just introduce a new zombie, a sapper type zombie
https://en.wikipedia.org/wiki/Sapping
This zombie would do major damage to blocks (50% more than strongest basic unit), but would be weak in player damage, they would path like normal, so no extra behaviors, maybe they stay in destruction mode longer if it activates, giving them extra time to do the best they can
make them spawn as often as normal units, so we see them everywhere, not just a a horde night spawn or a high level spawn
making this kinda unit, you could reduce block damage among normal zombies by 25%, but by mixing in the sapper, the same damage to blocks would happen, and add another "priority" target to focus on
make him/her based on the construction worker, but instead of a yellow hat, it would be a foremans' hat (white/red) and they could carry either a pickaxe or hammer or even a sledgehammer (think demolition before construction etc) {this would essentially create a zombie pairing, and maybe even have him/her spawn "naturally" in the construction site POI at the loot location as a location specific spawn}