287-CCS : Early age and long-term crack width analysis in RC Structures
Technical Committee 287-CCS
Deputy Chair: Dr. Fragkoulis KANAVARIS
Even though reinforced concrete (RC) is one of the most used manmade materials in the world, and adequate models exist for the prediction and design of the ultimate capacity of RC structures, the prediction of service life behaviour is still not mature enough for actual design purposes. This may lead to immediate repair needs, inadequate service life behaviour even when regulatory prescriptions for design are strictly followed, or at other times to unnecessary overdesign of reinforcement, which has negative consequences on both sustainability and economic aspects. This is amplified by development of new more sustainable cements and supplementary materials since the range of material properties needed for SLS-design is considerably wider than for ULS design. The problem stems to a more fundamental set of mutually influencing factors that clearly require further development and integration: (i) lack of proper understanding of the fundamental mechanisms involved in the processes of hydration-induced temperature, shrinkage, creep and herewith caused cracking; (ii) lack of integrative developments combining material scientists and structural engineers for the relevant concerns in research; (iii) lack of definitions/recommendations for collaborative developments of field-involved stakeholders towards better behaviour (material technologists, structural designers, contractors, material suppliers); (iv) lack of integration of experimental developments for restrained behaviour in complex reinforced systems with predictive/simulation methodologies; (v) lack of benchmarking and integration of existing methodologies for simulation/prediction of stresses and crack widths during service life, including simplified code-based approaches and advanced simulations (e.g. backed by FE method), which are able to cope with the combined effects of applied load (sustained) and restrained deformation at both early ages and in the longer term.
The TC intends to contribute to the body of knowledge regarding the above-mentioned research/industry gaps, both on material and structural level, towards a better design for serviceability of RC structures, which in turn shall contribute for an overall improved service life. The TC will join binomials of experts: (i) from material science and structural design; (ii) focused mostly in early age behavior and those focused mostly in long term performance (iii) those focused in experimental approaches and those focused in simulation, and also; (iv) from academia/research and industry.
The topic of cracking in RC structures for serviceability has been addressed in the past, but never with the integrative perspective aimed with this TC, which is expected to bring about a significant number of new insights of important benefits for researchers and practitioners.
The TC excludes extreme loading situations related to fire, cryogenic temperatures, earthquake, fatigue and blasting, for example. Cracking due to swelling reactions (e.g. alkali silica reaction, delayed ettringite formation), other deterioration mechanisms, reinforcement corrosion and any type of volume change occurring in concrete before setting is also excluded.
Terms of reference
The TC is supposed to run for 4 to 5 years and intends to systematically address the set of knowledge gaps mentioned above, in a true intent to provide the basis for a ‘next generation’ approach to the problems that include restrained self-imposed deformations, and their impact on serviceability of concrete structures. It intends to bring experts from different fields in academia and practice towards a better understanding of phenomena and joint endeavours that further deepen knowledge in this complex context.
Due to the inherent continuity to the subjects covered by the recently closed RILEM TC 254-CMS (‘Thermal cracking of massive concrete structures’), this TC comprises a significant number of members of such TC. In fact, the TC stems from a set of activities that were set as future targets of development in the scope of the termination of TC 254-CMS. The proposed TC is also expected to have an international geographical reach, promoting an intercontinental collaboration of academics and practitioners. Right since its constitution, it includes participants from Europe, Asia, America and Africa with the intention to extend collaboration to Australia.
The work of the TC relies on the collaboration of subject matter experts, not necessarily with the same background, adding the interdisciplinary element required for approaching the complex topic of imposed strains at early age and long-term. The TC members shall be challenged for analytical and numerical benchmarking (estimation of stresses, strains, temperatures and crack widths under different conditions), as well as round robin testing (scale effect in tension). Depending on adhesion levels, which are strongly dependent on current research activity/funding of TC members, these tools might have smaller or wider reach.
The scope and aims of the TC resonate with industry needs in the field of crack control which adopts relatively unsustainable approaches to the problem, such as overdesigning or excessively repairing. The TC will also aide in identifying areas in which future research is needed.
Detailed working programme
This TC will operate combining physical meetings and meetings in an online environment to facilitate co-ordination of activities between members internationally.
A proposed timeline for the activities of the committee is:
- Start-up meeting (Nov. 2019 – Jan. 2020): introduction of members, suggestion of new members, plan future activities.
- First physical meeting and official inauguration of TC in RILEM Spring Convention in Guimarães (12-13 Mar. 2020). Agreement on book chapter and initiation of discussion of potential analytical/numerical benchmarks and round robin testing.
- At least one physical meeting per year, accompanied by one-two online meetings.
- Organisation of a relevant RILEM workshop (2021-2023).
- Publish book on crack control by 2024 (or up to 2026 upon potential extension of TC life).
The TC should be linked to obtain relevant information with the following present and past RILEM TCs:
- 254-CMS: Thermal cracking of massive concrete structures
- MDC: Multi-decade creep and shrinkage of concrete: material model and structural analysis.
- NUM: Numerical modelling of cement-based materials.
- 214-CCD: Concrete cracking and its relation to durability: Integrating material properties with structural performance.
- 238-SCM: Hydration and microstructure of concrete with supplementary cementitious materials.
- 259-ISR: Prognosis of deterioration and loss of serviceability in structures affected by alkali-silica reactions
RILEM strives for promoting a more sustainable and safe construction, improved performance and cost benefit for the society through a collaborative environment of international nature. This is in consonance with the goals of the TC which aims to achieve sustainable construction through enhanced understanding fundamental processes involved in crack control and disseminate guidance that can be used on academic and industrial level.
There is a potential of interconnection with fib TG 2.1, which is currently focusing on cracking as well, but with complementary methodologies. Cooperation and co-participation of members in both TC’s is expected with very positive impacts, particularly in view of the intended bridging between RILEM and fib, as independent but collaborative institutions.
The following deliverables are expected to be the output of the TC:
- A dedicated international RILEM workshop and workshop proceedings.
- Possible doctoral course in the scope of the TC to be evaluated
- Recommendations published in Materials and Structures on modelling of stresses in concrete from early ages with a thermo-chemo-mechanical approach (an ongoing process before the actual creation from this TC amongst several of its members).
- Publication of a final report summarizing the main results and the general conclusions
- A book on “Interdisciplinary approach to early age and long-term crack width analysis in RC Structures: from material science to structural design”. The book should cover not only state of the art matters, but also a collection of personal experiences, and points to joint conclusions reached by the Technical Committee. Therefore, the book will be a textbook (to be published through RILEM/Springer).
Tentative chapter structure for the proposed book:
- Cracking in RC structures: relevance and phenomenology
- Experimental insights in laboratory
- In-situ evidence repository
- Code-based approaches towards prediction of cracking and crack widths
- Analytical and semi-analytical approaches towards prediction of cracking and crack widths
- Micro and meso scale simulation approaches
- FE-based simulations
- Cracking performance requirements: aesthetics, durability, leak-tightness.
- Crack repair and sustainability
- Materials/techniques towards improved cracking performance
- Integrated measures on the supply chain towards better performance
Group of users
Academics working with fundamental materials properties and numerical simulation of materials properties, testing laboratories, industrialists working with e.g. materials development, scientists within engineering practice, structural designers, analysts and consultants.
Specific use of the results
The outcomes of the TC will pose substantial benefit to academics who work on multiphysics simulations of hardening and hardened concrete, as well as crack control due to imposed deformations. Furthermore, relevant, leading edge guidance for engineering practice will be established which will promote a more accurate and sustainable approach to control of cracking in reinforced concrete structures.