DURABILITY AND PERFORMANCE OF TITANIUM DIOXIDE IN PHOTOCATALYTIC PAVEMENTS

Transcription

1 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 Tel: (225)

2 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 (NO x ) 58% of the carbon monoxide Tall buildings prevent the dispersion of air pollutants in urban areas

3 Introduction 35 million Americans live within 300ft from roads Decomposition of pollutants by ultraviolet (UV) radiation is extremely slow 2008 Non-Attainment Areas (EPA)

4 Photocatalytic Uses of TiO 2 Architectural Facades Statues Highway Sound Barriers Tiles PAVEMENTS

5 Photocatalytic Mechanism Titanium dioxide forms highly oxidizing holes and photo-generated electrons resulting in powerful oxidizing and reductive agents hydroxyl radicals and superoxides. Conduction Band Light (hv) Valence Band E g =3.2 ev H 2 O TiO 2 e - h + Hydroxyl radical ( OH) Superoxides (O 2 -)

6 Photocatalytic Mechanism NO x, SO 2, VOC UV radiation Rain TiO 2 TiO 2 Surface NO 3 - NO 3 -

7 NO x Photodegradation NO x Degradation: Sulfur dioxide is decomposed to sulfate Hydrophobic or hydrophilic properties of the surface allow them to self-clean in the presence of rain

8 Photodegradation Efficiency TiO 2 crystal (anatase, brookite, rutile) Substrate Application method Concentration of TiO 2 Type and Concentration of Pollutants Flow Rate Relative Humidity Interaction between multiple pollutants UV light intensity Photocatalytic degeneration and regeneration.

9 Titania Research at LSU Laboratory evaluation of concrete pavement treated with TiO 2 : Methods of applications Impacts of environmental conditions (relative humidity, pollutants flow rate, solar radiation) Effectiveness on NOx and SO 2 degradation Design variables (aggregate gradation, TiO 2 concentration) Durability of Photocatalytic layer Photocatalytic Pervious Concrete Pavement

10 Titania Research at LSU Laboratory evaluation of asphalt pavement treated with TiO 2 : 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 TiO 2 on HMA and WMA aging

11 Titania Research at LSU Field evaluation of asphalt and concrete pavement treated with TiO 2 : Hassan and co-workers laid the country s first airpurifying asphalt and concrete photocatalytic pavements on Dec. 20, 2010

12 Phase I: Laboratory Evaluation

13 Sample Preparation Curing and sprinkling nano-sized TiO 2 particles 10mm thin surface mixture with TiO 2 Application of Water-Based TiO 2 Solution

14 Application Method HMA & WMA Spray-Coating Application of TiO 2 : A thin nano film is spray-coated on each sample a mixture of TiO 2 anatase nanoparticles with an average size of 6nm suspended in an aqueous liquid at 2% by volume.

15 Laboratory Setup NOx Analyzer Photoreactor Illustration of the Environmental Setup

16 Photocatalytic Efficiency NO Reduction Efficiency 500 NOx NO2 NO 400 Concentration (ppb) Average Reduction Trial ppb % Reduction Trial % 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: Light On duration (h:mm) Light Off

17 Results and Analysis Water vapor can have both negative and positive impacts on the environmental performance of TiO 2

18 Results and Analysis The longer the residence time the more NO reduced.

19 Experimental Setup Concrete Asphalt Hamburg Type Loaded Wheel Tester

20 Rut Depth (mm) NOx Reduction Efficiency Durability Results and Analysis WMA &HMA NOx Removal Efficiency decreased after 60 loading in the LWT Before LWT After LWT 25.0 HMA WMA SC-64L1 SC-64L2 SC-64L3 SC-70L1 SC-70L2 SC-70L3 Sample ID H64CO H64-7 H70CO H70-7 W64CO W64-7 W70CO W70-7 Mixture ID

21 Durability Results and Analysis - Concrete Durability: Loaded-Wheel Tester The measured rut depth for all specimens was minimal (less than 1mm).

22 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.

23 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.

24 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

25 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.

26 Removal Efficiency Effect of TiO 2 depth The increase in depth resulted in an increase in NO x removal efficiency 70% 60% 50% 40% 30% NOx NO 45% 39% 40% 34% 35% 30% 50% 53% 20% 10% 9% 9% 0% Control Depth (inch)

27 Phase II: Field Installation and Evaluation

28 Field Installation First field installation of TiO 2 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 TiO 2 anatase nanoparticles with an average size of 6nm suspended in an aqueous liquid at 2% by volume

29 Field Installation A customized distributor truck was used in the application of TiO 2 water-based solution

30 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

31 Field Effectiveness Indirect Method: Nitrate Analysis Field measurements were conducted to quantify the amount nitrate deposited on the pavement surface NO + O H T io 2 NO 2 + H. NO 2 + O H T io 2 NO 3 + H.

32 Average Nitrate (mg/l) 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 Day

33 Cost Analysis Cost Increase is 4.4% Costs will decrease significantly once TiO 2 is mass produced in the US reducing in both material and delivery costs. Cost Estimate Cost ($/yd 2 ) 2009 RS Means 10 inch concrete paving surface Photocatalytic Coating 1.88

34 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.

35 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

36 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 TiO 2 pavement surface coating on the aquatic environment

37 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

38 Thank You!