What is Residual Reactivity to Internal Alkali (RRIA) testing for concrete?
Residual reactivity to internal alkalis testing of concrete structures is used to identify the current state of concrete with regards to Alkali Aggregate Reaction (AAR) damage and predict the potential for further degradation over time to allow for educated maintenance and repair strategies.
How does the Residual Reactivity to Internal Alkali (RRIA) test work?
Samples are held in conditions designed to significantly accelerate the AAR process (38°C and >95% relative humidity) and the rate of expansion is measured.
This elevated temperature and pressure enhances the mobility of alkali ions and water molecules promoting contact between reactive silica in aggregates and alkalis from the cement paste.
The measurement of expansion is a direct indicator of the ongoing AAR within the concrete as a gel that swells upon absorbing water is generated, exerting expansive pressure within the concrete that can lead to cracking and structural damage.
Measurement of this accelerated expansion over the test time allows an expansion vs time curve to be plotted and the empirical prediction of future AAR expansion.
What is Residual Reactivity to Internal Alkali (RRIA) testing used for?
Deterioration process | Defects | Control of repairs |
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How do I carry out Residual Reactivity to Internal Alkali (RRIA) testing of concrete?
While no specific BSI or ASTM standards exist for this test, a procedure for successfully completing RRIA testing based on related standards, industry best practice and data from research papers involves the following steps:
Use a diamond-tipped coring drill to extract 100x200mm cylindrical samples from locations that accurately represent the entire condition, avoiding areas with visible damage or repairs.
Place cores in a sealed environment conducive to AAR expansion with controlled temperature (38°C) and high relative humidity (>95%) to accelerate any ongoing alkali-silica reactions (ASR) within the concrete.
Use vernier callipers to record the initial and subsequent dimensions of the cores daily until no significant change in mass is exhibited between two consecutive tests. This will indicate that their moisture content and temperature are stable and that any subsequent changes in dimensions or mass are due to the AAR process rather than the environmental conditions.
Monitor the temperature and humidity within the conditioning environment to ensure they remain constant. Fluctuations in these parameters could delay reaching equilibrium.
After equilibrium has been reached continue to record expansion and mass measurements periodically (typically monthly). Measuring techniques and timings should follow ASTM C1293.
Analyse the raw data to determine the rate of expansion and plot a curve of residual expansion overtime.
Utilize software for statistical analysis to model expansion trends and predict long-term AAR. Factors such as the variability in concrete composition, environmental exposure conditions, and the initial ASR gel content must be considered. Historical data from similar concrete formulations and exposure conditions can provide additional insights into the accuracy of the predictions.
What equipment and expertise are required for Residual Reactivity to Internal Alkali (RRIA) testing of concrete?
A diamond tipped concrete core drill for sampling.
- An environmental chamber capable of precisely controlling temperature and humidity levels at 38°C and over 95% relative humidity respectively.
Digital vernier callipers with an accuracy of 0.01 mm for precise dimensional measurements of concrete cores and detecting small changes over time.
Precision balances with accuracy of greater than 0.01g for mass change measurements
Digital software analysis tools such as MATLAB or Microsoft excel packages to collate data and create plots to predict future AAR behaviour.
Laboratory experience and expertise is required to accurately carry out RRIA testing. While the test procedure itself is relatively simple it is vital to precisely control conditions for the entire test time.
What are the advantages of RRIA testing of concrete?
This test allows for an assessment of the not just the current damage sustained by a concrete structure but also the future potential for ongoing deterioration, allowing precise assessment and tailored intervention strategies.
By identifying if the possibility for further damage exists, it helps in planning maintenance schedules effectively, potentially saving on extensive repair costs that are not necessary yet.
By monitoring and mitigating expansive reactions, the overall durability of concrete structures is improved, extending their service life and performance.
What are the disadvantages of RRIA testing of concrete?
The test procedures are relatively complex involving sample extraction, preparation, and controlled testing environments, which can be cost-prohibitive.
The need to extract concrete cores for testing is inherently destructive and may require further repair post-testing.
The accuracy of predictions from this test can be affected by the environmental conditions in which the concrete operates, which are not always controllable or perfectly replicable in lab settings.
How accurate is RRIA testing of concrete?
Expansion of concrete samples can be identified that is greater than 0.01mm and mass changes greater than 0.001g.
Expansion vs time is plotted and empirical equations derived to accurately predict the level of expansion into the future with slightly degrading certainty.
What are the limitations of RRIA testing of concrete?
The test's accuracy in predicting future expansion is contingent upon the level of restraint within the concrete tested and the degree of alkali leaching, which can vary significantly between structures and environmental conditions.
The process from core extraction to result interpretation is lengthy, which may not be suitable for urgent assessment needs.
While the test indicates the potential for future expansion due to AAR, it does not definitively predict whether, when, or to what extent this expansion will occur, as these outcomes heavily depend on numerous environmental variables that the test does not simulate.
Concrete properties can vary significantly within a single structure. The test results from a sampled core may not represent the entire structure's condition, potentially leading to underestimations of risk.
Ancillary information
Maturity of test: > 10 years
Qualification & interpretation : Specialised lab
Service disruption: No
Preliminary works: No
Time consumption High (> one day)
Cost High
Access to element 1 face
References and further information