Experimental Study On Testing Compressive Strength Of Mixture By Small Diameter Core Sample Drilling Method

Cement based grouting materials commonly used in replacement and reinforcement projects have good fluidity and early strength,but their strength values are usually higher than the compressive strength values of concrete commonly used in actual projects between 20MPa-40 MPa,which will cause strength redundancy,and the high price of grouting materials will increase the project budget.Mixing concrete and cement-based grouting material to prepare mixture can improve the fluidity of concrete,appropriately improve its strength,and reduce the cost.In this thesis,C30 concrete is prepared in the form of mixing cement,gravel,sand and water,and 30% and 50% of Class III cement-based grouting materials are added to prepare four solid walls of mixture and 144100 mm standard curing and curing cubes under the same conditions.Core drilling method and rebound method are commonly used on-site detection methods in engineering.Drilling small diameter core samples can effectively avoid drilling steel bars into the solid structure and can reduce the damage to the area of structural members to ensure that the members have sufficient bearing capacity.Therefore,96 core samples with a diameter of 70 mm and 96 core samples with a diameter of 50 mm are respectively drilled from four concrete mixed walls in this thesis.Through the rebound of the core drilling area,the special strength testing curve of the mixture is established with the rebound value and the strength of 70 mm core sample to achieve the purpose of testing the strength of the mixture by rebound method.The specific research contents and conclusions are as follows:The rebound test was carried out on the four prepared solid walls of the mixture according to the four ages of 3d,7d,14 d and 28 d to explore the influence of age and grout content on the rebound value of the solid wall of the mixture.It was found that the rebound value of the mixture increased with the increase of age and grout content.According to the age of 3d,7d,14 d and 28 d,core drilling sampling was carried out for the rebound area of four solid mixture walls.The compressive strength of 70 mm and 50 mm core samples drilled at each age and the test blocks of two curing methods were tested and compared.It was found that the strength of the test blocks of two curing methods was higher than that of the core samples of two diameters in each age.Because 50 mm core samples were more susceptible to the influence of processing precision and test instrument load,the compressive strength of 70 mm core samples was slightly higher than that of50 mm core samples.Compared with the 50 mm core sample of the mixture,the compressive strength of the 70 mm core sample and the test block of the two curing methods are close,so the70 mm core sample strength is taken as the actual strength of the wall.Since the compressive strength of 70 mm and 50 mm core samples of the mixture has a high correlation with the growth of age,in order to meet the needs of drilling 50 mm core samples to detect the actual strength of the solid structure of the mixture in the project,the strength conversion formula of 70 mm and 50 mm core samples of the mixture has been established.In order to enable the rebound method to detect the strength of the solid structure of the mixture,the average rebound value of the mixture wall and the 70 mm compressive strength value of the core sample were substituted into the national unified strength measurement curve of concrete.It was found that the average relative error and the relative standard deviation did not meet the specification requirements,so a special strength measurement curve for the mixture was established to meet the application of the rebound method.