Effect of Sodium Silicate Types on the High Calcium Geopolymer Concrete

Abstract

Geopolymerization is an innovative technology that can transform several solid aluminosilicate materials into useful products called geopolymers. Alkali activation of aluminosilicate precursors such as waste or by-product materials from other manufacturing processes is established as one of the methods of producing sustainable binders for construction. Most of previous studies focus on low calcium pozzolanic material and very little study on high calcium material. Waste Paper Sludge Ash (WPSA) were used as main pozzolanic material in this present study. The high-calcium WPSA essentially consists of aluminosilicate modified by the presence of large amounts of calcium. It can be categorized as cementitious and pozzolanic material when Calcium Oxide (CaO) varies between 10% and 20% or greater than 20%. The chemical composition of the WPSA used in this study contains approximately 53% of CaO, this value consider very high compared with other high calcium material used by other researchers. Alkali (Na or K) hydroxides or silicates are generally used as the activating agents. Based on previous geopolymerization studies, it was estimated that the most important production cost factor is the cost of used chemicals and especially the one of Sodium Silicate (Na2SiO3) solution. Sodium Silicate (Na2SiO3) are usually used as a alkaline activators in geopolymerization process. Na2SiO3 comprises a fundamental process in geopolymerization technology. Therefore, this study aims at experimentally the polymerization stage in Na2SiO3. In this study of geopolymer concrete using powder Na2SiO3 (which makes handling easier in practice and more economic) and compares it with waterglass (liquid Na2SiO3). In this study, WPSA and alkaline liquid are being used to replaced the Portland cement to produce geopolymer concrete. The alkaline liquid that been used is the combination of sodium hydroxide (NaOH) and Na2SiO3. Two (2) series of geopolymer concrete specimens composing two (2) different type of Na2SiO3 which are powder form solution (4 Molar) and waterglass ( ready made liquid form) were adopted. In addition, present study also examined the effect of using Recycle Concrete Aggregate (RCA) to produced more green concrete. There are 144 cube specimens at size 100mm x 100mm x 100mm were prepared. The compressive strength of the geopolymer concrete specimens is tested at the age of 3, 7, 14 and 28 days after cured in local laboratory ambient condition. The chemical analysis using XRF/XRD and morphorlogical structure view from SEM/EDX also been examined. The result shows that the silicate phases were characterized as X-ray amorphous to semi-crystalline structures materials and the strength effect using these both silicate types (liquid and powder) are not much differ. Consequently, more economic production of geopolymers by used Na2SiO3 solution (powder) for geopolymer production.