What is Chloride profile testing?
The chloride profile of concrete is measured by taking dust samples at progressive depths from the structures surface and measuring the total and free chloride levels present at each point to determinate the chloride diffusion coefficient and map how the chloride content changes with depth to the steel reinforcements.
How does Chloride profile testing work?
The total chloride content of concrete samples collected at different depths from the concrete surface is determined by nitric acid extraction and free chloride content by a water extraction.
The graphic representation of the chloride content (Kg/m3 or % / mass of binder) vs. depth in the concrete gives the chloride profile.
Based on the chloride profile and levels of free chlorides, the chloride diffusion coefficient , the chloride content at the steel reinforcement surface and the time expected for a critical chloride content reach the reinforcements can be predicted.
What is Chloride profile testing used for?
Deterioration process | Defects | Control of repairs |
How do I carry out Chloride profile testing?
BS EN 14629:2007 provides a codified procedure for chloride profile testing of a concrete structure. Steps include:
Identifying sampling locations and drilling cores from the concrete structure.
Mark the core at regular intervals to represent the different depths at which chloride content will be analysed. This can depend on factors such as the objective of the study or the cover depth of the element.
Carefully cut the drilled core into segments using a concrete saw where each segment corresponds to a specific depth range from the surface.
Wear appropriate PPE to protect against dust and ensure the cutting process does not contaminate the samples with external chlorides.
Clearly label each core segment with its corresponding depth range for accurate tracking and analysis.
Separately grind each core segment and separate the dust in half.
Expose each sample to water to remove the free chlorides and record their mass as per BS EN 14629:2007.
Expose each sample to nitric acid remove the bound chlorides and record their mass as per BS EN 14629:2007.
Add free chlorides to bound chlorides to get the total chloride content and calculate this as a % by mass and kg/m3 value for each depth range.
Construct a chloride profile graph to assess the penetration of chlorides over time and evaluate the risk of corrosion to the reinforcing steel.
Estimate the chloride diffusion coefficient.
Based on the chloride diffusion coefficient, surface chloride concentration, cover depth and the chloride threshold for the steel reinforcement (approximately 0.95% by weight of cement), use Ficks second law to calculate an estimated time until the onset of corrosion.
What equipment and expertise are required for Chloride profile testing?
To carry out chloride profile testing a significant amount of specialised equipment and a high level of expertise is required. Usually, this test is conducted by a specialised laboratory.
Equipment includes:
Coring equipment and a concrete saw for sample collection/preparation.
Mortar and pestle or ball mill to powder cores for chemical analysis.
- A precise electronic scale capable of measuring to at least 0.001 gram for weighing the samples.
Beakers of flasks for chloride extraction.
Nitric acid solution.
What are the advantages of Chloride profile testing?
This test can measure the free and total chloride to estimate the chloride diffusion coefficients.
Chloride profiles enable early detection of areas with risk of corrosion before it reaches the reinforcement and provide an estimated time to initiation of corrosion.
By understanding the chloride distribution within a concrete structure, repair strategies can be more accurately tailored to the specific needs of different areas, enhancing the effectiveness of remedial actions.
While initially the costs are high and the test takes a significant period of time, they can lead to significant long-term time and cost savings by extending the lifespan of the structure and reducing the need for frequent repairs.
What are the disadvantages of Chloride profile testing?
Time-consuming and costly test method which may limit applicability for large-scale structures when multiple samples are needed.
Obtaining concrete cores for chloride profile testing requires drilling into the structure, which can compromise its integrity and aesthetics.
Concrete carbonation and leaching can alter the chloride profile, affecting the accuracy of the test results. These "skin effects" may not accurately reflect the chloride levels at the depth of the reinforcements.
The need for specialized equipment and skilled personnel to conduct the testing and interpret the results adds to the overall expense.
Handling and preparing samples for analysis carries the risk of external contamination, which can skew results and lead to inaccurate chloride content readings.
How accurate is Chloride profile testing?
The accuracy of chloride profile testing in concrete is critically dependent on meticulous sample selection, cross-contamination prevention, and the precision of extraction and weighing processes. Precise drilling and handling are essential to prevent any bias in the results due to contamination. The extraction process, which involves dissolving chloride ions into a solution, is vital to accurately reflect the concrete's chloride content. Any inconsistency here can significantly affect the outcome, either underestimating or overestimating chloride levels.
Weighing plays a crucial role, demanding the use of highly sensitive analytical balances to ensure precise measurements of samples and solutions. This accuracy in weighing underpins the integrity of the data, influencing the calculation of chloride diffusion coefficients and, subsequently, the assessment of corrosion risks. Standardized and reproducible methods for extraction and weighing are paramount for the reliability of longitudinal studies and the evaluation of protective measures against chloride-induced corrosion.
Combining these elements—meticulous execution from sampling to analysis and expert data interpretation—ensures the reliability of chloride profile testing. This comprehensive approach provides a solid foundation for making informed decisions on mitigating corrosion in concrete structures, highlighting the intertwined roles of precision, consistency, and expertise in achieving accurate test results.
What are the limits of Chloride profile testing?
Chloride profile testing is a critical tool for evaluating the corrosion potential in reinforced concrete structures, yet it comes with certain limitations. The process is inherently invasive, requiring drilling that may compromise structural integrity or aesthetics.
Accurately representing the entire structure's condition through selected samples poses challenges, especially in complex or large structures. Environmental factors like carbonation and moisture can skew results, while the interpretation of these results demands expert knowledge to avoid misjudgements regarding corrosion risks and necessary interventions. Additionally, the testing is time-intensive and costly, with a risk of sample contamination during extraction and analysis. It also offers a snapshot of current chloride levels but lacks predictive power for future corrosion progression, necessitating further monitoring and modelling for a comprehensive risk assessment.
Despite these limitations, understanding and navigating these challenges is essential for leveraging chloride profile testing effectively in the maintenance and protection of concrete infrastructures.
Ancillary information
Maturity of test: > 10 years
Qualification & interpretation : Specialised lab
Service disruption: No
Preliminary works: Yes
Time consumption High (> one day)
Cost High
Access to element 1 face