Development of Low CO2 Durable Concrete Using Geopolymer and Related Chemically-Activated Cements

Knight, Richard L. (2017) Development of Low CO2 Durable Concrete Using Geopolymer and Related Chemically-Activated Cements. [USQ Project]

Text (Project)
Richard L Knight Research Dissertation_Redacted.pdf

Download (4MB) | Preview


Concrete is a vital construction material in modern society as it is used to shape the built environment in many ways. Its use can be seen in the construction of road and rail infrastructure, buildings, dams, runways, and water and sewerage systems. It is the most widely used man-made material in the world.

Not to be confused with cement, concrete is essentially a mixture of aggregates and paste which are combined to form a solid, rock like mass. Aggregates are typically sand and gravel or crushed stone, and the paste is typically water and Portland cement (more commonly known as ordinary Portland cement (OPC).

There are many aspects of OPC concrete production that appear to be coming under increased scrutiny from an environmental and sustainability perspective. OPC concrete traditionally relies on the quarrying of non-renewable raw materials, and significant amounts of coal are used in the production of Portland cement. Electricity is needed to run the machinery for grinding, blending, and processing, and the concrete industry typically has high fuel use and a need for heavy transport in the supply and distribution chain. These factors mean that concrete production is commonly associated with the depletion of the world’s natural resources and significant CO2 emissions.

The increased awareness of environmental and sustainability issues in the concrete industry is leading to the development of new source materials for concrete production. Recent innovations in this area include the use of Portland cement-free, low CO2 binders, commonly referred to as geopolymers binders, which result in concrete mixes (i.e. geopolymer concretes) with similar mechanical properties to OPC concrete, but which offer a lower carbon footprint.

Geopolymer concrete has garnered attention in recent years, mainly as a result of being more ‘environmentally friendly’ than OPC concrete. Sometimes referred to as ‘green’ or ‘low carbon’ concrete, previous studies have proven geopolymer concretes to be environmentally superior through the use of binders manufactured from waste / industrial by-products (e.g. fly ash and blast furnace slag), rather than virgin raw materials extracted by quarrying.

Previous experimental work has shown that geopolymer concrete can offer similar mechanical properties to OPC concrete, with comparable compressive strengths, elastic moduli, and Poisson’s ratio. In some instances, geopolymers can exhibit properties superior to OPC concrete, such as better heat resistance and low creep and drying shrinkage properties. Geopolymers can also offer enhanced resistance to many common concrete durability issues. With these factors in mind, vii geopolymer concrete appears to offer many of the attributes of OPC concrete and should therefore be considered as a suitable replacement.

Despite the potential advantages of geopolymer concrete, widespread acceptance and increased commercial use appears to be a long way off. The construction industry is often cautious and safety conscious when it comes to embracing new building materials. A thorough and detailed understanding of a new material and how it will react in critical design conditions may often be required before widespread utilisation and acceptance will take place. In this regard, it was the intention that this research project would assist in advancing the geopolymer cause.

With this in mind, the main objective of this research project was to strengthen the position of geopolymer concrete via experimental investigations that helped gain a deeper understanding of how differing activator solution ratios and their concentration affect strength, along with different binder ratios. Different geopolymer concrete mix designs were developed to have a target compressive strength of 30MPa, with varying activator solution ratios and binder ratios. Several important mechanical properties for the different mix designs were established via experimental testing (e.g. compressive strength, stress / strain characteristics, and modulus of elasticity). It was found that the tested geopolymer mixes were comparable with OPC concrete mixes in this regard.

During this research project one potential drawback discovered early on was the fast setting time for the tested mix designs, samples hardening to an unworkable hardness within minutes, even when submerged in water.

Results: During this project testing phase, some of the Compression results that did not fall into what was logical logically expected. Thus, there were no quantifiable results achieved and the findings to be presented. What did eventuate, using logic and the principle of differentiation, was to replace suspected corrupted data with predicted values and plot the hypothesized results. While not tangible they have resulted in a sound and intriguing hypothesis into a direct cause and effect ration for the change in modulus. Using data derived using this method, in the near future, it may be possible to predict the effect that changes to the modulus will have on different fly ash to blast furnace slag mix ratios.

Conclusion: While concrete results eluded the research project certain conclusions can be assumed, cursory evidence points to a direct relationship between the modulus and the compression strength of the viii casting. Currently, the data is insufficient to state this conclusively, but initial data indurates this to be the case. Industry acceptance and widespread use of fly-ash/slag based geopolymer concrete, as an alternative building material, is still some time away. At this stage of understanding, there are still too many unknowns and potential complications that need to investigated and rectified. However, fly ash/slag based Geopolymer concrete has demonstrated that it has exciting potential within the construction industry when these challenges are overcome.

Statistics for USQ ePrint 40824
Statistics for this ePrint Item
Item Type: USQ Project
Item Status: Live Archive
Additional Information: Bachelor of Engineering
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Civil Engineering and Surveying (1 Jul 2013 - 31 Dec 2021)
Supervisors: Wang, Hao; Zhang, Zahua
Date Deposited: 06 Sep 2022 03:24
Last Modified: 06 Sep 2022 03:28
Uncontrolled Keywords: concrete; geopolymers binders; environmentally friendly

Actions (login required)

View Item Archive Repository Staff Only