227-HPB : Physical properties and behaviour of High-Performance Concrete at high temperature

Technical Committee 227-HPB

General Information

Chair: Dr. Pierre PIMIENTA
Deputy Chair: Dr. Robert JANSSON MC NAMEE
Activity starting in: 2007
Activity ending in: 2014
Cluster A

Subject matter

The work program of the new TC comprises characteristic effects, physical properties and modelling of high performance concrete (HPC) at temperatures up to 1000°C. Five types of HPC will be investigated. These are high strength concrete (HSC), ultra high strength concrete (UHPC) and self-compacting concrete (SCC). Special type of HPC like special temperature resistant (STRC) and special aggregate concrete (SAC) will also be included in the subject of the program. The advisory group of the TC 200 HTC proposes to use the wording HPC in a broader sense than it is commonly used up to now.

The basis of modelling is closely related to the mechanical, physical and geometrical properties or characteristic effects under high temperature conditions. Therefore a state of art report (STAR) on HPC will be the first task of the TC. The specific aspects are e. g.:

- Strength, elasticity, plasticity, strain, transient creep and thermal strain
- density, conductivity, heat capacity, phase changes, fracture energy and permeability
- porosity, pore pressure, spalling, temperature fields and stresses, weight losses and energy adsorption

An updating of existing date will be done at first, thereafter follows the presentation of new test data of committee members and experts.

The modelling of concrete is the second main task of the TC. A START of modelling will be drawn up at the beginning of work, starting from simple models which are now in use, e. g. EC level two and level three, up to models with high levels of sophistication which are still a matter of investigations in concrete research.

Further tasks of the TC are devoted to experimental and theoretical aspects, whereby the spalling of concrete members and the measurement of pore pressures in HPC will be investigated. The following aspects will be taken into account with respect of spalling of HPC:

- temperature increase and stresses - moisture content of elements
- external load and prestress
- thickness of concrete members
- reinforcement
- heat exposure and geometry (2d or 3d)
- aggregate type
- mix proportion and porosity
- fibres and fibre content

The committee will also investigate the prevention of spalling by sacrifice layers or other means. A report and/or workshop on spalling of concrete are the aim of this task. There are four TC members which are working in the field of pore pressure measurements, whereby new technical methods are under development. A report of test methods and on new test results is proposed from the advisory group. The result may be also presented in the framework of the spalling workshop mentioned above.

The TC advisory group has not included the topic investigation of HPC structures under high temperature e. g. fire behaviour of structures or else in its program, because it was felt that there is still a lack of knowledge concerning the material properties at high temperatures and modelling, i. e. a calculation of structures at high temperatures is in many cases rather speculative than scientificly well-founded.

The final goal of the TC beside of the proposed state of art reports and the reports on spalling, pore pressure measurements and experimental methods is the organisation of one or two workshops in specifics fields like spalling or modelling of HPC, (HSC and UHPC) under high temperature.

Terms of reference

From experience with RILEM TC 200 HTC it is estimated that the life time of the new TC should be 5 years. For the bibliographical work at least one year is needed. New test results and test equipments will be available at 2009. The finalisation of reports according to paragraph 4 needs at least two years. Finalisation and an international workshop are planed for 2012.
The recruitment of members and experts for the new committee is based on the members of the TC 200 HTC and further correspondence to specialists in this field. An announcement in the RILEM Journal would be very much appreciated. The chairman proposed C. Andrade or co-worker (E), Prof. M. Schmidt, Kassel (G) and Prof. C. Bailey, Manchester (UK) to be asked for their participation.
The work implies bibliographical research but also experimental work and theoretical research on HPC concrete. The equipments for measurements at high temperatures are mostly available in the member institutions mentioned on page 6 and 7. New equipments for pore pressure and permeability measurements are being available in different institutes.

The German research Foundation (DFG) has established a research program on the 'Composition and Properties of fresh and hardened UHPC'. Up to now the DFG program is not extended to high temperature research. Nevertheless one participant in the German UHPC project (Prof. Schmidt) indicated his interest in the new committee (see list of scientists who have interest in the new TC).

Detailed working programme

The different tasks for the TC will be the following:

Assembling of known experimental data and presentation of new data.

Task 1: STAR on HPC Properties
Task 2: Report on spalling
Task 3: Report on pore pressure measurements
Task 4: STAR on Modelling
Task 5: Experimental methods
Sub-task 5.1: Fracture energy method
Sub-task 5.2: Thermal properties method (conductivity, heat capacity, density)
Sub-task 5.3: Permeability method
Sub-task 5.4: Temperature measurements
Sub-task 5.5: Weight loss measurements

Describing of test equipments and methods for high temperature measurements of the following properties and quantities:

- thermal conductivity and heat capacity
- weight loss and density
- permeability
- pore pressure
- fracture energy

Technical environment

The new TC is closely related to the TC 200 TC which will finalise its work on high temperature behaviour of concrete at the 31st of August 2007. There are 11 RILEM Recommendations and one STAR avaible from the work of this TC.

Further relations exist by members who are working in TC 205 SCC of RILEM. International exchange is supplied by RILEM members who are working simultaneously in the fib committee 'Fire Design of Concrete Structures'. Several members of the new TC are also members of the new Russian committee working on the 'Application of Fracture Mechanics in Civil Engineering' which was established by the Russian Academy of Architecture and Building Science (RASSN) in March 2007.

The new TC will be organised as indicated on a table of this proposal (see page 8). The possible members and their institutions are shown on the list given hereafter

Expected achievements

The new TC intends to work on HPC of different types based on the knowledge of experts who are working world wide. A condensation and publication of this knowledge by RILEM is the main objective of the new committee. With respect to this objective the TC intends to prepare the following documents:

- a state of the art report on the temperature behaviour of HPC (see Fig. 1)
- a state of the art report on modelling of concrete at high temperatures
- reports on temperatures effects on HSC, SSC, UHPC, STRC and SAC like
- spalling, pore pressure and permeability
- change of physical properties and weight loss

Group of users

The possible users of the research results comprise several groups. The first group mainly includes

- universities and test laboratories,
- material scientists and experts.

A second group includes persons and companies which are involved in practical building design and construction like

- designers and civil engineers
- building material companies and industry
- building authorities

Specific use of the results

The proposed TC is a relevant committee which covers economical and social needs because of the use of high performance concretes, which in many applications may contribute to the reduction of environmental effects of concrete constructions. Further it increases the safety and life-time of structures, which is of great importance for infra-structure buildings like bridges, tunnels and express-ways.

The new materials may be successfully applied in pre-fabrication because in this case a considerable reduction of manufacturing time of buildings can be achieved due to the rapid increase of concrete strength. Further the SCC is more and more used in practice, whereby the possibility of a combination of comparatively high strength with good workability leads to a very effective concrete production.

The results of the TC may be directly used in practice of concrete building design with HPC. Up to now the behaviour of HPC, especially under fire exposure, is not completely understood in practical design. HPC explodes usually under fire attack and safety measures must be applied. There are simple technological means to reduce or even avoid the spalling effect of HPC. The technological means are not widely known in the practical fields of HPC applications.

The results of the TC may also help to increase the knowledge of modellers with respect to the behaviour of concrete at high temperatures or under fire exposure and may be used to increase the level of safety and reliability of concrete structures.