## 1 Introduction
The above-mentioned previous work shows that AAM derived from industrial waste has excellent mechanical strength using a combination of NaSiO\({}_{3}\) and NaOH. Alkali silicates (NaSiO\({}_{3}\)) are expensive and have higher CO\({}_{2}\)-equivalent emission than that of OPC, in terms of production [15; 25]. Hence the utilization of AAM as compared to OPC has been limited to a small scale. Previous studies reported that sodium silicate is a more environmentally unfriendly solution than NaOH in terms of its carbon footprint [26]. Therefore, there is a need to investigate the use of the eco-friendly activating agent NaOH as a solo activating agent to synthesise AAM with excellent mechanical strength. [PERSON] et al. [15] investigated the possibility of using NaOH as a sole activating agent to synthesize alkali activated GGBFS composites at elevated temperatures. The developed geopolymer yielded a durable brick with UCS of 72 MPa. Furthermore, [PERSON] et al. [13] successfully developed BOFS based AAMs using a sole alkaline activator. The author then investigated the mechanical properties of BOFS/FA based AAMs using sodium hydroxide as an activating agent. The results showed that developed BOFS/FA AAMs met the minimum requirement as per ASTM C34-13, C129-14a and SANS227: 2007 [9]. [PERSON] [27] blended Taftan pumice (75%) and GGBFS (25) and then cured it for 28 days at ambient temperature. KOH and NaOH solutions were used activating agents; a UCS of up to 55 MPa was achieved [27]. [PERSON] et al. [28] studied the feasibility of using FeCr slag as a precursor and KOH as an alkaline activator; an alkali activated FeCr slag with a UCS of 24.5 MPa was developed. In another study [PERSON] et al. [29] reported that it is feasible to produce BOFS/GMT or Fly Ash/ GMT based AAMs that have good mechanical properties and are environmentally friendly. Most research reported in literature on alkali activated material use both NaSiO\({}_{3}\) and NaOH as activating agents. There is scarce and not well documented literature on using a sole alkali activator without addition of sodium silicate or silica reactive instead of a combination of silica and alkali solutions. Furthermore, many documented studies continue to investigate alkali activated binder cured at elevated temperature of which for a country like South Africa (SA) that is facing severe energy crisis. This practice can cause power cuts; the use of elevated temperatures will put more strain on the energy grid on a production scale. Furthermore, the concept of alkali activated material in SA has not gained much traction to date due to the expense of alkali activating agents such as NaSiO\({}_{3}\) as compared to NaOH. It is with this in mind that this study was pursued to demonstrate the feasibility to synthesize alkali activated GGBFS using NaOH as an alkali activator without addition of sodium silicate or silica reactive to produce green and sustainable alkali activated GGBFS composites cured at ambient temperatures to save energy. This study aims to produce a sustainable alkali activated GGBFS cured at ambient temperatures using a NaOH as an activating agent, without an addition of any silica reactive source or solutions. The dissolution of alumino-silicates from the GGBFS as a precursor under different NaOH concentrations was studied. The synthesised alkali activated GGBFS were evaluated for mechanical strength, durability, and microstructural performance. To establish the most favourable condition for geo-synthesis of GGBFS the following parameters were investigated: molarities of NaOH ranging from 5 to 15 M; the liquid to solid ratio (from 20% to 30%); the curing age (7, 28, 56 and 90 days). Lastly, the environmental effects of the synthesized alkali activated GGBFS geopolymer was also studied through 30 days of metal leachability testing.