196-ICC : Internal curing of concretes
Technical Committee 196-ICC
Autogenous shrinkage is a phenomenon, which is ingrained in high-strength/high-performance concretes of low water/binder ratio matrix. It is the result of chemical shrinkage, which cannot be avoided. In low water/binder ratio matrices it leads to considerable self-desiccation. This self-desiccation results in the development of capillary stresses causing autogenous shrinkage. Conventional curing procedures of ponding in water are not sufficiently effective in this case. They may eliminate the autogenous shrinkage in small cross-sections only, because the penetration of water from the external ponded surface is limited. In view of these limitations, different strategies have been developed in recent years, based on the use of internal reservoirs of water. One strategy, which has been investigated more extensively, is based on the use of lightweight aggregates, while the other is based on the use of water absorbing polymers. Both water saturated porous aggregates and water saturated absorbing polymers can act as internal reservoirs, providing a source of curing water to the paste volume in their vicinity, to offset self-desiccation. The main objectives of the committee are (1) to coordinate research efforts and compile the results of studying fundamental mechanisms responsible for internal curing, and (2) to develop practical recommendations for utilizing of advanced methods of internal curing of concretes. The focus will be on internal curing of high-strength/high-performance concretes of low water/binder ratio matrix, in order to counteract autogenous shrinkage caused by self-desiccation. These recommendations will include mainly technological procedures (preparation of raw materials, mixing, casting, vibration and curing) and concrete mix design (optimization of the type, dosage and properties of the water-deliberating phases). The geometry of cast and cured concrete elements has to be taken into account, as well as environmental conditions and using conventional curing agents. Numerous interacting phenomena such as shrinkage, creep, thermal effects, cracking, and interface quality will be investigated. The scope of the committee will extend also to the methods of internal curing of other concretes, such as normal-strength concrete made at water/binder ratio higher than ~0.4.
Terms of reference
Researchers in different countries around the world are presently on their way to develop practical solutions for different aspects of advanced methods of curing. The aim is to assemble the various pieces of knowledge generated and to ultimately produce a general guide to assist concrete technologists. 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, Japan, North American influence area (European standards, ASTM, ), the TC will include representatives of three different world regions: European, North American and Asian. The main goal of the TC is the elaboration of recommendations for engineers and practitioners; therefore their participation is necessary. 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. The work will require preparation of a state-of-the-art report, computer processing aimed to optimise type, dosage and characteristics of the materials used as internal curing agents, development of the new types of internal curing agents and special technological procedures providing the maximum effectiveness of internal curing.
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: - Modelling; - Experimental work; - Validation of the proposed computational modelling by cross comparison with the experimental results of other members; exchange of the results of the modelling and experiments and discussion at periodical working meetings of the TC; - Organizing international RILEM conference (workshop) on Internal Curing of Concretes; - Preparation of the state-of-the-art report and recommendations for the practitioner.
The proposed TC is a follow-up of TC 181-EAS "Early Age Shrinkage Induced Stresses and Cracking in Cementitious Systems" lead by Prof. A. Bentur, and it will develop further the methodology of internal curing formulated in the Part 7.2 of the TC 181-EAS state-of-the-art report, which will be published soon by RILEM. In part of the experimental investigation, the work of the proposed TC will be coordinated with TC 185-ATS "Advanced testing of cement based materials during setting and hardening" lead by Prof. H.-W. Reinhardt. The work will provide input to relevant standardisation work within ACI, ISO and NIST. The TC fits into the RILEM's technical programme, in particular the items "Performance, maintenance and repair of building materials and structures during the service life" and " Updating of test methods". 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 dealing with other advanced methods of concrete curing will be made.
Expected achievement A general guideline for internal curing of concretes. It will propose: · Computational calculations; · Harmonised test methods; · Recommendations for the practitioner; · International RILEM conference (workshop); · State-of-the-art-report. Results diffusion 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" and "Concrete Science and Engineering"; · At the end of the TC tenure: publication of a final report summarizing the main results and the general conclusions in a dedicated conference or workshop.
Group of users
Academics, testing laboratories, industrialists, practitioners, general public ... The targeted users are industrials and practitioners involved in the field of concrete technology.
Specific use of the results
Reliable rules and recommendations for durable concretes, 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.