Study On The Supramolecular Hydrogels For Self-healing Of Cementitious Materials

In the construction field,cementitious materials are one of the most widely used materials.However,cementitious materials are prone to cracks,which can reduce the durability of building structures.In order to repair the cracks in cementitious materials,new intelligent cementitious materials with self-healing function have been widely studied.Self-healing technology of cementitious materials is generally divided into autogenous self-healing and autonomous self-healing.The autogenous self-healing technology is mainly through the cement hydration process to produce Ca CO3 precipitation to fill the cracks,and the autonomous self-healing technology is to add engineering cementitious crystal admixtures,polymers,shape memory alloys and microorganisms in the cement matrix to produce physical and chemical reactions with the cement matrix,to achieve the effect of healing cracks.Based on the basic theory of bone self-healing,this paper studies self-healing cementitious materials.The 4-Hydroxypyridine/Pyromellitic acid supramolecular hydrogel was designed and embedded in the supramolecular hydrogel with a repair agent in cement.The supramolecular gel can respond to environmental changes after cracks occur in cement,release repair agents,and repair cracks.Studies on the repair products and self-healing effects show that the supramolecular hydrogel system can effectively repair cementitious materials,and the results are as follows:(1)Preparation of 4-Hydroxypyridine/Pyromellitic acid gelator,which can form supramolecular hydrogels through self-assembly in water.Through infrared and micrograph analysis,it is known that supramolecular hydrogels with fibrous threedimensional network structure can effectively incorporate the repair agents.Through the study of the thermal properties of supramolecular hydrogels,it is known that the gel transition temperature increases with the increase of gelator concentration,and the structure of supramolecular hydrogel formed by high concentration gelator is more stable.The release kinetics results showed that the release of the reagents by hydrogel followed the diffusion-erosion model.(2)To simulate the self-healing of cementitious materials: firstly,the supramolecular hydrogel embedded with repair agents was embedded in cement to obtain self-healing cementitious materials,and then a large amount of repair products could be obtained in deionized water.The results of IR,Raman,X-ray diffraction and SEM showed that the self-healing products were mainly hydroxyapatite with lamellar spherical structure.(3)Further study on the self-healing process of cementitious materials shows that after cracks in cementitious materials,supramolecular hydrogels respond and release repair agents.The ammonium ion in the repair agent can promote the calcium ion leaching in cement matrix,promote the phosphate ion react with the calcium ion in the pore solution to form hydroxyapatite,and heal crack surface,and then grow to the middle,so as to repair the cracks.(4)The compressive strength,permeability and carbonation resistance of selfhealing cementitious materials with cracks were cured after 28 days.The self-healing cementitious material can completely repair 600 μm cracks.The research results of selfhealing mechanism show that the self-healing is mainly due to the formation of hydroxyapatite and partial autogenous self-healing.