Photocatalytic concrete for reducing traffic NOx on urban roads

PGR-P-798

Key facts

Type of research degree: PhD
Application deadline: Ongoing deadline
Funding: Non-funded
Supervisors: Dr Emilio Garcia-Taengua and Dr Yue Huang
Schools: Institute for Transport Studies, School of Civil Engineering

<h2 class="heading hide-accessible">Summary</h2>

Road pavements provide a means to convert vehicle tailpipe pollutants to less harmful substances. For instance, reducing the concentrations of nitrogen oxides (NOx) in cities can be achieved by photochemical conversion of NOx to nitrate ions (NO3-), using semiconductors such as titanium dioxide (TiO2). Previous experiments (de Melo et al., 2012) tested road pavements overlaid with cement mortar which contained TiO2 for their photocatalytic efficiency. Other studies examined the effects of environmental conditions such as ultra-violet (UV) radiation and relative humidity. Conflicting results are sometimes found in the literature. Besides, different practice was carried out, for example by TiO2 spray coating or by TiO2-intermixed surface (Guo et al., 2017). Similar experimental trials were carried out for asphalt (Fan et al., 2017, Fan et al., 2018). Removal of air pollutants by both types of pavements was also measured in an environmental chamber (Toro et al., 2016). However, details of the pavement materials and traffic environment are unknown. The challenges are multiple. For instance, the efficiency in the degradation of NOx decreased significantly with time. The high maintenance needs and costs can only be justified for locations where public health is of high concern and other means to improve air quality prove inefficient. Besides, the safety requirements for pavement surfaces need to be considered, such as skid resistance, which is critical at locations often coinciding with higher concentration of pollutants. Resistance to vehicle abrasion and the self-cleansing ability (with aid of rainwater) are important to ensure benefits of the novel concrete pavement can be sustained. This project will explore the novel concrete pavement further in urban street cannons that call for reducing the NOx concentration from vehicle emissions. There was preliminary work (Hao et al., 2019, Xie et al., 2020) in this field that models the dispersion of pollutants using computational fluid dynamics (CFD). Variation of TiO2 in the concrete mix and the environmental (e.g. humid, temperature) factors need to be considered in the concrete mix design. Besides, the influence of traffic (speed, volume, fuel mix) will be quantified using micro-simulation and instantaneous emissions model. The aforementioned safety requirements and maintenance needs will refer to pavement design and asset management practice, such as DMRB (Design Manual for Roads and Bridges) in the UK. Whole life cost of the pavement can be studied and compared with conventional pavement using life cycle analysis.

<h2 class="heading hide-accessible">Full description</h2>

Road pavements provide a means to convert vehicle tailpipe pollutants to less harmful substances. For instance, reducing the concentrations of nitrogen oxides (NOx) in cities can be achieved by photochemical conversion of NOx to nitrate ions (NO3-), using semiconductors such as titanium dioxide (TiO2). Previous experiments (de Melo et al., 2012) tested road pavements overlaid with cement mortar which contained TiO2 for their photocatalytic efficiency. Other studies examined the effects of environmental conditions such as ultra-violet (UV) radiation and relative humidity. Conflicting results are sometimes found in the literature. Besides, different practice was carried out, for example by TiO2 spray coating or by TiO2-intermixed surface (Guo et al., 2017). Similar experimental trials were carried out for asphalt (Fan et al., 2017, Fan et al., 2018). Removal of air pollutants by both types of pavements was also measured in an environmental chamber (Toro et al., 2016). However, details of the pavement materials and traffic environment are unknown. The challenges are multiple. For instance, the efficiency in the degradation of NOx decreased significantly with time. Previous studies (Osborn et al., 2014) on the durability of a TiO2-treated photocatalytic pavement under field conditions suggested that the service life of TiO2 coating is 6-11 months for concrete and 10-16 months for asphalt. The high maintenance needs and costs can only be justified for locations where public health is of high concern and other means to improve air quality prove inefficient. Some studies (Shen et al., 2012) recommend the TiO2 treated pavement surface be used at locations such as bus (diesel-driven) lane in the vicinity of schools where the maximum conversion efficiency and health gain can be obtained. Besides, the safety requirements for pavement surfaces need to be considered, such as skid resistance, which is critical at locations often coinciding with higher concentration of pollutants. Resistance to vehicle abrasion and the self-cleansing ability (with aid of rainwater) are important to ensure benefits of the novel concrete pavement can be sustained. This project will explore the novel concrete pavement further in urban street cannons that call for reducing the NOx concentration from vehicle emissions. There was preliminary work (Hao et al., 2019, Xie et al., 2020)(Hao et al., 2019) in this field that models the dispersion of pollutants using computational fluid dynamics (CFD). Variation of TiO2 in the concrete mix and the environmental (e.g. humid, temperature) factors need to be considered in the concrete mix design. Besides, the influence of traffic (speed, volume, fuel mix) will be quantified using micro-simulation and instantaneous emissions model. The aforementioned safety requirements and maintenance needs will refer to pavement design and asset management practice, such as DMRB (Design Manual for Roads and Bridges) in the UK. Whole life cost of the pavement can be studied and compared with conventional pavement using life cycle analysis. Nevertheless, the use of photocatalytic nanoparticles as a pavement coating to trap and decompose air pollutants provides a promising technology to mitigate the harmful effects of vehicle emissions. Results will be useful to transport authority who can make informed decision on air pollution control and asset management.   Reference DE MELO, J. V. S., TRICHÊS, G., GLEIZE, P. J. P. & VILLENA, J. 2012. Development and evaluation of the efficiency of photocatalytic pavement blocks in the laboratory and after one year in the field. Construction and Building Materials, 37, 310-319. FAN, W., CHAN, K. Y., ZHANG, C. & LEUNG, M. K. H. 2017. Advanced Solar Photocatalytic Asphalt for Removal of Vehicular NOx. Energy Procedia, 143, 811-816. FAN, W., CHAN, K. Y., ZHANG, C., ZHANG, K., NING, Z. & LEUNG, M. K. H. 2018. Solar photocatalytic asphalt for removal of vehicular NOx: A feasibility study. Applied Energy, 225, 535-541. GUO, M.-Z., LING, T.-C. & POON, C. S. 2017. Photocatalytic NOx degradation of concrete surface layers intermixed and spray-coated with nano-TiO2: Influence of experimental factors. Cement and Concrete Composites, 83, 279-289. HAO, C., XIE, X., HUANG, Y. & HUANG, Z. 2019. Study on influence of viaduct and noise barriers on the particulate matter dispersion in street canyons by CFD modeling. Atmospheric Pollution Research, 10, 1723-1735. OSBORN, D., HASSAN, M., ASADI, S. & WHITE, J. R. 2014. Durability Quantification of TiO2 Surface Coating on Concrete and Asphalt Pavements. Journal of Materials in Civil Engineering, 26, 331-337. SHEN, S., BURTON, M., JOBSON, B. & HASELBACH, L. 2012. Pervious concrete with titanium dioxide as a photocatalyst compound for a greener urban road environment. Construction and Building Materials, 35, 874-883. TORO, C., JOBSON, B. T., HASELBACH, L., SHEN, S. & CHUNG, S. H. 2016. Photoactive roadways: Determination of CO, NO and VOC uptake coefficients and photolabile side product yields on TiO2 treated asphalt and concrete. Atmospheric Environment, 139, 37-45. XIE, X., HAO, C., HUANG, Y. & HUANG, Z. 2020. Influence of TiO2-based photocatalytic coating road on traffic-related NOx pollutants in urban street canyon by CFD modeling. Science of The Total Environment, 724, 138059.

<h2 class="heading">How to apply</h2>

Formal applications for research degree study in the Institute for Transport Studies should be made online through the <a href="http://www.leeds.ac.uk/rsa/prospective_students/apply/I_want_to_apply.html">University's website</a>. Please state clearly in the research information section that the research degree you wish to be considered for is Protocatalytic concrete for reducing traffic NOx on urban roads as well as Dr Yue Huang as your proposed supervisor. If English is not your first language, you must provide evidence that you meet the University's minimum English language requirements (below). As an international research-intensive university, we welcome students from all walks of life and from across the world. We foster an inclusive environment where all can flourish and prosper, and we are proud of our strong commitment to student education. Across all Faculties we are dedicated to diversifying our community and we welcome the unique contributions that individuals can bring, and particularly encourage applications from, but not limited to Black, Asian, people who belong to a minority ethnic community, people who identify as LGBT+ and people with disabilities. Applicants will always be selected based on merit and ability.

<h2 class="heading heading--sm">Entry requirements</h2>

Applicants to research degree programmes should normally have at least a first class or an upper second class British Bachelors Honours degree (or equivalent) in an appropriate discipline. The criteria for entry for some research degrees may be higher, for example, several faculties, also require a Masters degree. Applicants are advised to check with the relevant School prior to making an application. Applicants who are uncertain about the requirements for a particular research degree are advised to contact the School or Graduate School prior to making an application.

<h2 class="heading heading--sm">English language requirements</h2>

The minimum English language entry requirement for research postgraduate research study is an IELTS of 6.0 overall with at least 5.5 in each component (reading, writing, listening and speaking) or equivalent. The test must be dated within two years of the start date of the course in order to be valid. Some schools and faculties have a higher requirement.

<h2 class="heading">Contact details</h2>

For informal enquiry, please contact Dr Yue Huang, e: <a href="mailto:y.huang1@leeds.ac.uk">y.huang1@leeds.ac.uk</a> For further information please contact the Graduate School Office e: <a href="mailto:ENV_PGR@leeds.ac.uk">ENV_PGR@leeds.ac.uk</a>,