Dear Vivek,

geopolymer technology isn’t like Portland cement technology, so rules to follow are different . Every checking has to be referred to alumina silicates used. Fly ash is really general term you must be more precise to obtain so precise answer fit to your case. I mean :

1. What type of fly ash (only class F, because with class C isn’t possible to obtain geopolymerization)

there are Class F with less than 4% of CaO that are better than fly ashes with 8-9%.

2. Temperature of calcining of fly ash (950°C is too low , only alkali activation with weak and inconstant properties, more than 1300°C are better , without pollution of coal and sulphur but 1500°C or 1600°C are the best, for reactivity and amorphous content)

3. Size of fly ash particles

4. Reagent pH of silicate used for alkalination that is directly connected to Molar Ratio. If too low you haven’t any geopolymerization and if is too high you will have too corrosive system till obtaining only alkali activated materials (incostant and with efflorescence).

5. Type of alkaline cation chosen : sodium based (cheap but not easy to manage) or potassium based (stable but more expensive)

6. Type of curing , probably heat aging because fly ashes can’t develop enough strength at room temperature (what T° , for how many hours and why that time)

7. Type of aggregates used to create bricks (size, rounded , scattered, wastes and so on) .

What do you mean with homogeneity of mix? If you need to know if is Geopolymer brick or not you have simply to put in water after hardening and to compare mechanically after 24h, 7 and 28 days with samples aged under air .

You must find similar strength between them (less 5 to 10% of tolerance is quite normal , more isn’t acceptable ). No hydrate minerals are allowed in geopolymer products so no CSH or KASH or NASH , (are terms from alkali activation and from Portland cement technology) you haven’t obtained geopolymer but only alkali activated bricks that aren’t the same.

Other test of durability are possible to do only after complete aging (frost - defrost cycles and so on).

As you know one of the most big problems about diffusion of geopolymer products is related to missing of precise standards . This fact depends on choice of precursors ,so you must find a method fit to your raw materials (fly ash, silicates and type of aggregates) and test till you will find the right way.

Hoping to be useful for your work.

Best regards

Alex Reggiani

Dear Vivek,

in case if you wish to study the homogeneity of this kind of material in hardened state you may use:

- ultrasonic testing along the thickness of the material to see the changes in the velocity and also density and compressive strength. For example see here:

https://www.ndt.net/article/ecndt2018/papers/ecndt-0456-2018.pdf

- micro-CT to see the changes in porosity kf the material along the thickness. For example see here:

https://www.researchgate.net/profile/Krzysztof_Ostrowski4/publication/326882112_The_Effect_of_the_Morphology_of_Coarse_Aggregate_on_the_Properties_of_Self-Compacting_High-Performance_Fibre-Reinforced_Concrete/links/5b6a0ef992851ca650514267/The-Effect-of-the-Morphology-of-Coarse-Aggregate-on-the-Properties-of-Self-Compacting-High-Performance-Fibre-Reinforced-Concrete.pdf

I was working mainly with cement-based material but maybe it will be helpful for your study.

Best regards

Łukasz

Thanks. I have gone through this. But can you able to identify any standard data for comparison of quality of geopolymer mortar as UPV require comparison with standard data.

Dear Vivek,

Unfortunately I do not havy any standard data for geopolymer mortar.

Best regards

Łukasz