Freedom of design, mass customisation, waste minimisation and the ability to manufacture complex structures, as well as fast prototyping, are the main benefits of additive manufacturing (AM) or 3D printing. A comprehensive review of the main 3D printing methods, materials and their development in trending applications was carried out. In particular, the revolutionary applications of AM in biomedical, aerospace, buildings and protective structures were discussed. The current state of materials development, including metal alloys, polymer composites, ceramics and concrete, was presented. In addition, this paper discussed the main processing challenges with void formation, anisotropic behaviour, the limitation of computer design and layer-by-layer appearance. Overall, this paper gives an overview of 3D printing, including a survey on its benefits and drawbacks as a benchmark for future research and development.

Additive manufacturing (3D printing): A review of materials, methods, applications and challenges

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

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

Precursors for the preparation of one-part geopolymers are synthesized by thermal activation of albite with sodium hydroxide and sodium carbonate, then cooling and crushing the resulting product. Albite is stable under thermal treatment up to 1000°C, but is able to be converted to depolymerized, disordered, and X-ray amorphous geopolymer precursors in the presence of sodium hydroxide or sodium carbonate at elevated temperatures. The geopolymer precursors react with the addition of water (i.e., form a “one part geopolymer mix”), forming geopolymers with acceptable compressive strength. One-part geopolymers synthesized via thermal activation of albite with NaOH show a higher compressive strength than those produced with Na2CO3 at the same dosage. Some crystalline sodium-aluminosilicate hydrates (zeolites) are also formed in addition to geopolymer gel in the geopolymers synthesized from albite activated by NaOH, compared to predominantly amorphous phases in the samples activated by Na2CO3. The activation of natural aluminosilicates including albite by thermal treatment with alkalis has great potential in the development of novel one-part mix geopolymers.

Thermal Activation of Albite for the Synthesis of One‐Part Mix Geopolymers

The interrelationship between surface chemistry and rheology in alkali activated slag paste

Few attempts have been made to understand the effect of the structural and surface properties of source materials on geopolymerization. In the present work, kaolinite, albite, and fly ash have been chosen for a case study to answer this question. X-ray diffraction, X-ray fluoresence, X-ray photoelectron spectroscopy, 27Al and 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, and scanning electron microscopy (SEM) have been used to characterize the source materials and geopolymers. The fly ash that has an amorphous structure and possesses the lowest binding energies in its structure shows the highest reactivity during geopolymerization. Apart from the reactivity, the desired Si/Al molar ratio in the gel phases and the leaching of the source materials are observed to significantly affect the geopolymerization. The geopolymerization of mixtures of two or three source materials demonstrates the benefits derived from the interaction between the source materials. Such interactions cou...

Effect of Source Materials on Geopolymerization

By scanning electron microscopy and microanalysis of fly ash-based and mixed fly ash-slag inorganic polymer cement (i.e., “fly ash geopolymer”) binders, a more detailed understanding of the gel structure and its formation mechanism have been developed. The binder is predominantly an aluminosilicate gel charge balanced by alkali metal cations, although it appears that calcium supplied by slag particles becomes relatively well dispersed throughout the gel. The gel itself is comprised of colloidal-sized, globular units closely bonded together at their surfaces. The microstructure of the binder resulting from hydroxide activation of fly ash is much less uniform than that which forms in a corresponding silicate-activated system; this can be rationalized in terms of a newly developed explanation for the differences in reaction mechanisms between these two systems. In hydroxide activation, the newly formed gel phase nucleates and grows outwards from the ash particle surfaces, whereas the high silica concentration in a silicate-activated system enables a more homogeneous gelation process to take place throughout the inter-particle volume.

Microscopy and microanalysis of inorganic polymer cements. 2: the gel binder

Drying of cement paste, mortar, or concrete specimens is usually required as a pre-conditioning step prior to the determination of permeability-related properties according to standard testing methods The reaction process, and consequently the structure, of an alkali-activated slag or slag/fly ash blend geopolymer binder differs from that of Portland cement, and therefore there is little understanding of the effects of conventional drying methods (as applied to Portland cements) on the structure of the geopolymer binders Here, oven drying (60 °C), acetone treatment, and desiccator/vacuum drying are applied to sodium silicate-activated slag and slag/fly ash geopolymer pastes after 40 days of curing Structural characterization via X-ray diffraction, infrared spectroscopy, thermogravimetry, and nitrogen sorption shows that the acetone treatment best preserves the microstructure of the samples, while oven drying modifies the structure of the binding gels, especially in alkali-activated slag paste where it notably changes the pore structure of the binder This suggests that the pre-conditioned drying of alkali activation-based materials strongly affects their microstructural properties, providing potentially misleading permeability and durability parameters for these materials when pre-conditioned specimens are used during standardized testing

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Jannie S.J. van Deventer

Papers

Thermal Activation of Albite for the Synthesis of One‐Part Mix Geopolymers

The interrelationship between surface chemistry and rheology in alkali activated slag paste

Effect of Source Materials on Geopolymerization

Microscopy and microanalysis of inorganic polymer cements. 2: the gel binder

Drying-induced changes in the structure of alkali-activated pastes