In my research, I find that the w/b and exhibited a more prominent effect on workability than the other parameters. The effect of Na2O content on workability was not significant.

Article Chloride diffusion in alkali-activated fly ash/slag concrete...

It is not really something to have an opinion about. It is easily proven that adding more water makes something flow faster. So yes, adapt the workability by adapting the water/binder or water/solids ratio.

However, always report both ratios and more information to completely define the mixture. The influence of the alkali/binder ratio on the workability might be small, but it certainly has an effect on other properties of geopolymer or alkali-activated concrete.

Arne Peys , it is the least attended factor by the researchers. I have observed that most of the researchers just talk about strength and other parameters instead of giving due attention to the workability. However, during execution of concrete construction works it appears to be the first challenge for the concerned people.

Your view on the a/b or w/s ratio is very trivial.

Both these ratios have a considerable effect on both strength and workability of the concrete. The water to binder ratio, however, is more significant. The alkali to binder ratio increases the strength until an optimum alkali content is reached and then decreases afterward. In terms of workability, the increase of this ratio increases the flow/slump of the concrete, however, one has to be careful to differentiate between alkaline liquid to binder ratio and alkali solid to binder ratio. Despite its different role in OPC and geopolymer (in terms of chemical reaction), the increase of water to binder ratio significantly reduces the strength of GPC, similar to that of OPC, due to the increase in the porous structure after evaporation. Similar to conventional concrete, the increase of this ratio also increases the workability of the concrete. Current researches in this area are using a one-part geopolymer cement in which case the water to binder ratio is treated similar to the water to cement ratio in the case of OPC concrete. The alkali to binder ratio is important while trying to optimize the proportion of the different solid ingredients in the alkali cement.

In most of the papers that i have read, liquid alkaline binder to solids ratio holds more importance in geopolymerisation process, while in curing using OPC water to cement ratio is important. No water is added in geopolymerisation method thus water to solids ratio is irrelevant here.

Dear Sulaem,

To answer this question, you have to be familiar with the chemical reactions occur in geopolymerization process. First of all, geopolymers are not alkali activated materials. You have to identify what kind of system you are working with. Generally speaking, there is no alkali activator as per your question, because there is nothing to activated. The aluminosilicate precursors are naturally reactive with alkaline. It is like Portland cement and water. Portland cement is naturally reactive with H2O, but no body use water as an activator for Portland cement. Water is a reagent in this case, so the alkaline (Na2O, K2O, etc.) for aluminosilicate precursors. "Alkali activator" is a misleading phrase and creates confusion around the terminology of this process. I highly recommend Dr. Joseph Davidovits book, Geopolymer Chemistry and Application, for this manner.

In case of geopolymer system, considering physical ratios such as alkali/binder ratio or water/solid ratio, lead to significant variations in the final results. The reason is, chemical reactions in geopolymerization would fluctuate a lot with a minor change in physical factors such as precursor weight or water/solid or alkali/binder ratios. Therefore, you need to consider chemical factors in order to obtain a stable-form geopolymer material. I highly encourage you to initiate with chemical ratios such as silica/alumina, alkaline/silica or alumina, H2O/alkaline, rather than simply considering physical ratios such as the one in concrete technology (water/binder ratio, cement content, etc.).

If there was any question left regarding mix designing approach, you are welcome to have a look on our recent publications about different geopolymer binders derived from different construction and demolition waste materials. The proposed mix design approach in these publications, would help any researcher to consider chemical process for designing geopolymer materials.

Bests,

Sina Dadsetan

In my view, I would like to maintain distinct differences between geopolymer concrete and cement-based concrete. Therefore, the alkaline-binder ratio would be preferred over the water/solids ratio, to have a clear understanding that the role of the alkaline activator is very much crucial.

Thank you.

what is the optimum solid binder ratio in alkali activated binder, using slag as a precursor