Effect Of Steel Fibers On Self-monitoring Of Crack For Smart Concrete

Concrete structural members are inevitably cracked due to the effects of factors such as load,fatigue,and environmental corrosion in service life.The appearance of cracks will lead to structural damage and degrade load bearing capacity of structure.It will also ease the ingress of water and harmful ions into concrete matrix,which may cause the durability deterioration of the concrete structure.If the crack can be detected in its early age,repair and strengthening can be carried out as soon as possible,which greatly reduced the maintenance cost in later stage.This fact indicates the great significance of real-time crack monitoring of structural components.In this context,a method of pre-embedding electrodes when preparing a specimen,and monitoring the crack formation and development by measuring the electrical resistance is proposed.In order to ensure the incorporation of steel fibers meet the in-situ project quality requirement,steel fiber dosage was chosen as variable.The workability,mechanical properties and flexural toughness of specimens with different steel fiber dosage were tested and analyzed.In addition,some factors that may affect the resistance measurement of concrete specimens,such as steel fiber dosage,curing age and frequency were also studied.The main contents of this paper are as follows:(1)With slump and air content tests,workability of fresh concrete with different steel fiber dosage was investigated.The results showed that with the increase of steel fiber dosage,the slump of the mixture showed a downward trend,and the air content showed an increasing trend.(2)With cube compressive strength test,compressive strength of concrete specimens with different steel fiber dosage were investigated.The results showed that the incorporation of steel fiber has no significant effect on the compressive strength of the concrete.(3)With the third-point bending test,flexural toughness of concrete with different steel fiber dosage was investigated.It was shown that with the increase of steel fiber dosage,the flexural toughness of concrete was gradually improved.A good linear relationship between energy absorption index and fiber dosage can be found by linear fitting.(4)With bending test and synchronous electrical resistance measurement.The electrical resistance of specimen before and after cracking was studied.Results of double crack and double section experiment were also analyzed.It can be concluded that,the formation of crack or new crack in muti-cracks specimen can be promptly detected by monitoring the change of electrical resistance.With double section monitoring test,it was found that the electrical signal difference between cracked and uncracked section after specimen cracking was obvious,which means that crack section can be determined by monitoring the electrical resistance of specimen.(5)With the electrical resistance measurement performed among variation of influencing factors such as steel fiber content,curing age,and alternating current frequency.The influence of these factors on concrete specimen resistance measurement were explored.It was shown that,with the increase of steel fiber dosage,the electrical resistance of concrete specimens decreases;the electrical resistance of concrete increases with the increase of curing age;measured conductivity was affected by AC frequency,and the influence degree increases with the increase of steel fiber dosage.