Subject matter

So far durability design is based on different single processes such as carbonation, chloride penetration and freeze-thaw cycles. In the meantime, however, it has been shown that combined actions can be much more severe than each single deteriorating process. In many areas a high percentage of chloride and sulphate ions can be found in the marine and ground water. This situation is even more severe in the neighbourhood of salt lakes. But even in coastal areas high concentrations of aggressive ions can be observed. In all of these areas service life of reinforced concrete structures can be shortened considerably. According to results reported by Qinghai Salt Lake Institute of the Chinese Academy of Sciences, cracking and spalling can be observed on traditional concrete structures without special protective measures after not more than two or three years if exposed to groundwater with high salt concentration.
Besides, there are other places in the globe where this is also of concern: e.g. the Dead Sea next to Israel; Salt Lake in USA; parts of the Middle East (e.g. Iran) and Australia. Aggressive processes of combined sulphate and chloride attack are rather complex. Sulphate ions migrate into the pore space of concrete and react with the ions dissolved in the pore liquid. As a consequence chloride penetration into the pre-damaged concrete is facilitated. As a consequence corrosion of steel reinforcement will start at an early stage, causing crack formation and spalling of the concrete cover. This TC will focus on deterioration of reinforced concrete structures situated in an aggressive environment and in particular exposed to a combination of sulphate and chloride containing water.

Objectives:

1. To develop a standardized test method to determine service life of concrete structures under the combination of mechanical load and a combination of sulphate and chloride ions
2. To quantify the influence of type of salt, study in detail the combination of sulphate and chloride ions, influence of drying and wetting cycles, influence of imposed mechanical load on the corrosion of steel bars and deterioration of concrete
3. To determine time dependent changes of the microstructure and transport properties of concrete under the above mentioned conditions.
4. The major aim of this TC will be to increase service life of reinforced concrete structures in aggressive environment.

In this way durability and service life of reinforced concrete structures situated in aggressive environment can be significantly extended.

The focus will be placed on concrete made with Ordinary Portland Cement (OPC), and several widely used mixtures of supplementary cementitious materials, such as 50 % of OPC, 30 % of slag and 20 % of fly ash. If the number of active participants of the new TC will be sufficient, supplementary cementitious materials (binary system of fly ash, slag, and silica fume) will be considered in addition by members of this TC.

• Transport properties, changes of microstructure, migration of chloride through the concrete cover will be studied in detail.
• Ion migration, chemical reactions in the microstructure, penetration of the concrete cover, will be studied in detail first.

Then the obtained results will be critically compared with site observation.

Terms of reference

The TC is planned to run for 5 years.

Members have been recruited from universities, research centres, design offices and industry, based on their experience with sulphate attack and chloride transport in cement-based materials.

Detailed working programme

1st year: Literature review on degradation mechanisms and establishment of a bibliography covering most relevant papers;
Preparing experimental programs for testing chloride penetration in presence of sulphate ions; if possible, tests of concrete with SCMs may be included.
In addition comparative tests shall be run with reinforced concrete specimens placed under load.

2nd year: Comparative test series to observe combined sulphate and chloride migration into concrete, run by at least five laboratories in different countries.
Investigation of damaged structures under the influence of combined actions of chloride sulphate migration,

3rd year: Evaluation of first results and necessary improvement of the test method, new run with the revised test method.

4th year: Critical discussion of results obtained so far, continuation of test series, comparison with observations on real structures.

5th year: Finalizing the test method and drafting of recommendations. In addition, an international conference or workshop will be held in order to present the results to the interested public.

Proposal of a standardized test method for concrete under combined action of combined sulphate and chloride attack; if possible the influence of an applied load shall be included.