Mortar Deformation Under Freeze-thaw Cycle And Design Of Its Measuring Sensor Research

Freeze-thaw damage of concrete is an important factor affecting the durability of concrete.At present,the evaluation methods of freeze-thaw damage are mainly mass loss rate and dynamic elastic modulus.Both of these two methods have their limitations and can not understand the actual damage inside the material.Based on the existing studies on the mechanism of freeze-thaw failure,it can be found that the essence of freeze-thaw failure is matrix deformation and cracking caused by freezing expansion and transportation of internal pore water during cooling.Therefore,the monitoring of freeze-thaw deformation has important research significance for the mechanism of concrete freeze-thaw failure,evaluation index and material modification,and the monitoring means of freeze-thaw deformation is an important factor limiting its further research.In view of the above problems,this paper will study the structure design of thick film resistance sensor and the monitoring of freeze-thaw deformation of different types of mortar.The main research contents and research results are as follows:Firstly,two strain amplification structures of the thick film resistance sensor,I-shaped and sawtooth,were designed,and the compatibility and coordination of the two structures embedded in concrete for deformation testing were investigated by using finite element simulation.The simulation results show that the serrated thick film resistance sensor can enhance the deformation coordination and meet the compatibility between the sensor and the measured substrate.Through orthogonal test,the influence degree of the three parameters of the diameter,spacing and layout range of the serrated hole on the strain transfer rate is obtained,and the optimal structural design scheme is obtained.Secondly,according to the designed structure,the corresponding serrated thick film resistance sensor is prepared,which is embedded in the mortar specimen to test the freeze-thaw deformation,and the measured results are compared with those measured by the metal strain gauge under the same conditions.Results showed that the sawtooth thick film resistor sensor inside the embedment mortar specimens after to test out the law of changes with the temperature deformation of freezing and thawing,but thick film resistance of metal strain gauge is small compared to the test results,the deformation value in the first 10 times of freeze-thaw cycle with metal strain gauge measured deformation value,with the increase of freeze-thaw cycles deformation value is gradually increasing the gap between the two.Finally,the internal deformation of ordinary mortar,internal curing(SAP)mortar and air mortar under different freeze-thaw cycles was tested,and the evolution law of freeze-thaw deformation of the three mortar materials was studied,and the freeze-thaw resistance of the three mortar materials was evaluated from the perspective of freeze-thaw deformation.The results show that the freeze-thaw deformation of the three mortar materials increases gradually with the increase of the number of freeze-thaw cycles.The addition of air entraining agent and SAP can reduce the freeze-thaw deformation of mortar and improve the freeze-thaw resistance,and the effect of the former is better than the latter.The linear fitting effect of the internal limit deformation of mortar and the number of freeze-thaw cycles is better.In addition,the freeze-thaw deformation of mortar and its mass loss rate have similar development rules,that is,with the increase of the number of freeze-thaw cycles,both of them gradually increase.