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Modeling the Time-to-Corrosion Cracking of the Cover Concrete in Chloride Contaminated Reinforced Concrete Structures

by

Youping Liu

Dissertation submitted to the Faculty of the Virginia Tech in partial fulfillment of the requirements for the degree of

Ph.D

in

Civil Engineering

Approved

Richard E. Weyers, Chair
Imad L. Al-Qadi
Richard M. Barker
Jesse J. Brown, Jr.
Richard D. Walker

October 21, 1996
Blacksburg, Virginia


Abstract

Modeling the Time-to-Corrosion Cracking of the Cover Concrete in Chloride Contaminated Reinforced Concrete Structures Youping Liu Richard E. Weyers, Committee Chairman Department of Civil Engineering


Abstract

Significant factors on steel corrosion in chloride contaminated reinforced concrete and time-to-corrosion cracking were investigated in this study. Sixty specimens were designed with seven admixed chloride contents, three concrete cover depths, two reinforcing steel bar diameters, two exposure conditions, and a typical concrete with water to cement ratio of 0.45. Corrosion current density (corrosion rate), corrosion potential, ohmic resistance of concrete and temperature were measured monthly on these specimens using both the 3LP and Gecor devices. Metal loss measurements were performed in accordance with ASTM G1-90, method C3.5, after specimens cracked. The actual corrosion weight loss of the steel reinforcing bars was then compared to the result obtained from the corrosion rate measurement devices. An interaction model for characterizing the dynamic corrosion process was developed based on the five-year corrosion database. The model demonstrates that the corrosion rate is a function of chloride content, temperature at reinforcement depth, ohmic resistance of concrete, and corrosion time after initiation. A time-to-corrosion cracking model was suggested based on a corrosion-cracking conceptual model and critical mass of corrosion products. The model predicted times to corrosion cracking are in good agreement with the observed times to corrosion cracking of the cover concrete.

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