Experimental Research On The Special Strength Curve Of The Mixture Used For Replacement And Reinforcement

When the building fails to meet the requirements of the specification due to design errors or improper operation during the construction process,it is often necessary to adopt a replacement reinforcement scheme for the structure.Existing buildings will also have problems such as wall cracking,local instability and durability degradation due to aging,natural disasters and other reasons during use.Replacement and reinforcement are required.The completed building can continue to be used,which not only saves funds,but also protects the environment.Cement-based grouting material has the advantages of early strength,convenient construction and good fluidity,which can effectively shorten the construction period and is widely used in the field of replacement reinforcement engineering.However,due to its high strength,it is easy to cause strength redundancy,so that the mixture of grouting material and concrete is gradually used in replacement reinforcement engineering.As the most commonly used method of on-site detection,rebound method is often used in engineering detection before and after replacement and reinforcement.However,there is no systematic study on the on-site detection of mixture rebound method,and when using JGJ/T23-2011’Technical Specification for Testing Concrete Compressive Strength by Rebound Method ’ to infer the compressive strength of the mixture,there is a large error in the result.Therefore,this paper conducts experimental research on the mixture and establishes a special rebound strength measurement curve,which ensures the detection accuracy and improves the work efficiency.It has guiding significance for practical engineering.The main research contents and conclusions are as follows :(1)Through the analysis of the advantages,disadvantages and errors of the field detection method,the rebound-drilling core method is selected to conduct the strength detection test on the wall made of the mixture with the mixing ratios of 30%,50% and70% of the grouting material.Through the test data,it is found that the shape of the compressive strength growth curve of the mixture is similar to that of the concrete strength growth curve,and increases with the increase of the age and the mixing ratio of the grouting material.The growth rate of the first three days is the fastest,which can reach65%–70% of the final strength.The growth rate of the first 14 days is fast,which reaches90%–95% of the final strength.The growth rate is proportional to the content of the grouting material.In the age of 14 days to 28 days,the strength increases to about 99% of the final strength.(2)Through economic analysis,when the mixture is used in replacement reinforcement engineering,the cost savings can reach 26%-62%,and 50% grouting material mixing ratio can meet most of the replacement reinforcement requirements,and the cost savings are about 44%.(3)Based on the regression analysis of the rebound of the mixture and the compressive strength of the core sample,and the comparison of multiple regression models,the special strength measurement curve suitable for the rebound method to detect the mixture structure is selected.The average relative error of the curve is 3.2%,the relative standard deviation is 3.0%,and the determination coefficient is 0.963,which all meet the requirements of the special strength measurement curve in the technical specification of JGJ/T23-2011’ rebound method to detect the compressive strength of concrete.(4)The comparison between the conversion strength of the special strength curve and the measured strength shows that the higher the grouting material content is,the longer the age is,the better the fitting is.After 7 days of age,the presumption error of the mixture components with 50% and 70% grouting material is roughly within 3%,which is very close to the actual strength of the structure.The rebound value is substituted into the national unified strength curve of pumping concrete to verify the applicability of mixture structure detection.It is found that the error is large,so it is necessary to establish a special strength curve of mixture,which has practical engineering significance.