Welding areas are very difficult to deal with in terms of floor toppings for obvious reasons. The high heat/ sparks can cause a lot of damage -- to bare concrete, as well as to any epoxy coatings. There are other industrial flooring materials that are intended for very high temps, such as...
Wow, alpha, great visuals! For a floor crack like this, an epoxy and graded aggregate mixture like Quikpatch also works very well. Florogel (http://www.florock.net/pdfs/FloroGelrev3.pdf) is another option and both are made in the Chicago headquarters, where they know a little something about...