Dear Ruba Palanivelu ,

I red the article but I cannot find any Geopolymer material inside, just an Alkali Activated Concrete.

The raw material used as precursor and the pH used aren’t correct to obtain mineral polymerization also called Geopolymerization. There is big lack of alumina and the pH is so high that only dissolution can be obtained. This means that , as proved from your analysis, you found CSH (calcium silicate hydrate) that comes from an hydraulic reaction, not from polymerization of mineral sources. Geopolymers aren’t hydraulic products but polymers and aren’t Alkali Activated Materials at all (can be also obtained in acidic medium).

The firing testing done, are also too much short in time and have been done at quite low temperatures to be considered fireproof test. Usually these kind of materials must resist at 1000°C and every 30 minutes you have achieved a class of fire resistance (30, 60, 90, 120 till 240 minutes). Optionally can be tested the mechanical strength after the firing and cooling down, that progressively with the time of staying at high temperature, will be lower.

Geopolymer materials for fireproofing don’t spall at all, because they don’t have hydrated minerals like CSH or NASH and usually GP can resist till more than 1000°C. But you need to know that the aggregates must be more selected for this purpose. Using standard silica sand and calcium carbonate or silica gravel, you won’t reach the best results. Calcium carbonate will be transformed in CaO at 850°C (not at 300 or 600°C as mentioned) releasing the 41-42% of CO2 that ,as every gas, in temperature will expand trying to exit from the concrete. Silica sand instead starts changing even early, because at 573°C the alpha quartz becomes beta quartz modifying its crystallography with a great peak of dilatation (other expansion). Both these stresses can let creep or explode the concrete, but of course maybe not within 15 minutes only of heating time.

I suggest to have a look at www.geopolymer.org the site of Geopolymer Institute where Professors Davidovits (Joseph and his son Ralph) work, to understand how really works the geopolymerization process.

To improve the fireproof ability you need to update your raw materials selection and the mix design that are wrong and you should substitute also the standard aggregates, with raw materials more refractory. Basalt fibers cannot do miracles alone 🤷🏻‍♂️.

When correctly formulated and properly mixed, Geopolymer Materials for fireproofing can achieve good stability till temperature between 1300 to 1600°C, for more than 4-6h of testing. Of course this comes from my professional experience.

I wish you good luck for your future work

Best regards

Dr. Alex Reggiani

CTO GeoMITS