Study On Early Crack Resistance Of Concrete Based On Crack Resistance Grading

With the rapid development of Chinese infrastructure construction,concrete is widely used in engineering construction,but there will be a series of problems in the process of concrete application,especially the problem of concrete cracking,which leads to the durability and applicability of the construction is seriously affected,has become a hot topic of concern in engineering circles.Generally speaking,the concrete structural members are working with cracks,there is almost no concrete structure without cracks,but for the special building and special environment needs,the preparation of concrete early crack resistance requirements are more strict.According to the different requirements of crack control in engineering,the classification of concrete crack resistance is conducive to the formation of a one-to-one correspondence between the crack resistance of structural members and the grade of crack resistance.It is beneficial to maximize resources and interests,and realize the production mode of "high quality and high price" of concrete.At the same time,it also saves a lot of costs for the construction unit.In the event of concrete cracking at the site,it is helpful to clarify the responsibilities of the parties involved.The existing "Technical Regulations for the Prevention and Control of Cracks in Building Engineering" JGJ/ T317-2014 classifies the crack resistance of concrete into five grades.However,there are some deficiencies in the practical engineering application,so as to improve the shortcomings,so that it can be implemented in field engineering.This paper mainly does the following four work:(1)The optimal dosage of fly ash and mineral powder in the early crack resistance of C30,C35 and C40 concrete is determined by the concrete slab test.The test results show that: when fly ash and mineral powder are only mixed,the optimal single content of crack resistance is 40%,and when fly ash and mineral powder are mixed,the composite ratio of 1:1 replaces 40% cement,the crack resistance of concrete is the best.When different mineral admixtures are added,the crack resistance is as follows: single fly ash > equal amount of compound fly ash and mineral powder > single mineral powder > non-mineral admixtures.(2)The influence of wind speed,temperature,humidity and other factors on the early crack resistance of C30,C35 and C40 concrete was studied.The test results show that the crack resistance of concrete deteriorates gradually with the increase of wind speed.The early cracking resistance of concrete under high temperature environment is worse than that under low temperature environment,and the early cracking resistance of concrete under normal temperature environment is the best.With the increase of ambient humidity,the early cracking resistance of concrete gradually increases.With the increase of strength,the influence of wind speed,temperature and humidity is greater.(3)Study the influence of six curing methods including no curing,coating curing,moisturizing curing,secondary curing,simultaneous moisturizing curing and secondary curing,and standard curing on the early cracking performance of C30,C35 and C40 concrete.The test shows that the relationship between different curing methods and crack resistance of concrete is as follows: no curing < coating curing <moisturizing curing < secondary coating < moisturizing + coating < standard room curing.(4)By studying the test results of the early crack resistance of C30,C35 and C40 concrete under the influence of wind speed,temperature,humidity and different curing methods,the critical control indexes of the wind speed,temperature,humidity and different curing methods on the crack resistance of concrete under the crack classification standard were obtained.