259-ISR : Prognosis of deterioration and loss of serviceability in structures affected by alkali-silica reactions
Technical Committee 259-ISR
Deputy Chair: Prof. Leandro SANCHEZ
Activity ending in: 2019
With aging infrastructures, instances of Alkali Silica Reaction (ASR) and Delayed Ettringite Formation (DEF), broadly covered under the term Internal Swelling Reaction (ISR), are increasingly being detected. They have been observed in bridges, dams, and most recently in nuclear power plants. Concrete swelling may result in bridge partial failure, dams with structural cracks and misaligned turbine shafts, and locked slice gates. For nuclear reactors micro-cracks may cause increased gas permeability which will jeopardize the containment integrity and may decrease the residual structural resistance under accidental loading. This TC, which limits its activity to structures with known expansive concrete, seeks to address two complementary but fundamental questions: a) What is the kinetics of the reaction and b) How would it affect the integrity of the structure (serviceability and strength) and thus establish a science based prognostic to the structure owner.
The activities of this Technical Committee will be subdivided in six major topics:
- Topic 1: Selection and interpretation of optimal monitoring system for structures undergoing expansion [2, 3] (optical, acoustic and others). This is essential to monitor the progress of the swelling evolution and its consequences.
- Topic 2: Development/refinement of existing laboratory procedures to determine the kinetics of the reaction i.e. expansion vs (future) time [4-6]. Procedure to determine the kinetic characteristics of the time dependent reaction to be used in a finite element simulation. But also critical to estimate when the reaction will be exhausted.
- Topic 3: Extrapolation of results from structural component laboratory testing .
- Topic 4: Selection of material properties based on data from existing structures undergoing ASR  or DEF. This is a critical step in the performance of a reliable finite element simulation.
- Topic 5: Identification of critical features which should be present in a finite element code; Development of test problems for validation; Survey of relevant programs which can perform a transient structural analysis of a structure undergoing a chemically induced expansion.
- Topic 6: Guidelines for finite element codes. [6,7].
The activities of this proposed TC will not cover: petrography, chemistry, causes, material selection (for construction), prevention measures, remediation, or numerical micro-models.
Terms of reference
Estimated time needed: Three years.
Membership: Will be limited to few members with an international geographical distribution, who are specialist in related fields, and few stakeholders from the hydroelectric, nuclear and transportation industries. It is expected that much of the work will be done by electronic correspondence. Conference calls will be held as well. The committee meetings will be planned, as much as possible, in conjunction with the conferences with maximum participation by committee members, to minimize the travel costs and raise attendance, and the semi-annual RILEM conferences will be preferred for the committee meetings.
All RILEM members are eligible to join the committee.
Detailed working programme
1) Comprehensive and detailed literature search on:
- Degraded mechanical properties (tensile strength, elastic modulus, fracture energy and others) to be used in a numerical study of a structure.
- In-situ measurements and interpretation (acoustic, optical, others) to assess extent and evolution of the reaction.
- Finite element numerical models.
- Kinetics of the reaction and long term prognostics.
2) Recommendation of a procedure to assess future expansion. Identical tests will be performed in multiple laboratories to assess and refine an existing procedure.
3) Recommendations for in-situ monitoring.
4) Numerical benchmark studies.
5) Synthesis of the above, and guidelines for the prognosis of swelling concrete.
6) Publicize results in ACI, RILEM, FraMCoS conferences.
RILEM TC 219-ACS is about to wrap its activities. Though it had a Modeling working group (M) which was supposed to issue a report on existing numerical models, this task was never completed and it was stated that this should be left for future TCs. Furthermore most/all of its activities focused on prevention (petrographic studies) of AAR and management of existing structures suffering from AAR. It did not address prognostic.
ASR has been identified by a recent report by the U.S. Nuclear Regulatory Commission and the nuclear industry as a major degradation mode that can potentially impact concrete nuclear structures.
ASR has long been identified as a major aging problem for dams.
Two major achievements are expected form this research:
- RILEM Recommendation on a methodology to develop a science-based prognosis for infrastructures undergoing internal swelling.
- Organization of, at least, one international symposium on the subject (main target FraMCoS).
Group of users
a) Engineers assessing aging of structures.
b) Academic and institutional researchers in the field eager to adopt and improve the suggested recommendations.
c) Members of various engineering society committees preparing design recommendations or codes.
Specific use of the results
Proper use of the outcomes of this research will be guided by those committee members who are also referred as the “Stakeholders”. That is when confronted with an existing structure subjected of ISR, stakeholders would be in the position to assess its structural integrity to their respective regulatory bodies through continuous monitoring, laboratory testing which will provide the kinetics of the expansion (i.e. expansion vs. time), and recommendations on how to perform an adequate and credible finite element simulation to assess serviceability and strength as a function of time. The economical impact of that research is directly tied to the licensing renewal and safe long-term operations of electricity generation hydro- and nuclear stations.