Is it possible to use a penetrating sealer, such as those used on driveways, to make shotcrete repel moisture? If so, will the sealer improve the shotcrete’s freezing-and-thawing performance?

It is possible to use a penetrating sealer on shotcrete in the same manner as cast-in-place concrete. We are not aware of research on the durability of such a sealer and do not know if it would enhance the freezing-and-thawing characteristics. A high-quality shotcrete mixture that is properly placed will exhibit excellent freezing-and-thawing characteristics with or without a sealer.