As part of my project, I aim to develop the lightest possible concrete while reducing the associated carbon footprint. I plan to completely replace Portland cement with blast furnace slag (GGBFS) and use lime as a chemical activator. I would like to hear your opinions on the feasibility of such an approach, as well as any information on its potential impact on density and environmental benefits (e.g., CO₂ emission reduction). Do you have examples of successful applications or recommendations on optimal dosages and potential challenges to anticipate? Thank you for your contributions!
Your approach of replacing Portland cement with ground granulated blast furnace slag (GGBFS) activated by lime is both feasible and promising, particularly for reducing the carbon footprint of concrete production. GGBFS is widely recognized as a sustainable alternative to Portland cement due to its lower embodied energy and significant reduction in CO₂ emissions when utilized effectively. Chemically activating it with lime is a common strategy, as it promotes the formation of calcium silicate hydrates (C-S-H), which contribute to strength development.
In terms of density, fully replacing Portland cement with GGBFS can result in a slight reduction in density, especially if combined with lightweight aggregates or foaming agents. This aligns with your goal of developing lighter concrete. However, achieving optimal mechanical properties and durability requires careful selection of the activator dosage and curing conditions.
Challenges to anticipate:
1. Setting time and early strength: GGBFS-based concrete often exhibits slower hydration and delayed strength development, particularly at early stages. This can be addressed by optimizing the lime-to-slag ratio and potentially incorporating alkali activators like sodium silicate.
2. Workability: The mix may require superplasticizers to maintain adequate workability.
3. Durability: While GGBFS generally enhances resistance to sulfate attack and chloride penetration, ensuring adequate curing is crucial to achieving these benefits.
Examples of successful applications include alkali-activated slag concretes used in infrastructure projects, such as marine environments and precast elements. These applications highlight its potential for both performance and sustainability.
I recommend starting with experimental trials to determine the optimal activator dosage and mix design for your specific requirements. Testing should focus on achieving the desired balance between strength, density, and durability while maintaining environmental benefits.
Yes, it is possible to make concrete without using Portland cement at all, by using chemically activated BFS. This class of concrete is also referred to as alkali-activated concrete. It has numbers of very desirable advantages as compared to Portland cement concrete: much lower carbon emissions, improved resistance, and far superior strength over time.
According to properties the composition of such a slag may affect besides the final content of the activation solution, properties may vary.
Therefore, it is very important that careful designs are made with the necessary testing to ascertain that the concrete will achieve the required performance specifications.
I recommend this article for you:
Article Properties of alkali-activated slag mortar and prediction of...
Using these percentages mentioned in the article proved to be the best
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