The geopolymer was made with a high calcium fly ash and an alkaline activator. The activator was a solution consisting of NaOH and Na2SiO3, where the NaOH was solid while the Na2SiO3 was an aqueous solution containing 63% water. A particular geopolymer mixture was determined by a SiO2/Na2O mole ratio (Module), solute (NaOH and Na2SiO3) concentration in alkaline solution (Con- centration), and liquid (activator)-to-fly ash mass ratio (L/F).
Dear Taher,
you are misunderstanding concepts. Geopolymer technology isn't synonymous of Alkaline Activation technology and high calcium fly ash, for sure, can't give you Geopolymer material because hasn't enough good mineralogy to react correctly. If you want to work with AAM activator is necessarily very high pH so corrosive, while to obtain Geopolymerization you can work with user friendly reagent called also hardener (system with lower pH) only classified as irritant. Mix design of these materials is different as stability and performances. Geopolymers don't need heat curing while for AAM is strongly suggested to avoid efflorescences and other high carbonation on surface due to alkalis migration in presence of humidity (air is enough humid to promote these processes).
Geopolymer technology isn't calcium based like you wrote, this could be valid for AAM but they aren't condensed mineral polymers, but still hydraulic, following reactions quite comparable to Portland cement but with higher alkalis content.
Put in water your product, if well mixed and is Geopolymer after 28 days in water, strength development will be comparable or just little different to air cured sample (due to lac of aerial carbonated micro-minerals that need CO2 from air to be stabilized, like sodium or potassium carbonates) ; on contrary if AAM , where alkali ions weren't involved in the reaction but only used as binder to glue all together randomly without any organized polymerization , your material will lose the most of its strength or usually will fail during water curing. This because alkaline ions ,if not linked to binder matrix can be easily leached out from material ,so mechanical properties become unstable till to the complete failure of the structure.
Geopolymers aren't Portland like materials like AAM, they can be used to obtain concretes and several types of mortars with superior durability and really high performances, but can be done even in acidic medium for more high tech uses (so if acid how they can be AAM?)
Try to verify your material and select the process that you want to develop, but check before at terminology because are technically different and to realize genuine geopolymers you must find other powder precursor. Using fly ash class C, even for AAM, you will have big problems about flash setting so you must study how to retard the Alkaline Activation ,but finally you won't have never a mineral polymer, so fire resistance can be better than Portland cement material, but spallation will occur ,because of crystalline water inside hydrate minerals, while with Geopolymers there aren't hydrates at all, then resistance to fire can be optimized to reach heat resistance (up to more than 1200-1500°C depending on type of binder and quality of aggregates used).
Hoping to be useful
All best,
Alex Reggiani
Dear Taher,
This is indeed a very complex question. To answer this question, you have to be familiar with different chemical reactions in geopolymer binders. I strongly agree with Alex Reggiani . The mistake in your question is that alkali-activation is similar to geopolymerization. This is not the case. They end up with entirely different products.
The very first step is to quantify the precursor mineralogy and its respective reactive components. There are too many papers dedicated to this concern. Without this information, most likely you will face with a lot of fluctuations and instability in the final products. If you proceed with high calcium fly ash, try to consider a highly reactive alumina source along with it. Otherwise, the whole reactions during alkalination and hardening move toward an instable material which the network would be eventually demolished in the presence of moisture. After identifying the precursor properties, you will be able to decide about alkaline reagents (not activators). I highly encourage you to read Dr. Davidovit's book about Geopolymer chemistry and applications.
If you still have any concern, you can check our recent publications regarding geopolymer binders with different precursors derived from construction and demolition wastes. In these publications, you will find step by step mix designing procedure starting from precursors chemical components.
Good luck!
Sina
Hello,
how did you determine the solution for NaOH? for example if you have 1000 g of cement
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Inorganic Materials
- Metals
- Alloys