Hello,

Generally the lye is prepared from leaching process of wood ash/fly ash.MOst of the Wood ash is having 30-45% of calcium carbonate and 10% of KOH as a major compound

As u have noticed difference in compressive strength may be due to the following reasons.

1) Basically Lye is composed of KOH and while preparing lye it requires high PH ,But concrete requires neutral PH. Increase in PH may decrease the strength.

2) As it is said before ,Lye is genarally the product of KOH,compared to NaOH, KOH has lower bond strength.so please check the composition of the lye u bought for the experiment.

The composition of the supplied sodium hydroxide (solution  and pellets form) should be checked with great care, since the molarity has a large effect during the geopolymerization process.

Dassekpo

Thanks for useful discussion.

Mr Mithun

Our Lye is actually a 48% concentrated NaOH solution obtained from Chlor-Alkali factory and hence, it is different from what you are referring.

Dear Dr Jean-Baptiste Mawulé Dassekpo ·

Sodium hydroxide  pellets are pure whitish with more than 98% purity.

Sodium hydroxide  solution had 48% concentration obtained from Chlor-Alkali industry.

 In geopolymer mix preparation, Na2O content of Activator Solution is kept same when prepared from Lye or pellets. Chemically, the sodium hydroxide solution  prepared is same as seen from titration against HCl

If you want to do an alkaline activation of fly ash with sodium hydroxide palets , is necessary to lead the palet to the same particle size of the precursor and homogenize the mix. In addtion i think what is necessary to keep the molar ratio of Al2O3 and Na2O between 0,9 and 1,1 for guarantee the electrostatics balance. This ratio can be estabilshed with a solution with am adequate molarity or with a mass of ground palets to a right particle size.

Then, the water can be added in the moment of  cast with out generate problems in the activation process.  

We prepare first NaOH solution. Then add to it sodium silicate solution after 24 hrs. This mixture is used for geopolymer concrete making. Now the question is if the two NaOH solutions, onemade from sodium hydroxide flakes and another one made by diluting lye which is a commercially available 48% solution, will these two behave differently in geopolymer mixes?

Dear Prof Nagashree Balasubramanya · M.S. Ramaiah Institute of Technology

(1)    The lye  I had mentioned  was Sodium based and not prepared from leaching process of wood ash/fly ash  (could be useful to get Potassium Hydroxide solution since it has  30-45% of calcium carbonate and 10% of KOH as a major compound)

(2)    Your observation  “Basically Lye is composed of KOH and while preparing lye it requires high PH ,But concrete requires neutral PH. Increase in PH may decrease the strength” is interesting. You may note:

·          KOH itself produces high pH in solution since it dissociates fully in water.

·          I did not understand “concrete requires neutral PH”.

·          Did you mean the solution or water used to make concrete must be neutral pH. This is not necessary condition.

o     Higher pH does not matter much in Portland cement based concretes and

o    in geopolymer concrete formulation, high pH is essential to dissolute alumina and silica from geopolymeric source material such as fly ash.

·          In our case, there can not be neutral PH and also there is essentially no difference in pH of solutions prepared from Sodium Hydroxide pellets or Lye.

(3)    I did not understand your statement “,Lye is generally the product of KOH, compared to NaOH, KOH has lower bond strength. so please check the composition of the lye u bought for the experiment”

·          Lye is a Sodium Hydroxide solution made in Chlor-alkali industry during electrolysis of brine (NaCl solution). I did not follow when you say ‘Lye is generally the product of KOH’.  

·          I did not follow your statement ‘compared to NaOH, KOH has lower bond strength’; which bond strength you are referring here?

·          I did not follow your statement ‘please check the composition of the lye u bought for the experiment’. I had informed above that  our Lye is a 48% NaOH solution

Mixing sodium hydroxide pellet with water produces a significant heat which affects the performance of the mixture. Did you allow the mixture to get cool to the room temperature before introducing it to the mixture? 

In a same research, we noticed this temperature could affect the compressive of the geopolymer mortars.

Dear Hassan Rashidian-Dezfouli,

As I have written earlier,  sodium hydroxide  solution is prepared one day before mixing sodium silicate solution into it to obtain a Geopolymer Reaction Generating Liquid (G-RGL) which is kept for one more day further to get homogenised liquid with hopefully chemical specis being stabilised. Thus, while preparing the geopolymer mix with fillers such as sand, the RGL is perfectly at room temperature.