The role of inorganic polymer technology in the development of ‘green concrete’
Introduction
Inorganic polymer concretes, or ‘geopolymers,’ have emerged as novel engineering materials with the potential to form a substantial element of an environmentally sustainable construction and building products industry [1], [2]. These materials are commonly formed by alkali activation of industrial aluminosilicate waste materials such as coal ash and blast furnace slag, and, as will be discussed in detail in this paper, have a very small Greenhouse footprint when compared to traditional concretes. Given correct mix design and formulation development, geopolymeric materials derived from coal ash (Class F and/or Class C) can exhibit superior chemical and mechanical properties to ordinary Portland cement (OPC) [1], and be highly cost effective. A key attribute of geopolymer technology is the robustness and versatility of the manufacturing process; it enables products to be tailor-made from a range of coal ash sources and other aluminosilicate raw materials so that they have specific properties for a given application at a competitive cost. Applications of particular interest at present include low or high strength concretes with good resistance to chloride penetration, fire and/or acid resistant coatings, and waste immobilization solutions for the chemical and nuclear industries. The specific properties of geopolymers which lead to particular suitability in each of these applications will be outlined briefly in this paper.
Despite these key technological attributes, and environmental and cost savings compared to OPC, the main drivers for the uptake of the technology by existing players in the cement and concrete products industry may not form a compelling business case for geopolymer production by these organizations at this time. This is particularly so for large cement companies, where the low profit margins and high financial risk involved with the introduction of a revolutionary (rather than evolutionary) technology in low- and high-strength concrete applications respectively must be taken into account. The successful adoption of geopolymer technology in the future will be governed by a host of factors to be discussed here, including the ability to add significant value to coal ash and/or slag waste streams, wider understanding of the benefits of the technology, as well as the potential to significantly reduce carbon dioxide emissions compared to OPC manufacture. This paper discusses the practical technical, environmental, and commercial drivers in more detail, as well as how geopolymer technology may form part of an overall ‘Green Concrete’ industry. Later in the article, the commercial drivers for adoption of geopolymer technology are explored in a broader context that takes into account not just the desirable application of the material, but also the market reality.
Section snippets
Performance, properties and applications
There is now a significant yet still modest amount of scientific literature exploring the properties of geopolymeric materials on the laboratory scale. However, more significantly, there is a growing understanding of the real world-scale capabilities of the technologies being developed through plant trials and commercial rollouts, most of which are naturally protected by confidentiality agreements. Nonetheless, it is clear that materials exhibiting the following performance properties can be
Technical challenges
The greatest challenge for any technology looking to be adopted in the construction industry is fundamentally two-fold. The key technological and engineering aspect of this challenge relates to product certification in each market. As geopolymers are made from ashes and/or metallurgical slags, these raw materials vary from source to source, requiring a large investment in formulation and certification from each source. However, it must be noted that this issue is largely the same as that faced
Environmental benefits
One of the primary advantages of geopolymers over traditional cements from an environmental perspective is the much lower CO2 emission rate from geopolymer manufacture compared to OPC production. This is mainly due to the absence of a high-temperature calcination step in geopolymer synthesis from ashes and/or slags, whereas the calcination of cement clinker not only consumes a large amount of fossil fuel-derived energy, but also releases CO2 as a reaction product. While the use of an alkaline
Regulatory issues
Probably the single greatest hurdle facing the emerging geopolymer industry in terms of application in the construction industry as a load-bearing material is not technological, but rather regulatory. In the developed world, there are very specific standards for what is considered ‘acceptable’ performance for a cementitious binder. These have clearly been developed over many years, with input from cement manufacturing companies with the behavior of OPC-based concretes specifically in mind.
Concretes or ceramics?
One of the primary decisions facing the geopolymers research community at the current point in time is that the applications for inorganic polymer technology are effectively divided between two distinct fields — cement replacement, or utilization as a low-cost alternative ceramic. While the product can be tailored to be ideally suited to one or the other of these fields of application, it is a challenge for the research community as a whole to make clear the distinction between the specific
Summary — Current challenges and obstacles
In order to develop a geopolymer industry, it is necessary to gain the greater acceptance of the technology by potential manufacturers and end-users, i.e. the technical virtues need to be “de-risked” and the commercial and environmental value of the technology quantified so that this can be accurately incorporated into the value proposition. This can be achieved through a more open-dialogue approach between academia and industry, and also the wider dissemination of basic knowledge. The current
References (63)
- et al.
The effect of ionic contaminants on the early-age properties of alkali-activated fly ash-based cements
Cem. Concr. Res.
(2002) - et al.
Reduction in wear of metakaolinite-based geopolymer composite through filling of PTFE
Wear
(2005) - et al.
Chemical stability of cementitious materials based on metakaolin
Cem. Concr. Res.
(1999) - et al.
Alkali–aggregate reaction in activated fly ash systems
Cem. Concr. Res.
(2007) - et al.
Corrosion resistance in activated fly ash mortars
Cem. Concr. Res.
(2005) Industrially interesting approaches to “low-CO2” cements
Cem. Concr. Res.
(2004)- et al.
The potential use of geopolymeric materials to immobilise toxic metals. 1, Theory and applications
Miner. Eng.
(1997) - et al.
An XRD study of the effect of the SiO2/Na2O ratio on the alkali activation of fly ash
Cem. Concr. Res.
(2007) - et al.
Geopolymerisation kinetics. 2. Reaction kinetic modelling
Chem. Eng. Sci.
(2007) - et al.
Alkali-activated cementitious materials: alternative matrices for the immobilisation of hazardous wastes — Part I. Stabilisation of boron
Cem. Concr. Res.
(2003)
The effect of metal contaminants on the formation and properties of waste-based geopolymers
Cem. Concr. Res.
Alkali-activated fly ash: effect of thermal curing conditions on mechanical and microstructural development — Part II
Fuel
Durability of geopolymer materials in sodium and magnesium sulfate solutions
Cem. Concr. Res.
Synthesis and thermal behaviour of potassium sialate geopolymers
Mater. Lett.
Thermal evolution of metakaolin geopolymers: part 1 — physical evolution
J. Non-Cryst. Solids
Immobilization of cesium in alkaline activated fly ash matrix
J. Nucl. Mater.
Quantitative determination of phases in the alkali activation of fly ash. Part I. Potential ash reactivity
Fuel
Alkali-activated fly ashes — a cement for the future
Cem. Concr. Res.
Engineering properties of inorganic polymer concretes (IPCs)
Cem. Concr. Res.
Geopolymer materials prepared using Class F fly ash and elevated temperature curing
Cem. Concr. Res.
Optimization of geopolymer synthesis by calcination and polycondensation of a kaolinitic residue
Resour. Conserv. Recycl.
Alkali activation of fly ashes. Part 1: effect of curing conditions on the carbonation of the reaction products
Fuel
Investigations about the effect of aggregates on strength and microstructure of geopolymeric mine waste mud binders
Cem. Concr. Res.
The composition range of aluminosilicate geopolymers
J. Eur. Ceram. Soc.
Reaction mechanisms in the geopolymeric conversion of inorganic waste to useful products
J. Hazard. Mater.
Geopolymer technology: the current state of the art
J. Mater. Sci.
Do geopolymers actually contain nanocrystalline zeolites?— A reexamination of existing results
Chem. Mater.
Fire-resistant aluminosilicate composites
Fire Mater.
Geopolymers — inorganic polymeric new materials
J. Therm. Anal.
Thermal conductivity of metakaolin geopolymers used as a first approximation for determining gel interconnectivity
Ind. Eng. Chem. Res.
Use of geopolymeric cements as a refractory adhesive for metal and ceramic joins
Ceram. Eng. Sci. Proc.
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