Mono-block, di-block and joint sleepers are the most common forms of concrete sleepers. Concrete sleepers are produced in woven or non-compound forms. Di-Block sleepers are mainly made of crack-resistant blocks which are connected by steel rods. 180 kg U-31 concrete sleepers which are used in the UIC 3,4,5 lines allow for transportation of 19 to 22 ton axial loads at up to 200 km / s and transportation of 17-ton axial loads at up to 220 km/s. 260 kg U-41 sleepers are usually used in Lines that can carry heavier loads at more than 200 km/s