Research on failure of cementitious materials under rotary cavitation test

Utilizing the rotating cavitation erosion test device invented by Nanjing Hydraulic Research Institute (NHRI) to perform the persistent cavitation experiment on hardened cement paste and mortar, observing and analyzing the differences and similarities between cavitation and abrasion zone. Observing the cavitation erosion on the surface of cement-based materials and researching on the destruction of cement hydrations under cavitation process by adopting multiple modern material analysis apparatus, such as Scanning Electron Microscope (SEM), Energy dispersive X-Ray(EDX), X-Ray Diffraction(XRD) and thermal analysis(TG&DSC). Results implied that after continuous cavitation test for 2 hours, the microscopic structure of original defects becomes smooth, to be specific, the flake, rod shape-crystals are basically disappeared and the bottom of cavitation pits are shaped like some melted organizations. Hence the cavitation erosion on cement paste is not only a simple mechanical failure but also lead to the thermal decomposition on hydrations, which could cause the remarkable loss of hydration products on the surface of test blocks. The specific figures are as follows: the mass loss of cementitious substances is no less than 40% so as the loss of slaked lime is more than 25% during a 2 hours cavitation experiment. In that way, the considerable hydration mass loss is capable to cause a huge affection on deterioration of concrete structures.