Experimental Study And Mechanism Of Cracking Resistance Research On The Early Plastic Cracking Of Fiber Reinforced Concrete

The early plastic cracking phenomenon of concrete is very common in practical engineering.In order to solve the above problems,most of the project adopts the incorporation of chopped fibers into concrete to prevent and suppress the early plastic cracking of concrete,and the actual engineering effect is good.At present,most of the practical engineering uses the empirical methods that is first using test method and then adopting the specifications of the fiber,and the guidance of fiber application given by the corresponding standardized design and technical standards is not detailed.And the fiber crack resistance mechanism-fiber spacing theory does not take into account the influence of the fiber length and the interfacial bonding between fiber and concrete on early plastic cracking,the theory can’t fully reflect the fiber parameters on the crack resistance of concrete,it is not helpful for engineers and researchers to understand the fiber crack resistance in depth.These problems have hindered the extensive application and in-depth study of fiber concrete.In addition,due to the early plastic shrinkage cracking of concrete mainly caused by plastic deposition and water evaporation,but the fiber is how to affect the plasticity of sedimentation and water evaporation has not yet explored clearly,in order to achieve a comprehensive understanding of role of fiber in cracking of concrete,so the study needs to be systematically explored.The fibers adopted in this paper are used polypropylene fiber commonly employed in engineering.Based on the early plastic cracking test of fiber concrete,this paper focuses on the crack resistance mechanism of fiber in the early stage of plastic cracking.This paper focuses on 3 aspects: the improvement of the fiber space theory in the plastic cracking stage,the influence of the fiber on the plastic settlement and the effect of the fiber on the evaporation of water.After a large number of experiments and experimental data analysis,the main results of this paper are as follows:(1)Considering the parameters such as fiber content,length and diameter,the product of fiber length to diameter ratio and fiber content percentage P is simplified as parameter G,and the formula(2.9)is well fitted with the total area of the fracture.This proposed formula can better reflect the effect of different parameters of fiber on crack suppression,which can provide reference for the design application of fiber in engineering.(2)The improvement of fiber spacing theory based on linear elastic fracture mechanics makes the fiber spacing theory more fully reflecting the mechanism of fiber cracking resistance in the early stage of plastic cracking of fiber reinforced concrete.And the concept of fiber stress ratio area T is proposed,which is the size of the fiber bonding force per unit area perpendicular to the fiber length.(3)The incorporation of fiber into the concrete can effectively connect the concrete interior pores between the concrete surface.In the early stage of concrete plasticity,the fiber acts as a channel of the concrete bleeding,and it could enhance the bleeding rate of the concrete internal,which be higher than that of the water evaporation rate of concrete surface.The experimental results show that the incorporation of concrete into concrete could effectively reduce the development of capillary negative pressure,thus reducing the early plastic shrinkage of concrete,in this regard also reducing the probability of early plastic shrinkage cracking of concrete,and then improving the early plastic shrinkage cracking of concrete.(4)In the early plasticity stage of the concrete,the fiber acting as a water delivery channel,the incorporation of the fiber will aggravate the early plastic settling of the concrete and deteriorate the early plastic settling cracking of the concrete.