For the alkaline activated material study, we usually find the researchers keep the mass ratio of Na2O to slag/ fly ash constant, rather than pH or SiO2. What is the consideration for this kinds of design and what is the advantage?
The Na2O is the major component affecting the dissolution process of the aluminosilicate from the slag, and so reaching an optimum ratio is of great importance to the strength of the final product. while the pH value is a dependent factor on the Na2O content. when talking about the SiO2 content its presence affects the nucleation and gel precipitation phase rather than the dissolution which means that it is possibly to use an activator which contains no silica if the leached silica from the slag is enough for the polymerization process to produce a quiet sound matrix.
Alkali oxide dissolve easily in cementing solution as well as sodium ion replaces metal ions from their silicates and form sodium silicate which is partially soluble and decrease the gel formation of C-S-H.
- both Na2O and SiO2 to slag in mix design of Alkali-activated slag cement are constant. but mix design starts from Na2O to slag. because it calculate Na(OH) required. with knowing Na(OH) and ratio SiO2 to slag you can compute soudium silicate required. if you start from SiO2 to Na2O, mix calculation becomes hard.
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