Corrosion of steel reinforcing bars is a major problem in concrete bridge decks that are regularly exposed to chloride-based salts. Vertical electrical impedance (VEI) measurements quantify the level of protection offered to rebar against chloride ion ingress. Like most other electrochemical assessment tools, VEI testing requires a connection to the rebar. Instead of a direct connection to the rebar at a fixed point, however, a semidirect, low-impedance connection to the rebar can be made through placement of a sliding large-area electrode (LAE) on the surface of the concrete deck. Importantly, the LAE connection is completely nondestructive and can be rapidly deployed. In this work, a complete multichannel VEI scanner and LAE were constructed and demonstrated in the field. For all of the test sections, the VEI measurements obtained using the LAE connection were comparable to those obtained using a tapped connection and were also consistent with visual observations of deterioration.
The use of small specimen geometries in asphalt mixture performance testing to enable the testing of as-built pavement layers has been gaining attention in recent years. Small specimens could also improve the testing efficiency of laboratory-fabricated specimens by allowing the extraction of multiple test specimens per gyratory-compacted sample. Rigorous assessment of the small specimen geometries is required before the use of such geometries is standardized. In this study, small specimens were evaluated for dynamic modulus and simplified viscoelastic continuum damage fatigue. Three specimen geometries (100-mm- and 38-mm-diameter cylindrical specimens and 25- × 50-mm prismatic specimens) were compared by using five mixtures with a nominal maximum aggregate size (NMAS) ranging from 9.5 to 25.0 mm. The results show that the dynamic modulus and phase angle master curves agreed at low and intermediate temperatures, regardless of the NMAS values of the mixture. At the high temperature, the small specimen dynamic modulus values were slightly higher and the phase angle values were slightly lower than those of the large specimens. The specimen-to-specimen variability for the large and small specimens was comparable. The fatigue test results for the mixtures evaluated were comparable, except for the 25-mm mixture, which proved problematic in the testing of both small and large specimens. Pavement performance was predicted by the layered viscoelastic analysis for critical distresses program by using the test results for the small and large specimens. These results suggest that specimen geometry had a minimal effect on pavement fatigue damage predictions, which indicates promise for the use of small specimen geometries in practice.
Excess porewater pressure induced by rapid shearing often leads to liquefaction of granular deposits, resulting in excessive deformation and loss of stability of supported structures. Practitioners and researchers have developed and evaluated numerous approaches for the mitigation of liquefaction and its deleterious effects on civil infrastructure. Innovations include vibro-compaction and vibro-replacement of granular deposits, compaction and permeation grouting, deep soil mixing and jet grouting, and installation of large-diameter, high-density polypropylene earthquake drains. These mitigation techniques attempt to improve the ground such that the soil is densified, reinforced, or drained, lowering the potential for excessive ground deformation. Although the foregoing mitigation techniques enjoy strong theoretical and empirical evidence of their effectiveness, each of the methods exhibits the limitation that they use one mode of treatment (densification, reinforcement, or drainage). To overcome these limitations, the effectiveness of conventional and novel drained timber pile ground improvement for the mitigation of liquefaction was evaluated. The results of this study showed that drained and conventional piles could effectively densify liquefiable soils, with increases in relative density ranging from 60-95% immediately following installation of timber piles, depending on the pile spacing and use of pre-fabricated vertical drains (PVDs). Long-term measurements of corrected cone tip resistance showed increases of approximately 30% for piles spaced at four to five diameters, D, with and without PVDs, 125% for piles at 3D without PVDs, and about 145% for piles spaced at 3D with drains and 2D without drains. Closely-spaced drained piles produced larger improvements in cone tip resistance than conventional piles at the same spacing (i.e., 3D). Controlled blasting of the timber pile treated areas showed that the treated soils responded in a dilative manner, resulting in decreases in excess pore pressure relative to an unimproved zone, and resulting in significantly smaller vertical ground deformations. Although areas for improvement in the drained pile prototype were identified, there are no barriers to the immediate implementation of drained and/or conventional, driven timber displacement piles.
This work investigates the potential use of an intrinsically conducting polymerpolyanilinethat, when mixed in polyvinyl-butyral and top-coated with an acrylic resin layer, demonstrates comparable performance to the existing coating systems, according to the experimental data from two ASTM standard tests performed to evaluate its overall corrosion durability and tensile adhesion (pull-off strength). Formulation of the polyaniline-based wash primer was provided. Scanning Kelvin probe force microscopy (SKPFM) was used to analyze the microscopic mechanisms of the superior performance. The polyaniline-based primer demonstrated potential surface ennobling and oxygen smearing-out capabilities in this study. Under the protection of a top coat, the primer provided both preventive and corrective protection in a smart mode. The layered structure including an ICP primer, as demonstrated in this study, constitutes a viable smart coating system for corrosion protection of metallic materials.
This project proposes a bi-directional ductile end diaphragm concept to implement ductile end diaphragms in straight or skew bridge superstructures. The proposed concept relies on easily replaceable hysteretic energy dissipating devices (structural fuses) arrayed such as to provide ductile response to horizontal bidirectional earthquake excitations. Buckling Restrained Braces (BRBs) are explored here as a possible solution to serve as the ductile diaphragm’s seismic fuses. In Stage 1 of this research project, bi-directional ductile end diaphragm systems were designed for benchmark skew- and nonskew bridges and analyzed using nonlinear time history analysis to examine their seismic performance. Variations in skew, fundamental period of vibration, and earthquake excitation characteristics were also considered. In Stage 2 of this research project, quasi-static experiments were conducted to subject BRBs to a regime of relative end-displacements representative of the results predicted from the Stage1’s parametric analytical studies. Detailed analyses of cumulative inelastic deformations and low-cycle fatigue life of all BRBs using data from the experiments were performed. A recommended design procedure is presented for the EDSs in both non-skew and skew bridges was developed based on the parametric analyses and experimental results.
