Water reducing admixtures or plasticizes can be used to increase the strength of concrete by reducing the water quantity. Many companies are making these products and you have to use them as per their instructions to get desired results.
In case you are using grouting material in cracks for water proofing you need to ascertain the cause of cracks and their nature e.g. cracks may be dormant then you can use epoxy grouts if cracks are active we may have to use flexible material like silicon based grouts.
Waterproofing for roof depends on flat roof or pitched roof. In Bhutan probability of pitched roof may be more likely and therefore foot steps are not possible and you can have any effective water proofing.
These material are site specific and condition specific and therefore has to be selected carefully.
Types and dosages of admixture is depending upon the requirement and grade of concrete one has to used for various purpose. As far as water proofing is concern it depends upon situation and environmental condition of structures for which it has to used.
If you narrate with specific detail appropriate solution can be suggested.