Study On Crack Resistance Of High Performance Fair-Faced Concrete

Fair-faced concrete is a form of architectural art of modernism.It does not use any decorative materials such as paints.It directly expresses the original texture of concrete.It is widely loved and sought after by its unique expression and simple architectural style.In recent years,there have been more and more buildings using clear water concrete structures,but many clear water concrete projects are facing serious structural cracking problems.If the cracking problem of the fair-faced concrete structure is not solved,and the crack resistance of the structure is not improved,the development and application of the fair-faced concrete will be seriously restricted.Therefore,the fair-faced concrete must achieve high performance.It is necessary to combine high-performance concrete technology and application characteristics to prepare a facing concrete that meets the performance and evaluation criteria of high-performance concrete,with smooth surface,no obvious chromatic aberration and significant cracking.This project aims to study the high-performance technical route of fair-faced concrete and to study the structural crack resistance of fair-faced concrete.In this paper,the crack resistance of fair-faced concrete is studied in terms of the type and amount of cement and mineral admixture,aggregate quality,concrete workability and durability.The cracking properties of mortar and concrete with different composition and dosage of cementitious materials were studied.The slump,age of acceptance,natural sand content,mechanical sand grading,coarse aggregate irregular particle content and aggregate quality were studied.The effect on the crack resistance of fair-faced concrete.The test results show that the limestone powder is mixed to make the crack narrow and wide.The first cracking time is close to the reference group.The total area and total length of the crack in 28 d are improved compared with the reference group.The total length of the crack is reduced by 40% and the total cracking area is 28 d.It is reduced by 13%;the addition of magnesium oxide expansion agent prolongs the first cracking time and the total length of cracks is the smallest in 28 d,and the total length of cracks in spring is reduced by 55%,and the crack resistance effect is obvious;the incorporation of quartzite powder only improves the surface texture of clear water concrete.The apparent texture is relatively white,but the first cracking time is the earliest.The total length and width of the crack are the largest in 28 d.The first cracking time of S105 is extended,and the total length and total area of cracks are greatly shortened in 28 d,and the total length of crack is reduced 48%,the total cracking area is reduced by 45%,the surface texture is also more white and brighter than the reference group;as the fineness of the cement increases,the first cracking time is significantly shortened,and the total area of cracks increases with the crack width,although the crack width is relatively reduced,It is still not conducive to the crack resistance of fair-faced concrete.The fineness of cement should be controlled and the amount of mineral admixture should be increased.The fair-faced concrete prepared by using crack-resistant cement has better working performance and the surface is smooth and bright.Uniform,no cracking within 28 d,significantly improving the crack resistance of fair-faced concrete.The test results show that the crack resistance of plastic concrete is better than that of large fluid concrete;the amount of cementing material increases and the risk of cracking increases in the same grade concrete;the use of long-term age is increased with the increase of fly ash content.Cracking sensitivity;the less mud content of natural sand,the better the crack resistance,the mud content 3% is 15% than the mud content,the total area of cracks is reduced by 35% in 28d;The standard high-quality mechanical sand can improve the work performance,strength and crack resistance of concrete;with the optimization of coarse aggregate size,the first cracking time is prolonged and the total cracking area is reduced;the concrete prepared with fine aggregate is satisfied.In the case of the strength grade requirement,the workability and crack resistance of the inferior aggregates were remarkable,the first cracking time was reduced by 57%,and the total area of 28 d cracking was reduced by 72%.The durability test results show that with the increase of the amount of cementitious materials,although the crack resistance is reduced,the compactness is improved and the carbonization resistance is improved;the irregular aggregates of irregular aggregates and needle-like content are increased,and the concrete compactness is poor.Crack resistance and carbonization resistance are poor;improve aggregate quality,reduce coarse aggregate void ratio,improve concrete crack resistance and chloride ion diffusion resistance,and improve concrete surface water absorption,should be used to meet high performance Standard high quality aggregate for concrete aggregates.This paper proposes a high-performance clear-water concrete evaluation method,which provides a basis and reference for the construction unit to carry out the technical route of the fair-faced concrete project.