CTE TUNNEL CEILING SLAB COLLAPSE LTA to take preventive measures
The Straits Times Wednesday, 23 May 2007

 
CENTRAL Expressway (CTE) tunnels will now be inspected more closely and frequently, the Land Transport Authority (LTA) said yesterday - two weeks after a concrete slab the size of a car"s bonnet fell from a tunnel ceiling.
The checks will be carried out every three months on stretches which are under waterways, and every six months in other areas. Previously, the inspections were conducted once a year. The LTA said also that it will apply an electrochemical treatment - zinc hydrogel anode - to tunnels located under waterways. The zinc reacts with the steel in the concrete to form a weak electrical current - as in a battery - which helps impede corrosion. On the evening of May 9, chunks of concrete from the ceiling of a south-bound tunnel, which goes under the Singapore River - fell onto the road. Miraculously, no vehicles were hit. The cause has been identified as concrete spalling, which happens when steel beams in concrete rust and expand. The tunnels have been troubled with water seepage since the CTE opened in 1991, though millions of dollars have been spent to arrest leaks at nearly 2,000 points.
Yesterday, the LTA reiterated that the tunnels are structurally safe. It said that spalling "will not lead to a reduction in strength of the structure if attended to with proper repairs". However, certified corrosion specialist Qiu Jianhai told The Straits Times that "spalling concrete is just a visible surface problem signalling the start of the deterioration of the structure". He said that if corrosion control had been incorporated at the point of construction, it would have been cheaper. Dr Qiu, incidentally, also advocated the zinc hydrogel treatment.