Study On The Fracture Toughness Of Polypropylene Fiber Concrete By Acoustic Emission

Recently, polypropylene fiber concrete (PFC) developed rapidly, and has been widely used,and the technology of acoustic emission (AE) has a good application prospect in concrete filed. But there are a few studies on the fracture property of PFC by AE, and they can't meet the practical need.Introduced double-K fracture criterion used in concrete and considered softening characteristic of PFC, and based on the difference between concrete and PFC, amended the relative parameters, this paper tries to find the proper way to calculate the fracture toughness of PFC.AE technology can reflect the damage situation in metal, by comparing the position map of fracture process zone and the practical damage graph, can find both are consistent, therefore, applying AE position technology to study on fracture process zone is feasible. The initial cracking load of concrete beam is determined by AE method in this paper, then the measured solution of initial fracture toughness is obtained.The fracture parameters such as fracture energy, unstable fracture toughness and critical crack tip opening displacement are obtained by using the modified double-K fracture criterion and the data of experiment. Compared K IiCni ,e calculated from differentλvalue with K IiCni ,t calculated by AE, theλvalue of each group specimen is obtained, the real softening curve of material can be found.By comparing standard with non-standard PFC, the change low of each parameter with specimen size is gained, that is whether water reducing agent is added or not, every influence coefficient of different size specimen almost is same, and the fracture property of non-standard beam is better than the standard beam's.By comparing plain concrete with PFC of different fiber volume rate, the change low of each parameter with fiber volume rate is gained. And can find according to analyzing change law that polypropylene fiber having grate toughening effect for concrete, there is one best fiber content, and it is 0.9kg/m3, and adding water reducing agent, the fracture energy and unstable fracture toughness and initial fracture toughness of concrete are remarkably increased, but the critical crack tip opening displacement becomes lower. The analysis of double-K fracture criterion have showed that the modified model is suitable for describing the fracture of PFC.The studies can provide parameters for study of PFC fracture mechanism, structure design calculation of PFC, structure stability evaluation and damage prediction.