The work described in this paper is part of a research program aimed at establishing the factors which give a good durability to pavement repairs made with metallic fiber reinforced concrete. The experimental study shows that fibers, as they do not significantly reduce the shrinkage of concrete, have a positive effect by enhancing (by 15%) its relaxation and creep capacity. On the other hand, one must not ignore the indirect effects of cracking which may be of major importance. A finite elements study demonstrates that, among these effects, the stresses induced by the passage of vehicules, very dependent on the cracking characteristics, give a significant advantage to the fiber reinforced overlays.

In order to find an alternative to the more heavily regulated titanium dioxide (TiO2 P25) and to reduce the concentration of nitrogen oxide (NOx) in indoor environments, gold nanoparticles-decorated ZnO composite materials (Au/ZnO, 1 wt% Au) were successfully prepared by photodeposition (PD) or urea depositionprecipitation (UDP) methods. The resulting Au/ZnO catalysts showed excellent photocatalytic performance (around 40 %) for the degradation of 400 ppb nitrogen dioxide (NO2) at a laboratory reactor scale under UV-A irradiation as low as 0.1 W/m2 at 50 % relative humidity. The high activity was attributed to the Au-ZnO heterojunction formation, which significantly promoted the transfer of photogenerated holes from ZnO to Au and the water oxidation process on Au nanoparticles, improving the NO2 photocatalytic oxidation reaction due to a higher generation of OH center dot radical. The NO2 degradation was also investigated under realistic indoor visible light irradiation with NO2 concentrations found indoors (40 and 100 ppb). This work showed the prospects of applications of Au/ZnO materials in the field of indoor photocatalytic purification and gave a new insight into the study of ZnO-based composites for the photocatalytic degradation of NOx.

In urban environments, various pollutants generated by road traffic, human, and industrial activities degrade outdoor and indoor air quality. Among these pollutants, nitrogen oxides (NOx) are subject to air quality regulations designed to protect human health and the environment. It is therefore crucial to keep their concentration as low as possible. Advanced oxidation processes are a practical choice for the degradation of NOx; among them, heterogeneous photocatalysis has proven to be a viable route. However, while the efficiency of this process has been widely demonstrated on a laboratory scale, it is still the subject of debate for real-life applications. The purpose of this study was to present a new field experiment on the application of a photocatalytic coating to outdoor walls. Air quality monitoring stations were used to evaluate the NOx concentration reduction instead of the chemiluminescent analyzer, in order to increase the number of sampling points. Statistical analysis was carried out to interpret the results. Density probability functions were plotted and showed a positive impact of the coating, leading to lower NOx concentrations. This work was completed by a laboratory-scale assessment of the coating’s durability using abrasion, QUV, and immersion/drying tests. The air depollution capacity of the chosen coating was significantly reduced after QUV testing.

Self-cleaning products are commercially available to protect surfaces against soiling and avoid the high consumption of energy and chemical detergents necessary for cleaning. They are based on semiconductor oxides, mostly titanium dioxide (TiO2), which induce photocatalytic oxidation activity and superhydrophilicity. Therefore, we present an experimental procedure at a lab scale to assess the self-cleaning ability of various photocatalytic coatings (five TiO2-based commercial products and one lab-grade zinc oxide (ZnO) product) applied to mortar surfaces. The samples were artificially stained with three types of soiling: Congo red dye, diesel soot, and motor oil. They were exposed to the environmental cycle of UV illumination and water flow for two weeks and the changes in stain colors were first assessed with visual inspection. Then, spectrophotometry measurements were conducted before and after the self-cleaning experiment to calculate the color differences for each stain in the CIELab color space data. In addition, the coatings were characterized via X-ray diffraction analyses and water contact angle measurements. Results highlighted color changes for each stain and higher wettability (induced by OH radicals) of the coated surfaces, which favored surface washing and thus stain removal. Light also had a positive effect on the attenuation of the stains, particularly for the Congo red dye.

This study compares the (nitrogen oxides) NOx photocatalytic degradation performance of the commer-cial bare semiconductors, titanium dioxide (TiO2 P25) and zinc oxide (ZnO), with that of the homemade gold (Au)-decorated semiconductors, Au/TiO2 and Au/ZnO (1 wt% Au). A plasmonic absorption band was observed at 550 nm for Au/TiO2 and around 700 nm for Au/ZnO. Aqueous dispersions based on these oxi-des were sprayed on mortar surfaces. The results revealed that Au/ZnO had a high NO degradation capa-bility, comparable to that of TiO2 P25, and the best selectivity towards the formation of nitrates instead of NO2. The Au decoration clearly improved the photocatalytic response of ZnO, notably by avoiding the pro-duction of NO2. This positive effect was attributed to the better charge carrier separation and higher OH. production induced by the presence of Au. To the best of our knowledge, this was the first study on Au/ ZnO used for NO photocatalytic degradation. (c) 2022 Elsevier Ltd. All rights reserved.

This paper was focused on the possible chemical synthesis routes to obtain titanium dioxide, TiO2, from hexafluorotitanate waste and it was aimed to identify the parameters affecting the formation of crystalline titanium dioxide, TiO2, phases (anatase or rutile). An experimental design method, inspired from the Taguchi approach, was used to assess the positive or negative impact of input factors on the formation of rutile and anatase, which were the output factors of interest. An experimental matrix was built up with coded values for each factor and coefficients were computed to point out a correlation between outputs and inputs. Particular attention was paid to the chemical compounds (decomplexing agents) added to precipitate TiO2 from hexafluorotitanates and to the dehydration temperature used to obtain TiO2 crystallized phases. The powders resulting from the syntheses were investigated by X-Ray diffraction analysis. Their chemical compositions were determined by Inductively Coupled Plasma Atomic Emission Spectroscopy. Data-matching revealed the best synthesis conditions in terms of crystallized TiO2 content, and this was confirmed by calculating the processing yields. The results showed that silica and calcium hydroxide were the most efficient decomplexing agents leading to the formation of anatase.

WO3 is a known photocatalytic metal oxide frequently studied for its depollution properties. However, it suffers from a high recombination rate of the photogenerated electron/holes pair that is detrimental to its performance. In this paper, we present a new chemical method to decorate WO3 nanoleaves (NLs) with a complementary metal oxide (ZnWO4) in order to improve the photocatalytic performance of the composite material for the abatement of 400 ppb NO2 under mild UV exposure. Our strategy was to synthesize WO3·2H2O nanoleaves, then, to expose them, in water-free organic solution, to an organometallic precursor of Zn(Cy)2. A structural water molecule from WO3·2H2O spontaneously decomposes Zn(Cy)2 and induces the formation of the ZnO@WO3·H2O nanocomposite. The material was characterized by electronic microscopy (SEM, TEM), TGA, XRD, Raman and solid NMR spectroscopies. A simple thermal treatment under air at 500 °C affords the ZnWO4@WO3 nanocomposite. The resulting material, additionally decorated with 1% wt. Au, presents a remarkable increase (+166%) in the photocatalytic abatement of NO2 under UV compared to the pristine WO3 NLs. This synthesis method paves the way to the versatile preparation of a wide range of MOx@WO3 nanocomposites (MOx = metal oxide).

“Almost real-life” experiments of abatement of a pollutant, actually nitrogen monoxide, were carried out in a 10-m3 chamber, the walls of which were covered with plasterboard samples, themselves coated with a photocatalytic dispersion. The experimental protocol consisted in first injecting NO polluted air into the chamber to a certain level, then maintaining a steady level of pollution by tuning the flow rate to balance the leaks and, finally, illuminating the chamber. In a first stage of analysis, a three-flow (injection, leakage and renewal flows) model was used in order to characterize the leakage flow rate. This model was based on the difference of NO concentration between the interior and the exterior rather than on a pressure difference. A two-parameter empirical law was specially formulated for this purpose. In a second stage, the photocatalytic phenomenon was described by a four-flow model completing the previous one, the fourth flow being associated with the photocatalytic oxidation of NO. This flow was described by a rate law derived from the Langmuir-Hinshelwood (L-H) law, which was generalized to the experimental chamber. The parameters K (adsorption constant) and k (abatement kinetics constant) of the rate law were identified using a standardized lab-scale reactor. The equations, integrated by finite differences, fitted the experimental results correctly. The “diffusive zone thickness” was introduced as the thickness of the air layer potentially concerned by the photocatalysis and was quantified. This first attempt to model photocatalysis on a large scale was promising. However, further research work is needed to enable the model to take more parameters into account.

Titanium metal is widely used in the aeronautical sector for its specific properties and corrosion resistance. The design of titanium workpieces is based on chemical milling: a fast, precise, low cost technique popular in the aerospace industry. Material is removed from selected areas of a part by immersing it in a strong chemical reagent. This process produces shallow cavities on plates and sheets or removes shallow layers of materials from large aircraft components to optimize the strength/weight ratio. However, it leads to large volumes of wasted acid baths, which are harmful to the environment and have to be sent to an approved waste facility. The objective of this paper is to highlight a cleaner production process based on the circular economy concept, i.e. reduce, reuse and recycle to limit environmental pollution and operating costs. Waste from chemical milling baths used in the design of titanium parts was recovered with the aim of synthesizing titanium dioxide and using it for air depollution applications. The waste consisted of hexafluorotitanate compounds. Various processing techniques to synthesize titanium dioxide from hexafluorotitanate compounds were tested and resulted in powders having different physicochemical characteristics. The synthesis parameters studied were the nature of the decomplexing agent, the dehydration temperature and the heating period. Photocatalytic coatings were then formulated on the basis of the synthesized powders. They were applied to a mortar surface to evaluate their efficiency to degrade nitric oxide under two UV lighting intensities, 5 and 20 W/m(2). Depending on the synthesis process conditions, the concentration and crystal form of titanium dioxide particles varied, leading to more or less efficient photocatalytic coatings. The proportions of anatase and rutile phases in the synthesized powders were between 3 and 13%, and 5 and 30%, respectively. Concerning the particle size distribution, the variations observed were dependent on the D-values. D-10% was quite similar for all powders. However, D-50% and D-90% differed by a factor of two for some powders, notably because of the presence of impurities or remaining decomplexing agent particles. NO degradation varied depending on the photocatalytic dispersions and could reach 7% under an irradiation of 20 W/m(2). This article highlights the possible valorization of a massive industrial waste for specific applications provided that the conditions of processing techniques are optimized. (C) 2019 Elsevier Ltd. All rights reserved.

Indoor air is contaminated by numerous pollutants, which impact human health, comfort and productivity. These pollutants have various indoor sources such as building materials, furniture, combustion appliances or tobacco smoke. However, the pollution also comes from outside. In urban area, nitrogen oxides (NOx) emitted into the atmosphere can reach alarming levels. These traffic-related pollutants, which seriously impact the global environment and human health, can infiltrate inside buildings. Therefore, limiting the amount of breathable NOx in outdoor and indoor environments is an important priority for the modern society. The photocatalytic process has attracted particular attention in the last two decades and has proved to be efficient to reduce the concentration of NOx. However, further work has to be conducted to assess its efficiency in real indoor environments. The purpose of this paper was to report on the indoor air quality in an open space office in Manchester, UK. Focus was made on nitric oxide (NO) and nitrogen dioxide (NO2). The indoor concentrations of both gases were monitored from 14 January 2019 to 7 April 2019. During this period, a photocatalytic coating was applied to a part of the indoor wall. The influence of this coating on the level of NOx was assessed by comparing the indoor concentrations before and after the application. An attention was paid to the correlation between outdoor and indoor pollution and to the effect of other parameters such as temperature, humidity, pressure and O3 concentration. The results showed that the photocatalytic process led to a decrease in the NOx concentration. The likelihood to find concentrations above 35 ppb for NO and 7.5 ppb for NO2 was clearly reduced after the coating application.

Corrosion of steel in reinforced concrete structures is a recurrent problem affecting civil engineering structures and costing the world billions of dollars per year. This physical phenomenon mainly results from chloride ingress or concrete carbonation. Corrosion can be diagnosed through a nondestructive method such as half-cell potential measurements. The present paper studies this method on a reinforced concrete wall containing eighteen unconnected steel bars and subjected to chloride-induced macrocell corrosion. Three corrosion systems with different configurations of connections between the steel bars are generated, involving three different anode-to-cathode surface ratios. Then, half-cell potential variations are observed versus macrocell corrosion current. The results lead to a critical discussion regarding the physical relevance of the usual potential threshold method to detect corroding rebars in reinforced concrete structures. In addition, the experiments demonstrate that electrical continuity between reinforcing steel bars is not necessary to get meaningful information about the macrocell corrosion system. At last, the paper show that the electric field (potential gradient) relative to a macrocell corrosion system may be measured by connecting the measurement system (reference electrode + voltmeter) to any electrochemical system in electrolytic contact with the concrete.

The objective of this study is to develop bio-sourced waste chemicals for use as asphalt release agents. Glycerol was extracted from bio-sourced waste and transformed by transesterification into the surfactants undecenoates of glycerol (MUG) and undecenoates of diglycerol (MUDG). They were composed of glycerol, monoglycerol, diglycerol, triglycerol, tetraglycerol and water. The formulations were mixed separately with water at quantities of 5–50%, along with acetone and commercial bio-sourced ARAs in order to observe the effects. The formulations were subjected to performance testing with the asphalt slide test, finding significant reduction in adhesion for a number of different formulations. The interaction of the formulations with bitumen was tested by the bitumen degradation test, which was combined with FTIR–ATR analysis, finding that the formulations do not dissolve the bitumen, but rather were adsorbed by the bitumen. The effects on asphalt mix of the best performing formulation, MUG at 20% in water, was tested by indirect tensile strength, determining that the formulation was acceptable for use in the field.

Air pollution is a serious public health concern in France and many other countries. Nitrogen oxides (NO x ) include nitrogen monoxide (NO) and nitrogen dioxide (NO 2 ). They are mainly outdoor pollutants produced during combustion of fossil fuel. These gases can easily infiltrate buildings and thus increase indoor pollution. The recommended guideline values for NO 2 are 200 μg/m 3 (short-term exposure) and 40 μg/m 3 (long-term exposure). Although no guideline values exist for NO, this gas can be oxidised by atmospheric ozone and thus produce NO 2 . This paper studies the depollution efficiency of photocatalysis towards indoor NO. Experiments were conducted at real scale, in a 10-m 3 experimental chamber developed at the LMDC and used as a reactor. The interior walls of the chamber were equipped with painted plasterboards treated with photocatalytic coating (3 g/m 2 of TiO 2 ). Gas was continuously injected into the chamber according to a specific procedure: (1) pollutant injection at high flow rate to reach 200 ppb of NO, (2) pollutant injection at low flow rate in order to keep the NO concentration constant at 200 ± 10 ppb and (3) photocatalysis activation by switching on the light. Typical indoor lighting systems (fluorescent tubes, LED and halogen bulbs) were tested and UV fluorescent tubes were also used to optimise the photocatalytic efficiency. Results showed that NO indoor concentration was reduced by photocatalysis in real-world conditions. Significant NO degradation was obtained under visible light. In addition, using the experimental procedure presented in this paper, a new method for evaluating air depollution efficiency by photocatalysis at real scale is proposed.

This paper deals with the degradation of NO by photocatalytic oxidation using TiO2-based coatings. Tests are conducted at a laboratory scale through an experimental setup inspired from ISO 22197-1 standard. Various parameters are explored to evaluate their influence on photocatalysis efficiency: TiO2 dry matter content applied to the surface, nature of the substrate, and illumination conditions (UV and visible light). This article points out the different behaviors between three kinds of substrates which are common building materials: normalized mortar, denser mortar, and commercial wood. The illumination conditions are of great importance in the photocatalytic process with experiments under UV light showing the best results. However, a significant decrease in NO concentration under visible light is also observed provided that the TiO2 dry matter content on the surface is high enough. The nature of the substrate plays an important role in the photocatalytic activity with rougher substrates being more efficient to degrade NO. However, limiting the roughness of the substrate seems to be of utmost interest to obtain the highest exposed surface area and thus the optimal photocatalytic efficiency. A higher roughness promotes the surface contact between TiO2 and NO but does not necessarily increase the photochemical oxidation.

The aim of this paper is to assess the degradation of formaldehyde using various coatings, including photocatalytic dispersion. The experiments were conducted at a laboratory scale in a standardized photoreactor based on the procedure described in the ISO 22197-4 standard. Various illuminations conditions were explored: UV and visible light. The dispersions tested were applied to common building materials using a coating method. The abatement values were determined by high performance liquid chromatography according to ISO 16000-3 standard. Results showed that parameters such as nature of substrate, type of dispersion and product layer thickness on surface played an important role. Moreover, formaldehyde adsorption on substrate was observed. This phenomenon was far from being negligible and contributed to decrease formaldehyde concentration. Limiting the amount of formaldehyde in indoor environment is a necessary priority for the modern society as this gas known as being carcinogen diminishes the life quality of occupants and poses serious health risks.

This paper investigates a new test method to assess the photocatalytic activity of plasterboards coated with a TiO2 dispersion under real-world conditions. The degradation of nitrogen oxides NO x (NO and NO2) is studied and the photocatalytic efficiency under UV illumination is evaluated in a 10-m3 room after a constant gas injection. Two ultrafine TiO2 dispersions are used: 0.85% TiO2 and 5% TiO2, and three types of gas are tested: an NO/NO2 mixture (8/8 mol-ppm), NO (45 mol-ppm) and NO2 (45 mol-ppm). The test method presented here is midway between laboratory and real-scale procedures and allows better control of the experimental parameters than a real field experiment. Testing a mixture of NO and NO2 is a way to get closer to real-world conditions as air is polluted by various gases. This study focuses on the degradation of NO and NO2 under UV illumination when two types of TiO2 dispersions are used and highlights the difference in behaviour between these two molecules in terms of photocatalytic degradation. The results show that photocatalytic activity does not appear to be efficient to degrade NO2 molecules. Another mechanism seems to be responsible for the reduction of the concentration of NO2, namely adsorption. Encouraging results are obtained with NO molecules, which can be degraded by photocatalysis. The degradation observed is even greater with the more concentrated TiO2 dispersion.

The recycling of asphalt is a process where old pavement is broken up and used as reclaimed asphalt pavement (RAP) in new asphalt pavement, often with the aid of recycling agents. The goal of asphalt recycling agents is to reintroduce the properties lost in bitumen and asphalt during aging such as penetration, softening point, viscosity, ductility, cohesion and adhesion to aggregate, reducing the performance of asphalt and requiring its replacement. The purpose of this study is to observe the chemistry of bitumen aging and the effects of recycling agents may have in reversing it. Fourier transform infrared spectroscopy (FTIR)-attenuated total reflectance (ATR) was used to analyse the bitumen aging and regeneration in terms of the evolution of carbonyl, sulfoxide and other bands. FTIR-ATR microscopy was used to study the distribution of these bands between the aggregates in order to understand the remobilization of the old asphalt (RAP) by the recycling agents through observing their penetration into the RAP. A method for aging bitumen and mastic in a ventilated oven was developed. An increase in C = O and S = O indices was observed with aging, plateauing after 7d.

The objective of this study is to develop testing methods of asphalt release agent (ARA) performance and the degree to which they may damage the asphalt. The testing of ARA performance demonstrated their ability to reduce the adhesion between the asphalt and the surface of steel (asphalt tools, truck beds…) by the asphalt slide test, which provided two indicators for quantifying performance. The testing of the their damage to asphalt consisted of the measurement of the degree to which the compacted asphalt is damaged by the ARA including CBR resistance, indirect-tensile strength and bitumen degradation testing, the latter also serving as a test to find the most effective bitumen remover (BR). For asphalt degradation, the indirect tensile strength test provided more consistent results than CBR resistance.

Asphalt release agents (ARAs) are used for reducing the adherence of asphalt residue to tools used for asphalt mix production, while bitumen removers (BRs) are used for cleaning the asphalt residue from the tools after their use. In order to be able to formulate well performing and safe bio-based ARAs and BRs, the performance, safety and chemistry of the currently available bio-degradable ARAs and BRs from both French and American construction industry were analysed. This provided insight into how ARAs and BRs functioned, insight that is as of now, not available. In addition to these, biodegradable short-chain esters were also tested. The testing of the damage to asphalt pavement by ARAs and BRs and of the quantification of their performance, were developed in Part I of this article. In this paper, gas chromatography examined the chemical composition of the agents while Fourier transformed infrared spectrometry was used to chemically investigate the agents’ chemical modification of the bitumen. It was found that commercial ARAs can be classified by their functioning as either surfactants or softeners. Additionally, it was found that short-chained esters are very effective as BRs.