Research On Embedded Concrete Strain Sensor With Low Elastic Modulus

The accurate measurement of deformation of concrete including the deformation at early age is one of the important premise to evaluate service performance of concrete structure. However, most of existing instruments for measuring deformation of concrete are set on the external, the ways are not applicable to the early age concrete due to its unsound internal structure, low strength and wet surface, so it is difficult to realize the measurement of deformation accurately, economically, conveniently and on-line with the existing instruments. Embedded sensor appearing recently could solve the above questions, but the elastic modulus of embedded sensor is about 300~800 MPa, it is too large to response sensitively the deformation of concrete at early age, leading to the lag of capture of the deformation.In order to solve these questions, based on the principle of deformation amplification with elastic element of double ? type, the embedded strain sensor with low elastic modulus(ESS) is developed in this study. In this paper, firstly the basic principle, design method and assembling procedure of ESS in detail are introduced; then calibration device for ESS is developed, and coefficient for modifing the deformation of ESS is obtained with the device; finally the basic performance of ESS is investigated, and the reliability and advantage of ESS are discussed by comparing the measurement results of ESS with that of CDP.The conclusions derived from the investigation are as follows:1. The design of ESS based on the principle of deformation amplification with elastic element of double ? type is reasonable and feasible. Further, The simulation results of ABAQUES and checking test prove this conclusion.2. The calibration device for ESS is developed and used to calibrate the deformation of ESS. The coefficient for modifing the deformation of ESS obtained with the device can be used to measure and calculate the deformation of concrete.3. The relationship between ESS strain and the external strain is linear, the proportional coefficients are about 0.835~0.962.4. The data of calibrate shows some differences between ESS due to handwork, in order to accurately monitor the strain behavior, every one of ESS must be calibrated.5. The maximum elastic modulus of ESS is 35 MPa, the value is not only lower than the elastic modulus of mature concrete, but also lower than that of concrete during hardening period. It just is an advantage of ESS in the sensitive deformation monitor of concrete at early ages.6. Comparison experiment shows that ESS can catch the deformation of concrete at early ages better than the traditional way.