Study On Estimating The Compressive Strength Of Class Ⅳ Grouting Materials In North China By Rebound Method

Class IV grouting is a new type of construction material with similar properties to concrete.It is characterized by early strength,high strength,high fluidity and slight expansion,it is widely used in the field of concrete structure and masonry structure reconstruction and reinforcement.The compressive strength of grouting material is the most important index among its many properties.It is very important for the whole project quality to master the strength of grouting material and its changing law with age,the 21st century,the rebound method in the determination of concrete strength,sintered brick symbols,mortar strength aspect have the corresponding national standards and local standards,However,there is no relevant standard for testing the compressive strength of Ⅳ grouting materials by springback method.In this paper,a large number of springback and compression test data of four kinds of common Ⅳgrouting materials in northern China were analyzed by regression analysis:(1)The analysis of the age-compressive strength test data shows that the strength of four kinds of IV grouting materials commonly used in northern China can reach more than 20MPa after Id,40MPa after 3d and 60MPa after 28d.The strength of IV grouting materials increases rapidly in the early stage of curing,and the average strength growth value within Id to 7d reaches 50.8%of the strength of 28d.In the middle curing period,the strength growth rate slows down,and the average strength growth value in 7d to 21d is 11.4%of that in 28d.At the later stage of curing,the strength growth rate slows down further,and the average strength increase within 21d to 28d is 5.9%of the 28d strength.During curing from 120d to 180d,the average increase in strength was only 0.7%of that of 28d.(2)The regression analysis of the average compressive strength of four kinds of IV grouting materials at each age and the corresponding curing time in the northern area is carried out.The logarithm function relationship between them is given,that is,f=31.481+12.2151n(t0.592),and the correlation coefficient t is as high as 0.97.The mean relative error δ(%)and relative standard deviation er(%)were 4.3%and 5.5%,respectively.By using the logarithmic function relation between age and compressive strength and the error analysis of the compressive strength of IV grouting material with a long age of 180d,it can be seen that the logarithmic function relation between age and compressive strength is in good agreement within 120d of curing.The compressive strength of IV grouting material with curing age beyond 120 days can be stabilized at about 80 MPa.(3)Through the error calculation,it is verified that the strength measurement curves of national unified pumping and non-pumping concrete are not suitable for the prediction of the compressive strength of IV grouting materials in northern China.After fitting the curves of 468 groups of average springback compressive strength,the parabolic function relationship between them is given:f=-0.088R2+9.166R-167.309,the correlation coefficient t is 0.95,the average relative error δ(%)and the relative standard deviation er(%)are 11.2%and 14.8%,respectively,which meet the requirements of regional intensity curve for errors.(4)After systematic test and analysis of the factors affecting the compressive strength ofⅣ type grouting material,it is known that there is no obvious carbonation phenomenon in the early stage of the ore type grouting material.After curing for 21d,the carbonation depth of about 1mm will appear in some specimens.The material of mould test will not affect the strength change of Ⅳ grouting material;The ratio of rebound value to compressive strength ofⅣ type grouting material measured by ordinary concrete rebound instrument and high strength concrete rebound instrument is very close within 7～28d of curing.