were investigated.AN1 hydrogels buried in the paste could preserved 51wt%of the phosphate after the age of 28 days,but the AN2 hydrogels were the least,only 16%;the morphology of the hydrogels was not changed when they were placed in the samples for 48 days.The results show the good stability of hydrogel in the slurry.The mechanical properties,durability and working properties of the samples will be adversely affected with the addition of hydrogel,The more the hydrogel is added,the stronger the adverse effects;the cumulative heat of the slurry hydration will be reduced in the early stage and the slurry will be maintained in the later stage.?2?In order to verify the feasibility of bone mimic self-healing cementitious materials,this study explores the influence of HA growth environment on its morphology and chemical stability under synthetic conditions.The morphology and growth mechanism of HA formed by hydrogels in simulated cracks were explored under synthetic conditions.The small range change of Ca/P in environment had little effect on the phase morphology of hydroxyapatite.It is easy to form OCP impurities in low pH environment,But carbonate is easy to be introduced to HA to form carbonate calcium-deficient hydroxyapatite?CCDHA?at high pH environment.With the increase of deposition time,the crystallinity and Ca/P of hydroxyapatite gradually increase,the particle size of product gradually increases.However,the morphology of hydroxyapatite synthesized at room temperature is not regular;Cl^-in the environment can not affect the crystallization of hydroxyapatite,but CO₃^2-will hinder the formation of a good lattice structure of HA.The higher the degree,the higher the Ca/P.HA is produced in the three hydrogels under simulated environment,the products are calcium-deficient hydroxyapatite?CCDHA?,the higher Ca2+concentration,the higher the yield on the test block.The more things we have.?3?In order to study the self-healing performance and its influencing factors of self-healing materials,four methods were used to test the self-healing efficiency:from visualization and determination method,the self-healing efficiency of three self-healing materials is similar,but from the method of water permeability,the self-healing efficiency of AN2 samples are better;the wider the crack,the lower self-healing efficiency of materials;The crack at 300um width is completely repaired.The crack at300-400 um width is repaired by 70%with water permeability method.When the width of crack increases to 400-500 um,the self-healing efficiency of crack decreases to51.7%.The longer the cracking time is,the lower the repair rate of crack area is;adding Ca?OH?2 to the sample can promote the self-healing efficiency.?4?In order to study the self-healing products and the self-healing mechanism,The XRD,FTIR,Raman and SEM were used to characterize the healing products.The repair mechanism was explored by studying the changes of healing products at different ages and SEM graph of healing cracks.The actual repair products of the three hydrogels were composed of CaCO3 and CCDHA;At the healing age of 7 days,the repair products were initially spherical cluster-shaped CCDHA,Then the product gradually contacts and fuses to increase its particle size.After 14days,CCDHA on both sides of the crack grew and contacted with each other to repair the crack.Finally,CaCO3 began to form and tend to contact and wrap spherical CCDHA.After 28 days,A large amount of calcium carbonate is produced.