I've a small crack in the surface of my front porch/step:
It does not appear to be cracking on the side of the step.
That slab appears to be about 6+ inches thick; I can't see how it is cracking but it is.
Before freezing weather/water get into the crack, I thought I'd fill it with something. I'd appreciate suggestions for the right material; I'm assuming some kind of on grade/below grade material caulk or elastomer.