| There is a large amount of cement slurry in bridge concrete,so there must be a curing period in the pouring process.At this stage,a series of physical and chemical reactions will take place inside the concrete,and various parameters such as humidity and temperature will also change accordingly.At the same time,this stage is also an important stage of concrete strength development.Therefore,it is of great significance to monitor the solidification stage to predict the strength development of bridge concrete.However,there is still a lack of a reliable real-time monitoring method for the internal humidity of concrete.Based on this,this paper tries to develop a set of plastic fiber optic humidity sensing system that can be embedded in concrete,and on this basis,it tries to explore the relationship between the change of various parameters and the strength development of concrete during the curing process by experiment.The specific research contents are as follows:In this paper,a humidity sensing system based on plastic optical fiber with good toughness and high stability is proposed.The basic working principle can be explained by the fiber loss theory.The loss caused by grooving in plastic fiber can be regarded as the loss of fiber connection,the loss formula is derived from this.It is also concluded that the refractive index at the groove,the fiber diameter,and the size and number of grooves will all affect the loss value.Therefore,when the external humidity changes,the refractive index in the groove will change accordingly,resulting in the received light power will also change.In the process of sensor design,the influence of groove size and fiber diameter on sensor accuracy was explored through experiments,the results show that the deeper the groove depth,the larger the groove width,and the smaller the fiber diameter,the higher the corresponding sensor sensitivity.In the subsequent calibration test,the sensor element was placed in a temperature and humidity box,and the response curve between relative humidity and relative optical power was measured.Multiple sets of tests were conducted for plastic optical fibers with different number of grooves,the test results show that the two have a good linear relationship.According to the test results,a grooved fiber with a groove width of 80 um,a groove depth of 100 um,a groove number of 15,and a fiber diameter of 1000 um is used to make the sensing element.Finally,experiments have confirmed that the sensor has good stability in the temperature range of 10 ? 80 ?.In the monitoring test of the concrete curing process,the grooved optical fiber humidity sensor was embedded in three sets of concrete samples with different water-cement ratios,and the relative optical power change within 28 days was monitored and converted into humidity change.Compared with the measured results of TH22R-EX automatic temperature and humidity recorder,it is found that the data change trend of the two is basically the same,which confirms the feasibility of the sensor.In addition,the development of compressive strength and temperature change at28 d were also monitored.The development of relative humidity,temperature and compressive strength of concrete during curing is summarized based on the above experimental data.At the same time,comparing the different test data of the water-cement ratio of each group,it is found that the lower the water-cement ratio of the concrete specimen,the lower the peak temperature that can be reached during the curing process,and the greater the change in the relative humidity.Finally,the relationship between the compressive strength and the change in humidity during the stage of relative humidity reduction in the curing process is fitted,and it is found that the two have a good linear relationship,and the relationship between the two is obtained.This relationship can be used to predict the development of concrete strength by monitoring the changes in humidity during the curing process of concrete. |
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