Effect Of Loading On Permeability Of Fiber Concrete

This thesis presents an experimental study on permeability of concrete under and after loading. Permeability of fiber concrete, including polypropylene fiber(PP fiber) concrete, steel fiber concrete and hybrid fiber (PP fiber and steel fiber) concrete, is measured by means of the Germanns water permeability test method and the chloride ion penetration test method (CECS 207:2006), after loading at various stress levels. Permeability of hybrid fiber concrete is evaluated by means of the water absorption test method under loading at various stress levels. The goals of this thesis are to study the effect of loading on permeability of concrete and that of fiber (PP fiber and steel fiber) on permeability of concrete subjected to loading.The experimental results indicate that, for a few types of concrete, i.e., steel fiber concrete at W/B ratio of 0.60, hybrid fiber concrete at W/B ratio of 0.26, permeability of concrete was influenced by loading at a certain stress known as the critical stress. When the compressive stress is lower than it, an increase of permeability of concrete is small; when the compressive stress exceeds it, a noticeable increase in permeability of concrete can be measured.The fact that permeability of concrete after loading was lower than that under loading, indicates that cracks closed partially after loading. Therefore, a test method to measure permeability of concrete under loading should be established.Permeability of PP fiber concrete was almost the same as that of plain concrete at a given stress; compared with plain concrete, permeability of concrete incorporating steel fiber decreased significantly when concrete was subjected to loading. These experimental results indicate that, steel fiber plays a more significant role than PP fiber in terms of permeability of concrete subjected to loading.If steel fiber is used to improve the cracking resistance, the W/B ratio of control concrete should be an important factor to be considered. Only in the control concrete with a lower W/B ratio (for example, a W/B ratio of 0.26 in this thesis) that is the effect of steel fiber on resisting cracks significant.For the same batch of specimens, the data (relative water absorption) of the water absorption test under loading can't be correlated with those after loading for the data are limited, and thus whether the test can be used to measure permeability of concrete under loading is uncertain. So that, more data are needed in further research to make a correlation between the data of the water absorption test under loading and those after loading, i.e., choose more stress-strength ratios.