MOTORWAY signing structures from Southampton to Portsmouth will have to undergo extensive testing after it was revealed that they have been constructed with faulty concrete.

Every single new gantry from junctions four to 12 of the M27, from Southampton Airport to Portsmouth, has rogue concrete in its foundations, which could develop concrete cancer within a decade.

The gantries, which straddle the M27 carriageways at junctions and display blue motorway information signs, were only built a few months ago and have a 60-year life expectancy.

However that could be drastically cut in the light of this week's announcement.

However, a Hampshire gantry expert has reassured motorists that the huge steel structures are still safe.

Last month, it emerged that workers at Wiltshire-based Lafarge Cement had falsified test results for two years.

One million tonnes of cement made at the Westbury plant had too much alkali, making it susceptible to crumbling.

Thousands of private builders were affected, with Lafarge pledging to monitor everything from major construction sites to domestic house extensions.

This week, the Highways Agency released for the first time a list of the major road and rail schemes which also used the faulty cement - and Hampshire's M27 gantries are pinpointed.

The Highways Agency sought to reassure drivers, saying: "At present the agency's investigations indicate there are no concerns for safety.

"We are aware that there is a risk in the future of ASR (alkili silica reaction, or concrete cancer), but ASR is a relatively slow process usually taking several years to manifest itself.

"We have met with Lafarge to discuss the implications. Over the coming months, the agency will be examining the occurrences of the cement in more detail, to assess the structural and durability implications, and the overall risks."

Gantry expert Simon Benfield, from Hampshire engineering firm Giffords, told the Daily Echo: "It's more likely to affect the lifespan of the gantries. They are designed to be there for 60 years, but you might find that the concrete would deteriorate and the gantries would lose strength.

"However, the concrete is not going to have as much effect on gantries as other structures because gantry foundations are designed to be resilient to alkaline conditions."

Lafarge UK's managing director Jean-Francois Sautin said: ""We are a responsible company and are continuing to work with our customers and their customers - like the Highways Agency - on each case to assess the likelihood of any reaction developing and ensuring that the structures are appropriately managed."