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Pozzolanic activity of clay minerals with respect to environmental geotechnics


The chemical interaction between clays and calcium hydroxide, a major component of Portland cements, influences the mechanical properties of the composite material and is therefore of special interest for many geotechnical engineering applications. Cements and clays are e.g. applied as composites in engineered barrier systems. For these systems, it is expected that beneficial clay properties such as

  • low hydraulic conductivity
  • low diffusive solute transport
  • high sorptive capacity
  • swelling ability
  • high plasticity

will markedly change upon contact with the high pH cement pore solution. The high pH value during cement setting in the presence of calcium hydroxide (portlandite) may even cause destabilisation of clay minerals and formation of additional cement hydrates (pozzolanic reaction).

The investigation of the pozzolanic reaction of various clays will include chemical analysis (ICP-AES) of the pore solution as well as quantitative mineralogical and chemical analysis of the corresponding solids. Thermoanalytical, infrared spectroscopical, X-ray diffraction techniques and environmental scanning electron microscopy will be applied.

Model calculations in order to predict mechanical and hydraulical behaviour of composites of known mineral content will be performed.


Hermanns Stengele, Rita and Müller, Christian

Index Terms:

ClayGroup; cement; pore solution; portlandite; calcium hydroxide; pozzolanic; quantitative mineral content; engineered barrier; environmental geotechnics

Further Information:

Date published: 07.04.2002