Modular wall or fence construction system

A modular wall or fence construction system comprising:

• at least first and second I-profile blocks,
• said first and second I-profile blocks each having an I-shape in planform so as to define a parallel pair of flanges across opposite ends of a web extending between said flanges, said I-profile blocks having generally planar and parallel upper and lower surfaces and a uniform vertical height,
• wherein each of said flanges of said first and second I-profile blocks have radiused rib keys formed in opposite parallel edges of said flanges, said edges distal on said flanges from said web, a first pair of said radiused rib keys being a pair of convex rails along said parallel edges on a first side of said web and a second pair of said radiused rib keys being a pair of concave channels along said parallel edges on a second side of said web opposite said first side of said web so that each flange of said pair of flanges has oppositely disposed on opposite said edges one convex rail of said pair of convex rails and one concave channel of said pair of concave channels,
• wherein an adjacent pair of said first and second I-profile blocks may be interlocked to form a rotatable joint, rotatable in one degree of freedom during construction of the wall or fence, by cupped mating said one convex rail of one of said adjacent pair of said first and second I-profile blocks with a corresponding said one concave channel of the other of said adjacent pair of said first and second I-profile blocks,
• wherein said flanges of said first I-profile blocks are substantially identical, and wherein one of said flanges of said second I-profile blocks is a wider flange which is wider than the other narrower flange of said flanges of said second I-profile blocks so that said radiused rib keys for said wider flange are spaced laterally further apart than said radiused rib keys for said narrower flange.