De or het betonverharding?

The correct Dutch article is:

de betonverharding

Rule Words ending in -ing: almost always de. See the rule

How to use betonverharding

the betonverhardingde betonverharding
this betonverhardingdeze betonverharding
that betonverhardingdie betonverharding
our betonverhardingonze betonverharding
your betonverhardingjouw betonverharding
every betonverhardingelke betonverharding
which betonverharding?welke betonverharding?
a big betonverharding / the big betonverhardingeen grote betonverharding, de grote betonverharding