Research On Embedded Geopolymer Sensor And Self Sensing Concrete Column Component

Most modern large concrete structures require service for decades or even hundreds of years.Due to the combined effects of structural fatigue,environmental erosion,and other factors during use,concrete structures can experience fatigue damage.Therefore,it is necessary to implement health monitoring for major engineering buildings.Sensor is the main functional component of Structural health monitoring system,but the existing sensors generally have shortcomings such as short service life and poor compatibility with concrete structures.Selfsensing concrete material is an intelligent material that meets the structural strength requirements and has sensing function.It can monitor its stress state or damage situation in realtime by monitoring its own resistance changes,and has advantages such as good durability,high sensitivity,and natural compatibility with concrete structures.Geopolymer materials are rich in a large amount of alkaline ions due to their alkaline activation properties,which gives them inherent advantages in conductivity and lays the foundation for their further development as intrinsic self-sensing materials.However,there is currently limited research on geopolymer sensors,let alone exploration of their structural applications.In this paper,slag(SL),fly ash(FA)and fly ash microsphere(FAM)were used as precursors,and carbon fiber(CF)and steel fiber(SF)were used as conductive phases,On this basis,the geopolymer sensor is embedded in concrete to prepare a self-sensing concrete column and its self-monitoring performance corresponding to stress/strain is studied.The main conclusions are as follows:(1)Fly ash microspheres can improve the conductivity and pressure sensitivity of geopolymer sensors.When the carbon fiber content increases to 0.3%,the electrical resistivity of the sensor decreases by 1-2 orders of magnitude,reaching 9.4 Ω· cm.Quartz sand is helpful to improve the compressive strength of the sensor,but its small particle size distribution increases the resistivity of the sensor by two orders of magnitude.Steel fibers have no significant improvement effect on improving the conductivity of geopolymer sensors.When the peak stress is 12.5 MPa,the resistance change rate(FCR)of the geopolymer sensor prepared with carbon fiber,fly ash microspheres,and standard sand can reach 19.5%,and the strain sensitivity(GF)can reach 388.48.The barrier effect of quartz sand on the conductive network will affect the sensing performance of the sensor.The FCR of the geopolymer sensor made of quartz sand as fine aggregate is only 3.7%,and the GF is only 48.37.The stability of the pressure sensing performance of steel fiber polymer sensors is poor.(2)After embedding different sizes of polymer sensors(S-type: 20 mm × 20 mm × 40 mm,M-type: 40 mm × 40 mm × 40 mm,L-type: 40 mm × 40 mm ×160 mm)into C50 concrete column components,the FCR of the sensors can be used to monitor the stress state of the concrete column.The resistance change rate of the L-type sensor has a good correspondence with the stress/strain of the concrete column and has the most stable pressure sensitive performance.When the stress amplitude is 20 MPa,the FCR value of the L-type sensor is around 4%,and the GF can reach 83.61.The repeatability and stability of the sensing signal of the M-type sensor are the worst.As the number of cycles increases,the perceived signal stability of the S-type sensor gradually deteriorates.M.The embedding of S-type sensors has a relatively low impact on the ultimate strength of concrete columns,while the embedding of L-type sensors results in significant fluctuations in the ultimate strength of concrete columns.(3)Combined with digital image analysis(DIC),it was found that monitoring the FCR changes of steel fiber polymer sensors under bending can provide early warning of the appearance of initial cracks,and the FCR show a significant upward trend before the cracks appear.Steel fiber geopolymer sensors can monitor the width of crack propagation,while carbon fiber geopolymer sensors exhibit brittle failure.There is a good linear correlation between the resistance change rate and the crack width of the flat steel fiber polymer sensor.