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Sulfate resistance of concrete: improved method based on the test according to SIA 262/1, appendix D: (FGU2010/001)

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Vehicle design and manufacturing (VDM)
Infrastructure (INF)
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Transport sectors
Passenger transport,
Freight transport


Background & Policy context

The vital importance of tunnel systems for traffic and energy production using water-power is undisputed. These concrete structures can be damaged by an interaction with sulfate-bearing groundwater leading to a decreased service life. Cases of such interactions have been documented for example in an ASTRA project done at Empa. Therefore, effective concrete concepts preventing damages are mandatory (eventually in combination with sealing systems). Testing such concrete concepts are currently not possible because the usability of the results obtained with the test according to SIA 262/1 is very limited as shown in the current ASTRA project (see provisional report in appendix). As a result, concrete concepts that have been optimised according to the SIA 262/1 test are related to a significant uncertainty concerning durability. Therefore, expansive repair work necessary in the future is probable. The improved test procedure will increase the meaningfulness of the results considerably. Moreover, the probability of damages caused by concrete concepts optimised according to wrong criteria will be decreased.


The usability of a test determining the sulfate resistance of concrete exposed in the tunnel environment has to be ensured. In 2003 such a test was defined in the SIA 262/1. Because the decisive parameters influencing the test results were poorly understood and the usability of the test had to be clarified, a project financed by ASTRA was started in 2008. After finishing the experimental part and analysing the results of this current project, it became clear that the procedure and data analysis according to SIA 262/1 are of limited value.

However, the results of the current project show a way how to adapt the test. Such an improvement has to be optimised and validated with experiments. The goals of the follow-up project are:

  • adaptation of the test procedure with
  • optimisation of the sulfate ingress
  • determining the influence of concrete composition and sulfate solution composition
  • analysis of chemical and physical processes during the test
  • definition of test procedure and data analysis
  • definition and verification of limit value for expansion

The project is carried out in four phases:

Phase 1:

As demonstrated in the current project, the sulfate entry is very low when dense concrete systems in the current standard test. The reason is that dense concrete systems, despite the small size specimen at the remedies provided by standard drying contain a lot of water. Thus, the entry is very low sulfate by capillary suction. The planned additional storage, it is now possible to cycle the initial drying and watering optimise. On concrete mixes with a binder and three different w / c ratios therefore different combinations of drying and impregnation in sulfate solution are investigated. In this case, the drying behaviour and the change in mass of the test specimens is determined in function of time. In addition, the sulfur profiles are determined and used to calculate the optimum storage regime for customised sulfatesulfate resistance examination by electron microscopy.

Phase 2:

In practice, the concrete is in most cases not with a pure sodium sulfate solution into contact, but there are almost always also magnesium ions present. However, various binders behave quite differently with respect to these different ions in the solution. The specific in Phase 1 storage regime is therefore investigated the solution to be used in the adapted sulfatesulfate resistance test. These are concrete with three different w / c ratios and two different binders, which behave differently with respect to the test solutions known to be used, produced. At these concretes a customised sulfatesulfate resistance test is carried out (preliminary storage and optimised four-week extra storage) with the following test solutions:

  • Pure sodium sulfate solution, as used in the current standard test
  • Pure magnesium sulfatesulfate solution
  • Mixture of sodium sulfate and magnesium sulfate

In addition to the measured length and mass changes in the dynamic modulus of elasticity is measured as particular injury is not necessarily associated with the magnesium sulfate with a large stretch. Using electron microscopy also the reaction products can be determined. For these studies, the test solution to be used for the customised sulfate resistance test is then derived.

Phase 3:

With the optimised in phase 1 storage regime and the particular in Phase 2 testing solution that matched sulfate resistance test is validated with subsequent four weeks additional storage. These different concretes with three differen


Parent Programmes
Institution Type
Public institution
Institution Name
Swiss Government: State Secretariat for Education and Research
Type of funding
Public (national/regional/local)


It was found that the mechanisms basically are in agreement with the experience made with the analysis of different damages in tunnels. However, the assessment of the data with the proposed formula revealed results which were, in case of normal concrete, contradictory to the experience of long term tests.

Additionally, it was found that the ingress of sulfates has to be increased and more time for the chemical reaction has to be provided. This was the basis for starting the present research project. The aim was to develop an adopted testing procedure, which should mainly be based on the existing procedure but improve the significance of the results.

In a first part, a limited matrix of concrete mixtures was used to apply different variables in the testing procedure and to study their effects on parameters like length change, uptake of sulfate solution, change of mineral phases, etc. Based on these results, the final testing procedure was defined. The main differences to the existing procedure is, that for the four drying and wetting cycles the drying period is extended while the wetting period is shortened.

This increases the uptake of sulfate solution. Moreover, the drying and wetting cycles are followed by an 8 week storage in sulfate solution without further drying and wetting. As a result, the reaction time for the sulfates is increasing and the resulting expansions as well. The sulfate resistance is assessed using the expansion during the additional storage in solution without drying and wetting cycles. This value is used as decisive parameter without using a formula with correction factors for concrete mix design as in the former test.


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