VÖGELE In-Line Pave places asphalt hot on hot at a width of 7m
First published in Road Surface Technology 2015 as Hot-on-hot for Horb
Horb is a picturesque south-west German town on the upper reaches of the Neckar River, 437m above sea level, at the northern edge of the Black Forest. The region has a vibrant agricultural economy and is also a heavily visited tourist area. So when securing a slope below the B-14 trunk road between two parts of Horb Dettingen to Ihlingen the roadway also had to be renewed to a high quality
The Karlsruhe regional authority tender specified that the binder course and surface course had to be built “hot-on-hot” as compact asphalt pavement. This was in accordance with regulation ZTV Asphalt-StB 07 – the German terms and guidelines for construction of asphalt roadways. It meant using either one module paver or two pavers.
Contractor Reif, from nearby Baiersbronn, won the tender based on the use of an InLine Pave train comprising three machines: a VÖGELE PowerFeeder MT 3000-2i Offset, a VÖGELE Super 2100-2 IP with AB 600 TP2 Extending Screed for the binder course and a VÖGELE Super 1800-3i with AB 500 TV Extending Screed for the surface course.
“InLine Pave was the obvious choice for rehabilitating the B-14,” explains Thomas Nagel of Reif. “Firstly, ‘hot on hot’ was specified by the customer. Secondly, our experience has shown that InLine Pave ensures an absolutely perfect layer structure and an intensive bond between the layers – two essential prerequisites for more durable roads.”
Importantly for Reif, the machines making up the company’s InLine Pave train are conventional machines that have been only slightly modified. This allows their use for regular work on construction projects, said Nagel. “As a medium-sized enterprise, that improves our chances of winning tenders for two-layer asphalt pavements.”
InLine Pave is a particularly efficient means of building durable roads. Paving the binder and surface courses “hot-on-hot” offers several advantages. For example, instead of the usual 8cm binder course and 4cm surface course, different thicknesses can be chosen for the individual layers.
When using InLine Pave, the hot binder course prevents the surface course cooling too quickly. The higher temperature of the pavement makes it possible to pave thinner surfaces. In Horb, the surface course was only 2cm thick. The higher temperature of the surface course means that a higher density with fewer voids can be achieved during final compaction by rolling.
The most important issue when paving the wearing course of stone mastic asphalt on the B-14 trunk road was to ensure that the amount of binder complied with the German terms and guidelines and that the voids content in the surface course did not exceed 5% by volume.
A lower content of voids counteracts pavement ageing due to oxidation. High compaction increases the pavement’s permeability to water and its thermal stability, very effectively counteracting the formation of rutting.
The Inline Pave Train
For the binder course, the contractor used a Super 2100-2 IP paver with a transfer module to move the surface course mix supplied by the feeder directly into the material hopper of the paver that was placing the surface course. The transfer module had a heated conveyor to prevent the mix from sticking.
The Super 1800-3i used to pave the surface course was an all-rounder with a wide range of applications. With a maximum pave width of 10m and a machine length of just 6m, it can handle motorway sites and trunk roads as easily as tight traffic roundabouts. For hot-on-hot paving, the Super 1800-3i was equipped with a water spraying attachment for the crawler tracks, as well as with a particularly large, insulated extra material hopper for 25tonnes of mix.
The third machine – or more accurately the first machine – in the InLine Pave train was a VÖGELE PowerFeeder MT 3000-2i Offset. It received the binder and surface course mixes supplied by feed vehicles. It alternately transferred the mix with its pivoting conveyor directly into the large extra material hopper of the paver for the binder course or to the transfer module for the paver placing the surface course.
The paver operator used a system of lights to signal to the driver of the feed lorry whether binder course mix or surface course mix was required.
Height and distance of the conveyor were adjusted automatically, for example when the operator changed the position of the distance control switch from binder course mix to surface course mix. The feeder concept of the MT 3000-2i Offset meant that the complete system comprising material feeder and paver could stock up to 45tonnes and transfer up to 1,200tonnes of mix per hour. A 25tonnes feed lorry could be emptied in only a minute.
Road construction by conventional methods admittedly produces an outstandingly even pavement. A base course, binder course and surface course are paved in three passes. The paver’s auto-levelling properties ensure that the evenness improves from layer to layer.
But the InLine Pave process moves this process ahead by using two mutually independent pavers with floating screeds. Any unevenness is levelled out to the same degree as during conventional paving. For InLine Pave, there are no special requirements made on the evenness of the base course.
When using InLine Pave, the usual tolerance of up to 10mm is absolutely acceptable for producing a final surface course with maximum evenness.