Flyash Based Geopolymer Concrete – A State of t he Art Review

Abstract

Concrete usage around the world is second only to water. Ordinary Portland Cement (OPC) is conventionally used as the primary binder to produce concrete. But the amount of carbon dioxide released during the manufacture of OPC due to the calcinations of lime stone and combustion of fossil fuel is in the order of 600 kg for every ton of OPC produced. In addition, the extent of energy requires to produce OPC is only next to steel and aluminum. On the other hand, the abundant availability of fly ash worldwide creates opportunity to utilize (by-product of burning coal, regarded as a waste material) as substitute for OPC to manufacture concrete. Binders could be produced by polymeric reaction of alkali liquids with the silicon and the aluminum in the source materials such as fly ash and rice husk ash and these binders are termed as Geopolymer. In Geopolymer Concrete, fly ash and aggregates are mixed with alkaline liquids such as a combination of Sodium Silicate and Sodium Hydroxide. United Nation's Intergovernmental panel on Climate Change (IPCC) prepared a report on global warming during April 2007 which enlists various methods of reduction of CO2 emissions into atmosphere. As per that report, unmindful pumping of CO2 into the atmosphere is the main culprit for the climate change. Large volume of fly ash is being produced by thermal power stations and part of the fly ash produced is used in concrete industry, low laying area fill, roads and embankment, brick manufacturing etc. The balance amount of fly ash is being stored in fly ash ponds. Hence it is imperative on the part of Scientists and Engineers to devise suitable methodologies for the disposal of fly ash. Disposal of fly ash has the objective of saving vast amount of land meant for ash pond to store fly ash. Further, use of fly ash as a value added material as in the case of geopolymer concrete, reduces the consumption of cement. Reduction of cement usage will reduce the production of cement which in turn cut the CO2 emissions. Many researchers have worked on the development of geopolymer cement and concrete for the past ten years. The time has come for the review of progress made in the field of development of geopolymer concrete. Consequently 102 papers pertaining to the ingredients and technology of geopolymer concrete have been reviewed in this state of the art paper.

A state of the art review into the use of geopolymer cement for road applications

“…The aluminosilicate materials are divided into two main categories: industrial by-products and raw, rock-based materials (Davidovits 2013). The majority of research has considered the use of industrial byproducts such as fly ash or blast furnace slag as potential precursor materials (Rangan, 2014;Duxson & Provis, 2008;Saravanan et al, 2013;Jayaranjan et al, 2014). Although Zeobond, an Australian geopolymer cement producer, use fly ash as an aluminosilicate constituent, (Zeobond, 2014), Heath et al (2013) argue that fly ash production in the UK is decreasing, reducing the potential for long term use of this source.…”

“…A geopolymer is defined by the Geopolymer Institute (2014a) as an inorganic polymeric material which is formed through geopolymerisation. The term geopolymer cement refers to binders formed as a result of this geopolymerisation process (Saravanan et al, 2013). The mixture of this binder with aggregate and water forms geopolymer concrete.…”

Global CO2 Emission-Related Geotechnical Engineering Hazards and the Mission for Sustainable Geotechnical Engineering

“…Geopolymers, a substitute for Portland cement, are alkali-activated, cementitious binder materials produced by a reaction called geopolymerization that occurs between aluminosilicate materials containing high levels of silicon and aluminum oxides (i.e., slag, fly ash, and metakaolin) and alkali-activating agents (i.e., alkali hydroxides) [93,98]. Alkali-activated geopolymers consist of three-dimensional structures of sodium aluminosilicate hydrate (N-A-S-H) gel along with calcium-silicate-hydrate (C-S-H) gel, which make up the Portland cement [94]. These geopolymerized gel binders, formed through a polycondensation process, fill the pores between soil particles to reduce the void ratio and increase bulk density, resulting in enhanced strength.…”

Importance of Cation Species during Sulfate Resistance Tests for Alkali-Activated FA/GGBFS Blended Mortars

“…Some studies [4,6,7,8,9,10,11] have proposed the use of calcium sulfoaluminate (CSA) cement to reduce the firing temperature and total CaO content, resulting in fewer CO 2 emissions during production as compared to OPC. By contrast, alkali-activated materials (AAMs) have also been considered as a candidate to replace OPC because AAMs can be manufactured through the recycling of industrial by-products, such as ground granulated blast-furnace slag (GGBFS) and fly ash (FA) [12,13,14,15,16,17,18].…”