Repair Properties Of Crack Restorative Agents And The Effects On Properties Of Cement-based Materials

Cracks are unavoidable hazards in cement-based materials.If the cracks in cement-based materials can be effectively repaired at the stage of micro-cracks,and are environmentally responsive to automatic repair,then not only can prevent micro-gradual,avoid more serious consequences of component damage,but also through the self-environmental response of materials to repair,reduce the use of human and material resources.It is very meaningful.In this paper,the repair properties of polymer based environmental responsive repair materials for cement based materials are studied.The ideal microcracks were prefabricated by adding steel wire into the mortar blocks.The self-repairing experiments were carried out by placing the cracked specimens in eight different environments(tap water,6% sulfate,artificial seawater,pH = 12 alkaline solution,pH = 5 acidic solution,pH = 7 neutral solution,99% humidity,60 humidity).Assessment of Repairing Degree of Repairing Agents in Different Environment by Acoustic Emission Detection,Crack Width Detection and Moisture Transfer Experiment.Through the analysis of gas permeability and pore structure of concrete structure,the influence of repairing agent on the properties of cement-based materials was studied.The effect of repairing agent on the properties of cement-based materials was also studied by means of microscopic analysis,such as scanning electron microscopy(SEM),X-ray diffraction(XRD),thermogravimetric analysis(TG).The interface model of polymer repairing agent for crack repairing of mortar was established,and the repairing mechanism of polymer repairing agent was established.The experimental results show that: under different environments,the degree of repair of mortar cracks is different.In the tap water environment,the repair effect of the restorative agent is higher than that of the test block itself.In sulfate and seawater environment,the repair effect of the test block without repair agent is similar to that of the test block with repair agent.Under different pH values,the test piece with added reagents has better repair effect than the test block without addition of reagents,and can reduce the erosion effect of the solution environment.The alkaline environment of pH=12 is the best environment for repairing effect,Acidic environment and neutral environment both have the same degree of repair,and are not as effective as alkaline environment.The repairing effect of the repairing agent in the humidity environment is lower than that in the solution environment,and the lower the environmental humidity,the worse the repairing effect ofthe repairing agent.Through the analysis of gas permeability and pore structure of concrete structure,it is found that under normal water curing environment,the use of repairing agent will slightly increase the internal pores of concrete structure,and lead to a slight decrease in the impermeability of concrete.In the simulated harsh environment,the use of repairing agent can reduce the damage of concrete structure in extreme environment.Compared with the sample without repairing agent,the porosity of the sample increases less,and the permeability of the sample is smaller than that of the sample without repairing agent.It is feasible in practical engineering.At the same time,the repairing mechanism of polymer repairing agent was analyzed,including the physical adsorption of polymer,the interfacial binding between polymer functional groups and the complexation between polymer functional groups and metal ions.Through the interaction of substances,a network connection structure is formed at the interface of cracks in mortar test blocks.Through the environmental responsiveness of macromolecule,the polymer repairing agent expanded to fill the cracks by absorbing water in the environment.It can not only prevent the continuation of cracks,but also isolate the inner and outer space of mortar test blocks,avoid harmful substances in the environment intruding into the interior,reduce the durability of the structure,so that the cracks can be repaired.