A 17-story reinforced concrete structure with prestressed concrete floor slab, clad with an architecturally pleasing white cement and calcined stone aggregate, exhibited signs of deterioration after 30 years exposure to central London environment. The investigation was instigated after a piece of concrete spalled from a high level and crashed down. After the investigation, when the cause of the deterioration was established, recommendations were made to the client and specifications for repair were made. After the repair specialist was selected the author supervised the repair ensuring that the specifications were strictly followed. The paper describes the investigations and the rehabilitation of the structure.

Soldier Field, located on Chicago's lakefront, is one of the most historically significant buildings in the city. Opened to the public in 1924, the stadium features classic Roman colonnades above the main stands on each side of the playing field. Sixty years of exposure to harsh northern climate took its toll on the reinforced concrete structure. The tread-and-riser system was deteriorating due to reinforcement corrosion and freeze-thaw exposure. Also, ground water fluctuations accelerated the deterioration of the highly permeable concrete at the base of the columns. A major rehabilitation effort was started in the early 1980s. The concrete frames were strengthened and the stands were reinforced with an overlay of latex-modified concrete. The overlay system was designed to support its own weight, the weight of the original stands, and the expected live load. The underside of the structure was repaired with shotcrete. Circularly reinforced collars were installed at the deteriorated column bases, and the existing wood pile foundations were tested to verify their capacity to support the additional dead load. The repairs are holding up very well after 10 years of service.

As the results of CEN/PC directives in 1986 and subsequent decisions, the work of CEN/TC 104 "Concrete Performance, Protection, Placing and Compliance Criteria," was extended to cover standardization work on admixtures for concrete (TC 104/WG 3) fly ash for concrete (TC 104/WG 4), mixing water for concrete (TC 104/WG 5), grouts for prestressing tendons (TC 104/WG 6), and sheaths for prestressing tendons (TC-104WC 7). In June 1989, TC 104/WG 8, protection and repair of concrete structures, was formed.

A design method has been proposed that considers the interaction of the superstructure with the abutments. The superstructure sways freely under moderate intensity ground shaking. At this stage, the piers are considered to be taxed at 70 percent of their capacity. Under the design earthquake, the piers hinge and bang against the abutments. The soil passive resistance behind the abutment back wall is mobilized, which is considered as elastic springs in the computer model. The sway of the superstructure is carefully monitored to limit the displacement of the abutment to avoid stability problems. The maximum resistance of the soil behind the backwall is also limited. Since the maximum longitudinal sway is known, the demand on ductility of the pier is quantified by plastic analysis. This demand is checked against the realistic thrust-moment-curvature relationship of the pier. Iterations may be performed to satisfy the constraints and achieve acceptable results.

Concrete structures, old or new, often experience formation of cracks, even though these are accounted for by the designer at the time of construction. To repair these cracks, a large number of injectable inorganic materials (cements and cementitious grouts), organic materials (epoxies, polyurethanes, polyester, etc.) and mixtures of both have been used successfully and unsuccessfully. Cementitious materials seem to arouse great controversy among engineers, especially with regard to the acceptance levels of the consistency (water-cement ratio) to be used for injection. A hydraulic facility in Quebec is therefore evaluating a number of cementitious materials as well as various epoxies and polyurethanes for repairing its concrete structures. The paper describes the results of a study performed in the laboratory using normal portland cement (Type 10) and high early-strength cement (Type 30) both with and without superplasticizers, and two ultrafine cements, and recommends an arbitrary lower and higher limit of the water-cement ratio, which could be suitable for crack injection. It also presents some physical and mechanical data on these cements. 110-691