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Washington Metropolitan Area Transit Authority
	Where:	WMATA Rail Platform, Washington, D.C.
	Problem:	On-grade platforms suffered server premature deterioration from ASR
	Solution:	Performed in-situ repair using Vacuum Impregnation restored structure’s compressive strength to 6,200–7,400PSI.

Rehabiliation of WAMATA Rail - Transit Structures

Washington Metro’s program for heavy-rail system rehabilitation of deteriorated platform concrete, at on-grade stations, took on a completely new perspective. Pre-construction investigation and testing identified concrete deterioration resulting from alkali-aggregate reaction. Deicing salts, in conjunction with the freeze-thaw cycles further exacerbated the extent and severity of the platform deterioration.

Under the investigation phase, core samples were taken to develop a rule of measure for strength and durability. Several cores had deteriorated to the extent that sample extraction revealed conditions of total disintegration, seriously compromising the platform structural integrity.

In light of this distressing information, implementation of a retrofit design and repair program required an in-situ methodology that restored structural integrity. The concern for concrete restoration with advanced AAR and ASR was provisional. Industry standards No reliable history of restoration materials and particularly technology addressed this type of deterioration.

Like so many structures in a heavily popularized area, the concern for the impact on the surrounding community and particular the demand for public transportation weighted heavily on the method of repair. The options for restoration of the deteriorated platforms were all but limited to conventional removal and replacement, or employment of an in-situ repair process that minimized the excessive intrusion and operational issues.

With minimal impact on the operating schedule and without compromise of the operating-system safety and reliability, as the first most concern, every consideration was given to minimize the construction period and facilitate construction economy.

After an exhaustive investigation of technology, the Balvac Process of Vacuum Impregnation was chosen as the only feasible means of in-situ repair that would meet the stringent objectives of reconstruction.

As a means of quality control and evaluation of the Balvac Process of Vacuum Impregnation, cores samples were extracted pre and post repair. The platform concrete that all but disintegrated in the investigation phase now yielded cores samples having compressive strength ranging from 6,400 to 7,200 psi. Thus, indicating that the method was completely successful in restoring the structural integrity of once highly deteriorated concrete.

Upon successful completion of the initial platform restoration program, use of the Balvac Process of Vacuum Impregnation was specified with WAMATA as the only repair method for rehabilitation of concrete where presence of AAR, in its various stages of development, had been identified.

Nearly 20 years latter, the Balvac Process of Vacuum Impregnation has stood the test of time. To date the AAR and ASR has been mitigated, if not totally arrested. No further deterioration from this internal reactive condition of disintegration has occurred.

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