Notwithstanding the uncertainties regarding aspects of the mechanism of formation of thaumasite, several measures have been suggested to minimise the risks of TSA (Bensted, 1998), namely: ·
Lower water/cement ratio as far as is practically possible coincident with good concrete (or mortar) workability with a suitable superplasticiser in the mix, so as to minimise internal transport of ions in the pore solution of the hardened material. ·
Reduce permeability of the concrete (or mortar) with ground granulated blastfurnace slag (ggbs) or fly ash (pfa) additions, or else by utilising blended cements like Portland-slag cement (e.g., CEM II/A-S) or Portland-fly ash cement (e.g., CEM IIB-V), as given in the European standard for common cements BS EN 197-1 (2000). ·
Seek to reduce the C3S (alite) and C3A (aluminate) levels as far as is practical or feasible.
Amend codes of practice for producing concrete (or mortar) liable to be exposed in sulfated environments where temperatures of 15ëC or less are likely to be encountered on a regular basis each year. This fourth recommendation has been subsequently enacted, following the publication of the `Thaumasite Expert Group Report’ in 1999.
