Corrosion resistance in different fly ash based geopolymer concretes

Geopolymer concrete produced using 100% fly ash as the main binder has recently been introduced as a sustainable construction material capable of replacing Portland Cement (PC) concrete. At the same time the corrosion of steel in reinforced concrete structures is one of the major durability issues with reinforced concrete structures. A major challenge faced by the construction industry in adopting geopolymer material is the variability of fly ash from different sources, which affects the properties of the geopolymer concrete produced. Hence, the question of whether reinforcing steel can be protected with geopolymer concrete produced from a range of fly ashes as effectively as with PC concrete is a key question. In order to investigate this, a series of geopolymer concrete specimens containing a range of cast in chloride contents (0-5%) were prepared using three different low calcium (Class F) fly ashes obtained from Australian power stations. The corrosion potential (Ecorr), polarisation resistance (Rp) and corrosion current (Icorr) for steel embedded in the geopolymer concrete over the initial three months are reported in this paper. The geopolymer concrete is found to passivate steel reinforcement to a slightly lesser degree than a similar binder content PC concrete in this initial stage. In addition the steel in the geopolymer displaying the highest compressive strength (Gladstone) was observed to display the most negative Ecorr and highest Icorr values in this period, indicating the greater susceptibility to corrosion.