The influence of the stabilizing agent SDS on porosity development in alkali-activated fly-ash based foams

Alkali activated foams (known also as “geopolymer foams”) are formed by the adding of a foaming agent, such as Al powder or H2O2, to an alkali activated matrix which can be based on, for example, fly ash, slag or meta-kaolin. The foaming agent decomposes and reacts inside the matrix, resulting in the release of gasses which form pores within the structure. Such pores have to be created before the alkali activated foams harden. In order to prevent the escape of these gasses from the foam, a stabilizing agent can be added to the foam mixture. This paper presents the results of tests involving the pore-foaming process in the case of highly porous, alkali activated, fly-ash based foams. Between 0.5 and 1.5 mass % of H2O2 was added to the fly ash precursor as a foaming agent, as well as different amounts (varying from 0.1 to 4.0 mass %) of the selected stabilizing agent, which is known as SDS - sodium dodecyl sulfate. The physical, mechanical, and microstructural properties of the hardened alkali-activated foams were determined. Their pore structures were characterised by SEM, as well as by a three-dimensional (3D) technique, X-ray computed micro-tomography. The advantage of the latter method is that a better insight can be obtained into the characteristics of the hardened pore structure, including information about its homogeneity and the pore size distribution. The influence of the amount of the added foaming agent, as well as that of the amount of the stabilization agent, was evaluated, and optimal addition mass percentages were determined. In the case of the best mixtures, the investigated hardened pore structures showed relatively good mechanical properties, and could therefore be used for various applications in the building industry.