Application of Photocatalytic Concrete Paving Blocks in Poland—Verification of Effectiveness of Nitric Oxides Reduction and No

materials

Article Application of Photocatalytic Concrete Paving Blocks in Poland—Veriﬁcation of Eﬀectiveness of Nitric Oxides Reduction and Novel Test Method

Hubert Witkowski 1,2,*, Janusz Jarosławski 3 and Anna Tryfon-Bojarska 4,5

1 Department of Building Physics and Building Materials, Łód´zUniversity of Technology, Al. Politechniki 6, 90–924 Łód´z,Poland 2 Consulting for Construction Hubert Witkowski, 92-511 Łód´z,Poland 3 Institute of Geophysics, Polish Academy of Sciences, Ksi˛eciaJanusza st. 64, 01–452 Warszawa, Poland; [email protected] 4 Innovation Management Unit, SGH Warsaw School of Economics, Al. Niepodległo´sci162, 02–554 Warszawa, Poland; [email protected] 5 Skanska Property Poland sp. z o.o., Al. Solidarno´sci173, 00–877 Warszawa, Poland * Correspondence: [email protected]

Received: 12 October 2020; Accepted: 5 November 2020; Published: 17 November 2020

Abstract: Photocatalytic concrete is one of the most promising concrete technologies of the past decades. Application of nanometric TiO2 to cement matrices enables the reduction of harmful airborne pollutants. Although a number of implementations of this technology are described in this paper, problems related to test conditions are also reported. One major issue is the sufficient light irradiation that for higher latitudes can be significantly reduced. In this paper, a field campaign on the implementation of photocatalytic concrete pavement in Warsaw (52.23◦ N) is briefly described. Based on experience from the field campaign, a novel test method is developed. In the research, the effectiveness of nitric oxide reduction is verified at natural light irradiation for various dates of solar position at noon in central Poland (51.83◦ N). The results confirm the benefits of using photocatalytic materials at higher latitudinal locations. The experimental setup presented in the study combines the advantages of controlled measurement conditions typical in laboratory tests with the possibility of including natural sunlight conditions in the investigation process.

Keywords: photocatalytic concrete; NOx reduction; solar UV irradiance

1. Introduction According to the European Environmental Agency’s 2018 report on air quality in Europe [1], the air pollutants most hazardous to human health are PM’s (particulate matter), NO2, and ground-level O3. The estimated impact on the population of European countries from exposure to NO2 concentration in 2015 alone was approximately 79,000 premature deaths. Consequently, the problem of air quality has become one of major importance. In urban areas, one of the dominant sources of airborne pollution is traﬃc. Hence, air quality has been analyzed using direct measurements [2–4], as well as numerical simulations [5–7]. Analysis of air pollution in Europe described by Koolen and Rothenberg [8] indicated that among a variety of airborne pollutions, reduction of NOx (a sum of NO and NO2) emissions is the most urgent needed response and potentially the most beneﬁcial. The application of photocatalytic materials based on the cement matrix enables the reduction of nitric oxide concentration in the presence of UV light during the process of photocatalysis. Therefore, the number of implementations of this promising technology have increased in the last decade. The wide range of applications includes using vertical

Materials 2020, 13, 5183; doi:10.3390/ma13225183 www.mdpi.com/journal/materials Materials 2020, 13, 5183 2 of 13 elements such as façade panels and coatings as well as horizontal elements such as concrete pavements. Photocatalytic properties in concrete are provided by the addition of a nanometric catalyst to the cement matrix. One widely known and used photocatalyst is nanometric titanium dioxide (TiO2). The main advantages of TiO2 are: high chemical stability, nontoxicity, and high oxidizing power. TiO2 exists in three diﬀerent forms: anatase, brookite, and rutile. Anatase exhibits the highest overall photocatalytic activity [9]. In the late 1960s, Fujishima and Honda [10] described the mechanism of the photocatalytic reaction of TiO2. In the process of photocatalysis, certain atmospheric pollutants can be degraded—such as nitric oxides, volatile organic compounds (VOCs), and non-volatile organic residues—due to charge transfer (redox) on the catalyst surface [11]. The simpliﬁed mechanism of nitrogen oxide reduction can be described as follows:

hV, TiO NO + OH 2 NO + H+ (1) → 2

hV, TiO2 + NO + OH NO− + H (2) 2 → 3 The NO3 formed on the photocatalytic concrete surface reacts with the calcium in the cement matrix to form a water-soluble calcium nitrate. Next, the salt is removed with rainwater [12]. The effectiveness of photocatalytic concrete technology has recently been the subject of a number of laboratory and field studies. The most significant factors affecting NOx degradation are irradiance, relative humidity, pollutant concentration, and flow rate over the photocatalytic surface. In laboratory tests, the impact of various factors has been studied, such as the type and amount of TiO2 added to concrete [13], UV radiation wavelength range [14], concrete surfaces [15], humidity [16], temperature [17], and the carbonation process of concrete [18]. Test methods have been described in standards such as: ISO 22197–1 [19], UNI 11247 [20], JIS R 1701–1 [21]. The test setup described in standards is designed to provide a laminar flow of the gas along the surface of sample; therefore, the space between sample’s surface and the glass covering is very narrow (about 3 mm). This system provides the ideal conditions to measure the reduction of NOx concentration during constant gas flow. However, the real conditions are more complex, which has been confirmed in field studies. A number of projects on the application of photocatalytic materials have been conducted recently across Europe, the United States, and China. Although general observations of field campaigns are in accordance with the findings of laboratory studies, the measured values of pollutant reduction substantially vary in particular cases. The influence of dirt deposits on photocatalytic road pavement in Bergamo resulted in a reduction of approximately 16% photoactivity a few weeks after the completion of the installation of photocatalytic concrete pavement [22]. After one year of service of 10,000 m2 photocatalytic pavement blocks on the parking lanes in Antwerp, a 20% reduction in purification efficiency was measured [17]. The application of photocatalytic cement-based paint on walls and ceilings in the “Umberto I” tunnel in Rome resulted in a NOx reduction of over 20%, measured in two monitoring campaigns [23]. George et al. [24] and Boonen et al. [25] have described no significant pollutant reduction during the field campaign at the Leopold II tunnel in Brussels. In most cases, in-situ tests have proven the effectiveness of photocatalytic technology in NOx reduction. However, the results indicated that the ability to reduce pollutants with the use of photocatalytic concrete is highly vulnerable to various external factors such as wind speed, dirt and humidity that occur at the particular moment of testing. Therefore, to achieve reliable data, a long-term campaign is needed. The first commercial large-scale application of photocatalytic concrete for an office building in the center of Warsaw Generation Park was preceded by research carried out by the Skanska Property Poland and the Góra˙zd˙zeCement consortium, together with scientific partners: the Institute of Geophysics of Polish Academy of Sciences, the Warsaw University of Technology, and the Geology Department of the University of Warsaw. Although the effectiveness of NOx reduction on the applied concrete blocks was proven in laboratory tests according to standard UNI 11247 [20], the effectiveness of the location of the pavement application had to be verified. The first concern was related to the Materials 2020, 13, 5183 3 of 13

Materials 2020, 13, x FOR PEER REVIEW 3 of 13 availability of suﬃcient solar irradiance to trigger photocatalytic reactions at the latitude of 52.23◦ N.

Thewas nextconditioned concern by was the related result of to the land field relief tests; around a minimum the measurement 15% of NO point—thex abatement roundabout was an assumed is an openrequirement crossing for of further two city implementation traffic arteries vulnerable of the new totechnology. wind impact. For Thethe field target campaign, large-scale about application 350 m2 wasof public conditioned sidewalk by next the to result the Daszynskiego of the field tests; rounda a minimumbout and 15% next of to NO thex abatementoffice building was was an assumed chosen. 2 requirementIn the period for from further the end implementation of June 2018 ofto themid- newSeptember technology. 2018, For several the field daily campaign, tests were about conducted. 350 m ofAir public quality sidewalk was measured next to theabove Daszynskiego both the regular roundabout and the and photocatalytic next to the o ffipavement.ce building Some was selected chosen. Inresults the period of this fromfield thecampaign end of are June presented 2018 to mid-September in this paper. 2018, several daily tests were conducted. Air qualityFolli and was Macphee measured [26] above described both thea simple regular model and to the obtain photocatalytic UV contributions pavement. to solar Some radiation selected resultsas a function of this of field geography campaign and are se presentedason. The inobtained this paper. results indicated that proper UV contribution is achievedFolli throughout and Macphee the [26 whole] described year only a simple at latitu modeldes tobelow obtain 35°. UV The contributions other factor to described solar radiation in the asmodel a function was the of geographylength of a and day. season. Folli and The Macphe obtainede results[26] discussed indicated an that exam properple of UV photocatalytic contribution ispavement achieved application throughout in the Copenhagen whole year at only a latitude at latitudes of 55.68° below N. 35 A◦. significant The other NO factor reduction described was in theachieved model for was a total the lengthUV daily of adose day. exceeding Folli and 600 Macphee kJ/m2 day [26]−1 discussed. an example of photocatalytic pavementExperience application from inthe Copenhagen field campaign at a latitude in the Gene of 55.68ration◦ N. Park A significant project and NO reductionthe aspects was mentioned achieved 2 1 forabove a total were UV the daily motivation dose exceeding to undertake 600 kJ/ mresearchday− .on a novel test method that would reduce the influenceExperience of various from external the field campaignfactors (such in the as Generation wind or variable Park project pollutant and the concentration) aspects mentioned and would above werereflect the a natural motivation UV irradiance to undertake occurring research in on the a novelconsidered test method location. that In would the paper, reduce a novel the influence method of variouseffective external air purification factors (such and as results wind orof variable NOx reduction pollutant measured concentration) at an and autumnal would reflect period a naturalat Central UV irradianceGeophysical occurring Observatory in the consideredof Institute location. of Geophysi In thecs paper, Polish a novel Academy method of ofSciences effective (Belsk, air purification Poland, and51.83° results N; 20.78° of NO E)x reduction are presented. measured The at results an autumnal obtained period were at compared Central Geophysical with the laboratory Observatory test of Institutemethod described of Geophysics in UNI Polish 11247 Academy [20]. of Sciences (Belsk, Poland, 51.83◦ N; 20.78◦ E) are presented. The resultsProperties obtained of applied were comparedphotocatalyt withic cement the laboratory were examined test method with described a scanning in UNIelectron 11247 microscope [20]. (SEM)Properties using SEM of applied elemental photocatalytic mapping. cementThe main were objective examined of with this a scanningresearch electronwas to microscopeverify the (SEM)distribution using SEMof nanoparticles elemental mapping. in cement. The main objective of this research was to verify the distribution of nanoparticles in cement. 2. Materials 2. Materials In the described research on the novel test method and field campaign, the same samples of In the described research on the novel test method and field campaign, the same samples of photocatalytic concrete paving blocks were investigated. The dimensions of the paving blocks were photocatalytic concrete paving blocks were investigated. The dimensions of the paving blocks were 500 mm × 500 mm × 70 mm. Photocatalytic concrete was applied only in the 5 mm of the top layer 500 mm 500 mm 70 mm. Photocatalytic concrete was applied only in the 5 mm of the top layer and and made× from CEM× II/A–S 42.5R with nano TiO2 (Heidelberg Cement TX Active). The pavement made from CEM II/A–S 42.5R with nano TiO (Heidelberg Cement TX Active). The pavement blocks were blocks were produced in accordance with 2standard EN 1339:2003 [27]. In the tests, samples were cut produced in accordance with standard EN 1339:2003 [27]. In the tests, samples were cut to dimensions of to dimensions of 180 mm × 150 mm × 70 mm to fit into measuring chamber dimensions, as shown in 180 mm 150 mm 70 mm to fit into measuring chamber dimensions, as shown in Figure1. Figure 1.× ×

Figure 1. PhotocatalyticPhotocatalytic concrete paving block studied in the research with a novel test method.

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In concrete paving blocks, the dominant constituent is an aggregate, and as emphasized by Petrounias et al. [28], aggregate has a major impact on a concrete’s properties. However, the goal of the research was to investigate the concrete pavement’s photocatalytic properties. Accordingly, photocatalytic cement was tested. As the content of the photocatalyst is a key factor affecting the effectiveness of photocatalysis, the distribution of TiO2 was verified. According to the manufacturer’s ® data in CEM II/A–S 42.5R, TX Active cement up to 5% of TiO2 P–25 of Degussa was added. To examine Materials 2020,, 13,, xx FORFOR PEERPEER REVIEWREVIEW 4 of 13 the distribution and size of nanoparticles, SEM analysis was applied. A pure sample of cement was effectiveness of photocatalysis, the distribution of TiO2 was verified. According to the manufacturer’s investigated.effectiveness The Sigma of photocatalys VP (Zeiss)is, equipped the distribution with of two TiO2 EDS was verified. XFlash According 6/10 (Bruker, to the Oberkochen,manufacturer’s Germany) data in CEM II/A–S 42.5R, TX Active cement up to 5% of TiO2 P–25® of Degussa was added. To detectors wasdata in applied CEM II/A–S in SEM 42.5R, analysis. TX Active Tocement determine up to 5% the of TiO chemical2 P–25® composition,of Degussa was aadded. 120 µTom aperture examine the distribution and size of nanoparticles, SEM analysis was applied. A pure sample of was used, and for high resolution imaging, a 30 µm was used. To ensure the discharge of the electric cement was investigated. The Sigma VP (Zeiss) equipped with two EDS XFlash 6/10 (Bruker, surface’s charges,Oberkochen, the Germany) sample wasdetectors sprayed was withapplied carbon in SEM and analysis. secured To withdetermine a special the chemical strip of electrical composition, a 120 µm aperture was used, and for high resolution imaging, a 30 µm was used. To charge. Thecomposition, results of a 120 SEM µm analysis aperture was (Figures used, 2and and for3 high) indicated resolution the imaging, grains a 30 of µm nanometric was used. To TiO 2 have ensure the discharge of the electric surface’s charges, the sample was sprayed with carbon and sizes of 20–50 nm and form agglomerates on the cement grains. Distribution of TiO2 in cement secured with a special strip of electrical charge. The results of SEM analysis (Figures 2 and 3) indicated is homogeneous.the grains of nanometric TiO2 have sizes of 20–50 nm and form agglomerates on the cement grains. the grains of nanometric TiO2 have sizes of 20–50 nm and form agglomerates on the cement grains. Distribution of TiO2 in cement is homogeneous. Distribution of TiO2 in cement is homogeneous.

Figure 2. SEM image of the cement sample with TiO2 distribution on the cement grain (Everhart– Figure 2. FigureSEM 2. SEM image image of of the cement cement sample sample with TiO with2 distribution TiO2 distributionon the cement grain on the(Everhart– cement grain (Everhart–ThornleyThornley type type detector detector at ETH at = ETH2.0 kV).= 2.0 kV).

(a) (b) Figure 3. SEM image of the sample surface (a) morphology and (b) EDS maps of titanium in the Figure 3. FigureSEM image3. SEM image of the of samplethe sample surface surface (a(a)) morphologymorphology and and (b) EDS (b) maps EDS of maps titanium of titaniumin the in the investigated region. investigated region.

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TheMaterials effi 2020ciency, 13, x of FOR photocatalytic PEER REVIEW paving blocks in air purification was investigated during5 of the 13 field campaign, in situ and with a novel test method. For compatibility of the obtained results, samples were The efficiency of photocatalytic paving blocks in air purification was investigated during the tested according to UNI 11247 [20]. In this reference test, dimension of the sample was in accordance field campaign, in situ and with a novel test method. For compatibility of the obtained results, with the standard requirements: 80 mm 80 mm 10 mm. samples were tested according to UNI 11247× [20]. ×In this reference test, dimension of the sample was in accordance with the standard requirements: 80 mm × 80 mm × 10 mm. 3. GenerationMaterials 2020 Park—Field, 13, x FOR PEER Campaign REVIEW 5 of 13 3. Generation Park—Field Campaign In the fieldThe campaignefficiency of (Figurephotocatalytic4), concentrations paving blocks ofin NO,air purification NO 2, and was NO investigatedx were measured during the at the regular sidewalkfieldIn with thecampaign, typicalfield campaign in concrete situ and (Figure pavingwith a 4),novel blocks concentrations test andmethod. at the Forof NO, photocatalyticcompatibility NO2, and of NO the pavingx obtainedwereblocks, measured results,both at 400the mm aboveregular thesamples pavement sidewalk were tested with surface, according typical where concrete to UNI the 11247 paving reaction [20]. blocIn this ofks referencephotocatalysisand at the test, photocatalytic dimension occurs. of the paving The sample distance blocks, was both between in accordance with the standard requirements: 80 mm × 80 mm × 10 mm. collecting400 mm points above was the ca. pavement 10 m. In thesurface, research, where the the two reac APItion Model of photocatalysis 200A NOx analyzersoccurs. The (Teledyne distance API, between collecting points was ca. 10 m. In the research, the two API Model 200A NOx analyzers San Diego,3. Generation CA, USA) Park—Field were used Campaign to determine the NO, NO2, and NOx concentrations. From continuous (Teledyne API, San Diego, CA, USA) were used to determine the NO, NO2, and NOx concentrations. measurements, 1 min and 1 h means were calculated for further analysis. From continuousIn the field measurements, campaign (Figure 1 min4), concentrations and 1 h means of NO,were NO calculated2, and NO forx were further measured analysis. at the regular sidewalk with typical concrete paving blocks and at the photocatalytic paving blocks, both 400 mm above the pavement surface, where the reaction of photocatalysis occurs. The distance between collecting points was ca. 10 m. In the research, the two API Model 200A NOx analyzers (Teledyne API, San Diego, CA, USA) were used to determine the NO, NO2, and NOx concentrations. From continuous measurements, 1 min and 1 h means were calculated for further analysis.

FigureFigure 4. Measuring4. Measuring station station atat thethe Daszynskiego roundabout roundabout in Warsaw. in Warsaw.

Among several daily tests during the field campaign, a number of days with unfavorable Among several daily tests during the field campaign, a number of days with unfavorable measurement conditionsFigure 4. occurred.Measuring station The majorat the Daszynskiego factors affecting roundabout the in resultsWarsaw. were wind and traffic measurement conditions occurred. The major factors affecting the results were wind and traffic intensity, which, during the summer period, were reduced, resulting in relatively low NOx levels. To Among several daily tests during the field campaign, a number of days with unfavorable intensity, which, during the summer period, were reduced, resulting in relatively low NOx levels. achievemeasurement representative conditions results, occurred. the Thedaily major traffic factors volume affecting from the previous results wereyears wind at theand Daszynskiego traffic To achieve representative results, the daily traffic volume from previous years at the Daszynskiego roundaboutintensity, which,was analyzed. during the Data summer were period, provided were byreduced, the Administration resulting in relatively of City low Roads NOx levels. in Warsaw. To An roundaboutaverageachieve daily was representative analyzed.traffic volume results, Data (Figure the were daily 5) was provided traffic assumed volume by as thefrom a representative Administration previous years level, at the of and CityDaszynskiego only Roads results in of Warsaw.the An averagecampaignroundaboutdaily withtra was comparativeffi analyzed.c volume Data traffi (Figure werec were provided5) assumed was assumedby the in Administrationthe asproject. a representative of City Roads level, in Warsaw. and onlyAn results of the campaignaverage with daily comparativetraffic volume (Figure traffi c5) were was assumed assumed as a inrepresentative the project. level, and only results of the campaign with comparative traffic were assumed in the project.

FigureFigure 5. 5.Traffic Traffic volumevolume from previousprevious years years measur measured edin thein vicinitythe vicinity of the of Daszynskiego the Daszynskiego Figure 5. Traﬃc volume from previous years measured in the vicinity of the Daszynskiego roundabout. roundabout.roundabout.

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4. Results of Field Campaign Materials 2020, 13, x FOR PEER REVIEW 6 of 13 MaterialsConsidering2020, 13, 5183 the issues described above, the results of the measurements from 12 September,6 of 13 2018 with the most representative conditions were chosen. In the tests at the Daszynskiego 4. Results of Field Campaign roundabout, concentrations of NO, NO2, and NOx in the air were measured from two collecting 4.points: ResultsConsidering above of Field the regular Campaignthe issues pavement described and above,above thethe photocatalytic results of the pavement.measurements Measurement from 12 September, results for NO,2018Considering NO with2, and the NO themostx are issues representativeshown described in Figures above, conditions 6–8. the results were of chosen. the measurements In the tests from at 12the September, Daszynskiego 2018 withroundabout, the most representativeconcentrations conditionsof NO, NO were2, and chosen. NOx in In the the air tests were at the measured Daszynskiego from two roundabout, collecting points: above the regular pavement and above the photocatalytic pavement. Measurement results for concentrations of NO, NO2, and NOx in the air were measured from two collecting points: above theNO, regular NO2, and pavement NOx are andshown above in Figures the photocatalytic 6–8. pavement. Measurement results for NO, NO2, and NOx are shown in Figures6–8.

Figure 6. Average concentration of NO on 12 September, 2018 from 10 a.m. to 6 p.m. at the regular pavement (blue) and photocatalytic pavement (red). Figure 6. Average concentration of NO on 12 September, 2018 from 10 a.m. to 6 p.m. at the regular pavementFigure 6. (blue)Average and concentration photocatalytic of pavement NO on 12 (red). September, 2018 from 10 a.m. to 6 p.m. at the regular pavement (blue) and photocatalytic pavement (red).

Figure 7. Average concentration of NO2 on 12 September, 2018 from 10 a.m. to 6 p.m. at the regular Figure 7. Average concentration of NO2 on 12 September, 2018 from 10 a.m. to 6 p.m. at the regular pavement (blue) and photocatalytic pavement (red). pavement (blue) and photocatalytic pavement (red).

Figure 7. Average concentration of NO2 on 12 September, 2018 from 10 a.m. to 6 p.m. at the regular pavement (blue) and photocatalytic pavement (red).

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Figure 8. Average concentration of NOx on 12 September 2018 from 10 a.m. to 6 p.m. at the regular pavement (blue) and photocatalytic pavement (red). Figure 8. Average concentration of NOx on 12 September 2018 from 10 a.m. to 6 p.m. at the regular Thepavement obtained (blue) results and photocatalytic indicated that pavement lower values (red). of nitrogen oxide concentration were collected from the photocatalytic pavement than from the normal sidewalk. The diﬀerence during the measure The obtained results indicated that lower values of nitrogen oxide concentration were collected period was varied. The average daily values are shown in Table1. The calculated average daily from the photocatalytic pavement than from the normal sidewalk. The difference during the measure reduction of nitric oxides was calculated as abatement A according to Equation (3): period was varied. The average daily values are shown in Table 1. The calculated average daily

reduction of nitric oxides was calculated as abatementCn Cp A according to Equation (3): A = − (3) 𝐶Cn−𝐶 𝐴 = (3) 𝐶 where A is nitric oxide abatement, Cn is the average daily nitric oxide concentration at the normal pavement,where 𝐴 is and nitricCp—average oxide abatement, daily nitric 𝐶 oxideis the concentrationaverage daily at nitric thephotocatalytic oxide concentration pavement. at the normal pavement, and 𝐶—average daily nitric oxide concentration at the photocatalytic pavement. Table 1. Average values of nitric oxide concentrations measured from 10 a.m. to 6 p.m. at regular and photocatalyticTable 1. Average pavement values at of the nitric Daszynskiego oxide concentrations roundabout. measured from 10 a.m. to 6 p.m. at regular and photocatalytic pavement at the Daszynskiego roundabout. Photocatalytic Parameter Regular Pavement Regular Pavement Photocatalytic Parameter Nitric oxides NO NO2 NOPavementx NO NO2 NOPavementx Average daily Nitric oxides 32.3 33.0 NO 65.2 NO2 20.8 NOx 24.4NO 45.2 NO2 NOx concentration (ppb) Average daily concentration (ppb) 32.3 33.0 65.2 20.8 24.4 45.2 Standard deviation 9.7 5.2 13.5 7.9 4.5 12.0 StandardAverage deviation daily 9.7 5.2 13.5 7.9 4.5 12.0 Average dailyreduction reduction of nitricof nitric oxides- (%) - - - - 36% - 26% 36% 31% 26% 31% oxides (%) The values of nitric oxides reduction by photocatalytic concrete pavement were higher than the assumedThe values threshold of nitric for oxidestarget large-scale reduction byapplication. photocatalytic concrete pavement were higher than the assumed threshold for target large-scale application. 5. Removal of Nitric Oxides by Photocatalytic Materials—Novel Test Method 5. Removal of Nitric Oxides by Photocatalytic Materials—Novel Test Method According to the findings of the field campaign from the Daszynskiego roundabout and describedAccording by toBoonen the findings et al. [25], of the the field pollutant campaign gas from flow the is Daszynskiego significantly roundaboutdifferent from and the described laminar byconditions Boonen et described al. [25], the in pollutantstandards gassuch flow as: isIS significantlyO 22197–1 [19], diff erentUNI from11247 the [20], laminar JIS R conditions1701–1 [21]. describedTherefore, in standardsto provide such conditions as: ISO 22197–1 more supportiv [19], UNI 11247e of natural [20], JIS Rgas 1701–1 flow, [ 21a ].testTherefore, setup described to provide by conditions more supportive of natural gas flow, a test setup described by Witkowski et al. [29] was applied as a base setup in this study. A general scheme of the method is presented in Figure9.

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MaterialsWitkowski2020, 13et, 5183al. [29] was applied as a base setup in this study. A general scheme of the method8 of 13is presented in Figure 9.

Figure 9. Test setup for laboratory conditions according to Witkowski et al. [29]. Figure 9. Test setup for laboratory conditions according to Witkowski et al. [29]. Although such a test system simulates gas flow reflecting in-situ conditions, artificial light sources provideAlthough only selected such spectraa test ofsystem UV light simulates with limited gas flow UV irradiance. reflectingAs in-situ described conditions, by Pierpaoli artificialet al. light [14], thesources results provide of different only lightselected sources spectra characterized of UV light by with various limited spectrum UV irradiance. peaks between As described470–370 nm by werePierpaoli different et al. in [14], terms the of results abatement of different indexes relatedlight sources to spectra characterized light range. byTherefore, various spectrum to verify the peaks air purificationbetween 470–370 effectiveness nm were of adifferent studied photocatalyticin terms of ab concreteatement sample,indexes the related described to spectra setup light was placedrange. outdoorsTherefore, and to exposedverify the to air natural purification solar light, effectiven as showness inof Figurea studied 10. photocatalytic During the study, concretea typical sample,autumn the (20described September setup 2019) was UV placed irradiance outdoors level forand clear-sky exposed conditions to natural for solar a latitude light, of as 51.83 shown◦ Nand in Figure longitude 10. ofDuring 20.78◦ theE occurred study, a for typical over 4autumn h of the (20 sample’s September exposure 2019) to UV the irradiance natural light level until for sunset. clear-sky Before conditions the test, anfor empty a latitude glass of reactor 51.83° was N and filled longitude with a gas of 20.78° up to100 E occurred ppb to verify for over maximum 4 hours gas of the concentration sample’s exposure and the tightnessto the natural of the light system. until Next, sunset. a studied Before sample the test, was an placedempty inglass the reactor glass reactor was fill anded coveredwith a gas to blockup to the100 sunlight.ppb to verify The reactormaximum was gas filled concentration again with gas. and Asthe the tightness concentration of the system. of the gas Next, reached a studied a maximum, sample thewas setup placed was in exposed the glass to reactor the sunlight. and covered to block the sunlight. The reactor was filled again with gas. AAs mixture the concentration of synthetic of the air gas (consisting reached a of maximum, 20% oxygen the andsetup 80% was nitrogen)exposed to and the NOsunlight. gas in a concentrationA mixture of of 100 synthetic ppb was air used (consisting during the of study.20% oxygen The gas and flow 80% rate nitrogen) was 4 L/ min.and NO In the gas study, in a NO,concentration NO2, and NOof 100x were ppb measured was used with during the API the Modelstudy. 200A The NOgas xflowanalyzer. rate was NOx 4levels L/min. were In measuredthe study, withNO, anNO accuracy2, and NO of aboutx were 5%.measured with the API Model 200A NOx analyzer. NOx levels were ± measuredThe measurement with an accuracy system of directly about ±5%. reflects UV-A and visible solar irradiance for natural conditions at a givenThe measurement geographical latitude.system directly However, reflects according UV-A to and the resultsvisible ofsolar measured irradiance spectra for ofnatural light sourcesconditions described at a given by Witkowskigeographical et al.latitude. [29], an However, applied glassaccording desiccator to the reducesresults of UVB measured radiation spectra levels, of whilelight sources UVA radiation, described after by Witkowski passing through et al. [29], the an glass, applied is not glass significantly desiccator changed. reduces UVB Furthermore, radiation thelevels, system whileexcludes UVA variable radiation, wind after effects passing and insu throughfficient pollutantthe glass, gas is concentrations not significantly that canchanged. occur inFurthermore, environmental the conditions. system excludes To verify variable the eff windectiveness effects of and the consideredinsufficient application,pollutant gas a limitedconcentrations surface ofthat the can considered occur in environmental photocatalytic materialconditions. is needed. To verify the effectiveness of the considered application, a limited surface of the considered photocatalytic material is needed.

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Figure 10. A novel test setup with a natural UV light source. Figure 10. A novel test setup with a natural UV light source. Figure 10. A novel test setup with a natural UV light source. Additionally, photocatalytic concrete’s ability to reduce NOx levels was measured with a test Additionally,method described photocatalytic by Witkowski concrete’s et al. [29] ability with an to artificial reduce light NO source.x levels Artificial was measuredUV light was with a test methodAdditionally, describedprovided with by photocatalytic an Witkowski OSRAM Vitalux etconcrete’s al. 300W [29 ]with withability nomi an nalto artificial reduce13.6 W UV-A NO lightx (315–4levels source.00 was nm) Artificialandmeasured 3.0 W UV-B UV with light a test was providedmethod with(280–315described an nm). OSRAM by Two Witkowski samples Vitalux collected 300Wet al. [29]from with withthe nominal same an concreteartificial 13.6 Wpavement light UV-A source. element (315–400 Artificial were nm) tested. andUV The 3.0light W was UV-B (280–315provided nm).time with of Two exposure an samplesOSRAM to artificial collectedVitalux UV 300Wlight from was with the 32–34 same nomi min. concretenal 13.6 W pavement UV-A (315–4 element00 nm) were and tested. 3.0 W The UV-B time (280–315 nm).As theTwo reference samples test, collected the air-purification from the perfor samemance concrete of the sample pavement was measured element according were tested. to The of exposurestandard to artificial UNI 11247 UV [20] light in the was Italcementi 32–34 min. laboratory in Bergamo. timeAs of the exposure reference to artificial test, the UV air-purification light was 32–34 performance min. of the sample was measured according to standardAs UNI 6.the Results reference 11247 of [the20 test, ]Novel in the Test air-purification Italcementi Method laboratory performance in Bergamo. of the sample was measured according to standard UNI 11247 [20] in the Italcementi laboratory in Bergamo. In the study of NOx abatement with the novel test method, global solar irradiance was measured 6. Resultsduring of the the Novel test. The Test measurement Method results are shown in Figure 11. Low values of UV irradiance in the 6. Resultsfirst of minutes the Novel of the Test test Methodresulted from an occurrence of thick clouds that reduced UV irradiance. In theVariability study of of NO NOxx abatementabatement and with natural the UV novel irradiance test method, changes globalwere in solargood accordance, irradiance with was a measured In the study of NOx abatement with the novel test method, global solar irradiance was measured during thedrop test. in Theradiance measurement of natural UV results light abatement are shown resulting in Figure in NO 11x decreasing.. Low values After ofsunset, UV irradiancethe in during the test. The measurement results are shown in Figure 11. Low values of UV irradiance in the the first minutesabatement of of the NO testx pollutant resulted was nearly from zero, an occurrence and the difference of thick in gas clouds concentration that reducedwas the result UV of irradiance. first minutesachieving of anthe equilibrium test resulted of gas from concentration an occurre in thence measuring of thick system. clouds that reduced UV irradiance. Variability of NOx abatement and natural UV irradiance changes were in good accordance, with a drop Variability of NOx abatement and natural UV irradiance changes were in good accordance, with a in radiance of natural UV light abatement resulting in NOx decreasing. After sunset, the abatement of drop in radiance of natural UV light abatement resulting in NOx decreasing. After sunset, the NOx pollutant was nearly zero, and the difference in gas concentration was the result of achieving an abatement of NOx pollutant was nearly zero, and the difference in gas concentration was the result of equilibriumachieving an of gasequilibrium concentration of gas inconcentration the measuring in the system. measuring system.

Figure 11. NO, NO2, and NOx abatement with natural UV irradiance measured with the novel test method.

Figure 11. NO, NO2, and NOx abatement with natural UV irradiance measured with the novel test Figure 11. NO, NO2, and NOx abatement with natural UV irradiance measured with the novel testmethod. method.

Materials 2020, 13, 5183 10 of 13

The obtained results of NO concentration reduction were calculated as an NO abatement A Materials 2020, 13, x FOR PEER REVIEW x 10 ofx 13 according to the Equation (4): Figure 11. NO, NO2, and NOx abatement with naturalC BUV irradianceCL measured with the novel test A = − (4) method. CB The obtained results of NOx concentration reduction were calculated as an NOx abatement A where A is NO abatement, C is NO reduced concentration in particular time unit, and C is NO according to thex Equation (4): L x B x concentration measured without UV irradiance (maximum entry value). 𝐶 𝐶 Next, the calculated solar zenith angle𝐴 characteristic to speciﬁc dates of the solar position(4) at noon 𝐶 with measured natural UV irradiance and NOx abatement is presented in Table2. where 𝐴 is NOx abatement, 𝐶 is NOx reduced concentration in particular time unit, and 𝐶 is NOx concentration measured without UV irradiance (maximum entry value). Table 2. NO abatement measured with a novel method at solar zenith angle characteristic to dates of Next, the calculatedx solar zenith angle characteristic to specific dates of the solar position at noon the solar position at noon for location with a latitude of 51.83 N. with measured natural UV irradiance and NOx abatement is presented◦ in Table 2. Natural UV Dates of Table 2. NOx abatement measuredSolar with Zenith a novel method at solar zenith angleNO characteristic to dates of Local Time Irradiance x Solar the solar position at noon for locationAngle with a latitude of 51.83° N. Abatement (hh:min:s) (290–400 nm) Position at ( ) (%) Solar ◦ (W/m2) Noon Local Natural UV Irradiance NOx Zenith Dates of Solar Time 15:09:05 60.63(290–400 nm) 10.89 Abatement 0 1 15 October Angle Position at Noon (hh:min:s) 15:25:30 62.55(W/m2) 18.12(%) 43.74 - 15:53:37(°) 66.09 14.12 47.54 31 October 15:09:05 16:10:0560.63 68.2910.89 12.6201 44.4815 October - 15:25:30 16:30:0862.55 71.0718.12 9.443.74 ‐ 45.07 18 November 15:53:37 16:57:4366.09 75.0514.12 6.7547.54 44.3531 15October December 16:10:05 17:04:3268.29 76.0512.62 5.9144.48 ‐ 42.92 - 16:30:08 17:19:1371.07 78.239.4 4.4545.07 43.9418 November 22 December 16:57:43 17:22:1175.05 78.686.75 4.1444.35 40.6615 December - 17:04:32 17:47:1876.05 82.465.91 2.3142.92 ‐ 32.96 - 17:19:13 18:07:1178.23 85.464.45 1.1843.94 24.0222 December - 17:22:11 18:44:3778.68 91.194.14 0.0940.66 ‐ 1.85 - 17:47:18 82.46 2.31 1 desiccators covered.32.96 ‐ 18:07:11 85.46 1.18 24.02 ‐ 18:44:37 91.19 0.09 1.85 ‐ 1 desiccators covered. The results are schematically presented in Figure 12. The results are schematically presented in Figure 12.

Figure 12. Results of NO abatement with the solar zenith angle characteristic to speciﬁc dates of the Figure 12. Results of NOx xabatement with the solar zenith angle characteristic to specific dates of the solarsolar position position at at noon. noon.

InIn the the study study with with the same same setup setup as asdescribed described by Witkowski by Witkowski et al. [29] et with al. [ 29an] artificial with an light artiﬁcial light source,source, the the obtained obtained resultsresults are are presented presented in Figure in Figure 13. The 13. achieved The achieved values of values NOx abatement of NOx abatement were were similarsimilar for for both both samples. samples.

Materials 2020, 13, 5183 11 of 13 Materials 2020, 13, x FOR PEER REVIEW 11 of 13

Figure 13. NO, NO2, and NOx abatement with artiﬁcial UV irradiance. Figure 13. NO, NO2, and NOx abatement with artificial UV irradiance. The result of abatement index measures according to standard UNI 11247 [20] is presented in Table3. The result of abatement index measures according to standard UNI 11247 [20] is presented in Table 3. Table 3. NOx abatement index according to Standard UNI 11247 [20].

NOx Abatement Index Table 3. NOx abatement index according to Standard UNI 11247 [20]. 28.2% NOx Abatement Index 28.2% 7. Conclusions

7. ConclusionsIn this paper, findings from the field campaign in Warsaw were presented. The results confirmed the effectiveness of photocatalytic concrete pavement in the reduction of nitric oxides. The calculated In this paper, findings from the field campaign in Warsaw were presented. The results confirmed average daily reduction of NO was 31%. the effectiveness of photocatalyticx concrete pavement in the reduction of nitric oxides. The calculated Problems that occurred during field measurements motivated the development of a novel test average daily reduction of NOx was 31%. method that was compared with the corresponding test setup with an artificial UV light source and Problems that occurred during field measurements motivated the development of a novel test measurement according to standard UNI 11247 [20]. The novel test method uses natural UV light method that was compared with the corresponding test setup with an artificial UV light source and irradiation in a laboratory test setup with a constant gas flow. The shape of the applied desiccators measurement according to standard UNI 11247 [20]. The novel test method uses natural UV light provides nonlinear gas flow that is typical in standardized test setups described in the standards [19–21]. irradiation in a laboratory test setup with a constant gas flow. The shape of the applied desiccators The research was conducted on 20 September at the Central Geophysical Observatory of Institute provides nonlinear gas flow that is typical in standardized test setups described in the standards [19– of Geophysics, Polish Academy of Sciences in Belsk (Poland) at a latitude of 51.83 N. In the study, 21]. The research was conducted on 20 September at the Central Geophysical Observatory◦ of Institute the abatement of the NO , NO, and NO concentrations as well as solar UV and global solar light of Geophysics, Polish Academy2 of Sciencesx in Belsk (Poland) at a latitude of 51.83° N. In the study, irradiation were measured. According to the described model of geographic location related to solar the abatement of the NO2, NO, and NOx concentrations as well as solar UV and global solar light radiation defined by Folli and Macphee [26], the best results for abatement efficiency are achieved for irradiation were measured. According to the described model of geographic location related to solar latitudes below 35 ; however, the obtained results with a novel test method indicated that even at low radiation defined◦ by Folli and Macphee [26], the best results for abatement efficiency are achieved for UV light irradiation, the values of measured abatement were above 40%. The calculated solar zenith latitudes below 35°; however, the obtained results with a novel test method indicated that even at angle characteristic to specific dates of the solar position at noon with measured natural UV irradiance low UV light irradiation, the values of measured abatement were above 40%. The calculated solar compared with the result of NO abatement demonstrated that, even for the winter solstice, values of zenith angle characteristic to specificx dates of the solar position at noon with measured natural UV abatement were significantly high (43.94%). irradiance compared with the result of NOx abatement demonstrated that, even for the winter The results of NO reduction by photocatalytic concrete observed in this study with a novel test solstice, values of abatementx were significantly high (43.94%). method applying natural UV light were lower than the results of an analogous test setup with an The results of NOx reduction by photocatalytic concrete observed in this study with a novel test artificial UV light source. The gas flow, the size of the specimens collected from the one paving block, method applying natural UV light were lower than the results of an analogous test setup with an and the glass desiccators were the same. The difference was the UV light source. However, the NO artificial UV light source. The gas flow, the size of the specimens collected from the one paving block,x reduction measured using this novel test method was similar to that obtained in the field campaign. and the glass desiccators were the same. The difference was the UV light source. However, the NOx reduction measured using this novel test method was similar to that obtained in the field campaign.

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Although the surface area of the studied samples in the study was significantly larger than the nominal surface area described in UNI 11247 [20] and the achieved results did not correlate, the proposed novel test method provides gas flow corresponding to natural conditions and applies natural light conditions with the entire spectra of UV wavelength range and light irradiation consistent to application conditions. The proposed test setup reduces negative wind effects and insufficient pollutant concentration. The described method combines the advantages of laboratory tests with field tests in specific sunlight conditions.

Author Contributions: Conceptualization, H.W.; methodology, H.W. and J.J.; validation, J.J.; formal analysis, J.J. and A.T.-B.; investigation, J.J. and H.W.; resources, A.T.-B. and H.W.; writing—original draft preparation, H.W.; writing—review and editing, J.J.; supervision, J.J.; funding acquisition, A.T.-B. All authors have read and agreed to the published version of the manuscript. Funding: The field campaign and related research received funding from Skanska and Gorazdze Cement; research on the novel method received support from Institute of Geophysics, Polish Academy of Sciences. Conflicts of Interest: The authors declare no conflict of interest.

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