Papers by Author: Chun Hua Lu

Abstract: In order to investigate the effects of polyvinyl alcohol (PVA) fibers on the performance of concrete, such as strength, crack resistance, permeability and chloride penetration properties, experimental research were carried out in this paper . Three types of fiber reinforced concretes with 0, 0.5%, 1.0% volume fractions were designed with the same water to cement ratio of 0.43. Flat band method was used to evaluate the cracking resistance, while AutoCLAM and ASTM C1202 were adopted to measure the permeability of concrete. The experimental results showed that the workability and the compression strength decreased as PVA adding volume increasing. However, the tension and the bending strengths increased for PVA fiber concrete. The number of cracks induced by the shrinkage of concrete was reduced by adding more PVA fibers. The permeability and chloride penetration ascended as PVA volume increasing. However, all the parameters with regards to strength, crack resistance, permeability and chloride penetration for fiber reinforced concrete were more reasonable than those for the specimens without PVA fiber. In additional, a very good correlation between the permeability and the electric flux was found in this paper, that means both AutoCLAM and ASTM C1202 could be used for concrete penetration test.

Abstract: Concrete cover cracking induced by reinforcement corrosion is an important problem in reinforced concrete structures. Several existing analytical models for cracking time are discussed, and it is found that the penetration of corrosion products into corrosion cracks is neglected in these models. Based on our study, a theoretical model that takes the ingress of rust into cracks into account is proposed to predict the cracking time. In order to analyze the amount of corrosion products deposited in cracks, an accelerated corrosion test was performed. Based on the experimental results, the parameter k, which deal with the ingress of corrosion products into cracks, is calibrated to be 0.1~0.3 for accelerated corrosion test. By comparing the predictions with the test results, it is found that the proposed model has high accuracy in analyzing the cracking time and that the mean absolute error between predictions and observations is about 9.4%.

Abstract: Based on chloride diffusion and random field theory, an analytical model of PC structures in erosive environment with chloride corrosion subjoining cyclic freeze-thaw was formulated. Models presenting the influence of chloride and cyclic freeze-thaw to failure probability are used to track the structural failure. It is found that cyclic freeze-thaw could be the driving force to damage of concrete in rigidity and mechanics. The computing results show that reliability index increases with the cover thickness, and cyclic freeze-thaw increases with decrease reliability. It is important to reliability calculation whether considering cyclic freeze-thaw.