Here is the full list of all 39 Outbreak achievements.
You failed to survive.
Defeated 20 undead threats.
Healed yourself.
Cleared your first scenario!
Cleared the Tutorial scenario.
Constructed your first barricade.
Defeated your first undead threat.
Successfully overcame a puzzle.
Defeated 100 undead threats.
Defeated 1000 undead threats.
Healed yourself 20 times.
Healed yourself 200 times.
Cleared 10 scenarios.
Cleared 100 scenarios.
Cleared the Outbreak scenario.
Solved 100 puzzles.
Cleared the Chasmal scenario.
Survived 5 scenarios on Normal Difficulty.
Survived 3 scenarios on Hard Difficulty.
Survived a scenario on Biohazard Difficulty.
Survived a scenario on Hard or Biohazard Difficulty with one or fewer kills.
Cleared the Miasma scenario.
Land 10 critical hits.
Cleared the Enkindle scenario.
Cleared all campaign scenarios.
Cleared a wave in Onslaught.
Survived the first five waves in Onslaught.
Survived the first ten waves in Onslaught.
Survived the first fifteen waves in Onslaught.
Survived the first twenty waves in Onslaught.
Survived the first twenty five waves in Onslaught.
Survived the thirtieth wave in Onslaught.
Constructed 10 barricades.
Constructed 50 barricades.
Constructed 100 barricades.
Purchased a piece of equipment in Onslaught.
Purchased 20 pieces of equipment in Onslaught.
Purchased 100 pieces of equipment in Onslaught.
Purchased 200 pieces of equipment in Onslaught.