Jieying Jane Zhang, Ph.D Research Officer and Adjunct Professor, Concrete Structures Institute for Research in Construction National Research Council Canada 1200 Montreal Road, Bldg M-20 Ottawa, Ontario, Canada, K1A 0R6 Tel/Fax: 613-993-6752 / 613-952-8102
Abstract: This paper presents an approach towards a performance-based durability design of concrete structures based on a simplified diffusion-based model, which overcomes some of the limitations of the current prescriptive rules of existing design standards. Numerical nonlinear relationships and relative sensitivities between the four parameters that govern the time to corrosion initiation of reinforced concrete structures are determined, including chloride diffusion coefficient, chloride threshold value of reinforcement, concrete cover and surface chloride exposure condition. To achieve a specified design life, it is found that in aggressive chloride-laden environments: (i) increasing the minimum concrete cover is more effective than selecting a corrosion-resistant steel; (ii) it is necessary to use both high performance concrete and corrosion-resistant steel; (iii) a relative decrease in the concrete cover has to be compensated by a much greater increase in the corrosion resistance of steel; and (iv) the variations in chloride diffusion coefficient has a large impact on required concrete cover and chloride threshold value, especially in increasingly aggressive environments. These relationships can be used to identify the most relevant parameters and serve as a guide for service life-based design for durable concrete structures.
Abstract: This paper presents a maturity concept and approach of applying the maturity method for predicting the development of mechanical properties of high-performance concrete over time. An examination of the activation energy and assumptions taken in the developmental process of the existing maturity method are first presented to better understand the capabilities and limitations of the maturity method, which is supported by new and existing experimental evidence. A practical approach is then proposed in which the activation energy is determined mathematically by minimizing the error between the predictions and experimental data. It is based on a new concept that the same maturity is defined only when different specimens of the same concrete have achieved the same level of a specified property under different curing temperatures. This concept makes the maturity approach more robust and more general for application to different concrete mix formulations and different types of property. The accuracy and feasibility of the proposed approach were successfully confirmed by experimental evidence.
Abstract: This paper evaluated relationships between four parameters that govern the time to corrosion initiation of reinforced concrete structures built in chloride-laden environments. Numerical nonlinear relationships between pairs of the governing parameters are determined based on a deterministic diffusion-based corrosion initiation model. The four parameters include chloride diffusion coefficient in concrete, chloride threshold level of steel reinforcement, concrete cover depth, and surface chloride exposure condition. The quantitative evaluations of these relationships can be used to identify the parameters that are more effective in achieving a specific design life of a concrete structure defined as the time to corrosion initiation. It was found that increasing concrete cover depth is more effective under heavier exposure to chlorides, while increasing the corrosion resistance of steel in terms of its chloride threshold value is more effective under lighter exposure conditions. The relationship between chloride diffusion coefficient and concrete cover depth implies that the use of high-performance concrete is more effective than increasing the concrete cover depth. The relationship between chloride diffusion coefficient and chloride threshold value suggests the concrete cover for normal concrete is more critical than for high-performance concrete. The relationship between concrete cover depth and exposure condition in terms of surface chloride concentration reveals the necessity of using both high-performance concrete and high performance steel under heavy and severe chloride exposure conditions. These relationships can also be used to determine most appropriate combination of values of the parameters for an effective design.
Abstract: durability in patch repair systems caused by new corrosion
attack is prevalent. From the prevailing understanding, the mechanism is attributed to macrocell
corrosion formed between repaired area (called patch) and its adjacent unrepaired area (called
substrate), and thereby ensuring electrochemical compatibility between the two areas is deemed
to be the key element to reduce the corrosion risk and thus to achieve a successful repair. This
paper examined the corrosion mechanism and the concept of compatibility in patch repair
systems from fundamental electrochemical principles and experimental verification. It was
illustrated that both macrocell and microcell corrosion mechanisms could play significant roles,
and the total corrosion could be underestimated if the latter is overlooked. Although the
incompatibility serves as the driving force for the macrocell corrosion, in light of corrosion
kinetics, it was shown that the corrosion magnitude depends more on the individual corrosion
kinetics of the anode or cathode.
