Concrete erosion

My attached garage concrete floor is emitting some type of white crystalline substance. When this substance is brushed away, I see a very thin layer of layer of concrete is flaking off. This floor is 28 years old. This started happening about 1 year ago. It is doing this in isolated spots. At present, I would say about 5 percent of the floor's surface is eroded.
I cleaned the floor with a good concrete cleaner and later applied a gray concrete sealer. About 1 week later, the same thing is happening, but now the sealer is lifting up with the white crystalline substance under it. Help with remedy would be appreciated.
Charles