Analysis of concrete in a vertical ventilation shaft exposed to sulfate-containing groundwater for 45 years

The concrete lining of a vertical ventilation shaft exposed to sulfate-bearing groundwater for 45 years was investigated. The concrete was characterized at several sites with different degrees of damage. Apart from strength measurements, optical and electron microscopy were the main tools used to assess the degree of damage and alteration of the concrete. The occurrence of damage appears to be related to the availability of sulfate-bearing groundwater on one side and the presence of poor-quality concrete on the other side. Most of the damage in the form of severe spalling is caused by ettringite formation. The impact of thaumasite formation with disintegration of the cement paste seems to be minor as it occurs after the concrete is already severely damaged. The mineral assemblages and the sequence of mineral formation caused by sulfate attack agree with the findings of laboratory studies and thermodynamic modeling.