The causes of ironwork failure

Failures of highway ironwork are unfortunately commonplace. Scott Wilson Kirkpatrick identified in a study that on principal routes, half of all of manholes will have failed within 2 years, but why?

The failure modes have been well studied and fall into three main areas:

How do you manage 100 million assets which have the propensity to ‘fail’ every 12-36 months, have an annual repair bill of £250million, can be dangerous when they fail and cause disruption when they are repaired? We believe we have the answer. 

The 100 million assets are the number of ironwork items in UK highways, the failure rate is taken from independent studies and the repair bill, a well publicised figure.

Today, there are over 5,000 Ironmaster systems installed on high trafficked carriageways stretching from Scotland to the south coast. The system’s five year guarantee has already saved local authorities almost £2.5m. The 407 systems installed in 2002 alone, generated a saving of almost £1m.

Since the 407 Irommaster systems were installed over seven years ago, they have been inspected, but there has been no reason to repair them because of the integrity of the structure. Other systems would (at best) have been re-repaired at least twice. Studies demonstrate that a conventional repair, on a principal route, lasts two and half years: therefore traditional ironwork would probably have been replaced in 2005 and again in 2008.

The audit of the 1100+ repairs undertaken in the three years spanning 2002-2004, revealed that no repairs had to be attended to. The cost benefits were more difficult to assess. Despite reviewing various methodologies, it was not possible to develop a robust analytical tool capable of accurately measuring:

• The costs of repairing the same piece of ironwork at least three times in the course of seven years
• The economic value of not inconveniencing road users – in terms of disruption caused by the need to ‘re-repair’
• The opportunity cost of reducing the health and safety risks, as well as legal claims from road users hurt and/or damaged by defective ironwork

The analysis therefore focused solely on the savings made from not having to restore the original repair. Based on the knowledge that:

• Traditional repairs on principal carriageways will conventionally last two and a half years
• The average cost of these repairs would be £1,200 each
• Traditional repairs undertaken in 2002 would require a re-repair in 2005 and again in 2008.

The total maintenance cost of the ironwork for the seven year period spanning 2002-2009 would therefore be £3,600. Using this formula, it was calculated that the 1100+ repairs undertaken between 2002 and 2004 saved the tax payer over £2.5m.

Commenting on the finding, Malcolm Chalmers, Managing Director, Rhino said “Asset management is critical to our customers. We know that they have to assess the long term benefits on every investment and sometimes make rational decisions based on calculated assumptions – but at the end of the day, they are assumptions".

“The results of this audit prove that the engineering behind Ironmaster’s repair methodology is robust and that purchasing decisions can now be made on verifiable proof, not just on assumptions based on the ‘science’ of this repair model."

“These results confirm that the quality of the Ironmaster workmanship and the quality of materials used makes the five year guarantee a reality. So, in addition to the £2.5m saved already, there is a further £8million in savings being made right now”.

Each and every Ironmaster installation comes with a guarantee certificate which is applicable to both the contractor and ultimate client, guaranteeing the performance of the Ironmaster installation for a period of 5 years.

This issued certificate is your legal right to claim a repair or replacement in the event of a failure of an Ironmaster installation.

There are some obligations on the owner of the ironwork to ensure the validity of that guarantee.

For example;

1. gulleys should be cleaned regularly and kept free of standing water, as the mortars used in the system are not designed to sit in standing water
2. the client should advise as soon as any failure is identified, so that the company can rectify the problem early on
3. new cast iron covers and frames were installed at the outset (the client does have the option to reinstall existing covers and frames but the 5 year guarantee would not apply in these instances)

If a failure is indentified, then we will, at our cost, replace or repair the installation without affecting the original terms of the guarantee, which will continue to run until 5 years from the date of the original installation.

Terms and conditions of the guarantee are included with the guarantee certificate or can be provided on request.

Structural

Until now, there has been no reliable, long-term treatment for failures around manholes and highway ironwork.

Conventional repair techniques have not provided a sustainable solution, leading to frequent repairs (sometimes after just 12-18 months) in order to maintain a safe and level running surface.

In addition, traditional repair methods utilise vibrating rollers and heavy compaction equipment, which themselves cause further damage to the substrate and the rigid materials used to support the structure. This undermines and hastens the re-emergence of defects.

These problems have been exacerbated by heavier HGV’s and subsequently compounded by the use of super single tyres, increasing loads on road pavements by 4 times that of traditional goods vehicles.

Financial

With a calculated average cost for an emergency repair and reinstatement of ￡1,200* and the average life of a manhole surround on a heavily trafficked route at 2.5 years, the annual maintenance cost per manhole equates to ￡480*.

The use of Ironmaster could represent an annual cost saving of up to 70%.

These figures do not include the hidden costs which are acknowledged but seldom calculated, such as the true cost of disruption to the travelling public and commerce.

Over ￡250 million is spent annually in the UK on installing and reinstating damaged and defective highway ironwork. That’s ￡½million each day.

*Optimising ironwork whole life cost using performance testing by Scott Wilson Pavement Engineering.

Litigation

Claims against councils, for damage to both road users and their vehicles (caused by deteriorating roads) have escalated dramatically in the past few years and in many cases the highway maintenance budget has been used to settle these compensation claims.

The system easily accommodates non-standard sizes, unforeseen structural conditions and localised surface deterioration.

Rhino installed the Ironmaster system using Pamrex 610mm x 610mm sealed units from Saint Gobain. This circular D400 unit incorporates an elastomer sealing ring.

There is no metal to metal contact. This ensures: (a) damping of mechanical stresses caused by repeated passage of vehicles (b) self centering and stability of the cover as the ring pinches the lower skirt and works agains the suction phenonmenon caused by vehicle tyres.