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Cementless “Geopolymer” Concrete for Sustainable Construction

School of Natural and Built Environment | PHD
Funding
Unfunded
Reference Number
NBE/MS/2020/05
Application Deadline
None specified
Start Date
None specified

Overview

The development of sustainable products is necessary for the continued success of the precast concrete industry. The project aims to develop sustainable technologies and products that: (a) reuse discarded materials and reduce the need to use expensive 'natural' materials (whose extraction can destroy natural habitats and which involve intricate supply chains) (b) have superior qualities compared to current best practice/products and extended lives (c) have a positive ecological and social impact (d) can offer value-added benefits and respond to a market need.

This project will focus on the production of Green Precast Concrete Products by investigating the possibility of completely replacing cement by waste materials of high silicon dioxide content, e.g., incinerator ash, basic oxygen steel slag, disposed ash, from coal-fired thermal power plants, into ash ponds or lagoons, together with waste alkali solutions from the chemical industry. The alkali activated ash may have cementitious properties similar to cement. The reaction has been shown to be possible but selection of materials to successfully achieve compressive strengths similar to cement remains a mystery, i.e. the process is based on trial and error of different combinations of materials. This is even with off the shelf alkali solutions of known concentration combined with ground granulated blast furnace slag (ggbs) that is known to be reactive in this way. Use of ggbs and commercially available alkali solutions make this type of concrete prohibitively expensive. Yet this same concrete can be made with 100% waste materials. There is a clear and urgent market need for cement free concrete products with reduced CO2 footprint. The testing and development will focus initialy on the production of ‘Green/Ecofriendly Paving Products' that use as a binder waste materials and thus do not require the use of cement. Cementless Concrete can use lagoon ash, basic oxygen steel slag, and ash from municipal waste incinerators, combined with waste alkali solutions from the chemical industry (production of one tonne of cement corresponds approximately to one tonne of CO2 released to the atmosphere). Research will concentrate on developing an understanding of the reaction mechanism between waste alkali solutions and industrial siliceous ashes. The mechanism of the reaction between these siliceous ashes and alkalis is not well-established. The work will be jointly supervised with the Earth & Ocean Sciences department which is exceptionally well equipped with two analytical scanning electron microscopes (SEM) and a new state of the art X-ray diffractometer (XRD), as well as other relevant facilities such as infra-red spectroscopy and cathode luminescence microscopy. The aim will be to use these techniques to characterise the material properties of the various concretes as well as the starting materials. XRD will be used to identify the range and quantities of minerals and materials in the concrete. SEM will be used to understand the distribution of the minerals and materials identified by XRD and to quantify grain sizes, shapes etc. The chemical analytical facility will not only allow correct identification of minerals developed in the geopolymer cement, but will also allow investigation of chemical interactions between the geopolymer cement and the different types of aggregate. One potentially exciting area of investigation is to see if the concretes can be suitably prepared for electron backscatter diffraction (EBSD) analysis, which allows quantification of crystal lattice orientations. It is well known that lattice preferred orientations (LPO) in both natural stone materials and in metals have profound effects on the engineering properties of those materials. This type of analysis, if it proves possible, could provide key evidence for understanding what microstructure develops in cementless "geopolymer" materials as a result of different sources of ashes which have different chemical and mineral compositions. This could allow blending of different materials so they produce geopolymer concretes with the desired engineering properties such as greater compressive strength, greater tensile strength, greater flexibility.

Project Summary
Supervisor

Professor Marios Soutsos

More Information

m.soutsos@qub.ac.uk

Research Profile


Mode of Study

Full-time: 3 years

Part-time: 6 years


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