International Concrete Abstracts Portal

Editor: Yail Jimmy Kim

This CD contains 15 papers that were selected from three special sessions sponsored by ACI technical committees 345 and 440 at the ACI Spring 2013 Convention in Minneapolis, MN. The papers emphasizes the concept, performance, evaluation, and repair of concrete bridges in conjunction with smart materials and sensors.

Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-298

Corrosion of prestressing steel strands in concrete bridge members may lead to the rupture of single strands and catastrophic collapse before visual inspection uncovers evident signs of damage, and well before the end of the design life. Recognizing corrosion in its early stage is critical to plan maintenance and repairs and prevent premature failures. The acoustic emission (AE) technique is a rational means to develop structural health monitoring and prognosis systems for the early detection and location of corrosion in prestressed concrete. It is sensitive to micro- and macro-damage, non-intrusive, and suitable for remote monitoring. However, there is little understanding of the correlation between AE and the extent of early damage in prestressing strands. This paper presents recent advances in AE monitoring of corrosion for prestressing strands embedded in concrete. The state of the art is reviewed, and results from recent research efforts are reported, in which prestressed concrete specimens representative of scaled bridge girders and piles were exposed to salt water through wet/dry cycles. The acoustic emission activity resulting from the early corrosion of strands was studied by evaluating AE data vis-à-vis electrochemical measurements and evidence from scanning electron microscopy.

This paper presents the results of an experimental study conducted to understand the stress-transfer mechanism of fiber reinforced concrete matrix (FRCM) composites externally bonded to a concrete substrate for strengthening applications. The FRCM composite was comprised of a polyparaphenylene benzobisoxazole (PBO) fiber net and polymer-modified cement-based mortar. Direct shear tests were conducted on specimens with composite strips bonded to concrete blocks. Parameters varied were composite bonded length and bonded width. Results were analyzed to understand the effective bonded length, which can be used to establish the load-carrying capacity of the interface to design the strengthening system. The normalized load carrying-capacity was plotted against the width of the composite strip to study the width effect. Finally, strain gage measurements along the bonded length were used to investigate the stress-transfer mechanism.

Overlays are installed on concrete bridge decks to improve ride quality, and in the case of impermeable overlays, also protect the deck from exposure to moisture and chlorides. Moisture and chlorides can penetrate over time into reinforced concrete, allowing for the initiation and progression of corrosion, which shorten the service life of a structure. To evaluate whether impermeable overlays are truly keeping moisture from penetrating into the concrete deck, researchers have implemented wireless moisture sensors in several bridge decks to monitor the moisture content of the deck below the overlay. In this study, the four overlays that are being monitored are a hot-mix asphalt wearing surface with a thermoplastic additive, an epoxy polymer concrete overlay, a fabric-reinforced liquid membrane with asphalt wearing surface, and a thin-set urethane membrane with an asphalt wearing surface. The moisture sensors have been installed at various locations in each deck including near the bridge joints, overlay construction joints, drainage paths, and under wheel paths. Results indicate that the hot-mix asphalt wearing surface with thermoplastic additive overlay only has moisture penetrating in regions that are near the joints. Measurements also indicate that the polymer concrete overlay has been effective at preventing the penetration of moisture. The latter two overlays, a fabric-reinforced asphalt membrane and a thin-set urethane, were recently installed and some preliminary conclusions may be offered about their effectiveness based upon early results.

Despite that steel fiber concrete (SFC) has been used in concrete structures during more than 50 years there is still a lack of practical recommendations. In Sweden, SFC has been used in concrete overlays on bridges during more than 25 years but the usage frequency is fairly low. The current Swedish guidelines for SFC overlays are based solely on empirically determined relationships between the amount of conventional reinforcement for crack control and amount of fibers. In a recent study at the Swedish Cement and Concrete Research Institute, the current recommendations have been critically reviewed. The experience shows that this empirical recommendation works fairly well for traditional concrete mixes and for the most frequently used fibers but there is a need of recommendations that promote the development of better concrete mixes and more efficient fibers. In order to reach this goal, guidelines which are much broader in their application field need to be developed. A novel approach taking the mechanical properties of the actual SFC into account has been proposed. This approach may also be used for concrete with synthetic fibers if their mechanical and long-term properties are proven to be sufficient.