Effect of different superplasticizers and activator combinations on workability and strength of fly ash based geopolymer

This paper evaluates the effect of different commercial superplasticizers (SPs) such as naphthalene, melamine and modified Polycarboxylate based on the workability and strength of a class F fly ash geopolymer paste activated by two different activator combinations, i.e. 8 M sodium hydroxide solution and a multi-compound activator composed of 8 M NaOH solution (28.6%) + Na2SiO3 (71.4%) with a SiO2/Na2O ratio of 2.0. These SPs at a dosage of 1% by mass of fly ash were added to the fresh paste and flowability of the activated fly ash paste was measured via mini slump test and compared with that of the paste without using any SP. The experimental results indicated that the effect of different SPs on the workability and strength of fly ash based geopolymer directly depends on the type of activator and the SP. In the case of using 8 M NaOH solution as the activator, naphthalene based SP was an effective type; whereas modified Polycarboxylate based SP was the most efficient type when the multi-compound activator was used. (C) 2014 Elsevier Ltd. All rights reserved.