Construction of concrete pavements in West Germany

In West Germany, the concrete pavements of the 'autobahns' are generally constructed by the slip form method, usually on top of a hydraulic- or bituminous-bound base. The thickness of these pavements has recently been increased from 22 cm (9 in.) to 24-26 cm (9.5-10 in.). To control the formation of cracks and to relieve the stresses caused by restraint of volume changes, these pavements are divided by joints into slabs 5 m (16.5 ft) long and 4.25 m (14 ft) wide. To withstand the effects of frost and deicing agents, the concrete must also contain entrained air. When old concrete pavements are renewed, either the old concrete is broken and new pavement laid on it, or the old concrete is crushed by a breaker and used as an aggregate for the cement-bound base.