Evaluating the effects of activating agents on the performance of geopolymer cements.

Abstract

Geopolymers are mineral polymers of inorganic polymer glasses with structure resembling natural zeolitic materials. Geopolymer formation uses source materials such as clay (e.g. kaolin and calcined kaolin) or industrial by-product (e.g. slag and fly ash). The source material provides silicon (Si) and aluminium (Al) for reaction by an alkali activator solution forming a polymeric Si-O-Al-O framework which becomes the binder. Geopolymeric materials are of great interest because of the reduced CO2 emission and energy requirement for their manufacture and the higher sustainability. The main objective of this study is to investigate different activating agents used in geopolymer cement formation and their effect on performance of these geopolymer cements. For this study, the Geopolymer cement is the mixture of metakaolin (source material) and alkaline solution of Sodium hydroxide (NaOH) or Potassium hydroxide (KOH) or Calcium hydroxide(CaOH2) and sodium silicate (Na2SiO3) or Potassium silicate (K2SiO3) or Calcium silicate(Ca2SiO3). A total of nine different trial combinations of alkaline activators are used having 50x50x50mm cubical samples cured at ambient conditions. From laboratory experiments and observations, it was determined how different alkaline activators affect the performance of Geopolymer cement. Mechanical properties were assessed by compressive strength while physical properties were assessed by setting time. It was found out that activating agents have a great impact on the performance of geopolymer cements i.e. NaOH+Na2SiO3 combination had the highest compressive strength while calcium based cements had the shortest setting time.