Advances in technology mean reinforcing steel can be added to existing concrete structures increasingly efficiently, and Hilti is opening up to clients a range of projects that were previously prohibited.
“If you can think of where rebar would go in a structure if it were being built from scratch, we can put that rebar in there now,” says Hilti engineering manager Paul Sleep.
“For a designer or contractor, knowing something can be modified or extended without needing as much work can give them the confidence to tackle things that may otherwise not be cost effective.”
Hilti has a range of products and services it believes represent a complete package for a project team looking to undertake the design and build of post-install rebar work.
“It’s a whole-system approach,” says Hilti engineering manager Khadije Bah. “From making sure the design is done correctly all the way through to training people on site so the installation is carried out properly.”
A key first step of the process is deciding on which design code to follow, as post-installed reinforcement can either be designed as an anchor, following European Technical Approval Guidelines (ETAG), or it can be treated as reinforcement and designed according to Eurocode 2. Hilti has developed software for either use: PROFIS Anchor and PROFIS Rebar.
“PROFIS software is used to do calculations,” says Bah. “You need clear information from designers, as you will be asked about the application, the concrete, the load, the dimensions and so on – then the software optimises the solution and gives you the minimum number of bars required, the depth of installation and the size of the bar.”
Displaying the workings and the outcome to the various parties is a critical next step.
“Once you have a solution that works, you can click on specification text and it will give you a clear text to paste into your own drawings,” says Bah. “You can also generate a full report. Designers often keep reports for their records.”
Ensuring site work is carried out correctly is critical to the success of the designs. The installation method is an important part of the full solution. It is therefore crucial that the installers follow the manufacturers’ instruction, says Bah.
“The contractor needs to be clear about what resin needs to be used, what size of bar is needed and what depth,” says Bah. “The cleaning method for the drilled holes is also important.
“You need to be drilling straight, that’s the first thing, then if you don’t remove dust from the hole, or have air bubbles in it, the resin will have a reduced bond strength, so the load transfer will not be what you have designed for, and you could risk failure.”
This is where Hilti equipment and training comes into play. Its SafeSet branding, for a system of tools and components used in anchor and post-installed rebar projects, is aimed at ensuring work on site goes as smoothly as possible and the finished structure matches designers’ intentions.
“Using SafeSet means you are following manufacturers’ instructions,” says Bah.
One key element of SafeSet is a hollow drill bit for hammer drilling.
Hilti in action
The Hilti-HIT rebar approach saves money
“This is connected to a vacuum dust extractor, which is cleaning the hole at the same time as it is being drilled, speeding up installation by removing the need for cleaning and the risk of people skipping a step,” says Bah.
For diamond drilling, there is a roughening tool that improves the strength of bond to that of hammer-drilled equivalents.
Then there are Hilti-manufactured resins to bond the materials.
“HIT-HY 200 A and HIT-RE 500 V3 are tested resins to give a similar strength as cast-in rebar if used correctly,” says Bah. “The bond strength of our resin is higher than that of concrete so we can use the real strength of the resin to reduce the depth of the rebar required. This can allow steel to fit into a wall where it may not have done using the concrete strength.”
Sleep adds that Hilti’s pure epoxy resins have a particularly high stated strength. “Because our installation process is fully tested and approved, we are more reassured about the bond strength we have and don’t need to have a margin for wet days, for example,” he says.
Air nozzles and piston plugs ensure drilled holes are completely filled with resin to maximise bond strength.
Even with the designs and the installation components all in place, Hilti’s involvement in a project does not stop.
Sleep says the firm employs more than 60 engineers across Great Britain, plus more than 380 technically trained account managers.
“With this many engineers locally and globally we are beginning to be considered an engineering consultancy resource in our own right,” he says. “We are happy to be involved at all stages to give reassurance to designers and customers. We can go anywhere in the country to make sure people have the right kit, awareness and training to install correctly.”
Hilti believes its input from the start of a project through to its conclusion can make a huge difference.
Sleep says traditional methods of adding rebar to a structure include breaking out the concrete to find the rebar, then using wire ties to attach new bars before re-pouring.
“This is a hand-arm-vibration heavy task, it affects time, cost and safety,” he says.
“We manufacture a range of detection systems, radar or magnetic tools that will find the existing rebar. If you can locate them you can put new bars in next to them – our system is like keyhole surgery, with minimum disruption.”
As well as making tools and products, creating software, training operatives and offering design and installation consultancy, Hilti also undertakes research in conjunction with top universities. As such it has developed some innovative methods.
“The Hilti-HIT rebar design method allows us to prove higher bond strength depending on bar spacings, so we can go beyond the Eurocode and take some provisions from US design codes,” says Sleep. “This allows lower volumes of steel and resin to save time and cost.
Hilti in action
“We also have a retrofit shear strengthening solution which involves access to a structure from one side only to fit additional shear-link strengthening bars, allowing a structure to be strengthened precisely where it needs it in a far less obtrusive way to other methods.
“We are now looking at drilling top down on road bridges without having to close roads underneath, which would be a huge saving.”