Marwa M. Hassan

Evaluation of Environmental Effectiveness of Titanium Dioxide Photocatalyst Coating for Concrete Pavement

Self-cleaning, air-purifying concrete pavement is a rapidly emerging technology that can be constructed with air-cleaning agents with a super-hydrophilic photocatalyst such as titanium dioxide (TiO2). Although this technology has the potential to support an environmentally friendly road infrastructure, several design and operational parameters may affect its effectiveness and need to be evaluated. The objective of this study was to evaluate the environmental and mix design parameters that may affect the effectiveness of the environmental performance of TiO2 coating. An experimental program was conducted: the effects of relative humidity level, flow rate of pollutants, and mix design parameters, including contents of TiO2 and aggregate sizes, were investigated. The environmental efficiency of the samples to remove nitrogen oxides from the atmosphere was measured by using a newly developed laboratory setup. Results of the experimental program showed that the mix designs without fines achieved the highest photodegradation rates. In addition, the increase from 3% to 5% TiO2 resulted in little improvement in the nitrogen oxide removal efficiency, which decreased with the increase in the humidity level and the pollutant flow rate.

Evaluation of the Environmental and Economic Impacts of Warm-Mix Asphalt Using Life-Cycle Assessment

The use of warm-mix asphalt (WMA) has received considerable attention in recent years to reduce energy consumption and air emissions. Despite these promising benefits, the promotion of WMA based on a single factor such as reduced energy consumption or reduced emissions does not provide a complete evaluation of this technology and may omit critical environmental factors that should be considered in the decision-making process. The objective of this paper was to conduct a life-cycle assessment of WMA technology as compared with a conventional hot-mix asphalt mixture. To achieve this objective, a life-cycle inventory (LCI) that quantifies the energy, material inputs, and emission during aggregate extraction, asphalt binder production, and hot-mix asphalt production and placement, was developed. Based on this inventory, life-cycle impact assessment of WMA technology was conducted. Based on this analysis, it was determined that WMA provides a reduction of 24% on the air pollution impact of hot-mix asphalt (HMA) and a reduction of 18% on fossil fuel consumption. Overall, the use of WMA is estimated to provide a reduction of 15% on the environment impacts of HMA.

Sustainable Photocatalytic Asphalt Pavements for Mitigation of Nitrogen Oxide and Sulfur Dioxide Vehicle Emissions

The ability of titanium dioxide (TiO2) photocatalytic nanoparticles to trap and decompose organic and inorganic air pollutants render them a promising technology as a pavement coating to mitigate the harmful effects of vehicle emissions. This technology may revolutionize construction and production practices of hot-mix asphalt by introducing a new class of mixtures with superior environmental performance. The objective of this study was to assess the benefits of incorporating TiO2 into asphalt pavements. To achieve this objective, the photocatalytic effectiveness and durability of a water-based spray coating of TiO2 was evaluated in the laboratory. This study also presents the field performance of the country’s first air-purifying photocatalytic asphalt pavement, located on the campus of Louisiana State University. Laboratory evaluation showed that TiO2 was effective in removing NOₓ and SO2 pollutants from the air stream, with an efficiency ranging from 31–55% for NOₓ pollutants and 4–20% for SO2 pollutants. The maximum NOₓ and SO2 removal efficiencies were achieved at an application rate of 0.05 L/m². The efficiency of NOₓ reduction is affected by the flow rate of the pollutant, relative humidity, and ultraviolet (UV) light intensity. In the field, NOₓ concentrations were monitored for both the coated and uncoated sections to directly measure photocatalytic degradation. Furthermore, nitrates were collected from the coated and uncoated areas for evidence of photocatalytic NOₓ reduction. Results from both approaches show evidence of photocatalytic NOₓ reduction. Further field evaluation is needed to determine the durability of the surface coating.

Field and Theoretical Evaluation of Thermal Fatigue Cracking in Flexible Pavements

Thermal cracking in flexible pavement occurs when the tensile stress exceeds the tensile strength of hot-mix asphalt at a given temperature or when fluctuating stresses and strains caused by temperature variation lead to a buildup of irrecoverable deformations over time. The objective of this study was twofold: (a) to quantify the measured strain magnitude associated with thermal fatigue through field measurements and (b) to present a three-dimensional, finite element (FE) model that accurately simulated thermal fatigue in flexible pavement. Results of the experimental program indicated that pavement response to thermal loading was associated with a high strain range, reaching a maximum recorded value of 350 um/m. This finding confirms the hypothesis that the criticality of thermal fatigue arises from the high stress-strain level exhibited in each cycle rather than its frequency, which is usually the critical factor in load-associated fatigue cracking. Moreover, the developed FE model accurately simulated...

Laboratory Investigation of the Effect of Mixed Nitrogen Dioxide and Nitrogen Oxide Gases on Titanium Dioxide Photocatalytic Efficiency in Concrete Pavements

Nitrogen oxides (NOx) emitted from vehicle exhausts are associated with adverse health effects on the public. Self-cleaning, air-purifying concrete pavement is a rapidly emerging technology that can be constructed by using a photocatalyst such as titanium dioxide (TiO2). The main objective of this study was to evaluate the environmental effectiveness of TiO2 coating in photodegrading mixed NO2 and NO gases from the atmosphere. Results of the experimental program determined that increasing the flow rate and NO2/NOx ratio negatively affect the effectiveness of the photocatalytic process. However, within the evaluated range, the titanium content and aggregate gradation had little effect on NOx removal efficiency. The highest photodegradation rate was observed at 25% relative humidity, which balances the availability of hydroxyl radicals at the surface with NOx contact with the photocatalytic surface.

Evaluation of Self-Healing Mechanisms in Concrete with Double-Walled Sodium Silicate Microcapsules

AbstractThe objective of this study is to evaluate a new generation of self-healing materials that hold promise for better durability and performance. The in situ polymerization method was used to develop double-walled microcapsules. The microcapsules were prepared in a single batch process containing sodium silicate as the healing agent encapsulated in double-walled polyurethane/urea-formaldehyde (PU/UF) microcapsules. Double-walled microcapsules provide enhanced durability at high temperatures compared with single-walled microcapsules while preserving adequate interfacial bonding of microcapsules. A parametric study was carried out to investigate the effect of different parameters such as agitation rate, pH, and temperature on the performance of the microcapsules and to determine the optimum microencapsulation procedure. The prepared microcapsules were then incorporated into self-healing concrete beams. To monitor the healing process of the cracks, microcracks were created by imposing a certain magnitud...

Effects of Shear Bond Characteristics of Tack Coats on Pavement Performance at the Interface

A finite element (FE) approach was used in a study to investigate the effects of interface shear bond characteristics of tack coats on pavement response at the interface. A two-dimensional FE modeling approach incorporated laboratory-measured bond characteristics of tack coats to describe the constitutive behavior at the interface. Two pavement structures typically used in Louisiana for low and medium traffic levels were simulated. The Louisiana interlayer shear strength tester was used to test three types of emulsified tack coat materials—CRS-1, SS-1h, and trackless—and a PG 64-22 asphalt binder at three residual application rates, 0.14, 0.28, and 0.70 l/m2 (0.031, 0.062, and 0.155 gsy). From the results of the FE simulation analysis, it was determined that the performance of tack coat materials at the interface was primarily dictated by the pavement structure with no pronounced change in the field stresses from one tack coat material to another. In addition, the influence of tack coat material type and application rate became more relevant in thin pavements and less dominant in thick pavement structures. For the thin structure considered in the study, it was determined that the majority of tack coat materials and application rates would experience fatigue damage at the interface. The minimum laboratory-measured interface shear strength to provide acceptable fatigue performance at the interface was 190 kPa (28 psi). For the thick structure considered in the study, the majority of the tack coat material types and application rates performed satisfactorily against fatigue damage at the interface. The minimum laboratory-measured interface shear strength to provide acceptable fatigue performance at the interface was 128 kPa (19 psi).

Heterogeneous Finite-Element Modeling of the Dynamic Complex Modulus Test of Asphalt Mixture Using X-ray Computed Tomography

Asphalt mixture is a heterogeneous, composite material consisting of aggregate, mastic, and air voids. Analysis of laboratory tests such as the dynamic complex modulus assumes that this material can be dealt with as a homogeneous material while overlooking the particulate nature of this composite. Because of the limitations of the elastic continuum theory, pavement engineers have recently paid considerable attention to the use of advanced modeling techniques for simulating the realistic behavior of asphalt mixtures. The objective of this study is to develop a three-dimensional (3D), heterogeneous model to describe the response of asphalt mixtures in the dynamic complex modulus test using an X-ray computed tomography image-based finite-element (FE)-modeling approach. Experimental testing results for two superpave mixtures, including one conventional hot-mix asphalt and one warm-mix asphalt, were used to validate and calibrate the developed FE models. Acceptable agreement between laboratory-measured and model-predicted dynamic modulus test results was achieved. Results of the developed FE models at different temperatures indicated that most of the deformations during the dynamic modulus test are derived from the mastic. In addition, the asphalt mastic had more influence than the aggregates on the results of the dynamic complex modulus test.

Durability Quantification of TiO2 Surface Coating on Concrete and Asphalt Pavements

AbstractThe use of nanosized titanium dioxide in photocatalytic pavements is a promising approach to combat air pollution. Past research focused on the effects of environmental and operational parameters on photocatalytic efficiency and its performance under laboratory and field conditions. Few studies have attempted to quantify the durability of the technology integrated with in-service photocatalytic pavements. This study developed and tested a new photocatalytic quantification method used to quantify the short-term durability of a TiO2 spray application on two pavement surfaces: concrete and asphalt. This was accomplished through developing a nitrate extraction method that could be used on in-service pavements without requiring core extraction. Results of the proposed method were compared to results obtained from the Japanese Industrial Standards (JIS) method. The experimental program included testing photocatalytic samples in the laboratory for NOx reduction and nitrate accumulation based on the JIS m...

Laboratory Evaluation of Environmental Performance of Photocatalytic Titanium Dioxide Warm-Mix Asphalt Pavements

AbstractThe use of titanium dioxide (TiO2) coating for pavements has received considerable attention in recent years to improve air quality near large metropolitan areas. However, the proper method of applying TiO2 to asphalt pavements is still unclear. This study evaluated the benefits of incorporating TiO2 in the preparation of warm-mix asphalt (WMA). Two application methods to integrate TiO2 were evaluated, a water-based TiO2 solution applied as a thin coating and using TiO2 as a modifier to asphalt binder in the preparation of WMA. On the basis of the results of the experimental program, it was determined that the photocatalytic compound was not effective in degrading NOx in the air stream when used as a modifier to the binder in the preparation of WMA. This could be attributed to the fact that only a small amount of TiO2 is present at the surface. When used as part of a surface spray coating, TiO2 was effective in removing nitrogen oxide (NOx-) pollutants from the air stream with an efficiency rangin...