Carbonate mineral addition to metakaolin-based geopolymers

The effect of adding significant percentages of alkaline earth carbonate minerals (calcite and dolomite) to metakaolin-based geopolymers is investigated by compressive strength testing, X-ray diffractometry and electron microscopy, with the aim of better understanding the role played by calcium ions, carbonate ions and mineral surfaces in geopolymers. Addition of around 20% calcite or dolomite is seen to improve the compressive strength of the geopolymeric material, although does induce additional shrinkage during the first 90 days of aging. More than 20% mineral additive has a deleterious effect on strength due to significant disruption of the geopolymer gel network and the reduced reactive aluminosilicate content. No distinct calcium silicate hydrate phase formation is observed in any of the systems studied. Some dissolution of the mineral particles is observed, however this is not a major effect in most instances. The mineral particles interact with the geopolymer gel predominantly via surface binding, which appears to be somewhat stronger in the case of calcite than dolomite.