Interaction with environment

Sulfates present in groundwater can pose a serious threat to the durability of concrete structure. The interaction of cement with solutions containing sulfate leads to the formation of a reaction front within the porous material and to the precipitation of gypsum and ettringite near the surface. Further within the sample the depletion of portlandite is observed. Significant damage due to sulfate interaction can result in the structural breakdown of the concrete structures e.g. tunnel linings within a few years.
Expansion of mortar bars in Na2 SO4
Thermodynamic modeling of the interaction with the environment

To test the “sulfate resistance” of a specific cement, mortar and concrete samples are generally submersed for a few weeks in concentrated Na2SO4-solutions and the mass and length gain is monitored as a function of time. High sulfate concentrations, as used in such tests, lead to the precipitation of gypsum, while lower sulfate concentrations, as present under field conditions, lead to no or only very little gypsum precipitation. The mortar samples show strongly differing expansion and mass gain depending on the reaction solution. Further factors influencing the expansion are the absence or presence of CO2 in the interacting solution, the amount of solution, the frequency of the exchange of the solutions, the sample geometry and the temperature. Considering all these factors it is not surprising that the tests carried out in different laboratories show large variations. In addition, the correlation of the test results with expansion and deterioration under field conditions is poorly understood.

The combination of thermodynamic modelling with experimental techniques such as XRD, SEM/EDS enables us to gain more insights into the process governing the interaction with the environment on a chemical level. Our studies in recent years focused on the effect of sulfate, chloride, carbonate and on alkali silica reaction.

Thermodynamic modeling of sulfate attack
Important publications
Prof. Dr. Barbara Lothenbach

Prof. Dr. Barbara Lothenbach
Senior Researcher / Projektleiterin / Adjunct Prof. NTNU

Phone: +41 58 765 4788

Dr. Andreas Leemann

Dr. Andreas Leemann
Deputy / Group Leader Concrete Technology

Phone: +41 58 765 4489