"Rehabilitation and retrofit of aged and distressed rail-transit structures and facilities often calls for unique and innovative engineering solutions, if the requirements of the operating-system safety and reliability, and the construction economy, are to be optimally realized…The concrete deterioration was caused by alkali-aggregate reaction and by the deicing salts, in conjunction with the freeze-thaw damage. The novel vacuum -impregnation method was used to successfully restore integrity of the affected concrete and thus obviate the need for platform demolition and reconstruction…The slab is cast in place using 3500psi concrete…In some instances the Minnesota Avenue structural slab had deteriorated to such an extent that the core recovery with sufficiently long pieces for compressive testing was not possible…In a generalized sense, only two basic options were available: Remove the defective concrete and repour, or utilize a procedure capable of in situ restoration of concrete…This method is based on first creating a partial vacuum in the concrete, a suitable polymer resin is then introduced into the concrete-matrix. The resin fills the cracks, including micro cracks down to 0.001 inch and less…Control cores were taken before and 8-hours after the completion of the impregnation operation. The cores were tested to yield a compressive strength ranging from 6,400 to 7,200 psi….the method was completely successful…susceptibility of rebar to corrosion was also significantly diminished…The rehabilitated slabs are reported to be performing well." ##

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