Unbound or hydraulically bound base layers supporting concrete pavements for road and rail infrastructure

Abstract

Most of the ballastless track systems built on earthwork sections for the German
high speed rail network are characterised by a pavement design using two bound layers.
The upper part of the pavement is designed as a continuously reinforced concrete layer
(CRCP) or as a prefabricated concrete slab system with coupled joints. They are supported by
cement treated base layers (CTB) or alternatively by asphalt base layers. There is also a
steady tendency observed in ballastless track construction to use cement treated base layers
with increasing requirements concerning strength or even using concrete base layers with respect
to bearing capacity and durability. But the interaction between the treated base layer and
the concrete pavement (CRCP or others) may lead to negative effects like reflective cracking,
which must be taken into account for the base layer and CRCP design to really improve the
entire two-layer system. For concrete road design Jointed Plain Concrete Pavements (JPCP)
on unbound base layers had been established during the last decades as a technical and economic
alternative. Technical and economic benefits for road construction were born by the
usage of unbound base layers instead of CTBs especially due to the shortage of construction
time and the usage of potential alkali-reactive material for unbound layers. Unbound base layers
offer a uniform and more flexible support especially for concrete slabs. But special requirements
to guarantee sufficient stability (resistance against erosion) due to repeated loading,
permeability etc. shall be applied on those unbound base course materials used to support
concrete pavements. Using synergetic effects between road and rail design unbound base layers
offer also alternative solutions for ballastless tracks. Designs and constructive features of
such multi-layer systems based on CRCP technology are shown achieving comparable bearing
capacity and durability.