185-ATC : Advanced testing of cement based materials during setting and hardening
Technical Committee 185-ATC
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 deter-mined 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 con-crete 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, flow table test, the compaction test and the penetration test. None of these tests give an objective result. The change of work-ability 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 us-ers 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. The velocity of the waves is clearly related to the setting and hardening state. Other 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. Since the RILEM workshop "Testing during concrete construction" in 1990 various research groups have been working on non-destructive testing of fresh and hardened cement based materials. These groups will be approached for participation in the new TC. They will supply the latest developments and guarantee a suc-cessful work of the TC.
Terms of reference
The work will start with a literature survey and lead to a state-of-the-art report. The topic refers to methods which can be used in the laboratory, on the building site in a control laboratory and during execution, for in-stance integrated in the formwork. Most prospective methods will be selected for round robin testing on cement, concrete and maybe other ce-ment based products. Round robin testing on fresh mixes is only possible if the test equipments are brought to the mixing place. Since it may not be assumed that all TC members were able to meet at the same place several sites will be selected where at least one member from a former test site will participate. 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 prac-tice. 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 equip-ment developers come from laboratories and universities. The time necessary is estimated at 5 years.
Detailed working programme
- Literature survey The starting literature are the proceedings of the RILEM Workshop "Testing during concrete con-struction" in 1990. Subsequent literature has been collected by the applicant. Other groups in various countries have published on the subject. The university of Stuttgart is connected to several literature data banks which can be approached from remote desk computers. - State-of-the-art report The results of the literature survey will be compiled in a state-of-the-art report. The report will also contain the experience of field and laboratory measurements carried out by members of the TC. The report will be continuously updated during the lifetime of the TC. - Round robin testing Round robin testing is a useful test to assess the capability of a test method. In case of fresh cement based materials round robin testing is complicated due to the continuous change of the state of hy-dration. Therefore, the test equipment of the participating group 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. It is anticipated that not all groups will be able to meet at the same site. Therefore, various sites will be selected such that at least one team will connect the test series (overlapping participation). - Test evaluation The tests will be evaluated with respect to as many parameters as possible, i. e. wave velocity, damping, 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. - Recommendation 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 recom-mendation will be submitted for publication in Materials & Structures. - Workshop A workshop is planned for presentation of the TC´s work and of the test recommendation. It is hoped that other experts which were not member of the TC will contribute to the workshop. The RILEM rec-ommendation could then be completed and offered to CEN or ISO as a pre-standard. The workshop should prepare proceedings which contain the scientific merit of the test methods, their principles and potential applications.
There is no direct link to previous RILEM TCs. However, a relation could be established to TC Nos. 145-WSM and 174-SCC.
The following results are anticipated: - state-of-the-art report - RILEM recommendation for testing of fresh and hardening cement based materials - Workshop proceedings Pre-standard to be submitted to CEN or ISO
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 struc-tures. 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.