Management and valorisation of wastes through use in producing alkali-activated cement materials

There is a growing global interest in maximising the re-use and recycling of waste, to minimise the environmental impacts associated with waste treatment and disposal. Use of high-volume wastes in the production of blended or novel cements (including alkali-activated cements) is well known as a key pathway by which these wastes can be re-used. This paper presents a critical overview of the urban, agricultural, mining and industrial wastes that have been identified as potential precursors for the production of alkali-activated cement materials, or that can be effectively stabilised/solidified via alkali activation, to assure their safe disposal. The central aim of this review is to elucidate the potential advantages and pitfalls associated with the application of alkali-activation technology to a wide variety of wastes that have been claimed to be suitable for the production of construction materials. A brief overview of the generation and characteristics of each waste is reported, accompanied by identification of opportunities for the use of alkali-activation technology for their valorisation and/or management

Waste glass from end-of-life fluorescent lamps as raw material in geopolymers

Nowadays the stunning volume of generated wastes, the exhaustion of raw materials, and the disturbing greenhouse gases emission levels show that a paradigm shift is mandatory. In this context, the possibility of using wastes instead of virgin raw materials can mitigate the environmental problems related to wastes, while reducing the consumption of the Earth’s natural resources. This innovative work reports the incorporation of unexplored waste glass coming from end-of-life fluorescent lamps into geopolymers. The influence of the waste glass incorporation level, NaOH molarity and curing conditions on the microstructure, physical and mechanical properties of the geopolymers was evaluated. Results demonstrate that curing conditions are the most influential factor on the geopolymer characteristics, while the NaOH molarity is less important. Geopolymers containing 37.5% (wt) waste glass were successfully produced, showing compressive strength of 14 MPa (after 28 days of curing), suggesting the possibility of their use in non-structural applications. Porous waste-based geopolymers for novel applications were also fabricated

Hydration and Physico-mechanical Properties of Blended Calcium Sulfoaluminate-belite Cement Made of Industrial By-products

Portland cement blended Calcium Sulfoaluminate-belite (CŜAB) cements were studied in order to improve its binding properties and workability for specific applications. The binders consisted of calcium sulfoaluminatebelite, Flue Gas Desulfurization-gypsum and Ordinary Portland Cement (OPC). In this research, effects of OPC contents (25, 50, 75 wt%) as a CŜAB replacement on hydration behaviors and physico-mechanical properties of the binders were observed. Used CŜAB cement was synthesized using industrial by-products viz., fly ash, Flue Gas Desulfurization-gypsum, Al-rich sludge as starting materials via hydrothermal-calcination method. The results revealed that the replacement of CŜAB cement with OPC extended the setting times of pastes. The reduction of hydration rate with higher OPC content was due to dilution of fast setting phases such calcium sulfoaluminate and mayenite. Hydration products of calcium sulfoaluminate cement were ettringite responsible for high early strength together with Al(OH)3. From 6 h onwards, hydration of tricalcium silicate phase from the OPC generated calcium silicate hydrate. Strätlingite was also found in low OPC content mix resulting from the reaction between the Al(OH)3 and either alite phase in OPC or belite phase in CŜAB cement. Ettringite could also react with Al(OH)3 to generate monosulfate at later ages. The calcium sulfoaluminate phase was mainly responsible for the early mechanical properties, while OPC played an important role to improve strength at later ages

Geopolymer/Zeolite composite materials with adsorptive and photocatalytic properties for dye removal.

This study investigated the adsorption capacities and photocatalytic activities of geopolymer-zeolite composite materials by incorporating different amounts of zeolite and TiO2 in a geopolymer matrix for dye removal. Geopolymers with SiO2/Al2O3 molar ratio of 2.5 were synthesized from metakaolin. The geopolymers containing zeolite and TiO2-doped zeolite exhibited similar behavior in terms of mineral compositions, microstructures and chemical frameworks. The compressive strength of geopolymer-zeolite composite materials decreased with increasing amount of zeolite and TiO2-doped zeolite (0-40 wt%) because of the increase in the porosity of composite materials. The maximum methylene blue adsorption capacity and photocatalytic efficiency of the powdered geopolymer composites with 40 wt% TiO2-doped zeolite was 99.1% and was higher than that of the composites with 40 wt% zeolite without TiO2-doping (92.5%). In addition, the geopolymer composites with TiO2-doped zeolite exhibited excellent stability after repeated usage as photocatalysts. The adsorption capacity and photocatalytic activity of pelletized geopolymer composites decreased because of the reduction in their specific surface area

Effect of High-Speed Mixing on Properties of High Calcium Fly Ash Geopolymer Paste

Geopolymers are produced by mixing alumino-silicate materials with alkaline activators, and the mixing process has a considerable impact on the dissolution of raw materials. This research studies the effects of mixing time, with a high-speed centrifuge mixer (1,000 rpm), on the setting and hardening properties of high calcium fly ash-based geopolymer paste. Setting time, strength, phase development, microstructure and porosity of the pastes were investigated. The results indicated that the increase in mixing time retarded the setting time which provided time for dissolution of starting materials. The optimum mixing time at high speed should be 1 min in order to obtain high strength and dense matrix in contrast to 10 min for the normal mixing. The mixing time also had an effect on the pore structure hence the total porosity of the paste