Alkali-activated bentonite clay-limestone cements

The development of sustainable cements requires the expansion and optimization of the mineral resources base. In this study, the medium-grade bentonite clay and limestone as a promising, available, low carbon, and abundant starting materials, were investigated as binary precursors for eco-friendly non-clinker alkali-activated cements development. Properties of fresh and hardened pastes of blended alkali-activated cements were investigated by standard techniques depending on the mineralogical assemblage, fineness of precursors, formulation details. The reaction products and microstructures of alkali-activated calcined bentonite clay-limestone hardened pastes were analyzed using thermal, XRD, and SEM/EDS analyses. As a result, calcined bentonite clays at 39–47 % content of clay minerals were stated to be suitable as a primary precursor for alkali-activated cements incorporated with high loading of raw limestone. Optimum compositions consisted of 20–30 % calcined clay and 70–80 % limestone with compressive strength up to 34.2 MPa. In the designed cement calcined bentonite clay is the main reactive precursor that forms a mineral matrix sodium aluminosilicate hydrate gel N-A-S-H, whereas calcium carbonate is a much less reactive secondary precursor that participates in the formation of sodium (calcium) aluminosilicate hydrate gel N-(C)-A-S-H.