Multiple casts of Bombardment only refresh the second bonus it does not stack. Blocking an attack also grants a stack, so a high blocking percentage is beneficial and maximizing block chance is advised.

The Thorns damage buff stacks up to 10 times (not refreshing earlier stacks).

The first bonus causes a splash of Thorns around the Crusader, not around the target (which coincidentally lines up with the Bane of the Trapped area of effect).

The attack speed of Punish and Slash are increased by 100%, and these skills deal 67,500% of effective Thorns damage to the first enemy hit (6 pieces).Take 50% less damage for 20 seconds after casting Bombardment (4 pieces).Each time an enemy is hit with Punish or Slash, or an attack is blocked, Thorns damage is increased by 90% for 2 seconds stacking up to 10 times. Thorns damage now hits all enemies in a 15-yard radius around the Crusader.The set consists of six pieces, all of which can be adapted for any class, and all six are required to complete it. Diablo II: Resurrected Review - Pile Of Old Bones

Diablo 3 might of the earth set dungeon