A brief history and review of geopolymer technology is presented with the aim of introducing the technology and the vast categories of materials that may be synthesized by alkali-activation of aluminosilicates. The fundamental chemical and structural characteristics of geopolymers derived from metakaolin, fly ash and slag are explored in terms of the effects of raw material selection on the properties of geopolymer composites. It is shown that the raw materials and processing conditions are critical in determining the setting behavior, workability and chemical and physical properties of geopolymeric products. The structural and chemical characteristics that are common to all geopolymeric materials are presented, as well as those that are determined by the specific interactions occurring in different systems, providing the ability for tailored design of geopolymers to specific applications in terms of both technical and commercial requirements.

Geopolymer technology: the current state of the art

http://www.personal.psu.edu/faculty/g/u/gur/cement%20for%20the%20future.pdf

Alkali-activated fly ashes: A cement for the future

The Role of Inorganic Polymer Technology in the Development of ‘Green Concrete’

Understanding the relationship between geopolymer composition, microstructure and mechanical properties

Carbon dioxide equivalent (CO2-e) emissions: A comparison between geopolymer and OPC cement concrete

Alkali aluminosilicate polymers, or ‘geopolymers’, a family of minerals with cementitious properties, constitute a promising future source of materials for the construction industry. These polymers combine certain properties of ordinary cements, traditional ceramic materials and zeolites. 29 Si, 27 Al and 23 Na MAS-NMR spectroscopy were used to characterise the reaction products resulting from the alkali activation of a type F fly ash. Specifically, analysis focused on the influence of the degree of polymerisation of the activating solution. The results obtained show that the nature of the alkali activator plays an important role in the kinetics, structure and composition of the gel initially formed. The alkaline aluminosilicate gel formed exhibits short-range order, with the silicon appearing in a wide variety of Q 4 ( n Al) ( n  = 0, 1, 2, 3 and 4) environments.

Nanostructure/microstructure of fly ash geopolymers

Alkaline activation of fly ashes

This study aimed to determine the physical-mechanical, mineralogical and microstructural properties of a pre-industrially manufactured hybrid cement (HYC) containing 5% alkaline activator and less than 30% clinker. The effect of the initial curing temperature (25 ± 1 or 85 °C for 20 h) on hydration kinetics and the development of compressive strength were also explored. The hydration products formed were characterised using XRD, SEM/EDX and 27 Al and 29 Si MAS-NMR. The findings showed that pre-industrial hybrid cement sets when hydrated with water and hardens to a 28-day mechanical strength of 35 MPa. The main reaction product formed was a mix of cementitious gels: C-(A)-S-H and C-A-S-H. Curing at 85 °C for 20 h, shows a behaviour similar to OPC, inhibited ettringite formation and generated more polymerised gels, enhancing 3-day but not 28- or 90-day mechanical strength.

Characterisation of pre-industrial hybrid cement and effect of pre-curing temperature

Alkaline cements consist essentially of two components: a cementitious material and an alkaline activator. Natural materials (metakaolin) or industrial by-products (such as slag and fly ash) with amorphous or vitreous structures are used as cementitious components, while the liquid or solid alkaline activators applied are generally alkaline salts or caustic solutions. This chapter discusses the most prominent characteristics and properties of both components: the [CaO]/[SiO2] and [SiO2]/[Al2O3] ratios in the cementitious materials; the best activator for each solid precursor; and the effect of anions (OH− (pH), silicates, carbonates and sulfates) and cations (Na+or K+).

Crucial insights on the mix design of alkali-activated cement-based binders

Alkali-activated fly ash is the primary component of a new generation of high-strength, durable binders with excellent mechanical properties and durability (on occasion bettering traditional Portland cement performance). Moreover, development of these cements may contribute to mitigating CO 2 emissions, since the base material is an industrial by-product. The present study was conducted to determine the effect of the composition of the initial materials (SiO 2 /Al 2 O 3 and Na 2 O/Al 2 O 3 ratios) on the mechanical properties, nature and composition of the reaction products. The results obtained indicate that there is no linear relationship between these ratios and mechanical strength, but rather a series of optimal values above and below which strength declines. In the specific case of the ratios studied in the present paper, these values were: SiO 2 /Al 2 O 3 = 4.0 and Na 2 O/Al 2 O 3 = 1.0 (molar ratios).

/pdf/activacion-alcalina-de-cenizas-volantes-relacion-entre-el-2jz8h0h2m5.pdf

Ángel Palomo

Papers

Nanostructure/microstructure of fly ash geopolymers

Alkaline activation of fly ashes

Characterisation of pre-industrial hybrid cement and effect of pre-curing temperature

Crucial insights on the mix design of alkali-activated cement-based binders

Activación alcalina de cenizas volantes. Relación entre el desarrollo mecánico resistente y la composición química de la ceniza