(Micro)-structural comparison between geopolymers, alkali-activated slag cement and Portland cement

Abstract

Concurrently to research conducted on ordinary Portland cement (PC), new types of binders were developed during the last decades. These are formed by alkali-activation of metakaolin or ground-granulated blast furnace slag (GGBFS) and are named, respectively, geopolymers (GP) or alkali-activated slag (AAS). Four different cementitious materials were synthesised: PC, AAS, GP, and a mix GP-AAS and fully compared about their compositions and (micro)-structures. X-ray diffraction has revealed the presence of semi-crystalline C{single bond}S{single bond}H gel binding phase in PC while AAS, GP and GP-AAS are nearly amorphous. Progressive structural changes have been observed between the different samples by means of infrared spectroscopy, 29Si and 27Al magic-angle-spinning nuclear magnetic resonance spectroscopy: there is a polymerisation extent of the (alumino)-silicate framework from PC [SiQ1 and SiQ2 units] to AAS [SiQ2 and SiQ2(1Al) units] and finally to GP [SiQ4(2Al) and SiQ4(3Al) units]. Scanning electron microscopy has shown that GP is a homogeneous matrix while the other materials are composites containing GGBFS grains surrounded by a binding matrix. Energy dispersive X-ray EDX analyses (line scans) have shown the absence of formation of any specific phase at the matrix-grains interfaces. © 2006 Elsevier Ltd. All rights reserved.