The joint comprises a pair (12, 14) of complementary engineering grade polymer injection moldings. Each molding is comprised of generally equal length oblique webs (15), set at 60 to a mid-plane (16) of the assembled joint, shorter, inner webs (17) and a longer, outer webs (18). Centrally of each outer web (18) is an aperture (21) and centrally of each inner web is a pin (22) with a step (23) and a pointed head (24). The heads of one molding clip into the apertures of the other while the steps determine their separation gap (25). The trapezium wave shape of the joint provides re-entrants (31) from the plane of the outer webs (18) towards that of the inner webs. Outwards of the re-entrants extend anchoring formations (33). Behind each re-entrant these formations are joined by a tab (34).

Edge protectors are useful to be cast into the edges of concrete slabs to prevent spalling thereof after shrinkage has occurred and a gap has formed between adjacent slabs. An alternative edge protector (10) is described which comprises a first folded sheet having, in use, an upper (35) and a lower portion (25), the fold being on a first side of the first folded sheet and being alignable, in use, with the sidewall of the slab, the upper portion being planar and being arrangeable, in use, with its upper surface coplanar with the upper surface of the slab, the lower portion extending at least partially under the upper portion in a direction away from the fold, and continuing from the end of the lower portion in the same general direction, without any further folds or bends greater than 90 degrees, as an anchor portion (20) such that the anchor portion is arrangeable within the slab.