Technical Committee 193-RLS
A cement-based material bonded overlay is often the first solution investigated when a concrete structure is in need of repair or strengthening. Lining is relevant to the same technique. In all cases, the result is an hybrid structure and the durability of such a system makes problem, specially because of the cracking of the overlay and its debonding from the overlaid structure.
The investigated technique mainly concerns slab and concrete pavement repairs. Millions of m2 of concrete overlays are performed each year throughout the world, still without much guarantee of success from a durability standpoint.
The main objective of the committee is to end up with design rules and practical recommendations specific to cement based bonded overlays, specially in the field of repairs in order to eliminate or reduce drastically hazard in the design and in the process. The many interacting phenomena such as shrinkage, creep, thermal effects, cracking, interface quality and fibre reinforcement of the overlay (which has proven to be beneficial) will be thoroughly investigated.
The scope of the committee may extend to other so-called hybrid structures, for instance asphalt road bases overlaid with Portland cement concrete.
Terms of reference
Many researchers around the world are presently on their way towards practical solutions in relation with different aspects of concrete repair durability. The aim is to assemble the various pieces of knowledge generated to ultimately produce a general guide helping the designer in most circumstances. The conclusions of the TC are expected within 3 to 4 working years.
The regular and correspondent members to be recruited are recognized experts in the domain. To account for the different practices and different standards in Europe and in North American influence area (European standards and ASTM), the TC will be built around two poles: a European Chairman (France) and a North American Secretary (Canada).
The main goal being the elaboration of design rules for engineers and recommendations for the practitioners, their participation is fundamental. Actions are expected in the different geographical areas covered by the members of the TC to initiate local (national or multi-national) groups involving practitioners. These groups will work complimentarily to the TC. They would provide the TC with the practitioners needs and expectations and carry the results of the TC through the standard making process until its achievement. A European Project could complete the system. It would be initiated and managed by the Polish partners.
Detailed working programme
The work of the TC will first focus on bringing together the expertise and knowledge of each participating member. This synthesis of expertise will be done at the first TC meeting. It will help identify the points of agreement and of disagreement among the participants.
On this base, the future work of the TC will process in parallel the following items.
- Validation of the proposed computational modelings (effects of shrinkage, temperature changes and external loading) by cross comparison with the experimental results of other members.
- Interface :
* different surface processing (from hydrodemolition to a smooth sandblasted interface), their respective advantages and problems,
* modelling of the interface, fundamental parameters: tensional or shear behaviour, or an association of both ?
* experimental characterization tests.
- Fatigue loading.
- Curing of the overlay, joints in the base structure and in the overlay.
- Overlay edges (probably the most critical zones).
Special attention will be paid to the effect (beneficial) of fibre reinforcement on the overlay behaviour and overall durability.
This work will be concluded by the proposal of quantitative design rules and recommendations for the practitioner.
This TC is complementary with TC 167-COM "Characterisation of old mortar with respect to their repair". The latter will provide useful guideline to prevent mismatches between the repair material and the original material. Besides, its expected applications are different from those of TC IFE "Industrial floors for withstanding harsh environmental attacks, including repair and maintenance". Indeed, although the repair aspect is present in both TC, the latter deals with chemically aggressive environment and the use of polymer or polymer-modified materials. It implies specialised workmanship and, in comparison with regular cement-based overlays (object of the proposed TC), shrinkage, cracking and bond at the base-overlay interface are of different nature, inferring different results and conclusions.
This TC will have connections as well with TC AES "Early shrinkage induced stresses and cracking in cementitious systems". The
The work will be carried out in connection with national or multi-national local groups involving practitioners as mentioned in 3. In addition, attempts to connect with researchers or groups already dealing with hybrid road structures (asphalt overlaid by concrete) will be made.
A general guideline for durable cement-based repairs or bonded overlays. It will propose:
- computational calculations,
- harmonised test methods, especially to characterise the interface,
- simplified designing rules for the practitioner,
- During the tenure of the TC: publication, by their respective authors, of the ongoing results (in scientific journals and conferences).
- Regular reports in Materials and Structures.
- At the end of the TC: publication of a final report summarizing the main results and the general conclusions in a dedicated workshop or symposium, or in special session of a conference on repairs.
Group of users
The targeted users are industrials and practitioners involved in the field of repairs.
Specific use of the results
Reliable rules and recommendations for durable repairs and thin bonded overlays, eliminating any hazard in their design and processing.
Through the local national or multi-national groups evoked in 3, the practitioners will, in their respective countries, implement the TC's recommendations until the adoption of national or international standards.