IN ACTION AGAIN :
Sligh Avenue over Hillsborough River
Bridges are designed to last for 50 or more years , but they still need regular maintenance and periodic repairs to stay in good condition and minimize expensive , major repairs in the future . The Sligh Avenue bridge in Tampa was ready for new concrete jackets around the concrete piles after the original concrete had been abraded over the bridge ’ s years of service . Concrete piles are common in Florida , as salt water corrodes steel . But the concrete piles have prestressed steel strands inside for flexural strength and support .
The inspection noted some deficiencies on the piles – concrete was delaminated , prestressing strands were exposed and corroded . As steel corrodes , it expands in volume by as much as three times the original steel volume . The additional room required by the corroded steel is what causes the concrete to delaminate and eventually pop off ( spall ). Nonstructural concrete pile jackets were recommended to repair the surface of the pile .
The Ayres structural inspection and structural design groups work seamlessly to conduct inspections , produce reports , develop cost estimates , and design repairs . Inspectors and engineers alike have completed the same two-week “ Safety Inspection of In- Service Bridges ” offered by the Federal Highway Administration ( FHWA ) National Highway Institute . Maslyn said this enables engineers to know what to look for when interpreting an inspector ’ s report , and they can also supplement the inspection team as team leaders .
Ayres partners with the County in many ways , Sunna said , including reviewing bridges to determine repair needs , prioritizing bridges and repairs , and preparing repair plans ;
However , when the contractor began removing the delaminated concrete , the team discovered the piles were in worse condition than originally thought . Ayres was tasked with redesigning the jackets to be structural – capable of resisting loads – and with cathodic protection . David Johnson explained that cathodic protection works to stop and potentially reverse the corrosion process of steel in reinforced concrete . The process of corrosion is similar to a battery , he said , so if you provide an anode of higher potential ( usually zinc ), then you stop the chloride ions from attacking the steel .
Once steel ( especially prestressing steel ) is exposed to chloride ions and the corrosion process begins , there is little you can do to stop the corrosion from progressing unless you use cathodic protection . Johnson said combining a structural jacket with cathodic protection will bring the deteriorated piles back to their original capacity and will serve as a permanent structural repair that should last decades with minimal maintenance .
“ Through the County ’ s diligent construction oversight , the County was able to respond to the changing situation in the field and respond with a forward-thinking solution that will save taxpayers money in the long run ,” Johnson said
– Wendy Kinderman www . AyresAssociates . com 13