Performance-Based Aspects and Structural Behavior of High Performance
Mohammad Abedalkareem Alhassan, Ph.D. Candidate, Advisor: Dr. Mohsen A. Issa
Bridge decks are deteriorating under repeated mechanical loading, shrinkage-induced stresses, thermal cycles, and environmental attack. Problems with corrosion of reinforcing steel and consequent spalling and delamination in reinforced concrete bridge decks are considerably intensified by the use of deicing salts. As a result, protective concrete overlays including latex-modified concrete (LMC) and microsilica concrete (MSC) overlays are being employed on bridge decks as part of rehabilitation and corrosion protection strategies. The overlay also provides an aesthetic product and a good riding quality. In addition to the typical advantages of the overlay; this study addresses the effect of bonded LMC and MSC overlays on the overall structural behavior of the bridge system and the advantages that can be gained from adding discontinuous synthetic and steel fibers to the LMC and MSC overlays.
This study encompassed extensive laboratory investigations and field application on a full scale prototype bridge system, 82 ft long and 18 ft wide with equal span lengths of 40 ft. As a result plain and fibrous LMC and MSC overlay mixtures were developed (plain LMC, LMC with synthetic fibers, LMC with steel fibers, plain MSC, MSC with synthetic fibers, and MSC with steel fibers) to meet target performance characteristics in terms of strength, permeability, hardened air-void system, bond strength, shrinkage, and crack arresting mechanism (toughness). Typically, the mixtures with synthetic fibers showed favorable performance over the mixtures with steel fibers due to the uniform distribution of synthetic fibers throughout the concrete, and LMC overlay mixtures showed superior performance over MSC overlay mixtures mainly in terms of permeability and shrinkage. The bond strength and the composite action between the overlay and the bridge deck were also evaluated under actual environmental exposures and full-scale low cycle fatigue load tests simulating AASHTO truck service load, overload, and ultimate load conditions. Following the laboratory and field studies, an innovative technique for casting LMC with synthetic fibers using mobile mixers is tried and proved to produce LMC with uniform distribution of the synthetic fibers and with high performance characteristics.
Experimental and Theoretical Behavior of Reinforced Concrete Beams and Columns Wrapped with CFRP-Composites
Rajai Alrousan, PhD Candidate, Advisor: Dr. Mohsen A. Issa
Many of the nation’s constructed facilities are in need of rehabilitation or strengthening due to their deterioration, aging, and underestimated design loads. To produce effective and durable repairs/strengthening projects, innovative construction materials with substantial bond characteristics, strength, and resistant to environmental exposures are required. This study deals with two major subjects: the application of carbon fiber reinforced polymer (CFRP)-composites for enhancing the shear strength capacities of reinforced concrete beams that are deficient in the shear behavior; and the use of the CFRP-composites for enhancing the ultimate axial strength capacity of the columns. The decrease in the costs of the composite materials as a result of the technology improvement has made the CFRP-composites an alternative to conventional materials with superior performance for many applications.
The major parameters that were evaluated are the effect of the number of applied layers of CFRP-composites and the fiber alignment on the behavior of the test specimens. In the beams, the CFRP-composites were applied in different number of layers and in different configurations that include U-wrapping and strips at varied spacing and orientation. In the columns, the number of layers of CFRP-composites was the major varied parameter. The initial phase of the study included fabrication and testing of large number of beams and columns; control and strengthened specimens. A total of 28 reinforced concrete beams; 5 ft-long with a cross section of 6 in. x 9 in., and 18 circular reinforced concrete columns; 24 in.-long with 6 in.-diameter, were tested to failure under monotonic loading. The experimental test results were then used to create and validate three-dimensional nonlinear finite element models identical to the tested specimens. The exact geometries, reinforcement details, and materials properties were employed in the nonlinear finite element analysis (FEA). After reasonable validation, the FEA were expanded to study the effect of various critical parameters on the behavior of the specimens; such as the effect of the thickness of CFRP-composites and orientation as well as the effect of the concrete strength. The current stage of research includes providing rational models that are capable of predicting the shear capacity of CFRP-strengthened beams and ultimate axial strength capacity of CFRP-strengthened circular columns based on the number of layers of CFRP-composites, concrete strength, and composites orientation. In addition, guidelines will be established to allow for optimum selection of the CFRP-strengthening scheme. At this stage, preliminary models were proposed, and their effectiveness and accuracy were evaluated based on the available experimental and FEA results. The preliminary models showed encouraging results and good agreement with the results available in literature. With further validation and calibration, the objective is to generalize the models to cover any CFRP-strengthening scheme and any member geometry and materials properties. The results of the ongoing research on CFRP for the last eighteen years at UIC were used to perform actual rehabilitation on many projects and mainly the rehabilitation of three damaged precast/prestressed concrete bridges in the State of Illinois.