A slab element for covering the ground is made e.g. of concrete and forms as a single piece. It has a head portion and a stem portion meeting at a notional meeting surface. The element is delimited by two opposite end faces of equal length joined by sides that form angled traces about a longitudinal axis common to the head at the stem, each said angled trace being formed by a succession of sides comprising at said head an inclined side face inclined in one direction relatively to the axis, a lateral side face extending lengthwise with respect to the axis and another inclined side face inclined in the opposite direction with respect to the axis, and comprising at the stem a lateral side face extending lengthwise with respect to the axis which is complementary to the lateral face of the head, the end face of the head together with its inclined sides and its lateral faces and the meeting surface describing a centrally symmetrical octagon, and the meeting surface together with the end face and lateral faces of the stem being symmetrical about the center of the stem. The head may describe a regular octagon. The stem may describe a square. But the stem may also describe a circle. The elements can be laid to form a composite ground covering structure, laid e.g. in herringbone bond pattern, and laid e.g. to include one or more supplementing slab elements of the same peripheral configuration as the stems of the elements.