Developing geopolymer concrete by using cold-bonded ﬂy ash aggregate, nano-silica, and steel ﬁber Jumah Musdif Their ⇑ , Mustafa Özakça Department of Civil Engineering, Gaziantep University, 27310 Gaziantep, Turkey highlights  GPCs have been synthesized using cold-bonded ﬂy ash aggregate (CFA).  No elevated temperatures have been used in this study.  The dosage of superplasticizer to achieve the target slump value is reduced by the use of CFA.  The pore structure of GPC incorporated permeable aggregate is signiﬁcantly improved by the utilization of nano-silica (NS).  Better performance of GPC is achieved by the use of 1% steel ﬁber and 2% NS. article info Article history: Received 30 January 2018 Received in revised form 11 May 2018 Accepted 30 May 2018 Keywords: Cold-bonded process Compressive strength Geopolymer Permeability properties Nano-silica Steel ﬁber abstract This experimental study presents the effect of nano-silica and steel ﬁber on the transport properties and compressive strength of alkali-activated slag/ﬂy ash concrete incorporated cold-bonded ﬂy ash aggregate. In order to reduce energy consumption and provide environmental impact, the cold-bonded process was used to manufacture cold-bonded ﬂy ash aggregate. Twenty four geopolymer concrete mixtures incorpo- rated cold-bonded ﬂy ash aggregate, nano-silica, and steel ﬁber were produced with sodium hydroxide concentration of 12 M and cured at ambient temperature. Transport properties of geopolymers were examined through water penetration, water sorptivity, and gas permeability at 28 and 90 days. Results indicate that geopolymer concrete incorporated cold-bonded ﬂy ash aggregate can be produced with compressive strength as high as 28.23 and 36.62 at 28 and 90 days, respectively. However, 2% nano- silica and 1% steel ﬁber volume fraction were the most signiﬁcant parameters that caused remarkable improvement of investigated properties. Moreover, the incorporation of waste materials in aggregate and geopolymer concrete production can alleviate environmental problems. Ó 2018 Published by Elsevier Ltd. 1. Introduction As in most of the industrialized countries, Turkey generates large amounts of waste materials. The annual production of Fly Ash (FA) and blast furnace slag in Turkey reach about 15 million tons and 600,000 tons, respectively. The disposal process of waste materials has been one of the most challenging matters in our country and worldwide [1]. Employing of solid waste materials in the construction industry are commonly used nowadays as it introduces usable construction materials. Concrete technology can introduce suggestions for recycling industrial wastes like FA and Ground Granulated Blast Furnace Slag (GGBFS). The scientiﬁc investigators reengineered some types of solid wastes in the production of artiﬁcial aggregate [2–4]. Several advantages of producing artiﬁcial aggregate from waste materials such as a promising an alternative to recycle waste materials, reducing the consumption of non-renewable natural resources, and producing lighter weight aggregate compared to the natural ones [5,6]. Three common different procedures used for manufac- turing artiﬁcial aggregate; cold bonding, autoclaving, and sintering. Using of these methods form spherical shape aggregates with a rel- atively smooth surface which are preferred because they more readily ﬂow past each other as the low speciﬁc surface area needs less binder and water in the design of concrete [7,8]. In addition, comparing to autoclaving or sintering method, the cold-bonding process method is the lowest energy consumption and has the least detrimental environmental impact [9,10]. Studies conducted recently by several authors with the use of Cold-bonded FA aggregate (CFA) in conventional concrete have revealed the performance of them to be satisfactory comparing to natural aggregate [9–13]. The studies reported the CFA to have https://doi.org/10.1016/j.conbuildmat.2018.05.274 0950-0618/Ó 2018 Published by Elsevier Ltd. ⇑ Corresponding author. E-mail address: mt45151@mail2.gantep.edu.tr (J.M. Their). Construction and Building Materials 180 (2018) 12–22 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat