No worries as earlier in this thread Gheckso linked to
this thread which has some images of troweled concrete, a trowel, and the scrapes on the chest. But look at the scrapes on chest, each one is deepest on one side and tappers off to the other, whereas the shape of the ridges in the troweled concrete would result in scrapes deepest in the middle and tapering off to both sides. The concrete would also leave scrapes between the those caused by the ridges as they aren't much higher than the rest of the concrete, whereas the the scrapes on the chest show unscraped sections between them.
Besides all that, the skin would have to be slid exactly on line with the ridges in the concrete to leave even vaguely comparable markings. So, it would be quite an amazing coincidence for such to result in scrapes which just happened consistent with the saw edge of the knife found behind Baldwin's house, and even more so an amazing coincidence that the saw edge and hilt of that knife is also consistent with wounds on Stevie Branch's forehead and cheek.
That said, for those who do prefer to believe the scrapes might have come from troweled concrete, the way to test that hypothesis is to get some fresh pig skin from a butcher and rub it up against such concrete to see what happens. I suspect that would be a fool's errand though, for the reasons I've previously explained.