Research On Self-healing Performance Of Concrete Mixed With Nano-modified Cementitious Capillary Crystalline Waterproofing

During construction and working condition,it is easy for concrete to crack because of physical and chemical reactions.The existence and development trend of cracks have inevitably influence on the mechanical properties and durability of concrete.Therefore,it is of great significance to improve and enhance the crack self-healing ability of concrete for improving the mechanical properties and durability.As a kind of green environmental protection of inorganic waterproof materials,Cementitious Capillary Crystalline Waterproofing Materials（CCCW）enter with water as a migration medium and move down the capillaries or cracks of concrete.This process facilitates hydration reaction between CCCW,unhydrated cement particles and water,forming an insoluble crystal to seal cracks and block up pores,improving concrete compactness and self-healing performance,so as to restore and improve the mechanical properties and durability of concrete.Nano-SiO₂（NS）belongs to an economical and practical nano materials with high activity and a high specific surface.It can not only promote hydration reaction of cement,but can also physically block up micro-pores,thus reducing the porosity of concrete and improving the compactness of concrete.In view of this,this article was supported by the National Natural Science Foundation of China（51778272）,the influence of CCCW and NS on the compressive strength,chloride corrosion resistance of damaged concrete after repairing and the flexural behaviors of damaged reinforced concrete beams after repairing was studied,and the microstructure of concrete crack hydration products was analyzed by SEM after repairing by experimental research.The main results are shown as follows:1.The influence of CCCW and NS on the compressive strength of concrete.CCCW has a certain weakening effect on the early strength of concrete,but improves the later concrete strength;NS can improve the compressive strength of concrete,especially the early strength,however,the compressive strength of concrete decreases with the increase of NS amount;Composite incorporating CCCW and NS can effectively improve the compressive strength of concrete;Compressive strength of concrete containing CCCW and NS is higher than single-doped CCCW concrete and the reference concrete,and the enhancement effect of composite incorporating CCCW and NS on concrete increases with ages.2.The influence of CCCW and NS on the compressive strength and microstructure of damaged concrete after repairing.The single-doped CCCW or composite incorporating CCCW and NS can effectively restore the compressive strength of concrete in water environment,and the self-healing performance of the concrete containing CCCW and NS is better than the single-doped case;The earlier the curing age is,the higher the repaired compressive strength is;The compressive strength of concrete after repairing increases with the increase of preloading stress level;The compressive strength,strength restoration ratio and ultrasonic velocity of concrete after repairing increases with the immersion time increasing;Compared with the reference concrete and single-doped CCCW concrete,it is found that the microstructure of the cracks of concrete containing CCCW and NS after repairing is more fully hydrated and more compact under SEM observation.3.The influence of CCCW and NS on the chloride corrosion resistance of concrete.The chloride corrosion resistance of single-doped CCCW concrete and composite incorporating CCCW and NS concrete is significantly better than the reference concrete,in which the chloride corrosion resistance of compounding CCCW and NS concrete is the best;The chloride corrosion resistance of concrete containing CCCW and NS after 30 days repairing in water environment is significantly better than that of unrepaired concrete containing CCCW and NS;The chloride concentration and chloride diffusion coefficient of concrete increase with the stress level increasing;With the extension of the erosion age,the difference of chloride concentration and chloride diffusion coefficient of concrete with different stress levels gradually decreases,while the chloride concentration of concrete shows an upward trend;The shallower the powder depth is taken,the more obvious the change of chloride concentration is;For the same powder depth of three mix ratios of concrete,the concentration difference between different erosion ages decreases with the extension of erosion age,and the downtrend of the concentration difference of concrete containing CCCW and NS is more obvious.4.The influence of CCCW and NS on the flexural behaviors of damaged reinforced concrete beams after repairing.The mid-span cross-section of the test beams better meets the assumption of a flat section;Under different exposure conditions,the flexural behaviors of three kinds of reinforced concrete beams have been repaired,among which the effect of compounding CCCW and NS is the best;The repairing effect of the flexural behaviors of reinforced concrete beams containing CCCW and NS in water environment is the most obvious;When the width of prefabricated crack is not more than 0.3 mm,the surface crack of reinforced concrete beams can be repaired obviously by compounding CCCW and NS.In this paper,the influence of CCCW and NS on the compressive strength,chloride corrosion resistance of damaged concrete after repairing and the flexural behaviors of damaged reinforced concrete beams after repairing were analyzed,which provides technical support for solving the practical engineering problems related to cracking,leakage and durability failure of concrete architecture.