To improve the workability of geopolymer concrete without altering the properties of the alkaline activator, consider the following practical and cost-effective strategies:

1. Optimize Aggregate Gradation: Use well-graded aggregates with a proper balance of fine and coarse materials to enhance packing density and reduce voids, thereby improving workability.

2. Increase Fine Content: Adjust the proportion of fine aggregates or add fillers like fly ash, silica fume, or ground granulated blast furnace slag to enhance lubrication within the mix.

3. Add Superplasticizers: Incorporate compatible superplasticizers designed for alkali-activated systems to reduce water demand while maintaining flowability.

4. Modify Water-Solid Ratio: Slightly increasing the water-to-solid ratio can enhance workability, provided it does not compromise the mix’s strength and durability.

5. Incorporate Lightweight Aggregates: Use lightweight aggregates with higher absorption properties to retain moisture and improve the mix’s overall flow.

6. Use Supplementary Cementitious Materials: Adding materials like metakaolin or Class C fly ash can improve particle distribution and reduce friction.

These approaches maintain the chemical integrity of the activator while improving the mix’s physical behavior, making them suitable for large-scale applications.

Hello! I have reviewed the latest research and practical approaches to improving the workability of geopolymer concrete without altering the alkaline activator properties. From my last three years of experiences, Here are some cost-effective and practical methods that can be applied on a large scale:

1. Use of Supplementary Cementitious Materials (SCMs)

• Fly Ash: Incorporating fly ash can significantly improve the workability of geopolymer concrete. Fly ash fills the voids between cement particles and aggregate, reducing internal friction and making the concrete more flowable. This is a cost-effective method as fly ash is often an industrial byproduct and readily available.
• Ground Granulated Blast Furnace Slag (GGBFS): GGBFS can also enhance workability by filling voids and reducing friction. A combination of GGBFS and fly ash can further optimize the workability of geopolymer concrete.

2. Addition of Fibers

• Glass Fibers: Adding graded glass fibers can improve the workability of geopolymer concrete. Glass fibers act as a lubricant, reducing the resistance between particles and making the concrete more flowable. The optimal amount of sand replacement using waste glass was found to be 20-25% with a target strength of 25 MPa.
• Steel Fibers: Steel fibers can enhance the cohesion of the concrete mixture, preventing segregation and improving workability. However, the dosage and length of steel fibers need to be carefully controlled to achieve the best effect.

3. Optimization of Aggregate Grading

• Well-graded Aggregates: Using well-graded aggregates can significantly improve the workability of geopolymer concrete. Well-graded aggregates have a continuous size distribution, which can fill the voids more effectively and reduce the demand for water and cement paste.
• Adjusting Aggregate Ratio: The ratio of fine to coarse aggregates can be adjusted to optimize workability. A higher proportion of fine aggregates can increase the paste content and improve workability, but excessive fine aggregates may lead to segregation.

4. Use of Superplasticizers

• Polycarboxylate Superplasticizers: These are highly effective in improving the workability of geopolymer concrete. They disperse the cement particles and reduce the water demand of the mixture. The recommended dosage of superplasticizer typically falls within the range of 0.8 to 1.5% of the binder content.
• Naphthalene-based Superplasticizers: They also have a good effect on improving workability. However, the dosage should be controlled to avoid excessive air entrainment, which may affect the strength and durability of the concrete.

5. Pre-soaking Aggregates

• Pre-soaking Aggregates: Pre-soaking the aggregates before mixing can improve the workability of geopolymer concrete. This is because the pre-soaked aggregates can absorb some water, reducing the water demand of the mixture during mixing.

6. Mechanical Mixing and Vibration

• Proper Mixing Time: Ensuring proper mixing time is crucial for achieving good workability. Insufficient mixing may lead to an uneven distribution of materials, while excessive mixing may cause segregation. Therefore, an appropriate mixing time should be determined based on the specific mix design and equipment used.
• Vibration: After pouring the concrete, proper vibration can help to remove air bubbles and compact the mixture, improving workability and reducing the risk of honeycombing and voids. However, over-vibration should be avoided to prevent segregation and bleeding.

7. Use of Waste Materials

• Waste Glass: Using waste glass particles as a replacement for fine or coarse aggregates can be a sustainable and cost-effective solution. The study found that the optimum amount of sand replacement using waste glass was 20-25% with a target strength of 25 MPa.
• Discarded Rubber Tire Crumbs: Incorporating discarded rubber tire crumbs can also improve the workability of geopolymer concrete. The freshly mixed geopolymer concrete can be transferred into pre-lubricated molds in layers and compacted with a vibrating table to remove air.

8. Mix Design Approaches

• Target Strength Approach: This approach involves designing the mix to achieve a specific target strength while optimizing workability. The mix design should consider the properties of the unprocessed materials, the kind and amount of the activator, and the cure program.
• Performance Approach: This approach focuses on the performance requirements of the concrete, such as workability, strength, and durability. It involves a systematic evaluation of different mix proportions to achieve the desired performance.

These methods can help improve the workability of geopolymer concrete without altering the alkaline activator properties. They are practical and economically viable for large-scale applications, making them suitable for use in various construction projects. I hope these suggestions are helpful for your work.

Hello,

I suggest you first to understand how Geopolymerization process works. I mean that Geopolymer precursor must be tailored to be the most reactive possible, my NDA prohibits to go deeper about formulations, but you can check at www.geopolymer.org there are about 27 articles free to be downloaded, that can be very helpful for your study.

Geopolymers are mineral polymers so their precursors don’t need to be activated by super alkaline liquids or solids (following the Alkali Acitvated Materials methods), because they are already reactive! Normally you need to activate something that is not enough reactive…

Geopolymerization isn’t hydraulic reaction so lot of balancing concerning water ratio, are not focused on what will be the correct chemical reaction between minerals. This confirms that GP aren’t AAMs where instead water is very important factor.

Remember also that all the admixtures like superplasticizers for example, work considering water as medium to obtain the best dispersion and have been created for OPC hydraulic systems. On the site you could buy the book of Professor Davidovits where you can find all the answers, obviously explained in very technical terms but are we talking of materials science or not? You will understand why: 1. the terminology is important for the related concepts that explain; 2. If the precursor isn’t adeguate to the application you cannot obtain good, stable and durable results and very probably you don’t obtain Geopolymerization but alkali activation that means inconstant result (every batch gives different data, but you don’t know why…), from very reduced to complete failure during water immersion curing (it’s mandatory to be stable in humid/wet conditions if your study must show the industrial feasibility of your material to be a sustainable alternative to Portland concrete) and lot of efflorescence, blooming and bad smells (even after prolonged aging). Just to list the most common side effects of alkali activation process; 3. to customize your recipe, matching your targets you must manage the technology knowing where operating and why.

Definitely, the most simple think is modifying your entire binding system. Treating a super high pH liquid or powder it doesn’t matter, like if it was water…it’s not the best choice. AAMs need higher pH than GP reaction (remember that the pH scale is logarithmic) and please take care about your fingers and breathing system because caustic fumes are very dangerous. Geopolymer reagents are not labeled as corrosive but only irritant, so you can touch by fingers without burning risks.

To delay the reaction you must think at the heat of the reaction, maintaining it under temperature controlled you will prolong your workability as well, without problems.

So first modify your precursor to be reactive, but with the speed of reaction you prefer. Using pH 14, everything will be dissolved and there aren’t admixtures that can help you. Davidovits coined the term of Geopolymer explaining that Geo meant geological source (natural or artificial minerals, that can be found EVEN from waste, but not mandatorily, because waste are inconstant aren’t selected at least if the target of your work is something that can be industrialized) and polymer because the chemical reaction and hardening followed the organic polymer process. So are called Geopolymers not Geoactivated or Geoprecipitates or Geodissolved materials. Technical words explain the technology behind are not synonymous. Acid Geopolymers are other example that they are not AAMs but it‘s really weird that I continue to read papers wrong written from the concepts point of view. I’m professional worker on GP materials, I’m not a professor so if you want to continue doing AAMs because your university thinks that are good, go ahead with no problem and good luck to solve all the side effects that will come from those systems.

But if you want to realize a GP concrete with enough workability and good stable durability the way isn’t adding admixture and working with the same alkaline system. Checking the particles size of the curve will help for sure, maybe letting you reduce the total binder, but won’t help you to solve the other issues.

Anyway, sorry for the long speech I hope you can resolve your problems but have a look on the site I mentioned, this would be very important and useful for your future studies and work.

Best Regards

Dr. Alex ReggianI