Using a simplified technology to make an alkaline binder from silica additives

Abstract

Introduction. The global expertise in the industry-scale application of alkaline composites in construction and their unique properties have proven strong prospects for and the relevance of a clinker-free technology and its development. The elaboration of alkaline-activated formulas for binders, containing fine powders of the aluminosilicate origin, allows making new efficient high quality products. New composite construction materials contain alkaline solutions of sodium silicate, although the large-scale application of this technology will require an alternative sealant. Materials and methods. The paper presents a method for the accelerated preparation of an alkaline-silicate sodium binder composed of a 40 % solution of caustic soda, having density of 1,430 kg/m3 and ultrafine powders featuring high silica content extracted from quartz glass sands and volcanic tuff. The resulting liquid-glass binder was studied using a special method to determine the concentration of SiO2 that reacted with NaOH and the SiO2/Na2O silicate module. Scanning electron microscopy is employed to study the synthesized alkaline solutions, or the filtrate and the suspension. Results. The results have proven the effectiveness of the “wet” method for preparing the alkaline-silicate sodium binder using the simulated compositions. Ultrafine microparticles are quite active and capable of rearranging in the suspension. As a result, hydrated nepheline compounds and hydro-alumino-silicate metastable phases of variable compositions are generated. The binder system has a sufficient amount of structureless silica that converts into a solution in the process of leaching; it is also capable of synthesizing new compositions corresponding to sodium hydrosilicate Na2[Si4O10]∙4H2O. Conclusions. The prospects for and availability of fine off-grade glass quartz sands are beyond doubt; the proposed “wet” method of making less energy- and resource-intensive liquid glass binders will expand the clicker-free technology of alkali-activated binders, thereby reducing the environmental load and promoting an alternative to expensive and energy-intensive Portland cement.