Microbial influenced corrosion can be caused for various microorganisms. Under humid conditions, Thiobacillus bacteria (microorganism) absorb hydrogen sulphide (H2S) gas on the sewer walls and excrete the corrosive acid which attacks concrete (Fig 1).

Reparation of such destructions produces high costs. Fot this suitable materials which could protect sewers in advance are therefore highly required.

A possible protection could be achieved by geopolymers, i.e. inorganic alumino-silicates polymer which is synthesised from minerals of geological origin or by product materials (metakaolin) under highly alkaline conditions.[1,2,3]

Geopolymerisation turns industrial wastes (ground granulated blast furnace slag, fly ash) into building materials with excellent chemical and physical properties. It is presently absolutely suprising that geopolymer can show increased acid corrosion resistance compared to concretes as well as to their crystalline counterparts, certain classes of zeolites.[4,5,6] These zeolites become to some extend acid resistant only by special treatments which transform the framework structure with low Si/Al ratios into those with high Si/Al ratios,[7,8] which indicates that the surface density and special binding of water and fixing of alkali and alkali earth cations in the pores are key properties which determines the desired advantages of geopolymers. The important question thus is in how far geopolymerisation can be tailored to form on one hand their optimal corrosion resistance against acid attack of microbial excrete and on the other hand to form an optimal protection layering to certain classes of concretes.

Within this collaborative project it is the aim to optimise geopolymers for concrete protection against MIC. Microbial effects are largely unknown for geopolymers and have not been investigated to any extend. Series of certain metakaolin/slag and metakaolin/fly ash based geopolymers will be prepared and their corrosion effects in bacteria produced acids will be investigated. The polymer characterization includes advanced methods of X-ray diffraction (Synchrotron), temperature dependent spectroscopy, and thermogravimetric analysis. Engineering characteristics such as flow, consistency change, adhesion in tension, and strength development; should be determined as well as pore structure characteristics; e.g. by mercury intrusion porosimetry and gas permeability. Furthermore, thermal expansion and contraction, elementary behaviour of structural members due to temperature change, cause stresses which tend to create cracks and decrease in long-term durability. Bacteria characterisation as well as the effect on bacteria produced acid on geopolymer will mainly be followed by spectroscopical means (IR and Raman Micro spectroscopy). Concrete bodies completely embedded within geopolymers and semi open samples will be investigated in cross section using different analytical techniques.

References

1. Literature: J. Davidovits, First Inter. Conf. on Alkaline Cements and Concretes, Scientific Research, Kiev, Ukraine: Properties of Geopolymer Cements, pp. 131-149.
2. F. Jirasit, C. H. Rüscher, L. Lohaus, 2006, Int. conf. on pozzolan, concrete and geopolymer, Thailand: A study on the substantial improvement of fly ash-based geopolymeric cement with the addition of metakaolin, pp. 1-15.
3. F. Jirasit, C.H. Rüscher, L. Lohaus, 2006, Abstract DMG 2006 Hannover Preparation and Characterisation of the Fly Ash- and Slag-Based Geopolymeric Cements with the Addition of Metakaolin
4. T. Bakharev, 2005, Cement and Concrete Research, Resistance of geopolymer materials to acid attack, 35(4), pp. 658-670.
5. S. E. Wallah, D. Hardjito, D. M.J. Sumajouw, B.V. Rangan, Fourth International Conference Geopolymer 2005, Saint-Quentin, France, Performance of fly ash-based geopolymer concrete under sulfate and acid exposure, pp. 153-156.
6. X. Song, M. Marosszeky, M. Brungs, Z. Chang, Fourth International Conference Geopolymer 2005, Saint-Quentin, France, Response of geopolymer concrete to sulphuric acid attack, pp. 157-160.
7. N. Salman, C. H. Rüscher, J.-Chr. Buhl, W. Lutz, H. Toufar, M. Stöcker, 2006, Microp. Mes. Mat. 90, pp. 339-346.
8. C. H. Rüscher, N. Salman, J.-Chr Buhl, W. Lutz, 2006, Microp. Mesop. Materials, Letter to the Editor 92, pp. 309-311.