There are many questions still to be answered or in need of a better solution. Here are just a few examples:

Definition of aggregate
How is the term "aggregate" defined? Is it defined in the same way in the USA as in West Germany, and is the aggregate from Berlin identical to that from Frankfurt? Certainly not. What effects does this inconsistency have on the surface quality and long-term durability, for example, of coatings. Similar questions can be asked about the cement.

Swelling of concrete
What is so important about the swelling potential? What impurities are permissible in concrete and water according to the national standard? What effect do they have?

Role of moisture
What role is played by moisture? Is it only important for the setting of the polymers or can it lead subsequently to loss of adhesion? What differences are there between outdoor and indoor building work? The latter problem is of major concern to factory managers and architects.