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.

Conduction

Band

Valence Band

Light (hv) Eg =3.2 eV

H2O

TiO2

e-

h+ Hydroxyl radical

(·OH)

Superoxides

(O2-)

Photocatalytic Mechanism

Surface

NOx, SO2, VOC

TiO2 TiO2 NO3-

NO3-

UV radiation

Rain

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

Application of Water-Based TiO2 Solution

Curing and sprinkling nano-sized

TiO2 particles 10mm thin

surface mixture

with TiO2

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

Illustration of the Environmental Setup

Photoreactor

NOx Analyzer

Photocatalytic Efficiency

NO Reduction Efficiency

-100

0

100

200

300

400

500

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

Con

cen

trati

on

(p

pb

)

duration (h:mm)

NOx NO2 NO

Average Reduction Trial 2 - 242 ppb

% Reduction Trial 2 - 56.4%

Light On Light Off

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

Hamburg Type Loaded Wheel Tester

Concrete Asphalt

Durability Results and Analysis –

WMA &HMA

NOx Removal Efficiency decreased after loading in the LWT.

0

10

20

30

40

50

60

SC-64L1 SC-64L2 SC-64L3 SC-70L1 SC-70L2 SC-70L3N

Ox R

edu

ctio

n E

ffic

ien

cy

Sample ID

Before LWT

After LWT

0.0

5.0

10.0

15.0

20.0

25.0

H64CO H64-7 H70CO H70-7 W64CO W64-7 W70CO W70-7

Ru

t D

ep

th (

mm

)

Mixture ID

HMA WMA

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

9%

30%

35% 39%

50%

9%

34% 40%

45%

53%

0%

10%

20%

30%

40%

50%

60%

70%

Control 0.5 1 2 3

Rem

oval

Eff

icie

ncy

Depth (inch)

NOx NO

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

𝑁𝑂 + 𝑂 𝐻𝑇𝑖𝑂2

𝑁𝑂2 + 𝐻.

𝑁𝑂2 + 𝑂 𝐻𝑇𝑖𝑂2 𝑁𝑂

3 + 𝐻.

Field Effectiveness

There is definite evidence that photocatalytic

degradation of nitrogen oxide is taking place

in the field in the treated section

0

0.1

0.2

0.3

0.4

0.5

1 2 3 4 5 6 7

Avera

ge N

itra

te (

mg/l

)

Day

Treated Section Untreated Section

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!