Construction and performance of concrete pavements in Bavaria

For economic and environmental reasons various motorways in Bavaria" have been provided with concrete pavements in recent years. In this form of construction the concrete slab and cement-bound sub-base are laid direct on the subgrade. On two new sections, near Regensburg CA 3) and near Rothenburg CA 7), the so-called "fully cement-bound pavement" was installed, comprising a 20 cm or 22 cm (respectively) thick concrete slab and a 25 cm thick cement-bound sub-base. The granulometrically graded mixture (0 - 32 mm particle size) for the sub-base was prepared, with about 3.5% of added Portland cement, in continuous mixers. At Regensburg the cement-bound sub-base was installed with a finishing machine in one layer over a width of 12 m . On the other hand at Rothenburg the sub-base was placed in two layers, .the upper layer being laid with two finishing machines travelling staggered in relation to each other. The concrete slab was then installed with the aid of big slipform pavers; it was provided with dowel bars and tie bars,but no expansion joints and no reinforcement. After completion of the concrete slab, longitudinal and transverse cracking was observed on both road sections, the causes of which are to be regarded as inherent in the system. On the basis of the knowledge gained on these jobs the following points are to be noted in connection with concrete pavement construction: - if the cement-bound sub-base has compressive strengths of more than 12 N/mm2, it should be systematically stress-relieved in the longitudinal and the transverse direction - notch cuts and construction joints in the sub-base should be located under the subsequent longitudinal and transverse contraction joints in the concrete s'l.ab - suitable measures for draining the concrete pavement are to be applied.