211-PAE : Performance of cement-based materials in aggressive aqueous environments
Technical Committee 211-PAE
Deputy Chair: Dr. Eric SAMSON
Cement-based and concrete infrastructure are having to operate in increasingly aggressive environments of an aqueous nature. These relate to natural environments such as the long-standing issue of concrete susceptibility to leaching in soft or aggressive waters; to public health environments with their associated drainage and treatment structures such as sewers, conduits, waste tanks etc; to water supply infrastructure with the provision of dams and canals; and to industrial and marine structures with natural or artificial highly aggressive environments.
In all these cases, concrete is subjected to a process of degradation whereby ion exchange reactions occur leading to a breakdown of the matrix microstructure and a weakening of the material. In some cases this can be extremely rapid and serious, such as in acidic environments, whether industrially or biogenically generated. In other cases degradation occurs over long periods of time, but the scale of the problem is such that the consequences are also severe, e.g. major dams, marine works, etc. Many industrial processes also generate aggressive aqueous solutions some of which can leach or attack concrete. Furthermore with increasing levels of acid rain being experienced worldwide, the ability of concrete to withstand this form of aggressive attack is also important.
The TC will focus on the broad issues concerning performance of cement-based materials in aggressive aqueous environments, where the main form of degradation relates to leaching or hydrate alteration by ion exchange.
Terms of reference
The objectives of the TC will be as follows:
· Characterisation of the nature of aggressive aqueous environments in the context of leaching and acid attack, including measures of aggressivity.
· Nature of degradation and deterioration mechanisms for different cement-based materials (including different cementitious systems) in such aggressive aqueous environments.
· Appropriate test methods to assess performance of cement-based materials in such environments, and which can be used to characterise and rate relative performance, as well as to inform long term predictions.
· Survey and analysis of the scale of the problem worldwide.
· Studies of in-situ performance of concrete structures in such environments.
· Service life prediction models for concrete structures in such environments and their effectiveness in being universally applicable.
Detailed working programme
It is proposed to finalise the detailed objectives and membership of the TC by the March 2004 meeting of RILEM. The TC is expected to have a three to four year operation, as follows.
· Year one. Form working groups (WG) to pursue the various objectives; agree on required outputs, initial report at end of year one.
· Year two. Further work by WGs. Preliminary reporting and decision on need for round-robin testing, as well as a possible proposal for a standard test procedure.
· Year three. Possible RR on test methods followed by recommended test procedure; all WGs to produce preliminary SOA reports.
At the end of the period of the TC, an international workshop will be organised to cover the detailed work of the TC, to publicise it's outputs including test procedures, and produce SOA documents.
The committee will deal with topics associated with deterioration and service life of cement-based materials and structures, subjects within the scope of RILEM as an organisation dealing with a range of construction materials and structural performance. The committee may have links with other RILEM committees, but no overlap is expected.
These would be
· Bringing together experts working in the area of degradation of cement-based materials under aggressive aqueous environments, with a view to understanding the phenomena better.
· Assessment of test methods for assessing performance of concrete in aggressive environments, with a possible proposed standard test procedure.
· A series of SOA reports on the nature of aggressive environments, performance of concrete in such environments, and suitable test methods.
· Possible round-robin test programme.
· An international workshop.
Group of users
Academics, test laboratories, industry and practising engineers.
Specific use of the results
With the urgent need to prevent rapid deterioration of concrete infrastructure worldwide, and minimise associated economic losses, it is important to understand deterioration mechanisms thoroughly and find cost effective ways of designing structures to resist such aggressive environments. In addition, such improved knowledge, including insights gained by appropriate test methods, will permit more effective and economical repairs to be carried out on deteriorated structures. Furthermore an understanding of the scale of the problem worldwide should assist infrastructure provide to consider better methods of providing durable structures.