Study On Design And Performance Of Self-healing Cementitious Materials Based On Hydrogel Carrier

Cement-based materials have outstanding advantages such as high strength,good durability and universal applicability,and are widely used in the construction field.During service process,subject to temperature,shrinkage stress or load fluctuations,cementitious materials are prone to cracking,which expands the channels and chances of chloride ions and water molecules invading the interior of the structure,intensifying the risk of reinforcement corrosion and causing great harm to the durability and service life of reinforced concrete.Traditional repair techniques require repair and reinforcement of damaged buildings with the help of manual labor,which has problems such as passivity,long implementation period,high cost,and inability to meet the demand for structural repair in special environments.Therefore,the development of self-healing cementitious materials with rapid self-sensing and self-healing of cracks is an important way to enhance the durability of structures.Mimicking the repair process of teeth and bones,the formation of hydroxyapatite products embedded in concrete matrix to repair matrix defects is a new strategy for self-healing technology of cementitious materials.A carrier with properties such as simple preparation process,high loading capacity,and intelligent response to cracks to release the repair agent is essential to enhance the repair efficiency of the matrix.In this paper,ammonium phosphate-induced hydroxyapatite was used to fill cracks as a cement-based autonomous repair method,and the repair performance and reinforcement protection properties were investigated.Firstly,2,6-bis[N-（carboxyethylcarbonyl）amino]pyridine（DAP）supramolecular hydrogel was synthesized by heating method.Then the DAP supramolecular hydrogel-driven self-healing cementitious material was prepared by adding DAP loaded with ammonium phosphate repair agent into the cement slurry.Crack repair and concrete reinforcement corrosion mitigation were achieved through the formation of well-stabilized hydroxyapatite minerals in the matrix cracks.The main research and conclusions of the paper are summarized as follows.（1）Preparation and performance study of DAP supramolecular hydrogels.The DAP supramolecular hydrogels were synthesized by a simple hydrothermal reaction,and the gelation behavior,microscopic morphology,thermal properties,rheological properties,and phosphate release behavior of DAP supramolecular hydrogels were characterized to investigate the feasibility and advantages of DAP as a carrier for phosphate-induced hydroxyapatite self-healing technology.DAP supramolecular hydrogel is based on the hydrogen bonding between the gel molecular groups to build a three-dimensional network structure,which provides a space for the restorative agent,and DAP is successfully loaded with 1 mol/L NH₄H₂PO₄.The super-molecular hydrogel is used to realize convenient and rapid coating of the repair agent by the dynamic reversible transformation of sol-gel during the heating and cooling process.Molecular hydrogel has the ability to release phosphate slowly in solution,and the release rate in alkaline environment is higher than that of deionized water,which can release 76%of phosphate content within 24 h,providing a continuous repair agent for the early repair of cracks.（2）Crack repair study.Firstly,the feasibility of using DAP as a carrier and NH4H2PO4 as a repair agent in hydroxyapatite self-healing technology was verified,and DAP supramolecular hydrogel-driven self-healing cementitious materials were prepared,while the chemical stability of repair products during carbonation and chloride incorporation was investigated.The results showed that the DAP supramolecular hydrogel loaded with NH₄H₂PO₄ reacted with fresh slices of cement to form a large amount of hydroxyapatite in a simulated pore solution environment;the self-healing member successfully repaired a 0.592 mm wide crack,and the repair product was hydroxyapatite accompanied with a small amount of calcium hydrogen phosphate dihydrate and calcium carbonate;carbonation had a small effect on hydroxyapatite in a dry environment and a larger effect on Carbonation has less effect on hydroxyapatite in dry environment and more effect on hydroxyapatite in wet environment,which easily transforms hydroxyapatite into calcium hydrogen phosphate dihydrate or calcium carbonate;the presence of chloride ions does not affect the nucleation and growth of hydroxyapatite.（3）Research on reinforcement corrosion inhibition.In order to promote the application of DAP supramolecular hydrogel-driven self-repair technology in large components and to investigate the reinforcement protection performance of self-repairing materials,self-repairing steel cement-based materials and self-repairing concrete beams were prepared to study and evaluate the differences in reinforcement corrosion behavior in the matrix before and after repair,and the following conclusions were drawn:by analyzing the results of X-CT of reinforcement,the self-repairing steel cement-based materials were subjected to chloride salt erosion for 84 days,the blank control The average thickness of the corrosion product layer of the built-in reinforcement was in the range of 70-100μm,and the thickness of the local product layer could be more than 200μm.The average corrosion thickness of the repaired specimens was 40μm,and the built-in self-healing member effectively slowed down the corrosion rate of the reinforcement;the resistance of the concrete beam matrix to chloride ion attack was also improved by adding the self-healing member.