The Remnants of Asgard will become available when the main storyline of the game is completed. After the credits the favor "The Last Remnants of Asgard" should appear in your journal. Your task is to find the remnants scattered throughout the realms and destroy the Einherjar guards in the area. Once you've done that you'll be able to loot the red chest you find nearby. In the chests you will find Fortified Remnants and Tempered Remnants - resources that can be used to upgrade your shields and armor.
