Abstract:Through NEL experimental method and scanning electron microscopy test (SEM), the resistance of chloride ion penetration in the concrete admixed with polypropylene fiber, complex minerals (fly ash/silicon ash with weight ratio of 4∶1), and polypropylene fiber under axial compressive loading or not was studied. The results show that, under no-load condition, the compactness between aggregate and cement stone improves, and the number and the width of the crevice obviously decrease in concrete specimens admixed with appropriate amount of polypropylene fiber and complex minerals. From the view of macro property, the diffusion coefficients of chloride ion decrease, and the anti-chloride ion permeability obviously increases when compared with that of the concrete admixed with polypropylene fiber or multiple minerals. The optimal proportion of the concrete for anti-chloride ion permeability is the composition of 0．1% polypropylene fiber and 25 % complex minerals co-doped. The diffusion coefficients of chloride ion slightly decrease firstly and then increase in concrete under axial compressive load. Under the same stress ratio, the chloride ion diffusion coefficient is the minimum for concrete with polypropylene fiber and complex minerals co-doped.

Abstract:In order to study the compressive properties of reactive powder concrete (RPC) at elevated temperature, 108 cube specimens (70.7 mm×70.7 mm×70.7 mm) were prepared to study the group compressive strength of RPC with polypropylene fibers (PPF) and steel fibers. The influences of temperatures, hybrid fibers content and explosive spalling principles were investigated. The experiment results show that a PPF volume content of 0.2% and a steel fiber volume content of 2% can prevent the explosive spalling of RPC and significantly increase cube compressive strength. The cube compressive strength decreased at 100℃, compared to 20℃ and increased from 200℃ to 500℃ as compared to 100℃, but decreased after 600℃. The cube compressive strength of RPC was lower as the fibers content increased before 300℃, but was higher as fibers content increased beyond 300℃ when steel fibers was the same content. Cube compressive strength of RPC was higher as the steel fibers content increased before 100℃, but was lower as steel fibers content increased beyond 200℃ when PPF was the same content. Compared with the normal strength concrete and high strength concrete, the cube relative compressive strength of RPC was lower before 400℃, but was higher between 500℃ and 800℃. The calculation formula of cube compressive strength at elevated temperature was obtained by fitting the curve of experiment data considering hybrid fibers content as temperature varied.