Experimental Study On Testing The Early Strength Of Grouting Material Specimens By Rebound Method

With the development of economy and the passage of time,more and more buildings need to be reinforced and reformed due to aging,natural disasters and changes in functions.Owing to its advantages of high early strength,good fluidity,micro-expansion and easy construction,grouting material has been widely used in the reinforcement,reformation and repair of existing structures with good results.And in order to effectively shorten the construction cycle and reduce the risk,the project depends more and more on the early strength of cement-based grouting material.In addition,the strength of grouting material is relatively high,and the factors such as water consumption,curing temperature and humidity,age etc.have great impact on the strength of grouting material in construction,so that the actual strength of grouting material in the construction site cannot reach the design value.In the meanwhile,it will also have a negative impact on the use of follow-up construction and cause potential safety hazards.Therefore,it is more and more important to evaluate the early strength of grouting material by on-the-spot testing.Furthermore,the rebound method is one of the non-destructive detection methods,which is widely used because of its convenient operation,low cost,wide detection area and no damage to the structure of the specimen.In this thesis,the rebound strength curve of early strength of grouting material is established based on the experiments,and the relationship between age and compressive strength of grouting material is further obtained.A formula for calculating age strength of grouting material is put forward,which provides basis and reference for judging construction cycle and testing strength of grouting material on site.The main research works are as follows:(1)The principle of rebound method and related concepts of rebound strength curve are introduced.Firstly,the basic principle of rebound method is introduced briefly,and the relationship between rebound value and compressive strength is clarified.Secondly,the relevant contents of three rebound strength curves are briefly described,and the calculation methods of compressive strength under specific conditions and the commonly used regression equations are given.Finally,the factors that influence the compressive strength of concrete measured by rebound method are summarized,and the reason why the carbonation depth is not considered in this thesis is clarified;(2)The experimental research scheme for testing the early strength of grouting materials by rebound method is set up.On the one hand,the test design and test instrument are described in detail,which provide technical support for the rebound test.On the other hand,based on the theory and technology mentioned above,the test methods are systematically introduced;(3)Based on the experimental data,the prediction of early compressive strength of grouting material is systematically studied.First of all,the experimental data are eliminated and sorted out,and the basic principles of fitting software and regression analysis are briefly introduced.Then,based on the test results and in conjunction with the least square method,regression and comparison analysis are carried out according to different expressions,and logarithmic expression is selected as the rebound strength curve of the grouting material.Furthermore,the relationship between age and compressive strength is analyzed,so as to explore development law of early strength of cement-based grouting material.At the same time,the formula for calculating the28-day compressive strength of grouting material from the compressive strength of grouting material at low age is derived by fitting.Finally,the influence of age on rebound value,measured and converted strength is analyzed.The results show that the error values of the two methods are small,and the fitting results are good.When the rebound method is used to measure the grouting material,the effect of age can be taken into account to correct the conversion strength,so as to reach the putative value which is closer to the measured strength.