Effects of accelerated carbonation on properties of ceramic-based geopolymers

Geopolymers are considered as environmentally friendly binders with a high potential not only to lower the prices of binders, but mainly to decrease the significant carbon footprint originating from the production of traditionally used Portland cement. Their production is very different compared to Portland cement as they are usually prepared by activating alumino-silicates in an alkaline solution. Similarly, to concrete, pozzolana active materials, such as fly ash, blast-furnace slag, or metakaolin were successfully used for geopolymer production. Nevertheless, the utilization of fine ceramic waste powder, also pozzolana active, has rarely been reported in geopolymer production. In this paper, series of ceramic-based geopolymers were prepared with the utilization of ceramic waste powder, alkali activated by the mixtures of sodium hydroxide and sodium silicate (water glass) with the silicate moduli ranging from 0.8 to 1.4. The studied samples were cured for 7 days at temperatures of 60 °C to speed up geopolymerization of ceramics, and after 28 days, they were exposed to 20 ± 2% CO 2 at 85% RH for 10 months. The effect of the accelerated carbonation conditions on the composition changes and thermal stability of the studied materials was determined by means of X-ray diffraction and thermal analysis. These results were supported by evolved gas analysis. Mechanical properties, such as compressive and flexural strength, were also analyzed. The accelerated carbonation conditions along with higher curing temperatures led to a partial enhancement of mechanical properties, reduction of efflorescence and non-negligible microstructural changes of exposed geopolymers compared to those stored in laboratory conditions.