Development of self-cured geopolymer cement

Abstract

To support the concept of environmentally friendly materials and sustainable development, the low-carbon cementitious materials have been extensively studied to reduce amount of CO2 emission to the atmosphere. One of the efforts is to promote alternative cementitious binders by utilizing abundant alumina-silicate wastes from the industrial sectors (e.g. fly ash or furnace slag), among which “Geopolymer (GP) cement” has received most attention as it can perform a wide variety of behaviours, in addition to cost reduction and less environmental impacts. The most common geopolymer production, fly ash-based, gained some strength with very slow rate at ambient temperature, while the strength is evidently improved when cured in high (above room) temperature, e.g. over 40°C. The major challenge is to step over the limitation of heat curing process and inconvenience in practice. In this study, the testing schemes of (i) GP manufacturing in various processes, (ii) inclusion of ordinary Portland cement (OPC) in GP mixture, called GeoPC and (iii) GeoPC manufactured with dry-mixing method, have been intensively investigated through mechanical testing (Setting time, Compressive strength and Internal heat measurement) and mechanism analysis (XRD, FTIR, SEM and EDXA) in order to develop the geopolymers, achieving reasonable strength without external sources of heat curing. It is found that the proposed (dry) mixing process could have generated intensive heat liberation which was observed as a comparable factor to heat curing from any other external sources, enhancing the curing regime of the mixture. The additional calcium content in the developed GeoPC system not only resulted in an improvement of an early strength by the extra precipitation of calcium compounds (C,N-A-S-H), but also provided a latent heat from the reaction of its high potential energy compounds (e.g. OPC or alkaline activators). The developments from these approaches could lead to geopolymer production to achieve reasonable strength in ambient curing temperature known as “Self-cured geopolymer cement”, without external heat, and hence provide construction industry viable technologies of applying geopolymers in on-site and off-site construction.