The most crucial aspect of relaying a concrete road surface is to ensure that the new and old layers act compositely. Otherwise, as heavy lorries apply large braking forces, the two layers can slide over each other.
The traditional method of concrete resurfacing involves removing the top 100mm of concrete pavement surface using high pressure water jets, drilling holes into the concrete and installing bent hooks of steel reinforcement. The hooks are set in place using a mortar system, which takes about a day to set. Bars of reinforcement are connected to the hooks to create another layer of reinforcement.
Concrete is then poured up to the original slab level, thus increasing the strength of the road surface.
However, things are often not straight forward on site, says Hilti applications engineer Camiel de Smet.
'Often the hooks don't set in the right position to receive the extra reinforcement layer, ' he says.
Since the concrete surface is uneven and the hooks are drilled down to the same depth, they are also often set at the wrong height. This means that some hooks end up being redundant and new ones have to be installed, adding to the time spent on site.
Hilti has produced a new steel shear connector - the snappily titled HCC-B known more commonly as the Hilti trumpet - to combat some of the shortcomings of the previous steel hook system.
Hilti's system has been used on numerous projects in Europe and is currently being installed on roads in Switzerland. But has yet to make its debut in the UK, despite being launched here earlier this year.
The 180mm long trumpets are so-called because they consist of a steel pin with a funnel shaped head.
The bottom section of the pin is proled to allow it to be screwed into the concrete, while the upper-ribbed section enables the height to be adjusted as easily. They are usually spaced at 700mm centres and every step of the installation has been carefully considered.
Take the way the mortar system is applied. De Smet noticed that when shear connectors were previously set, air gaps in the mortar could reduce the efciency of the bond between the concrete and steel.
So on the Hilti trumpets, mortar is injected down the funnel to the bottom of the pin where it spurts out through a hole and rises up to the surface of the hole.
'This avoids air gaps and creates a better bond, ' says de Smet.
The prole of the trumpet also allows reinforcement to either sit on the connector or be threaded through a hole at the top of the funnel. The system is more expensive, but de Smet argues the benets outweigh the cost.
'You can save up to 30% in labour costs by using the trumpets over rebar. But the big difference is the clear benet in increased quality, ' says De Smet.
'Ultimately you end up with as close as you can to monolithic concrete using a system you can rely on to be installed on time.'