Dear Adeyemi ,

I agree with you that at this moment Portland cement technology isn‘t still completely replaceable by other systems. This essentially because all necessary investments about Portland cement (horizontal kiln to calcine at 1450°C clinker , micronizing plants and all connections about stocking and transportation by train or truck and so on) have been already done and well absorbed , so the cost of Portland cement is quite cheap. This is well documented history of last 2 centuries. But ... first of all , geopolymer technology is completely different from alkali activation technology. Raw materials involved in 2 technologies can be similar , but proportions, dosages , ratio and pH of liquids (I don’t use “activators” because this therm has a meaning only for alkali activation, in geopolymer technology what is “re-active” are silicon aluminates powders , that are chosen and specific for geopolymerization and this process occurs not only in alkaline medium but also in acidic medium) for mixing are very different. So I can’t accept that definition of alkali activated materials is reported as the same of geopolymer products, because is wrong . I‘m researching , formulating and producing geopolymer mortars and concretes from several years and I have compared with alkali activated ones, the results of such long work are : 1. Geopolymers are stable and durable, with mechanical properties that continue to rise during time, with good resistance about chemical attacks , sea water and fire . Alkali cations are inside the matrix, so leached is almost nothing , carbonation and efflorescence are very low with sodium silicate , while zero with potassium silicate, there aren’t inside hydrated minerals . There is polymerization of minerals and pH is irritant like lime or Portland so user friendly . 2. Alkali activated are unstable , specially under water immersion (big lost of mechanical strength ) , efflorescence and carbonation are very visible ,because alkali cations are outside the bulk , so in surface can react with CO2 and humidity of ambient. Resistance to fire is reduced and not even the same, there Isn’t polymerization of minerals and pH is corrosive (user hostile). There are inside hydrate minerals (KASH , NASH where H means hydrate ). Leaching is high .

This long speech to say that geopolymer systems could grow up fastly , but now we need to understand that investments about process, mixing plant and selection of local raw materials must be done. This is the actual limit , but even Portland at the beginning needed time to be diffused , because everyone was using lime systems.

Alkali activated I noted that could be used with very good results for precasting , because heat curing permit to solve the main problems and increase the stability.

In any case , because I’m using and selling geopolymer solutions , I hope that this time to growing will be faster as possible ;D .

Sustainability of geopolymer technology has been already proved from the work of Prof. Davidovits during all his life. Silicates can be produced even from waste and raw materials are available worldwide (of course every local sources will produce different performances, but is the same for Portland that for sure is better in Germany than in Italy and so on).

Best regards

Alex Reggiani

Thank you Alex Reggiani

But do you think there will be steady supply of these aluminosilicater precursor such as fly ash for the future demand?

Dear Adeyemi,

Silica and Alumina are 2 of 8 most diffused elements on crustal Earth, so silicon aluminate minerals are worldwide diffused.

I think you are worried about wastes like fly ash class F, blast furnace slag that depend on coal and steel industry , but I think for many time we continue to produce electricity using coal or metals for constructions.

Fly ash is only one raw material that can be used and isn’t really the best .

Of course geopolymer made with waste can have locally different evolution depending on local sources. But rocks , clay and Caolinitic will remain at huge disposal .

All best

Alex Reggiani

Interesting

I agree with your question Adeyemi, Geopolymers and Alkali activated materials can only be partial substitution in concrete structures especially in places where industrial wastes or by-products are limited. And continental shipping of this calcio-aluminosilicates materials from a producing country to another country is not "sustainable". However, in major countries where these industrial side streams are produced, the utilization of geopolymer and AAM as an alternative to OPC ´should be encouraged politically. We have had success stories of these materials activation in construction applications in Australia and South Africa.

Alex Reggiani nice write-up, however he didn't mention that AAM and Geopolymers are the same..obviously they are not, but they are under the same category.

Dear Elijah,

I’m geologist specialized in raw materials for industrial uses, trust me , raw materials are sustainable because are present in situ worldwide. Of course every country can’t do everything, but if we are speaking about at least M30 concrete made with geopolymer , will be not a problem.

I have remembered that geopolymer aren’t alkali activated because often there is big confusion about that .

Geopolymers are stable and more durable materials than alkali activated for this reason I don’t consider both materials or same category.

All the Best

Alex Reggiani

Adeyemi Adesina Yes its been a nice thought you discussed. I agreed to your point but now a days innovations in the field of concrete technology has to happen and there is need to find alternate to that of conventional concrete.

A innovations has to given a equal solutions in all aspects, Time is also a major consideration with a Geopolymer and Alkali activated concrete. Hence within few years, this product will going to be the alternate for conventional concrete for sure....

Nice thought Alex Reggiani , Well said...

Thanks & Regards,

Basavakiran S J

The only real universal sustainable solution is not producing concrete.

In the comparison of binders, you have to look specifically to each location. Are you in a region where calcite and silicate minerals are abundant, but no producer of NaOH/Na-silicate or aluminosilicate can be found? In this case transport costs & footprint would shoot up for the alkali-activated material or geopolymer and might become less sustainable. In the situation of Belgium, which I know better, alkali-activated materials perform much better in comparison with Portland cement, because of the proximity of Na-silicate producers and the abundance of metallurgical residues.

Now, of course, there are other sustainable cements too, even OPC based systems, where the OPC is blended with high volume replacements of slag (blast furnace or others). In that case, comparing a 40%-60% blend (OPC-slag) with an alkali-activated material, the environmental gain is not that much anymore. Especially if you compare with geopolymer mixtures with metakaolin that you find in literature.

About the difference between geopolymers and alkali-activated materials, well, different definitions exist, which heat up discussions for some reason I never understand. So, just to be clear, the definition of alkali-activated material I used in this answer is "a material that becomes hard after mixing a powdered precursor and an alkali".

Cheerio,

Arne

Cement consumption must be stopped at all cost as or could be done so slowly by gradual implementation of GPC into the real practice. However, the absence of an universal makes it harder for GPC to be a viable option for the society as per immense opposition from cement manufacturers. Hence, we could have a good discussion after a general code has been formulated.

Valuable discussion

Best wishes