International Concrete Abstracts Portal

This paper presents on-site inspection techniques to examine a damaged prestressed concrete girder bridge. The bridge is 18.3 m [60 ft.] and consists of double-tee beams (DT3000 x 700 ) with a 50 mm [2 in.] topping concrete. To simulate the effect of deterioration for the girder, the leg member is intentionally damaged by cutting 2 prestressing strands. A load test is conducted to evaluate the flexural behavior of the bridge before and after the damage. A site inspection is conducted after 10 months of the load test. The inspection techniques used for this study includes the visual inspection, pull-off test, ultrasonic test, rebound hammer test, core test, and surveying. The bridge exhibits significant cracks and spalling of the concrete in the deck and the legs. Corrosion of the reinforcing steels is observed. The pull-off test shows that the bond strength between the flange of the girder and the topping concrete is adequate. The ultrasonic test exhibits some internal defects of the leg member, including an increased transmission time of the ultrasound. The in-situ concrete strength measured is reasonably close to the specified 28 day concrete strength, based on the rebound hammer test and the core test, with an average error of 2.1%. Permanent downward deflections are not observed, whereas a maximum camber of approximately 35 mm [1.4 in.] is measured by surveying. The inspection techniques reported in this study are reliable and recommended to examine concrete bridge elements.

This paper presents a case study in the evaluation and repair of precast prestressed concrete beams with moderate to severe deterioration due to Alkali-Silica Reaction (ASR). The subject of this study is a 25-year old, 15-span bridge in Texas experiencing deterioration characterized by longitudinal cracking along the bottom flange at the beam ends, vertical splitting in the beam web at the bearings, and general map cracking with discoloration on the beam surfaces. Evaluation methods discussed include crack and surface discoloration mapping and as well as procedures for excising samples for petrography and accelerated expansion testing to confirm the presence of ASR. A structural evaluation of the existing beams is also presented to study the potential capacity loss resulting from concrete deterioration. Detailed visual observations of distressed conditions, structural analysis of damage scenarios, and laboratory test results were considered to develop a repair course of action that included the application of crack fillers, concrete penetrating sealers, and coatings as well as the application of CFRP composites to confine the expansion in the concrete beams.

The historic bridge on Henley Street over the Tennessee River in Knoxville, Tennessee is a six-span, 1,389-foot (423 m) long open spandrel reinforced concrete arch bridge flanked by a 165-foot (50 m) long, three-span approach girder structure at each end. The arch span lengths range from 185 feet (56 m) to 317 feet (97 m) with an average rise-to-span ratio of 0.30. In an effort to accommodate six travel lanes, reduce the number of expansion joints in the deck, and use the existing arch structure in its present condition, a 1,720-foot (524 m) long continuous superstructure unit was designed with expansion joints located only at the abutments; however, analytical studies on the bridge showed that the combined effects of superstructure continuity and increased live load demands led to increased forces at various sections of respective structural components of the bridge. A combination of innovative design techniques were used to mitigate these adverse load effects. The bridge improvements were designed in accordance with the National Historic Preservation Act and the Department of Transportation Act of 1966.

Non-destructive evaluation techniques were used to assess the condition of a 40-year old concrete bridge operating in an aggressive marine environment. The bridge’s superstructure includes both reinforced and prestressed concrete one-way slabs, and experienced widening, repairs, and recently strengthening by means of externally bonded carbon fiber reinforced polymer (CFRP) laminates. Phase I of the investigation focused on evaluating deterioration of concrete and steel reinforcement by means of in-situ and laboratory testing. A 24 in. by 24 in. [610 by 610 mm] grid was marked on the bottom surface of the supporting slabs to map indicators of physical damage. Measurement of carbonation, pH, chloride content, corrosion potential, and visual inspection were implemented and rendered as layered maps to identify damaged areas. Phase II includes acoustic emission (AE) monitoring under service loads. AE amplitude, duration, energy and hits were analyzed to identify structural activity associated with damage phenomena, such as concrete cracking, slip between corroded reinforcement and surrounding concrete, and debonding of CFRP laminates. The database acquired from Phase I and Phase II was used for damage assessment. Combined results from the different techniques show promise in determining areas of concern with reduced uncertainty than when using a single measurement technique.

During the last decade, the Swedish Road Administration (SRA) has transferred resources from corrective to preventive bridge maintenance. Presently, 10 to 15 percent of the budget is devoted to preventive maintenance whereas corrective maintenance, repair, and reconstruction comprise the remaining 85 to 90 percent. This reallocation has resulted in considerable efficiency gains but further savings are likely to be large. Preventive maintenance aims at measures to maintain the function of the bridge structure. Frequent measures include water washing, cleaning, vegetation removal, crack repair, material refill, and stretching of bridge railings. SRA has defined a series of technical requirements to harmonize the preventive bridge maintenance. Several technical requirements state that a structural element or element part “should be 95 percent clean”. SRA has also developed methods to verify that the technical requirements are fulfilled. However, the scientific basis for the relationship between the technical requirements and the function of the bridge structure is unknown or weak. The verification methods are not always unquestionable. The paper contains a critical review of the technical demands for preventive bridge maintenance in Sweden. Do they adequately promote durability and long-lasting service life? Are the prescribed requirement levels appropriate? Could the technical requirements be replaced by other and better requirements? How do they look like in an international comparison? There is a general belief that performance-specified contracts would be more cost-effective than other contract types. Do the Swedish demands facilitate or obstruct performance-specified contracts for bridge maintenance? The questions are discussed in the paper that also contains a summary of a Swedish pilot study conducted at the Swedish Cement and Concrete Research Institute.