Influence Of Mineral Additives On Self-healing Effect Of Cement-based Materials And Investigation On Healing Mechanism

Concrete materials have the disadvantages of high brittleness,low tensile strength,and easy shrinkage.During construction and service,they tend to cause continuous accumulation of damage on the surface or inside,resulting in many different forms of tiny cracks,which cause serious damage to the concrete structure.At present,most of the crack treatment methods are passive treatment methods,that is,artificial cracks are repaired after the cracks of the concrete are generated.This method is difficult to find micro-cracks in the structure in time,and can not effectively repair the invisible micro-cracks.In addition,manual repair requires a lot of manpower and material resources,so there are certain limitations.In recent years,many foreign scholars have conducted research on the effects of mineral additives on the self-repair of micro-cracks in concrete,and have achieved some results.However,domestic research in this field is relatively small and insufficient.Therefore,based on this research background,this paper uses the evaluation methods of crack observation,water permeability test and mechanical property test to comprehensively evaluate the effects of mineral additives,types of mineral additives,crack age and maintenance environment on the self-repair of early micro-cracks of cement-based materials The law,and its repair mechanism is explained from a micro perspective.The main research contents and conclusions of this article are as follows:(1)Fly ash,ore powder,silica fume,metakaolin,quicklime and expansive agent were replaced by cement in different proportions in a single-mixed form,and pure cement specimens were used as a control group to observe the self-healing effect of specimens with different cracking age.The research results show that the early hydration of pure cement mortar specimens is stronger,and the best repair effect for early cracks is.With the extension of cracking age,the repair effect is getting worse;Quicklime,metakaolin and expansion agent can effectively improve the self-repairing effect of medium-term cracks,but its promotion effect on later-stage crack repair is low;The addition of fly ash and slag can effectively improve the development of volcanic ash reaction and promote the self-repairing effect of cracks in the later period;The addition of silica fume can promote the self-repair of cracks in the middle and later stages of the specimen.(2)The four additives(silica fume,metakaolin,quicklime,expansive agent)and Na2CO3 were used to replace 10%of the cement in the form of compounding,and the self-repairing effect of specimens with different cracking ages was observed.The results of the study indicate that the addition of quicklime and Na2C03 not only promotes the formation of calcium carbonate crystals,but also improves the alkalinity inside the cement-based material matrix under sufficient water conditions.;After the expansion agent is mixed with several other mineral admixtures,it has no good effect on the self-healing of micro-cracks;in addition,the activity of metakaolin is slightly higher than that of silica fume in the presence of alkali-stimulated substances.(3)Analysis of the crack self-repair data at different cracking ages shows that under the same maintenance conditions,the self-repair characteristics of the specimens are closely related to the cracking age:the cracking age is early,that is,the degree of hydration inside the matrix is low,so After cracks are produced,good self-healing characteristics are obtained;on the contrary,when the cracking age is late,the degree of hydration of the particles inside the cracks is high,resulting in poor self-healing effects.(4)Based on the two conservation environments of water conservation and standard conservation,the effect of conservation environment on the self-repair effect of cracks was studied.The research results show that the maintenance environment is directly related to the early self-repair ability of the cement-based materials.The repair rate in the immersed environment is significantly higher than that in the wet environment,especially in the early repair stage after the cracks are produced.(5)With the help of SEM scanning electron microscopy energy spectrum analysis and X-ray diffractometer technique,the mechanism analysis of single-mixed specimens with different ratios was carried out.The results show that the addition of mineral additives changed the composition of hydration products of cement-based mortar specimens.The newly generated crystals at the cracks are mostly calcium carbonate,containing a small amount of hydrated calcium silicate,ettringite,calcium hydroxide and other components,which work together to make the micro-cracks continue to heal.