Garage floor cracks happen no matter how carefully the concrete gets poured. Different factors cause cracks to appear. A common cause of heaved concrete is from temperature changes in the base material in an unheated garage, especially during the freezing and thawing cycles of the colder months. Another common cause of heaved concrete is an improperly placed expansion joint. Unless the crack creates several inches difference in the floor height, you can inject silica sand and floor crack repair compound into the crack to create a smooth surface on your garage floor.
Use a hammer and chisel to pry out all the loose concrete in the crack. Run a shop vacuum over the crack to remove small pieces of debris in the crack.
Wet both sides of the crack with crack weld resin.
Pour dry silica sand into the crack. Fill the entire length of the crack with sand.
Add more crack weld resin to the crack. Saturate the sand with the resin. Allow this mixture to set in the crack for 10 to 15 minutes.
Scrape the surface of the concrete level, using a putty knife. Use medium-grit sandpaper to sand the resin smooth. If you prefer, use a hand grinder to remove the rough edges.