Longfellow Towers (2001, 2005 and 2011)

LOCATION: BOSTON, USA

The Longfellow complex is in Boston overlooking the Charles River and comprises two 38 storey apartment buildings and an underground parking garage which were constructed between 1970 and 1972.

Inspections of the buildings were conducted in 1997 identified numerous areas of spalls due to corrosion of the steel reinforcement. Sealant joints at the sliding glass doors, ac units and windows were failing and allowing water to leak into the apartments. In 2001, the spalling had increased by 25% since 1996. Exposed column faces, balcony edges and floor slab edges had the least cover and most spalls. There was chloride contamination, carbonation and low cover throughout. Wherever the cover was less than 2” (50mm) there was high levels of active corrosion. Within the post-tensioned parking deck there was corrosion identified to the exposed tendon ends at 2ft centers and to around 12” from the anchor plate to the sleeve.

The complex received ICCP to protect the post-tensioned anchors within joints at the car park whilst monitoring the performance of surface-applied corrosion inhibitors and anti-carbonation coatings to reinforced concrete elevations for Longfellow Towers 1 and 4 was added.

Product / System Used

Corrosion management system (CMS) with embedded CP101 corrosion rate probes and AchillesICP and AchillesIES interoperable network management system with AiMS online performance management.

Project Details

Repair work to the apartments involved the delaminated concrete and the failed sealant being removed and the substrate properly prepared. Embedded corrosion rate monitoring probes were installed to monitor the initial and future effectiveness of the repairs as well as the performance of the surface-applied corrosion inhibitor applied beneath an anti-carbonation coating.

The Apartments were zoned every 5 levels with a zone of monitoring that housed 4no corrosion rate probes to assess environmental exposure conditions up the height of the building. Data were accessed on a schedule every day and uploaded to AiMS quarterly with annual reporting and archiving of trended behaviour.

The parking deck was repaired structurally and ICCP discrete anodes installed at 2ft centers along the line of the anchor plate between tendons to throw current to the exposed tendon ends for corrosion protection. The joints were zoned for ICCP to control specific positions and exposure conditions in a total of 5-zones.

All monitoring and control zones were bound on to a single interoperable open network and data accessed using AchillesICP and AchillesIES systems and uploaded to AiMS from the central Network Access Unit location.

Project Impact

Different corrosion mitigation strategies were adopted for the Towers and the parking garage to reflect the risk and need for control. Both strategies have operated for over 20 years to great effect achieving sustainable resilience without maintenance proven through performance data over the time since commissioning.

Awards

ICRI Award of Excellence – High-rise Buildings (2005)

ICRI Award of Merit – Longevity (2015)

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