The Test And Prediction Of Fly Ash And Polypropylene Fibers Affect Chloride Ion Permeability Of Burdening Concrete

Steel corrosion is one of the main causes of the reinforced concrete structuresdurability declining. The chloride ion is the primary factor of causing steel corrosion.It is of great significance to study the concrete chloride ion permeability.Concrete structures are often under load in the actual use. Load can cause theoccurrence and development of concrete internal micro cracks and the formation ofpermeable tunnels. And then load affects the chloride ion permeability. The actualloading conditions of concrete are simulated by imposing an axial load(40%,60%,80%of ultimate compressive load) on each test piece. The chloride ion diffusioncoefficient of burdening concrete is measured by NEL method. The results of loadaffect concrete permeability are studied.Fly ash and polypropylene fibers are two kinds of concrete admixture usedfrequently. Fly ash can reduce the dosage of cement and improve the performance ofconcrete to some extent. The polypropylene fibers incorporated into the concretemainly prevent cracking. Three water-cement ratio(0.30,0.40,0.50) of concrete aredesigned. Polypropylene fibers and fly ash are mixed into concrete in differentproportions. The work performance, compressive strength and chloride ionpermeability before and after loading of concrete in each group are studied. Theresults of water-cement ratio, fly ash, polypropylene fibers affect the permeability ofburdening concrete are further analyzed. The microscopic morphology of the concreteis observed simultaneously by scanning electron microscopy, which helps understandthe synergistic effect between fly ash and polypropylene fibers in macro.The study of neural network predicts chloride ion permeability of concrete isperformed in the end of paper. The prediction performance of BP neural network andRBF neural network is compared. The influence of increasing or decreasing stressratios of sample data covering to network prediction results is discussed. Through the work mentioned above, the following conclusions can be reached:Firstly, proper amount of fly ash and polypropylene fibers are mixed in concretetogether, which shows that the slurry dense is improved in micro and the concreteimpermeability is to improve in macro. Secondly, the results of polypropylene fibersaffect the permeability of concrete is associated with the size of water-cement ratio.Thirdly, when the stress ratio increases from0to0.6, the changes of concretepermeability show critical stress phenomenon. Fourthly, when both the stress ratioand incorporation ratio of fly ash and polypropylene fibers remain unchanged, theratio of concrete chloride ion diffusion coefficient shows downward trend withwater-cement ratio increases. Fifthly, when water-cement ratio, the incorporation ratioof polypropylene fibers (fly ash) and stress ratio remain unchanged, the results of flyash (polypropylene fibers) dosage affects the ratio of chloride ion diffusion coefficientare reversed to that of the chloride ion diffusion coefficient while no loading. Finally,RBF network is better than BP network in prediction accuracy and computing speed.With the addition of sample data covers stress ratio, the minimum prediction errornorm of RBF network increases. But the corresponding target value of mean squareerror decreases.