An Embedment Method Of Smart Aggregates By Precasting In Concrete Blocks

smart aggregate is a commonly used sensor for health monitoring of concrete structures,allowing ultrasonic monitoring of dynamic stresses and material properties.smart aggregates embedded in the structure often need to be fixed by bonding or tying to the reinforcement and other support structures,the support structure interferes with the monitoring area stress field and the sensor location stability is poor,thus affecting the monitoring accuracy.This paper proposes a novel smart aggregate embedding method——Concrete Block Casing method(CBC).Through numerical and experimental studies,it is found that the new embedding method significantly reduces the influence of stress field on the embedding region compared with the traditional embedding method,and the sensor position is more stable and the monitoring randomness is lower.The specific research results obtained in the paper are as follows.First,the randomness of sensitivity caused by the randomness of the Epoxy layer thickness of the commonly used normal and shear stress smart aggregates is analyzed.The range of possible variations of the Epoxy layer is considered,and the range of variations of the sensitivity of the piezoelectric smart aggregate is determined by finite element simulation and verified by loading tests.It was found that the coefficient of variation of the smart aggregate sensitivity is very small,no more than 3%,and the randomness of the sensor itself can be ignored when performing embedded randomness analysis.Secondly,this paper proposes the Concrete Block Casing method(CBC)for embedding precast concrete blocks with smart aggregates and compares it with the traditional embedding methods: Cross Joint Binding method(CJB)and Double Side Bonding method(DSB)to investigate the embedding interference level and its stochasticity.The effects of embedding in the monitoring of normal and shear stresses were verified in concrete column and deep beam specimens,respectively.It was found through experiments and finite element analysis that the CBC method has the least interference and embedded randomness in the stress field;when the positive stress is monitored,the influence of the support structure on the stress field in the monitored area is negligible,and the mean value of the CBC monitoring sensitivity is close to the theoretical value,and its sensitivity is 1.88 and 2.85 times that of CJB and DSB,and the coefficient of variation is 23% and 31% of both;when the shear stress is monitored,the CBC monitoring The coefficient of variation of sensitivity is 55% of that of DSB.Finally,the randomness of fluctuation parameters during fluctuation monitoring by the prefabricated block embedding method and the conventional method were compared and analyzed.The wave speed,center frequency and amplitude of the received signal were analyzed by performing 140 k Hz modulated Gaussian pulse excitation on six fluctuation monitoring paths spaced at 200 mm.It is shown that the use of CBC embedding can significantly reduce the randomness of fluctuation monitoring due to embedding,and its wave speed coefficient of variation is 28% and 25% of that of CJB and DSB,its center frequency coefficient of variation is 96% and 62.5% of that of both,and its amplitude coefficient of variation is 92.5% and 94%of that of both,respectively.