What is "Concrete Cancer"?
Corrosion of steel reinforcement in concrete structures is well known to be "Concrete Cancer", which is a significant worldwide problem and causes multi-billion dollars losses to the infrastructure and building owners each year. The detection, diagnosing and appropriate treatment of this complicated problem requires very special expertise in this field.
How the ACCI Can Help?
The ACCI is a leading group in research and consultancy on corrosion of reinforcement in concrete structures (see Papers and other reports under Publications in the menu). The special advantages of using the ACCI services include:
- Our extensive experience in condition survey, corrosion investigation, development of remedial and maintenance strategies and specifications.
- Use of state-of-the-art techniques, such as GECOR-6 on-site corrosion rate testing, half-cell potential mapping, chloride diffusion profile analysis, and material analysis by XRD, XRF and SEM and many more.
- Unique ACCI-developed techniques and softwares for effective investigations such as:
"Potential Curvature Method"
ACCI consultant (Tian) Z.T. Chang has developed a unique "Potential Curvature Method" for corrosion assessment based on extensive theoretical and on-site experiences. Tian's method greatly improves the accuracy to identify active corrosion sites regardless of whether the structures are in marine environments or mainly affected by carbonation. This overcomes the major limitations of the criteria of ASTM C876 on corrosion assessment based on half-cell potential values.
A paper of this new method is to be published in the "9th Durability of Building Materials and Components" (9DBMC), an international conference in Brisbane in March 2002.
The following is an example of corrosion assessment of a concrete pile in a marine wharf with the Potential Curvature Method.
Fig. 1 shows a half-cell potential map over the pile surface.
Fig 1. Half-Cell Potential Map over A Wharf Pile Surface
Fig. 2 is a Potential Curvature map plotted based on Tian's method for the same pile, where the active corrosion locations are clearly identified. An examination of exposed reinforcement on this pile showed good correlation with Tian's method.
Fig 2. Potential Curvature Map over the Same Pile Surface
[ Back to Top ]
"Cyclic Chloride Penetration Test"
High resistance to chloride penetration is an important property of quality concrete suitable for marine structures in order to provide long-term protection to steel reinforcement. BRC (ACCI) consultants have developed an accelerated salt-water ponding tests with wetting and drying cycles closely simulates the conditions in the splash and tidal zones.
In this test, concrete samples are subjected to 14 to 28 days cyclic exposure with 12 hours immersion in 15% NaCl solution and 12 hours drying under heating light. At the end of cyclic exposure, the samples are tested for chloride penetration depth. This test method and the assessment criteria have been included in the document "Performance Criteria for Concrete in Marine Environments" published by the Concrete Institute of Australia in November 2001.
The following figure shows typical chloride penetration profiles in concrete and mortar samples.
Fig-1. Chloride Penetration Depth in Samples after BRC Cyclic Test
[ Back to Top ]
"Chloride Diffusion Profile Analysis"
The transport of chloride ions into concrete is usually described by Fick's second law of diffusion. The mathematical solution to this problem is the "error function", which is very complicated. The chloride diffusion coefficient D can only be obtained by numeric approaches based on the results of analysis of chloride content at different depths in concrete samples.
The ACCI consultants have developed a unique numeric method, which is not only able to calculate the chloride diffusion coefficient D, but also to predict the time when the chloride concentration at the reinforcement level would exceed the threshold value for corrosion to initiate.
The following Fig-1 is an example of analysis of chloride diffusion coefficient with the ACCI method.
Fig 1. Analysis of Chloride Diffusion Coefficient with ACCI Method
[ Back to Top ]
|
