Construction of farm roads with cement-bound sub-bases used as pavement

Many minor roads are constructed with a cement-bound sub-base not provided with a surfacing. Two such experimental se~tions of road are described in this paper. One of these sections comprises a cement-bound crushed stone sub-base (shell limestone 0 - 45 mm size). It was constructed with a binder content of 4 - 5% by weight and is 20 em thick. The binder was a "road base cement" complying with DIN 18 506. Only slight weather deterioration effects have occurred after five winters. The experimental road section, which is used by farm traffic, has such a stable surface that the compaction marks made by the roller at the time of construction are still visible. The compressive strength measured o~ drilled cores was II N/mm2 on average at 28 days of age. Cores taken after one year were found to have an average strength of 15 N/mm2. There are no cracks. Another experimental road section was built in the autumn of 1984 as an access way to a quarry at an altitude of between 650 and 1000m, inclUding some steep gradients, on a northern slope of the Schwäbische Alp mountain range. The shell limestone used in this case was of 0 - 32 mm particle size and installed in a thickness of 20 cm with a binder content of 4 % by weight. This road section was exposed to extremely severe frost conditions in the winter of 1984/1985. Core specimens were drilled after 9 months and were found to have an average strength of 17.5 N/mm2 The minor roads construct~d with a cement-bound subbase without a surfacing are characterized by their "environmentally acceptable" appearance. They resemble crushed-stone macadam roads, but in terms of their load-carrying capacity they are almost as good as roads with bituminous or concrete surfacing.