Tentative Research On Non-destructive Detection Of Concrete Early-age Elastic Modulus

The cracks of concrete structure are mostly happened in the early stage. The parameters of early-age concrete are in continuous change, so it is evidently not in conformity with the reality to study the performance of early-age concrete by using invariable parameters. Young's modulus as an important parameter in the research of the mechanical property of concrete varies with the age increase. It's a time-consuming and effort-taking job to determine the elastic modulus of concrete in different age through traditional test method, and is hardly satisfactory to the requirement of application in reality. The use of Ultrasonic Non-destructive Examination (UNE) in detecting the the elastic modulus of early-age concrete has an extensive application prospect, thanks to its convenience and availability in any place at any time according to needs.This paper ,a sub-topic of Modern Concrete Crack Mechanism and Complete Set of Control Technology, which is an A class sponsored project of Jiangsu provincial Six Talent Peaks, has done some relative experimental research on the elastic modulus of early-age concrete. This paper firstly summarizes the relative research results of both domestic and overseas scholars. Then, it analyzes the feasibility of detecting the elastic modulus of early-age concrete using UNE, and determines the elastic modulus of concrete of various strength grades in different ages, using two methods, non-destructive examination and conventional pressure load test, and then compares the results from the two experimental methods, proposes the modified function relation between them, and obtains the formula of non-destructive detecting of the elastic modulus of concrete in different ages. Finally, in order to extend the application of the method mentioned above, this paper studies the influence of additive , water- cement ratio, aggregate size and strength grades upon the static elastic modulus of early-age concrete, and to make some applicable conclusions.Through the studies mentioned above, this paper obtains the following results:l.At the same age, the concrete elastic modulus through ultrasonic nondestructive examination is large than the static elastic modulus by pressure load test.2.Detecting the influence of density of compound material, wave speed of specimen and Poisson's Ratio of concrete upon early age elastic modulus of concrete through UNE, among the three, the wave speed has the greatest influence to the result.3.This paper brought forward the conversion relationship between the UNE elastic modulus and the static elastic modulus of same age concrete, thus made possible the calculation of the static elastic modulus of same age concrete through a known UNE elastic modulus and the application of the UNE elastic modulus detecting method directly to practice.4.Additive, water-cement ratio, aggregate size and strength grades exert certain influence upon the static elastic modulus of early-age concrete. In the same age, adding 1%JM-10 delayed coagulant, pump concrete enhancer could obviously reduce the value of the static elastic modulus of early-age concrete;along with the increase of water-cement ratio, the elastic modulus of concrete gradually decreases;along with the enlargement of aggregate size, the elastic modulus of concrete gradually increases;and along with the increase of strength grades of concrete, the elastic modulus of concrete gradually increases.