Carbonation in just add water geopolymer based on fly ash and dredged sediments mix
Elie Mahfoud, Khadim Ndiaye, Walid Maherzi, Salima Aggoun, Nor-Edine Abriak, Mahfoud Benzerzour
Abstract
This study aims to investigate the carbonation effect on microstructure and mechanical properties of One-Part-Geopolymer based on thermo-mechanical-synthesis sediments-fly ash mix. Four mixtures optimized in terms of mechanical performance and containing 0, 15, 30 and 50 % of sediments were exposed to accelerated (3 % CO 2 ) and natural carbonation. Using a phenolphthalein indicator on mortars (4x4x16 cm 3 ), the carbonation depth ranged from 4 to 6 mm. XRD, FTIR and TGA results showed that nahcolite is the main accelerated carbonation product, which lowers the pH but remains above the steel's depassivation limit. Natron is the most favored product in natural carbonation. In addition, calcite has been formed with the inclusion of sediments. SEM observations and MIP results show that pores and cracks are filled with carbonation products improving mortar density and hence mechanical performance. This outcome also showed that accelerated carbonation experiments are not illustrative of the natural reaction in geopolymer. • All mortars demonstrated good resistance to carbonation with a depth of between 4 and 6 mm. • The carbonation products formed are: nacholite, natron and calcite with the addition of sediments. • Accelerated carbonation favors nacholite formation which is responsible for the drop in pH. • pH levels remain below the depassivation threshold. • Carbonation products grow abundantly in pores and cracks, which has improved the mixes' mechanical properties and density.