Development of porous geopolymers foamed by aluminum and zinc powders

Abstract This study assesses the impact of synthesis factors (foaming agent type/content, alkali type and alkali concentration) on the compressive strength, density and porosity characteristics of fly ash geopolymers prepared by chemical foaming with the use of aluminum and zinc powders. The geopolymer synthesis was optimized through the application of multifactorial design of experiments. Image analysis was used to determine the porosity of the samples while the products were characterized by XRD, FTIR and SEM. Foamed geopolymers with a wide range of compressive strength (1.64–22.75 MPa), density (0.59–1.56 g/cm3) and pore area (3–76%) values were prepared. The foaming with Aluminum is more effective than Zinc powder since bigger volumes of gases are released during its chemical action. The foaming agent content is the determining factor of the properties while the alkali concentration has a great effect both on pore morphology and strength development. The incorporation of potassium ions seems to contribute to the development of porous structures. The macro-porosity of the products is governed by pores of 0.1–2.0 mm size.