Concrete is normally used for bridges, buildings and roads. Architects haven't had much luck making cement structures that age gracefully. After a few decades the raw cement looks cold, bleak, uninviting.
So, it is unusual to see concrete used to make rings, pendants and earrings. We buy jewellery for its beauty, and we intent to keep it for a long time. Concrete jewellery would seem to be a gamble: how will it look in twenty years?