Technical Committee 218-SFC
Deputy Chair: Prof. Dr.-Ing. Christian U. GROSSE
Activity ending in: 2011
The properties of cement based materials in the fresh and hardening state are currently being measured with rather conventional methods. The methods are not objective because the results are highly dependent on the measuring device and the measuring procedure. A few examples: setting and hardening of cement is determined by the Vicat needle. It measures the penetration resistance of a standardized needle under a defined force. Begin and end of setting is defined in the appropriate cement standard (for instance EN 196). The value of these two points during the hydration of cement is rather arbitrary and only useful for comparison of cements. However, there is no valuable relation between the results of the Vicat test and properties of concrete in the hardening state. Questions like end of workability of a concrete mixture cannot be answered from the Vicat test.
Workability is measured by various test methods such as the slump test, the flow table test, the vebe time, the compaction test and the penetration test. None of these tests give an objective result. The change of workability is assessed from tests at various times. However, there is no clear relation between workability test and practical workability at the site, for instance during slip forming.
What would be needed are objective, science based test methods with continuous monitoring of material properties from the fresh until the hardened state. There is a need by material producers, suppliers, and users to control production, mix, and execution.
New testing methods are available which could be used. They are based on the propagation of waves through a medium with time (or state) dependent properties or on the refection coefficient. This wave reflection coefficient as well as the velocity of the waves is clearly related to the setting and hardening state. Some acoustical methods use compressional waves while others use shear waves. Features like damping, dispersion, energy transport, frequency spectrum can also be measured and depend on the composition of a mix. Changes of the mix, either as the material or the amount (concentration) of a component is concerned can be detected. After having carried out numerous measurements it should be possible to control production and mixing rather accurately.
Control of cement based materials during production and execution leads to higher quality, more uniformity, and thus better durability. The control of high performance products is necessary in the light of structural safety. The increasing use of blends of binders asks for more control than today.
During the RILEM TC 185-ATC several procedures in non-destructive testing of fresh and hardened cement based materials using different techniques like NMR, acoustic emission or based on electrical or thermal effects have been investigated. Since there are already standards for some of these methods, there is a need mainly for recommendations regarding acoustical methods demonstrating their ability to be a standardized. The groups dealing with acoustical methods for quality control of fresh concrete and cement will be approached for participation in the new TC. They will supply the latest developments and guarantee a successful work of the TC.
Terms of reference
The work will start with a literature survey based on the state-of-the-art report compiled by TC 185-ATC and with new literature added by the members. It is expected that this report does not have to be rewritten but extended by a compilation of existing standards and recommendations. The topic refers to acoustical methods which can be used in the laboratory, on the building site in a control laboratory and during execution, for instance integrated in the formwork.
These methods will be selected for an additional round robin test on cement, concrete and maybe other cement based products. Round-robin testing on fresh mixes is only possible if the test equipments are brought to the mixing place. Since only a few different acoustical methods are addressed by this TC it is assumed that all TC members are able to meet at the same place. By this, the equipments can be calibrated to each other.
The round-robin tests will be evaluated and discussed in terms of applicability, versatility, usefulness for practice. These tests will be accompanied by individual tests at the site of the participants or at selected industrial sites.
At the end of the term of reference a recommendation will be written and proposed to RILEM.
The members will be recruited from laboratories, universities, and industry. It seems essential that material producers contribute to the work. Furtheron, one from the side of execution should participate. Test equipment developers come from laboratories and universities.The time necessary is estimated at 4 years
Detailed working programme
Literature survey and state-of-the-art of existing recommendations and standards
The starting literature dealing with acoustic methods are the according chapters of the state-of-the-art report to be compiled by RILEM TC 185-ATC. This report will be finalized in December 2004. Some literature has been collected by the applicant selected from this report. These literatures describe the state-of-the-art of techniques using acoustic methods for the quality control of cementitious materials.
The results of the literature survey will be extended by a compilation of existing recommendations and standards. The report will be continuously updated during the lifetime of the TC and published in form of an article.
Round-robin testing was a useful instrument during TC 185-ATC to assess the capability of the investigated test methods. A final round-robin test will be done to compare the actual status of the acoustical methods at one place. In case of fresh cement based materials round-robin testing is complicated due to the continuous change of the state of hydration. For this singular test, all groups will meet at the same site. Therefore, the test equipment of the participating groups has to be carried to the measuring site in order to supply each of them with the same batch. Various batches will be prepared such that a broad range of properties (or phenomena) can be investigated. The equipments should show their suitability, sensitivity, accuracy, and user friendliness. The tests will be evaluated with respect to as many parameters as possible, i. e. wave velocity, damping, and frequency spectrum. The experience during testing will be also evaluated and discussed. The aim is to select the most prospective method(s) for further detailing and development.
At the end of the evaluation and discussion of the several round-robin testing a recommendation will be prepared for standardized testing of fresh and hardening cement based materials. The recommendation will be submitted for publication in Materials & Structures.
A workshop is planned for presentation of the TC´s work and of the test recommendation. It is hoped that other experts who were not member of the TC will contribute to the workshop. The RILEM recommendation could then be completed and offered to CEN or ISO as a prestandard.
The workshop should prepare proceedings which contain the scientific merit of the test methods, their principles and potential applications.
There is a direct link to the previous RILEM TC 185-ATC. A relation could be established also to TC Nos. 188-CSC, 196-ICC and CUA as well as to the new TC’s ACD and INR.
- Compilation of existing standards (article) - RILEM recommendation for testing of fresh and hardening cement based materials
- Workshop proceedings
- Prestandards to be submitted to CEN or ISO
Additionally, the TC will organize a training course focusing on the industrial application of the methods.
Group of users
Testing laboratories, industrialists (mainly producers of mineral binders, additions, admixtures), construction companies, universities.
Specific use of the results
The economic impact is expected by better control of manufacture of components and execution of structures. High performance products need a close system of testing and monitoring in the fresh and hardened state of cement based materials.
CEN TC 104 "Concrete" has defined so-called concrete families with similar (but not equal) composition. Continuous testing would help to identify those mixes which do not belong to a family and thus to exclude wrong mixes.