Development of geopolymer mortar under ambient temperature for in situ applications

Abstract

Geopolymer concrete technology involves production of more environmentally friendly waste material-based concrete which could be a viable solution for conventional concrete replacement. Typical fly ash-based geopolymer concrete however requires high temperature curing treatment in order to develop sufficient early strength properties, which is considered a severe limitation for cast-in-place concrete applications. Most previous studies on geopolymer concrete have focused on the properties of concretes pre-hardened by heat curing and/ or by aggressive chemical treatment (e.g. alkali activation using concentrated sodium hydroxide (NaOH)). The current study presents an extensive experimental investigation on the mechanical and microstructural properties of geopolymer concrete mixes prepared with a combination of fly ash and slag cured under ambient temperature. 'User friendly' geopolymer mixes were produced using fly ash (FA) and Ground Granulated Blast furnace Slag (GGBS) mixed together with potassium silicate with molar ratio equal to 1.2 (as the activator) and water. The results indicated that heat curing treatment can be avoided by partial replacement of fly ash with slag. The compressive strength of the examined mixes was found to be in the range of 40-50MPa for 40 % and 50 % GGBS replacement mixtures respectively. Moreover, the flexural and direct tensile strengths of geopolymer mixes are considerably improved as the GGBS content is increased.Based on FTIR and SEM/EDS analysis, the inclusion of a higher content of GGBS resulted in a denser structure by formation of more hydration products.Keywords: Fly ash, slag, ambient temperature, user friendly geopolymer mortar *Manuscript Click here to view linked References 2 IntroductionThere are many environmental issues associated with the production of Ordinary Portland cement (OPC), such as consumption of 5% of natural resources, and generation of 5-7 % of total global anthropogenic carbon dioxide emissions [1][2][3][4]. This has led to an urgent need for the development of alternative materials that may provide technically viable alternative solutions to conventional cementitious concrete, with more favourable environmental credentials. Geopolymer concrete manufacture is one of the most promising techniques which has been developed in the last few years. Utilization of geopolymer materials can reduce 80% of greenhouse gas emissions associated with material production, and overcome issues related to cement production and unregulated disposal of industrial materials by recycling these materials in geopolymer manufacture [5][6][7].Geopolymers are inorganic by-product materials, rich in silicon (Si) and aluminium Five different mixtures of geopolymer mortar proportions were examined with various ratios of GGBS to total binder (10%, 20%, 30%, 40% and 50 %, Table 2). Based on preliminary experimental studies undertaken during the current project, the optimum mix design (in terms of mechanical strength and workability) was achieved using water, alkaline activator...

Tensile properties of a novel fibre reinforced geopolymer composite with enhanced strain hardening characteristics

“…SEM photographs in Fig.18a show the plain geopolymer mortar, and the images show a dark, well-connected structure and dense geopolymer microstructure. This mixture represents an optimum ternary geopolymer mixture based on earlier published studies [22]. Combining GGBS as a source of calcium, with FA and silica fume as source of silica leads to an increase in the formation of the geopolymerization product of a calcium alumino-silicate hydrate (C-A-S-H) gel.…”

“…Silica sand with a particle size less than 0.5 mm was used as fine aggregate. Total binder and silica sand quantities of 775 kg/m 3 and 1054 kg/m 3 respectively were used for the mixes in the current investigation, values based on a previous study [22].…”

“…Recently, the development of more user-friendly geopolymers has been proposed in order to enhance the strength of the geopolymer material as well as reduce costs and energy consumption, and promote easier handling application [11,22]. However, there are no published studies to date on user friendly geopolymer systems with strain hardening characteristics.…”

Effect of GGBS and curing temperature on microstructure characteristics of lightweight geopolymer concrete

“…However, a shift in the wave number of concrete 1-30 towards a lower wavelength was noticed, signifying a lower degree of silica polymerization [24]. However, with the incorporation of GGBS in mixes 2 and 3, the intensity of this vibration decreased due to the formation of C-S-H and N-A-S-H gels, associated with a reduction in the amount of Al [25]. When samples were cured in ambient conditions, a band at 1420 cm -1 was detected.…”

“…However, it was noticed the endothermic peak shifted towards higher temperatures (170-180°C) in mixes 2 and 3. The increase in GGBS content contributed to the degree of reactivity and reduced the setting time by developing aluminum-modified C-S-H (or C-(A)-S-H) gel [25,27].…”