Dear Gundupalli,

You did not mentioned what concentration of sodium hydroxide did you use. When you prepare the alkaline solution it heats up but if the alkali concentration is too high and reaches its maximum solubility the sodium hydoxide will crystallize out of the solution (supersaturated) especially if it cools down. I have used the same activator solution many times but I have not realized precipitation at all. I usually prepare activator using sodium hydroxide solution of 10 - 12 M and sodium silicate solution in a 1 : 1 ratio.

Best regards,

Attila Baranyi

Dear,

first problem you are misunderstanding 2 different technologies that have specific terminology. Alkali Activation needs an activator very high alkaline like the example of Dr. Baranyi uses (pH of this activator is very caustic it means classified corrosive and can burns your skin so pay attention).

Geopolymerization is totally other process, polymeric not hydraulic, where the liquid called technically reagent or hardener used can be alkaline or acid. But pH is user friendly so less alkaline, you can touch with fingers (I still have all my fingerprints ) without problems, classified as irritant not corrosive that is the same classification of Portland and limes.

AA materials are hydraulic so reaction is more close to Portland based products and also mix design can be similar, BUT AAM aren’t stable under humid conditions or if immersed in water (even if they are cured for 28 days, having high strength) and the lose lot of mechanical strength or fail but without any regular development (every mix is different).

Geopolymerization follows prof. Davidovits rules (check at www.geopolymer.org you can buy his book there is an entire chapter about reagent manufacturing) aren’t hydraulic and the mix design is specific and completely different from Portland and AAM. GP mix are repeatable, very stable under humid conditions and after demolding can cure without problems under water, maintaining very comparable strength to air cured samples.

Second thing, you must know your raw materials in terms of reactivity (mineralogy is more important than chemistry), amorphous content and particles size too. Chemistry only can be tricky to understand without knowing other important parameters.

Third , GP reagents are chemicals that must be done in the correct way and using industrial or semi industrial methods to be stable (avoiding any precipitation ) this means respecting the best temperature/pressure values (autoclave at least) to manage perfectly everything.

Last but not least when you will decide what technology using or studying you must evaluate which concentration of raw materials adopting like suggested by Dr. Baranyi

Hoping to be useful, have a good work

Best

Dr. Alex Reggiani

CTO GeoMITS

P.S. Check at my LinkedIn account ,some time ago I have published a study made for a client that ,like you ,had very confused idea about AAM and GP technologies. I compared some high strength AAM vs GP and I think you will understand better my words.