Inﬂuence of OPC replacement and manufacturing procedures on the properties of self-cured geopolymer Teewara Suwan, Mizi Fan ⇑ Department of Civil Engineering, School of Engineering and Design, Brunel University, Uxbridge, UB8 3PH London, United Kingdom highlights  OPC replacement shortened setting time and increased early strength of GeoPC systems.  Self-cured efﬁcacy could be tailored with different manufacturing procedures.  Pre dry-mixed process released intensive heat during synthesis.  Geopolymer was cured in ambient conditions without external heat supply (18–22 °C).  (#1) GeoPC and pre dry-mixed process can provide feasible production of self-cured GP. article info Article history: Received 15 July 2014 Received in revised form 18 September 2014 Accepted 25 September 2014 Keywords: Ambient curing Fly ash Geopolymer Manufacturing procedures Raw material combination Self-cured geopolymer abstract Geopolymer typically achieves its strength by heat curing, which is a limitation for in-ﬁeld applications. This study develops self-cured technologies for ﬂy ash-based geopolymer curing in ambient conditions without external heat supply. Two approaches, (i) the combination of OPC and Geopolymer (GeoPC), and (ii) different manufacturing procedures, were investigated. The results showed that the self-cured GeoPC could be developed with the setting time, early strength and microstructures of GeoPC enhancing when the amount of OPC replacement increased. The manufacturing procedure also directly inﬂuenced the solidifying behaviour and early strength development of geopolymer cement. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The Portland cement manufacturing is an energy intensive pro- cess and releases very large amount of greenhouse gas to atmo- sphere, and alternative cementitious systems have been studying to totally or partially replace the Ordinary Portland Cement (OPC) [1]. Alumina–silicate materials, especially ﬂy ash and other pozzolanic industrial wastes, have been identiﬁed as starting materials to produce OPC-less cementitious material, called ‘‘Geo- polymer Cement’’. The production of alumina–silicate based geo- polymer cement commonly use alkaline solutions, such as sodium silicate (Na 2 SiO 3 ) and potassium or sodium hydroxide (KOH or NaOH), mixing with raw starting materials to form homogenous slurry. Heat above ambient temperature is applied approximately from 60 to 90 °C for 24 to 48 h for curing purpose. Afterward, geopolymer will be continually cured or left in room temperature for further handlings [2] (Fig. 1). The properties of geopolymer cement, tested in accordance with the testing standard of OPC, are in the same order as or even better than those made from OPC. Moreover, geopolymer are using waste materials and manufactured without the energy intensive process like that of OPC. Replacing OPC with alumina–silicate waste brings about the beneﬁts not only for cost saving but also the reduction of environmental impact up to 9% less CO 2 emission when compared with OPC binder [3,4]. However, the requirement of heating for the curing process of the geopolymer has a signiﬁ- cant implication for on-site operation of construction and energy consumption. The typical ﬂy ash-based geopolymer paste cannot set within 24 h in ambient temperature [5], although adding some of calcium source can shorten the setting time of cement paste. Calcium content in geopolymer cement could be achieved by add- ing granulated blast furnace slag (GBFS), high calcium ﬂy ash, steel slag, calcium hydroxide (Ca(OH 2 )) or even OPC [6–9]. This paper http://dx.doi.org/10.1016/j.conbuildmat.2014.09.065 0950-0618/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author E-mail address: mizi.fan@brunel.ac.uk (M. Fan). Construction and Building Materials 73 (2014) 551–561 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat