DURABILITY AND PERFORMANCE OF TITANIUM DIOXIDE IN PHOTOCATALYTIC PAVEMENTS Marwa Hassan Performance Contractors Distinguished Assistant Professor Department of Construction Management 3128 Patrick Taylor Hall Louisiana State University Baton Rouge, LA 70803 Tel: (225) 578-9189 Introduction The US faces a significant challenge in controlling air pollution from transportation activities Road microenvironments contribute: 29% of the volatile organic compounds 35% of the nitrogen oxides (NOx) 58% of the carbon monoxide Tall buildings prevent the dispersion of air pollutants in urban areas Introduction 35 million Americans live within 300ft from roads Decomposition of pollutants by ultraviolet (UV) radiation is extremely slow 2008 Non-Attainment Areas (EPA) Photocatalytic Uses of TiO2 Architectural Facades Statues Highway Sound Barriers Tiles PAVEMENTS Photocatalytic Mechanism Titanium dioxide forms highly oxidizing holes and photo-generated electrons resulting in powerful oxidizing and reductive agents hydroxyl radicals and superoxides. Superoxides Conduction (O2-) Band Light e- Eg =3.2 eV (hv) TiO2 + h Hydroxyl radical Valence (·OH) Band H2O Photocatalytic Mechanism NOx, SO2, VOC UV Rain radiation NO3 - NO3 TiO2 TiO2 - Surface NOx Photodegradation NOx Degradation: Sulfur dioxide is decomposed to sulfate Hydrophobic or hydrophilic properties of the surface allow them to self-clean in the presence of rain Photodegradation Efficiency TiO2 crystal (anatase, brookite, rutile) Substrate Application method Concentration of TiO2 Type and Concentration of Pollutants Flow Rate Relative Humidity Interaction between multiple pollutants UV light intensity Photocatalytic degeneration and regeneration. Titania Research at LSU Laboratory evaluation of concrete pavement treated with TiO2: Methods of applications Impacts of environmental conditions (relative humidity, pollutants flow rate, solar radiation) Effectiveness on NOx and SO2 degradation Design variables (aggregate gradation, TiO2 concentration) Durability of Photocatalytic layer Photocatalytic Pervious Concrete Pavement Titania Research at LSU Laboratory evaluation of asphalt pavement treated with TiO2: Methods of applications Impacts of environmental conditions (relative humidity, pollutants flow rate, solar radiation) Durability & Effects on mix performance (fracture resistance, thermal cracking, and rutting performance) Photocatalytic Warm-Mix Asphalt Effect of TiO2 on HMA and WMA aging Titania Research at LSU Field evaluation of asphalt and concrete pavement treated with TiO2: Hassan and co-workers laid the country’s first air- purifying asphalt and concrete photocatalytic pavements on Dec. 20, 2010 Phase I: Laboratory Evaluation Sample Preparation Curing and sprinkling nano-sized TiO2 particles 10mm thin surface mixture with TiO2 Application of Water-Based TiO2 Solution Application Method – HMA & WMA Spray-Coating Application of TiO2: A thin nano film is spray-coated on each sample a mixture of TiO2 anatase nanoparticles with an average size of 6nm suspended in an aqueous liquid at 2% by volume. Laboratory Setup NOx Analyzer Photoreactor Illustration of the Environmental Setup Photocatalytic Efficiency NO Reduction Efficiency 500 NOx NO2 NO 400 Average Reduction Trial 2 - 242 ppb 300 % Reduction Trial 2 - 56.4% 200 Concentration Concentration (ppb) 100 0 0:00 0:30 1:00 1:30 2:00 2:30 3:00 3:30 4:00 4:30 5:00 5:30 6:00 6:30 7:00 7:30 8:00 -100 Light On Light Off duration (h:mm) Results and Analysis Water vapor can have both negative and positive impacts on the environmental performance of TiO2 Results and Analysis The longer the residence time the more NO reduced. Experimental Setup Asphalt Concrete Hamburg Type Loaded Wheel Tester Durability Results and Analysis – WMA &HMA NOx Removal Efficiency decreased after 60 loading in the LWT. Before LWT 50 After LWT 40 25.0 30 HMA WMA 20 20.0 10 NOx Reduction EfficiencyNOx Reduction 0 15.0 SC-64L1 SC-64L2 SC-64L3 SC-70L1 SC-70L2 SC-70L3 Sample ID 10.0 Rut Depth (mm) Depth Rut 5.0 0.0 H64CO H64-7 H70CO H70-7 W64CO W64-7 W70CO W70-7 Mixture ID Durability Results and Analysis - Concrete Durability: Loaded-Wheel Tester The measured rut depth for all specimens was minimal (less than 1mm). Experimental Testing Abrasion testing: according to ASTM C 944 Test method uses a cutter rotating at 200 rpm under a constant load of 98 N for 2 minutes to wear the coating surface. Durability Results and Analysis - concrete A thin coating would be more susceptible to abrasion than the photocatalytic compound applied using the sprinkling method or using the PT product. Effect of Weathering LWT slightly improved the NO removal efficiency of the different samples The weathering action exposed part of the embedded titanium dioxide particles at the surface Pervious Concrete Samples are prepared in two layers: Bottom lift: standard pervious concrete Upper lift: prepared with photocatalytic specialty cement Depth of the photocatalytic layer was varied between four levels: 0.5, 1, 2, and 3 in. Effect of TiO2 depth The increase in depth resulted in an increase in NOx removal efficiency 70% NOx NO 60% 50%53% 45% 50% 39% 40% 35% 40% 34% 30% 30% 20% Removal EfficiencyRemoval 9% 9% 10% 0% Control 0.5 1 2 3 Depth (inch) Phase II: Field Installation and Evaluation Field Installation First field installation of TiO2 on pavement in the US (12/2010) The test area is a pavement site located on LSU campus Many states (e.g., Virginia, Texas, Vermont, New York, and Missouri) will or are evaluating the technology The spray coating used was a mixture of TiO2 anatase nanoparticles with an average size of 6nm suspended in an aqueous liquid at 2% by volume Field Installation A customized distributor truck was used in the application of TiO2 water-based solution Field Monitoring : Direct Method NO concentration is measured at the pavement level by placing a perforated pipe at the surface in the middle of the lane Field Effectiveness Indirect Method: Nitrate Analysis Field measurements were conducted to quantify the amount nitrate deposited on the pavement surface 푇 푂 푖 2 . 푁푂 + 푂 퐻 푁푂2 + 퐻 푇푖푂2 . 푁푂2 + 푂퐻 푁푂 3 + 퐻 Field Effectiveness There is definite evidence that photocatalytic degradation of nitrogen oxide is taking place in the field in the treated section Treated Section Untreated Section 0.5 0.4 0.3 0.2 0.1 Average NitrateAverage (mg/l) 0 1 2 3 4 5 6 7 Day Cost Analysis Cost Increase is 4.4% Costs will decrease significantly once TiO2 is mass produced in the US reducing in both material and delivery costs. Cost Estimate Cost ($/yd2) 2009 RS Means 10 inch concrete paving surface 42.93 Photocatalytic Coating 1.88 Conclusions Applying TiO2 as close as possible to the source of pollution can remove a significant portion of NOx pollutants from the atmosphere when placed. Field measurements show that photocatalytic degradation of nitrogen oxide is taking place in the field in the treated section. Conclusions The NO removal efficiency decreased with the increase in humidity level Water inhibits absorption of NO by the photocatalytic compound As the flow rate increased, the percent NO removal efficiency decreased As the residence time decreased, it allows less time for the pollutants to be absorbed by the photocatalytic compound Additional work is needed.. Evaluate influence of other pollutants (VOCs) and mixed air pollutants. Full-scale controlled evaluation in accelerated facility is needed Long-term environmental performance and durability Assess the potential impacts of photocatalytic TiO2 pavement surface coating on the aquatic environment Acknowledgments This research was sponsored through LTRC, NSF, and the Gulf Coast Research Center for Evacuation and Transportation Resiliency The assistance of the concrete and asphalt laboratory staff at LTRC is greatly appreciated Thank You! .