233-FPC : Form pressure generated by fresh concrete
Technical Committee 233-FPC
Deputy Chair: Dr. Nicolas ROUSSEL
Activity ending in: 2016
Self-Compacting Concrete (SCC) is, in terms of a concept, one of the few truly revolutionary innovations within the concrete industry over all. Since its development in Japan in the mid-80s, research and use of SCC has increased and spread considerably throughout the world. This is displayed, for example, by the fact that RILEM has to date organised no less than four international symposia on SCC (Stockholm 1999, Reykjavik 2003, Chicago 2005, and Ghent 2007), while the fifth is scheduled for Montreal in 2010. In addition, RILEM has addressed the importance of SCC by forming a total of six technical committees so far: TC-174 on SCC and TC-188 on Casting of SCC, both chaired by Åke Skarendahl; TC-205-DSC on Durability of SCC, chaired by Geert De Schutter; TC-209-RFC on Rheology of Fresh Cementitious Systems, chaired by Olafur Wallevik; TC-222-SCF on Simulation of Fresh Concrete Flow, chaired by Nicolas Roussel, and TC-MPS on Mechanical Properties of SCC, chaired by Kamal H. Khayat. Of these six committees, the latter three are still active.
Adoption of SCC is, by far, most pronounced within the precast industry, where a number of factories in Europe are solely using SCC, while others use SCC in a majority of elements manufactured. Precast element factories built today are even deliberately designed to take full advantage of the superb qualities of SCC technology.
However, the use of SCC in the cast-in-place industry is, relative to the precast industry, much more modest, often limited to around 5-10% of total ready-mix concrete production. In fact, the choice of SCC over conventionally vibrated concrete is often governed by the nature of the application itself, when conventional concrete is impossible to consolidate (tunnel linings, narrow geometry, dense reinforcement, etc.) or when the scale of the project is large enough to gain considerable efficiency by using SCC. For so-called everyday use of SCC, one of the more obvious limiting factors is the prediction of form pressure, and thus, the optimal design of formwork. As a rule of thumb, the cost of the formwork system represents some 40-60% of total construction costs. This aspect alone shows the importance of formwork.
For approximately the last 10-15 years, form pressure generated by SCC has been reported in the scientific literature, and results show a broad span of pressures, from full hydrostatic pressure to as low as 20% of hydrostatic pressure. Some only report on the resulting pressure itself, while others have elaborated on approaches to also predict the pressure. In general, it is accepted that SCC (in fact all fresh concrete) is a thixotropic material that builds up a structure at rest, and this property is a common input to most of these approaches. However, besides material properties many other parameters also influence the resulting form pressure, such as formwork characteristics (surface roughness, form stiffness, reinforcement, etc.), casting procedure (disturbance of the concrete in the form, casting rate, filling from top or bottom, etc.) and environmental issues (temperature, mechanical disturbances on the construction site, etc.).
The development of new highly efficient synthetic dispersion admixtures, or superplasticizers, has been one of the key factors enabling the development of SCC, though they are also more and more commonly used to control the workability of conventional concrete. This means that most mix design actions, whose goal is to achieve different workability levels, are now done using superplasticizers. This implies that conventional concretes today are designed very differently than they were back in the 60s or 70s, when current design codes were developed. Consequently, recently published data from the literature indicate that conventional concrete results in far less pressure than the design codes predict. The conclusion must be that not only is there a need to develop new design codes for formwork for highly flowable concrete types such as SCC, but existing design codes for conventionally vibrated concrete must also be revised. Hypothetically, the same properties, material and other, apply for conventional concrete as well as for SCC in terms of form pressure; however the crucial difference is, of course, the deliberate disturbance when consolidating the conventional concrete mechanically by vibration.
The proposed new RILEM Technical Committee on Form Pressure Generated by Fresh Concrete would focus on gathering the available information on form pressure, from all relevant perspectives. It should be noted that the aim is to include aspects of conventional concrete and highly flowable concrete, as well as SCC in the work. The list of possible parameters affecting form pressure is long, and once defined; the relevant parameters to include in future design formulas will be considered and discussed by the TC members. In addition, existing codes and published material from conference proceedings and technical journals, etc., will be reviewed. As a natural outcome of the mapping of existing knowledge, the committee will suggest future research aimed at completing the knowledge necessary to create new formwork systems design formulas. Another focus will be on discussing possible new innovative changes to existing formwork systems and casting techniques, especially relative to SCC fresh properties
Terms of reference
The committee is composed of members selected from international organisations and research centres active in the field of formwork pressure. These include academia, research institutes, industry (contractors, formwork producers), public agencies, and other technical committees (for example ACI).
The estimated duration of the work is approximately 3.5 to 4 years, and the new committee could start its activities in the fall of 2009.
Detailed working programme
- Fall 2009: Seek consensus over committee’s work strategy and limitations.
- Two annual meetings during the years 2010 through 2012, in which the committee’s report on form pressure, future research and possible innovations will gradually be discussed and finalised, together with planning of the workshop/symposium.
- 2012: Publication of the report and organisation of the workshop/symposium;
This TC will be an extension of the work carried out by RILEM TC-CSC Casting of Self-Compacting Concrete. Its focus is identified as a highly important research area by ACI TC 237 - Self-Consolidating Concrete and ACI TC 347 Formwork for Concrete.
The TC fits into RILEM’s technical programme, in particular the items Materials Characterisation, Properties Evaluation and Processing.
Planned deliverables are:
- A committee report including:
1) State-of-the-art on form pressure generated by concrete,
2) Suggestions for future research to complete the knowledge necessary to create new formwork systems design formulas and
3) Possible innovations on formwork systems and casting techniques to fully utilise SCC in concrete construction.
- A workshop or symposium
Group of users
- Academics working with fundamental materials properties
- Standardization organizations
- Formwork system designers and producers
- Testing laboratories
- Concrete supplier
Specific use of the results
The outcome of the committee’s work will contribute to mapping the grey areas in the field of form pressure and highlight future need for research. The results will contribute to a deeper understanding of the mechanisms behind material properties, and how to characterise and use them together with formwork characteristics and casting procedures to optimise formwork systems and production techniques.
The work will contribute to a more optimised and widespread use of SCC within the concrete industry.