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

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.

The purpose of this study is to facilitate damage detection and health monitoring in concrete bridge girders without the need for visual inspection while minimizing field measurements. Simple span beams with different geometry, material and cracking parameters were modeled using Abaqus finite element analysis software to obtain stiffness values at specified nodes. The resulting databases were used to train two Artificial Neural Networks (ANNs). The first network (ANN1) solves the forward problem of providing a health index parameter based on predicted stiffness values. The second network (ANN2) solves the inverse problem of predicting the most probable cracking pattern. For the forward problem, ANN1 had the geometric, material and cracking parameters as inputs and stiffness values as outputs. This network provided excellent prediction accuracy measures (R2 > 99%). ANN2 had the geometric and material parameters as well as stiffness values as inputs and cracking parameters as outputs. This network provided less accurate predictions compared to ANN1, however, ANN2 results were reasonable considering the non-uniqueness of this problem's solution. An experimental verification program will be conducted to qualify the effectiveness of the method proposed. This test program is described in details in the present paper.

The technology of FRP strengthening has matured to a great extent. However, there is always room for performance improvements. In this study, external bonding of GFRP and near surface mounting of regular steel bars is combined to improve the behavior, delay the failure, and enhance the economy of the strengthening. E-Glass FRP is selected due to its inexpensive cost and non-conductive properties to shield the NSM steel bars from corrosion. On the other hand, the use of NSM bars gives redundancy against vandalism and environmental deterioration of the GFRP. An experimental program is conducted in which five rectangular cross-section beams are designed and built. The first beam is tested as a control beam failing at about 12 kips (53.4 kN). The second beam is strengthened using 5 layers of CFRP, which failed at 27.1 kips (120.5 kN). CFRP U-wraps were used to anchor this external reinforcement. The third beam is strengthened using two #5 steel NSM bars and 1 layer of GFRP, both extending to the support. GFRP U-wraps were applied to anchor this external reinforcement. This beam failed at 31.5 kips (140 kN). The fourth beam is strengthened with the same system used for the third beam. However, the NSM steel bars were cut short covering 26% of the shear-span only while the GFRP was extended to the support. This beam failed at 30.7 kips (136.5 kN) due to the lack of sufficient development of the NSM steel bars and the shear stress concentration at the steel bar cut off point. Nevertheless, the failure load developed was higher than that of 5 layers of CFRP used for beam 2. The fifth beam was strengthened exactly as the fourth beam, but once strengthened, was loaded five times to cracking load and then submerged in a highly concentrated saline solution for six months. The beam was then tested to failure with a failure load of 29.8 kips (132.6 kN), showing that the GFRP wrapping provided good corrosion resistance.