I am trying to find an optimum mix proportion for a rice husk ash - hydrated lime binder to be used with sand in the making of a building mortar. The pH of the mortar is around 12.6. Can I speed the hydration reactions by the addition of a bit of OPC so as to raise the pH through the sodium and potassium hydroxides found in OPC? If I do that what will be the consequences, positive or negative?
According to me the addition of OPC is not going to do anything regarding pH. because the pH of the OPC mortar is itself between 12-13. the alkalinity is mainly due to the presence of calcium hydroxide. For improving strength many people adopted an addition of 10-15% of OPC in the mix.
If you are concerned about any negative consequence, you do not have much to get worried. What is normally achieved in that situation is that the strength will be higher and the permeability will be reduced. But, in the other hand, the Young´s Modulus will be increased and it could increase the stresses originated in restrained shrinkage.
Already your mortar falls within the pH range that any addition of OPC would create. The only challenge you shall have to bear in mind will be shrinkage related, which is normal for any cement.
Could you share your findings on how it goes when you get through with it? I'm equally interested in the use of rice husks.
There should not be any effect to worry you.
Lime and ash from rice husk will be start reacting in high pH, adding cement will not change your pH, but rather help you with setting time and all around gain more compressive strength resistance.....
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