Hosin Lee

Development of a crack type index

Many automated systems for crack analysis have been developed to measure the extent and severity of pavement cracking objectively. However, the accuracy of such an automated crack analysis system has not been satisfactory. This paper presents a crack type index (CTI) that can be easily adopted to determine the crack type objectively as longitudinal, transverse, and alligator cracking. The CTI is based on the spatial distribution of the image tiles rather than image pixels, where a tile is defined as a subimage of a whole digital image. The spatial distribution of image tiles is analyzed vertically and horizontally, with a resulting single index, which can be used to identify a spatial orientation of cracking. To determine the accurate CTI threshold values for longitudinal, transverse, and alligator cracks, 150 pavement images were captured with a digital video camera mounted on a sport-utility vehicle: 50 images for each of three types of cracking. These 150 images were analyzed automatically to compute t...

Laboratory Evaluation of Color Polymer Concrete Pavement with Synthetic Resin Binder for Exclusive Bus Lanes

In the summer of 2005, exclusive bus lanes were constructed in the median of busy streets in Seoul, South Korea, as color polymer concrete pavements with a transparent synthetic resin binder and a red pigment. However, early distresses, such as shoving, potholes, stripping, and rutting have occurred from these color polymer concrete pavements. Potential causes for early distresses from color polymer concrete pavements were investigated: inadequate quality of color polymer concrete, inadequate quality control during construction, and insufficient subgrade support. Historically, polymer concrete mixtures have been designed and evaluated by using predominantly hydraulic cement concrete technology because polymer concretes are used in concrete structures. This paper adopted asphalt mix technology to evaluate polymer concrete for use in a roadway overlay. Laboratory evaluation was performed on color polymer concretes by conducting the following tests: Marshall stability test, indirect tensile strength test, and modified Lottman moisture sensitivity test. These test results of color polymer concrete mixes were significantly more positive than those of typical asphalt mixes, and the mixes met the minimum requirements. On the basis of test results, it can be concluded that the color polymer concrete with a synthetic resin is stronger and less susceptible to moisture than are typical asphalt mixtures.

Investigation of Bonding Condition in Concrete Overlay by Laboratory Testing, Finite Element Modeling, and Field Evaluation

To evaluate the effect of bonded versus unbonded condition in concrete overlay structure, a field evaluation, laboratory experiment, and 3-D finite element analysis (FEA) model were carried out. First, a field evaluation of bonded and unbonded pavement test sections in Iowa was performed. Cores were extracted from existing pavements and tested for their bond strengths with shear testing equipment. The bond strength between an overlay and the existing pavement gradually increased over time, regardless of the initial bond strength. In some cases, an insufficient bond shear strength at the interface between the concrete overlay and the existing pavement seemed to have contributed to increased distress on the overlay surface. Second, a laboratory experiment was conducted to investigate an effect of bonding in pavement structure. Concrete cylinder specimens that were one-half regular concrete and one-half polymer concrete were fabricated, and their indirect tensile strength was measured at the bonding interfac...

Concept of Film Thickness Applied to a New Approach for Polymer Concrete Mix Design for Airport Pavement Repair

Because of its superior ability to bond to substrate materials and its good resistance to freezing and thawing cycles, polymer concrete has been widely used for repairing airfield pavements. However, polymer concretes used in repairing airport pavements in South Korea have not lasted as long as originally predicted; this premature failure may be attributable to the incompatibility of the coefficient of thermal expansion (CTE) between the polymer concrete and the substrate concrete material. To lower the CTE of the polymer concrete, the amount of polymer must be decreased and the amount of coarse aggregates increased. To determine the optimum amounts of polymer and coarse aggregates, a new concept of film thickness is proposed. In this research, the laboratory evaluation was performed on the mixtures of polymer concrete to measure compressive strength and CTE. On the basis of these test results, it was discovered that a larger amount of coarse aggregates lowered the CTE value and increased the film thickness; these changes resulted in a higher compressive strength than that of a typical polymer concrete with fine aggregates. As expected, the CTE of the polymer concrete decreased as the amount of polymer decreased. On the basis of limited laboratory test results, a film thickness of 33.5 Μm is recommended to satisfy the minimum requirement of compressive strength (21 MPa) for repair material in South Korea. This minimum film thickness can be achieved with a mix of 8.2% polymer and 91.8% sand. However, if coarse aggregates are substituted for 40% of the sand, the same film thickness can be maintained if the amount of polymer is reduced to 6.35%.

Determining Timing of Overlay on Cold In-Place Recycling Layer: Development of New Tool Based on Moisture Loss Index and In Situ Stiffness

Cold in-place recycling (CIR) is one of the most popular rehabilitation techniques in Iowa. The Iowa Department of Transportation has increased the minimum moisture criterion from 1.5% to 2.0% because many overlays have been successfully applied on the CIR layer with moisture contents above 2.0%. However, a contractor must make daily measurements of the moisture content with a nuclear gauge. It is difficult to achieve 2.0% moisture content during a rainy summer in Iowa. For the curing issue to be addressed systematically, the moisture contents and temperatures of one project of CIR with emulsified asphalt and four projects of CIR with foamed asphalt were monitored. Capacitance moisture and temperature sensors were embedded at the midpoint of the CIR layer to measure moisture contents and pavement temperature. A GeoGauge was used to measure the stiffness. The field data obtained from the embedded moisture sensors and from a weather station were used to develop a moisture prediction model as a function of the initial moisture content, CIR layer temperature, wind speed, and humidity. With the developed moisture prediction model, a contractor can predict optimal timing for placement of the wearing surface without continually measuring moisture contents of the CIR layer with a nuclear gauge. The stiffness of the CIR layer measured with the GeoGauge was found to continue to increase as the curing period increased, despite an increase in moisture content caused by rainfall. The stiffness measured by the GeoGauge steadily increased during the curing period until it reached a value of 30 MN/m. For the optimal timing of an overlay to be determined, the stiffness, rather than the moisture, of the CIR layer should be measured.

Electrochemical Chloride Extraction Method to Control and Mitigate Corrosion in Rebar Embedded in Concrete : Laboratory Testing and Field Evaluation

This study determines the effectiveness of the electrochemical chloride extraction (ECE) method on a bridge deck with a high concentration of chloride. ECE was applied on a pedestrian bridge in Iowa to control and mitigate corrosion that occurred in the embedded reinforcing steel. First, chloride content was measured from the existing bridge deck; it ranged from 1.64 lbs/cy to 24.58 lbs/cy. ECE was applied to remove chloride from the bridge deck for 8 weeks. Afterward, chloride content was significantly reduced to 0.32 lb/cy and to 4.96 lb/cy. To simulate corrosion in the bridge deck, 2 reinforced slabs and 12 reinforced beams were prepared, cracked, and saturated with salt solution for 4 months, followed by ECE application. Initially, half-cell potentials were measured from test specimens; they all were below −200 mV; this indicated a 5% probability of corrosion. At introduction of 3% salt solution, the potential increased and remained at −500 mV for 4 months; this indicated 95% of corrosion. To remove chloride from test specimens, ECE was applied for 1.5 months. Afterward, average chloride content from the surface to 2 in. below the surface of test specimens with salt solution was significantly reduced from 10.68 lbs/cy to 4.12 lbs/cy, and half-cell potential decreased to below −200 mV. From limited laboratory test specimens, it can be concluded that the ECE method can effectively reduce corrosion activity by removing a significant amount of chloride.