In my experience the best option is to mix liquid sodium silicate with sodium hydroxide. Mixture of these two materials gives better compressive then using just one. Concentration of sodium hydroxide solution should be 6-12 mol/l depending on silica amount in raw material. Activator solution can consist 50/50 of sodium silicate and sodium hydroxide

Sodium silicate in liquid form and sodium hydroxide combination will yield better results. Adding sodium hydroxide to sodium silicate liquid just before preparing the mix is advised. A delay of 20 to 30 minutes may be allowed before preparing the mix. Strength gained by the geopolymer depends on a lot of factors which include Sodium silicate to NaOH ratio, raw material, curing temperature etc.

Execelente question. The main activator used in the geopolymer synthesis consists of mixing the NaOH solution and the Na2O solution. xSiO2. nH 2 O (gel). It is possible to buy alkali metal silicate in solid form.

This solid should be added in water and agitated to form a viscous solution. The molar concentration of silicate should be investigated. Generally a good parameter is to prepare alkali sodium silicate solution as follows:

- Viscosity * (cps) 800 to 1400

- Na2O (%) 14.00 to 17.00

- SiO2 (%) 31.00 to 35.00

- Total Solids 45 to 60

- Ratio (SiO2 / Na2O) 2.10 to 2.30

- pH 11-14

Attention to the viscosity it serves as quality control.

It is more ideal to use liquid sodium silicate. It may be necessary to consider the fineness property for powdered sodium silicate.

Sodium silicate in liquid form is better

Liquid sodium silicate is ready to use and give good results. To use Liquid sodium silicate alone as activator, the ratio of Na2O may be more than 12%. Solid sodium silicate is not completely soluble in concentrations over 10% at room temperature.

Anant L Murmu , DO you mean that mixing the NaOH Solution(Which is prepared one day prior) and Waterglass just before preparing the mix of the concrete?Is it ok to do that or we have to prepare one day before the mixture of NaoH Solution and water glass both ?Thank you

Dear @Jyoti Mahato, I found it more effective, if I mix NaOH solution (Prepared One day prior) with waterglass just before adding it to the prepared concred mixture. You may experiment with both the cases. On the contrary Davidovits do not reccomend the use of NaOH at all, due to its corrosive nature

I used liquid solution. It is a mixture of sodium silicate solution and sodium hydroxide solution.

Ideal form of mixing might be of Aqueous to gain higher strength but, when we are about to prepare in situ concrete it would be difficult as unskilled labours haven't any kind of understanding of actual amount. They may increase the amount to get enough workability or so.

So, if you are from a country where RMC isn't used much then you should go for a powder form.

So, I suggest to convert Aqueous form to powder form to assure the proper mix with proper amount of each content.

Anant L Murmu Bharat Bhushan Jindal Profs Davidovits mentions use of sodium hydroxide pellets to sodium silicate to adjust the SiO2 to Na2O ratio of the solution. it is also mentioned that these should be given a time period of 24 hrs for complete dissolution. You can refer to chapter 21 of the Geopolymer book for further understanding. He also mentions adding water (better workability) 24 hrs before use to allow it to be integrated in the chemical structure.

I usually used sodium silicate in liquid form with different SiO2/Na2O malar ratio

sometimes I added NaOH pellets to adjust the SiO2/Na2O ratio of solution.

In my view, the best form of sodium silicate (powder or liquid) depends upon the choice of application and the desired degree of user-friendliness. Using powdered form requires knowing of fineness and other physical properties while using the liquid form mainly requires knowledge of the chemical properties. The best form, however, is that which is easily available. Both forms are widely investigated in today's time, and the answer may not be that simple.

Thank you.

I deeply appreciate your interest in geopolymers.