269-IAM : Damage Assessment in Consideration of Repair/ Retrofit-Recovery in Concrete and Masonry Structures by Means of Innovative NDT
Technical Committee 269-IAM
Deputy Chair: Dr. Dimitrios AGGELIS
Huge numbers of infrastructures built in an era of rapid economy growth are deteriorating acceleratedly all over the world. Those can be regarded as ‘asset’ as they have a potential to change their values corresponding to the chosen maintenance program. In order to sustain the infra-asset, the maintenance philosophy to be taken shall be proactive maintenance rather than reactive/ corrective maintenance under the limitation of infrastructure investment particularly for new important structures. As for the infra-asset management such phases as design, construction, quality control and maintenance including repair shall be reasonably implemented; however, as repair/ retrofit has not so far been verified quantitatively, the suitable life-time scenario could not be determined for the individual structure. For the management of infrastructures, repair, reinforcement or sometimes retrofit would be thus crucial to maintain those as long as possible. As for crack repair works in concrete structures without any corrosion of rebar, various methods are employed such as crack coating methods, injection methods, and crack sealing/ filling methods. While for those with rebar corrosion, section repair methods or electrochemical repair methods are well applied. For the most advanced cases, self-healing concrete using un-hydrates of cement and mixture agent or bacterias’ metabolism, have been studied intensively all over the world in order to expect self-repair effect when cracking.
However, when those repair programs or self-healing effect are to be executed properly, there still a doubt about the efficiency of the works that have been carried out, and therefore quality assurance of those repair programs or self-healing effect shall be made quantitatively with non-destructive approaches.
In the past RILEM TC activities, damage identification has successfully been studied through TC212-ACD (Acoustic emission and related NDE techniques for crack detection and damage evaluation in concrete) and as for the fruitful outcomes, three recommendations have been issued, leading to be candidates (NP16836, NP16837, and 16838) of ISO standard currently. Furthermore, in the follow-up TC239-MCM committee (On-site measurement of concrete and masonry structures by visualized NDT), on-site NDT-utilized damage visualization techniques have comprehensively been studied, focusing on establishment of reliable interpretation procedure of the results measured by non-destructive testing (NDT), which will be summarizing as a state of the art report at present. As shown in the above, advanced NDT techniques and visualization of the result for concrete-deterioration have been established, and the resultant such parameters as velocities and attenuation rate of elastic waves can be indices to quantify the damage as well as to assure the repair works.
Again quantitative assurance of repair/ reinforcement/ retrofit programs or self-healing effect of concrete structures is a crucial issue to realize sustainable society all over the world, and RILEM TCs’ past activities will surely contribute to this issue, and accordingly in the follow-up technical committee dealing with those works will be mandatory established. The outcome of this follow-up committee will impact on life cycle scenarios for concrete structures, leading to establishment of ideal sustainable infrastructure. Several RILEM recommendations, aiming at being ISO standards will be made by the consequence of the TC activity.
Terms of reference
As for outcomes of TC239-MCM, damage visualization procedures will be systemized by such several promising NDT as AE Tomography, Radar, Thermography, and Impact Acoustics. Invisible damage existing inside of concrete could be quantified by the promising damage indices resulting from respective NDT. In this proposed TC activities, namely ‘Quantification of recovery effectiveness of concrete structures by means of NDT,’ with using some control specimens including several designated crack properties or crack network properties, several kinds of repair works will be conducted by using crack coating, injection, and filling methods, respectively. Section repair methods or electrochemical repair methods will be also applied for the specimens simulating rebar corrosion. For those repair works, repair efficiency namely recovery rate will be quantified by applying NDT. AE tomography, e.g., will visualize the recovery by elastic wave parameters as dominant frequencies, velocities, wave-attenuation and so forth. For comparatively shallow areas, repair works could be quantified by Thermography and Impact Acoustics. And for the surroundings of rebars, Radar will be utilized to quantify the recovery rate. Finally, for the self-healing concrete using un-hydrates of cement and mixture agent or bacterias’ metabolism, the self-healing effect including commencing timing of the effect, filling condition of crack interfaces as well as eventual performance-recovery will be evaluated by a variety of NDT by using their promising parameters. For recovery evaluation specific NDT parameters will be determined (e.g. advanced AE indices, ultrasonic pulse velocity, dispersive features) with the aim of evaluating mechanical properties like stiffness (elastic modulus) of the repaired structure, physical conditions like the percentage of sealing/filling of the open volume of cracks, while if possible, projections to the strength will be attempted.
Detailed working programme
-Literature survey and topical presentations
During each meeting, literature survey and associated presentations shall be planned. Subsequent literature will be also collected by members of the TC.
- State-of-the-art report
The results of the literature survey will be compiled in a state-of-the-art report or a final report. The report will also contain the experience in situ and on-site measurements carried out by members of the TC.
- Round robin testing
Round robin testing is useful to assure the resultant recovery rate corresponding to the type of repair works. With using control specimens installed by simulated defects, damage quantification before/ after repair works will be conducted by NDT in which the members are involved.
- Test evaluation
Through the testing, appropriate NDT and promising parameters to quantify the damage will be discussed by the members. And the most prospective method(s) to quantify the repair effectiveness will be proposed.
At the end of the evaluation and discussion of various round-robin tests, recommended practices will be prepared for standardized manuals. The recommendations shall be submitted for publication in Materials & Structures.
Several symposia and workshops are planned for presentation of the TC´s work and discussion of the recommended practices. It is hoped that other experts who are not member of the TC will contribute to the conferences planned. The RILEM recommendation could be associated with CEN or ISO as a pre-standard. The proceedings of the conferences shall be prepared, and possibly be published as the special issue of Materials & Structures.
This is a follow-up committee of TC 212-ACD and TC 239-MCM. This TC is linked well with such TC dealing with to quantify the concrete performance as well as NDT as 246-TDC 249-ISC. In addition, close working relations with ACI Committee 228, Acoustic Emission Working Group, USA, AE technical committee of JSNDI and IIIAE (International Institute of Innovative Acoustic Emission) are confirmed, because chairmen of these committees are key members of the proposed TC. Also ISO TC-135/SC9, Convener of WG4 is a chairman of this proposed TC, is an important role for the proposed RILEM committee because three ISO standards’ proposals using AE techniques for concrete materials/ structures have been cited from the three recommendations resulted from the activity of TC212-ACD.
The following achievements are promisingly expected and produced based on the past closely related TC activities:
• RILEM recommendations and recommended practices for quantification of repair/ reinforcement works by NDT
• Workshop proceedings, possible as a special issue of Materials & Structures.
• Training courses for one-site measurement by NDT
• Pre-standards to be submitted to ISO.
Group of users
Testing laboratories, Owners of infrastructure, Construction companies, and Universities.
Specific use of the results
In order to sustain the infra-asset, the maintenance philosophy to be taken shall be proactive maintenance rather than reactive/ corrective maintenance under the limitation of infrastructure investment particularly for new important structures. As for the infra-asset management such phases as design, construction, quality control and maintenance including repair shall be reasonably implemented; however, as repair/ retrofit has not so far been verified quantitatively, the suitable life-time scenario could not be determined for the individual structure. In the past decade, repair works have thus been intensively carried out all over the world for the likely deteriorated or damaged concrete structures; however, the quantification of damage/deterioration is still an issue to be studied in the present. This situation has been regarded as reckless and excessive execution of repair works without any assurance of the works. The proposed TC will be dealt with those unsolved issues to establish promising quality indices with innovative NDT so that life cycle scenarios could be established for every single infrastructure. The outcome will be used not only for developed countries where infrastructures have already been matured but for the emerging countries where life cycle scenarios containing maintenance programs shall be established in advance to ask loans for e.g., World Bank, Asia Development Bank and so forth. Accordingly the impact of TCs’ achievement will be huge for any country holding or constructing concrete infrastructures.