It does, but it will also bind a lot of the micro plastic pieces into the concrete matrix, which, I think (and, again, as I said, I haven’t actually gone looking for any research on this), would keep them from entering the environment. If the concrete is then recycled, typically by crushing and using as aggregate, it would further trap the particles. It’s not a perfect solution, but I don’t think there is a perfect solution to plastics in general, we just have to find less harmful alternatives.