Owner
United States Postal Service
Chicago, Illinois

Project Engineer/
Designer
Parsons Brinckerhoff
Chicago, Illinois

Repair Contractor
Allied Waterproofing, Inc.
Lyon, Illinois

Material Supplier/
Manufacturer
Degussa Building Systems
Shakopee, Minnesota

The Old Main Post Office was completed in 1932. With hundreds of train movements and thousands of passengers using the rail system daily, the Amtrak Station under the Old Main Post Office is a vital link between home and work for many Chicagoans. This 73-year old structure has survived the age of steam and coal fired trains and remains in relatively good conditions despite years of exposure to diesel locomotive exhaust. The ingress of carbon dioxide has reduced the pH of the parent concrete leading to severe corrosion of the structural reinforcing steel. This condition posed a serious risk to both passengers and trains alike.

The main challenge facing the engineer was determining the most effective methods of removing and replacing the damaged concrete. Several means and methods were explored over a two year period leading up to the development of the project specification. Ultimately, the engineer selected low velocity spray applied mortar for the replacement.

The contractors developed a plan to complete the work in a specified time, without shutting down the train station or creating disruption to commuters. All of the smaller equipment and manpower for each night’s work was loaded onto a converted school bus with folding platforms, and pulled to the work area on railroad tracks. The materials, mix water, and spray equipment were placed on a flatbed rail car and towed in behind the school bus. After the completion of each shift of work, the converted school bus drove out of the station and back to a staging area roughly one mile away.

The Old Main Post Office Plenum Ceiling Repair project was a complicated endeavor with many obstacles. By fostering a successful “partnership” between engineer, general contractor, subcontractors, and material supplier, the project was successfully completed on time and on budget.