Role of alkaline cations and water content on geomaterial foams: Monitoring during formation

The synthesis of an in situ inorganic foam based on alkaline polysialate was achieved at a slightly elevated temperature by alkaline activation of raw minerals and industrial waste based on a geopolymer synthesis process. To understand the formation of the foam, the differences induced by the variations in the alkaline element (sodium or potassium) and water content were investigated throughout XRD, in situ FTIR-ATR, volume expansion and thermal analysis coupled with mass spectrometry. The amount of water is the determining parameter for volume expansion but does not interfere with the structure formation of foams. The comparison between geopolymers and foams has elucidated the formation of at least two amorphous networks in the case of sodium foam and three in the particular case of potassium as the alkaline element.

Research Highlights
► Studied materials are prepared from silicate, hydroxide, metakaolin and silica fume.
► Study of formation reveals the reactions occurring and the contribution of water.
► Difference between foam and geopolymer lies in reactions of silica fume dissolution.
► Structure of foam consists on a mixture of at least two amorphous alkaline networks.
► Potassium introduction induces zeolite formation constituting the third network.