Several factors affecting the reactivity of fly ash (FA) as a precursor for geopolymer concrete have been investigated. These include physical and chemical properties of various FA sources, inclusion of ground granulated blast furnace slag (ggbs), chemical activator dosages and curing temperature. Alkali-activated FA was found to require elevated curing temperatures and high alkali concentrations. A mixture of sodium hydroxide and sodium silicate was used and this was shown to result in high strengths, as high as 70 MPa at 28 days. The presence of silicates in solution was found to be an important parameter affecting strength. Detailed physical and chemical characterisation was carried out on thirteen FA sources from the UK. The most important factor affecting the reactivity was found to be the particle size of FA. The loss on ignition (LOI) and the amorphous content are also important parameters that need to be considered for the selection of FA for use in geopolymer concrete. The partial replacement of FA with ggbs was found to be beneficial in not only avoiding the need for elevated curing temperatures but also in improving compressive strengths. Microstructural characterisation with scanning electron microscope (SEM) coupled with energy dispersive Xray spectroscopy (EDS) was performed on FA/ggbs pastes. The reaction product of FA and ggbs in these binary systems was calcium aluminium silicate hydrate gel (C-AS -H) with inclusion of Na in the structure.

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A simple process to produce sodium silicate powder from glass cullet has been developed. A mixture of glass powder, sodium hydroxide powder, and water was heated at temperatures of 150 to 330 °C. The effects of glass to NaOH ratio, temperature and duration, inclusion of water and fineness of NaOH were investigated. Fly ash and fly ash/GGBS blends were the precursors for alkali activated binder (AAB) mortars produced with this sodium silicate. Compressive strengths were similar to or better than those obtained with commercially available sodium silicate and sodium hydroxide solutions. FT-IR tests suggested that the reactivity of the glass derived sodium silicate powder was related to the number of non-bridging oxygen atoms in the silicate structure. Cost comparison between AAB and Portland cement concretes gave similar results for normal strength concretes (35 MPa). AAB concretes with higher strengths (50 and 70 MPa) can be cheaper than equivalent traditional concrete.

The effects of paste volume, water content and precursor blend on consistency, setting time and compressive strength of alkali activated concrete (AAC) produced with fly ash (FA) and ground granulated blast furnace slag (GGBS) have been investigated with the aim of developing a suitable mix design procedure. Paste volumes in the range 30%-33% were found not to influence the compressive strength but did influence the consistency of the mixes. The water-to-solid ratio was found to influence compressive strength and setting time. Increasing GGBS content in the binder blend resulted in an increase of the compressive strength, but higher GGBS content caused also early setting which may be undesirable. A mix design procedure has been developed and has been used to determine the constituent mix proportions for three classes of concretes, i.e. (a) a ready-mix concrete with nominal strength 35 MPa, (b) a typical structural concrete with nominal strength 50 MPa, and (c) a high strength concrete for precast applications with nominal strength 70 MPa. Cost analysis was carried out to compare the AAC with Portland cement concretes with similar properties. Normal strength Portland cement concrete (PC), as typically used in ready mix industry has been shown to be less expensive than AAC. However, alkali activated concrete can be competitively priced for high strength concretes. An empirical step-by-step procedure is presented for selecting trial mix proportions for concretes with a range of consistency values, setting times and cube compressive strengths.

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Geopolymer and Alkali-Activated Binders (AAB) has recently emerged as a new, green material with the potential to replace Portland cement in several applications. They can reduce the CO2 footprint of concrete by up to 80% and this is in addition to being more durable in certain aggressive environments. However, commercial alkaline activators contribute significantly to the cost and CO2 footprint of AAB concrete mixes. This research investigated the production of a low cost, low environmental impact sodium silicate solution (waterglass) from Rice Husk Ash (RHA) and more specifically RHA from Vietnam. A hydrothermal process for the dissolution of RHA in sodium hydroxide solution was developed. Sodium hydroxide solution concentration, process temperature and duration were studied. Optimised procedure parameters were found to be: NaOH concentration 3M, heating temperature 80 ℃ and heating duration 3h. The obtained solution was used for the production of AAB mortar made with a blend of fly ash and ground granulated blast furnace slag. Obtained compressive strength of mortar was in the range of 60 MPa at 28 days, matching the strength obtained from control samples produced with commercially available activators. Microstructural investigation (isothermal calorimetry, infrared spectroscopy, X-ray diffraction and thermogravimetric analysis) on pastes confirmed the equivalence between the solution produced with the optimised method and commercially available options. Cost analysis indicated that the proposed method could allow a reduction of almost 55% of the cost for the activation of AAB. Results from a simplified preliminary environmental analysis suggested increased sustainability of the RHA-derived solution when compared with commercially available waterglass.

Neat fly ash-based alkali activated binders require high activator dosages and high temperature curing in order to develop satisfactory mechanical properties. Blending ground granulated blast furnace slag (GGBS) with fly ash can give medium to high strengths without the need for high temperature oven curing. An extensive investigation was carried out for understanding the effects of GGBS substitution of fly ash in mortar. GGBS substitution in the mix has an impact on mix proportions, fresh and hardened properties, and microstructure of reaction products. The strength of fly ash/GGBS blends cured at room temperature increased with the increase of GGBS content, whilst setting time showed an opposite trend. Fly ash/GGBS blends required lower activator dosages for obtaining high compressive strength, which has cost and environmental benefits. XRD, FTIR, TGA, and SEM/EDX results confirmed the presence of C-AS -H gel as a reaction product with as low as 20% GGBS content.

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