We show record-highpeak power densities in comparison to the prior best literature onplatinum-based GD-supported materials which is promising informationfor future application.The lack of efficient and durable proton exchange membranefuelcell electrocatalysts for the oxygen reduction reaction is still restrainingthe present hydrogen technology. Graphene-based carbon materials haveemerged as a potential solution to replace the existing carbon black(CB) supports; however, their potential was never fully exploitedas a commercial solution because of their more demanding properties.Here, a unique and industrially scalable synthesis of platinum-basedelectrocatalysts on graphene derivative (GD) supports is presented.With an innovative approach, highly homogeneous as well as high metalloaded platinum-alloy (up to 60 wt %) intermetallic catalysts on GDsare achieved. Accelerated degradation tests show enhanced durabilitywhen compared to the CB-supported analogues including the commercialbenchmark. Additionally, in combination with X-ray photoelectron spectroscopyAuger characterization and Raman spectroscopy, a clear connectionbetween the  Closer to the operating conditions of PEMFCs at elevated temperatures(60–80 °C) in the potential window of 0.6–1.0 VRHE, Pt dissolution is the more dominant degradation process,with carbon corrosion becoming more significant above 1.0 VRHE, which reflects the fuel cell start-up and shut-down conditions.13 In particular, the temperature is of significantimportance when testing the durability of novel carbon-based supports,as the rate of carbon corrosion follows the Arrhenius law and increasesexponentially with temperature.14 Nevertheless,both mechanisms ultimately lead to the lowering of the electrochemicallyactive surface area (ECSA) of Pt and thus, loss of catalyst performanceover time.Proton exchange membrane fuel cells (PEMFCs)provide the zero-emissionenergy conversion solution critical to reaching complete decarbonizationof the automotive and other energy sectors.sp2 content, a higher 2D crystallinity, and fewer structuraldefects.16 These properties of GDs translate to betterthermodynamic stability.18 In principle, if GDsget appropriately exploited as supports for ORR catalysts, these benefitsshould provide significant improvements in terms of long-term durabilityresulting from increased resistance against carbon corrosion. Thisis of crucial importance to meet the ambitious targets of 30,000 hsystem lifetimes for HDV fuel cell applications.6Graphene derivatives (GDs) such as graphene, reducedgraphene oxide(rGO), and graphene nanoribbons possess specific chemical and physicalproperties compared to CBs. These include a higher specific surfacearea, better electronic conductivity, higher carbon 19 the more hydrophobic nature of GD materials and their restackingtendency20 make it extremely difficultto achieve both a high metal loading  and uniformdistribution of Pt-based NPs and thus a sufficiently high ECSA. Bothproperties are necessary for appropriately high roughness factorsof the catalyst layer and, subsequently, sufficient high current densityperformance.7 Furthermore, if one woulduse the oxidized version of the GD for NP deposition, improve hydrophilicity,and avoid restacking, the electronic conductivity of the carbon supportwould not meet the requirements for application in PEMFCs. Additionalchemical reduction or thermal treatment of the carbon support in furthersteps to improve the electronic conductivity would cause additionalstructural defects to the GD support due to the loss of oxygen functionalgroups.21 This would lead to agglomerationand detachment of NPs, namely, loss in the ECSA.7 Consequently, new synthesis pathways are required to enablethe synthesis of GD-supported analogues comparable with today’sstate-of-the-art CB-supported Pt-based catalysts. This has led tomany the strategies attempting to improve poor performance of theGDs using (i) various additives such as urea in the catalyst ink forthe electrode preparation22 or (ii) usingadditives such as CBs to act as spacers that prevent restacking ofGD-supported catalysts23 or (iii) synthesisof hybrid CB/GD26 or even MOx/GD-supported catalysts.27 Such strategies hypothesize the issues in the porosityof the catalyst layer and/or insufficient conductivity of the partly oxidized GD supports. Ideally, these issues should be resolvedat the catalyst level alone.7However, despite many efforts in recent years toutilize GDs asadvanced PEMFC catalyst supports, several major challenges preventedany significant breakthroughs. Namely, in comparison to CB-supportedcatalysts that are usually prepared with some of the existing industrialwater-based synthesis methods ,Inthe present study, we demonstrate a viable and scalable pathwayto produce multigram quantities of high-performance GD-supported Pt-basedORR catalysts. Using this method, we are able to show that properlyutilized GDs result in superior catalyst support, exhibiting bothenhanced durability when compared to CB-supported analogues and theability to reach a high current density performance comparable tothat of CB-supported catalysts, which has not been the case untilnow. Furthermore, this study provides a fundamental explanation forthe enhanced properties of GD-supported ORR catalysts.28 for the production of a wide variety of multigramquantities of M/GD composites ) and then using (ii) double passivationwith galvanic displacement (DP) methodology,29 enabling highly uniform deposition of Pt-based NPs on the GD supports.In the first step, graphite is used as a starting material for thesynthesis of graphene oxide (GO) . Because the oxidized GD materialsexhibit hydrophilicity, this enables good interaction with M-saltssuch as the Co or Cu acetates used in the present study to createhomogeneous aqueous M + GO/GONR suspensions.In this study, the productionof the GD-supported catalysts isbased on further development of procedures published in two recentpublications: (i) pulse combustion (PC) reactor technologyide (GO) 1a using Figure S1 for comparison). We note that the benefitof the fast partial thermal decomposition of oxidized GD in the (2)PC synthesis step is immediately followed by (3) thermally induceddecomposition of the M-salt, which prevents the GDs from restackingand allows for the formation of a highly exfoliated, homogeneous M/GDmaterial. Furthermore, even if a short reaction time could be reproducedin a batch mode setup, the reaction conditions would still not beas ideal as in continuous operating mode due to the varying localreaction conditions in the reaction vessel as the reaction proceeds.This would lead to the formation of a nonhomogeneous material, whichwould not meet the high requirements of a PEMFC electrocatalyst7 in further synthesis steps.The M + GO/GONR suspensions are then continuouslyfed through thePC reactor 1b. The P31 is then used to alloy the remaining M to obtainthe final intermetallic PtM ORR catalysts on both the CB and GD supportspresented in The PC approach,in combination with the Pt deposition using theDP methodology, provides an easily scalable commercial solution forthe utilization of GDs as an advanced catalyst support. Thermal annealingFigures S2–5 as well as Figures S6–10 for scanning electron microscope (SEM) characterization.Microscopy not only reveals the very high uniformity but also thehigh density of the PtM NPs for all the analogues prepared withinthis study—see particle size distribution derived from TEMimages . Most importantly,however, TEM microscopy reveals a clear structural distinction betweenrGO and CB-supported analogues. In the case of CB analogues, the structureconsists of 3D primary carbon particle agglomerates with a diameterbetween 30 and 50 nm . On the other hand, in thecase of the final GD-supported catalysts, the carbon primary particlesconsist of 2D carbon structures in the case of rGO-supported analogues and a ribbon-likestructure, evenly decorated with PtM NPs in the case of the rGONR-supportedanalogue .Figure S11) are in accordance with the wide XRDpeaks corresponding to the PtM crystal phases (S12). Thecomparison of the XRD patterns shows that PtCu analogues exhibit thepresence of the cubic (Pm-3 m) PtM3 intermetallic phase,whereas PtCo analogues exhibit the tetragonal PtM intermetallic phase(P4-mmm). In addition, XRD patterns of all the GD analogues preparedwithin this study are shown in Figure S12. It can be observed that regardless of the type of carbon supportused, the diffraction peaks corresponding to the metallic phases ofthese analogues are located at almost identical 2θ positions and exhibit a near-identical width of the mostintense peaks. Hence, while on the one hand the combination of PC28 and DP29 methodsallows one to vary the carbon support ;on the other hand, this synthesis approach is still flexible enoughto enable precise control over other parameters such as the metalloading and Pt:M chemical composition . XRD provides for the “fingerprints”of the crystal phases related to the PtM NPs, whereas Raman spectra. This is in accordancewith the prior studies, as GDs are expected to contain fewer structuraldefects and a higher degree of graphitization compared to partiallygraphitized CBs.32sp2 carbon content determination in the catalyst support.The sp2 content was calculated based onthe linear relationship between the extremes of pure sp2 and sp3 C atoms by employingthe eV difference between the minimum and maximum on the first derivativeof the Auger C KLL spectra.34 The value of the D parameter is noticeably higher for both rGO-supportedcatalysts compared to the CB-supported analogues. It is evident thatthe rGO-supported catalysts also have a higher sp2 content . This strongly agrees with the previousreport21 and corresponds well with theRaman spectra .36 The HT-DE setup enables performing accelerated degradation tests(ADTs) at an elevated temperature by using a reflux cooling condenserto avoid evaporation of the electrolyte (in this case 0.1 M HClO4). The use of high temperature provides the crucial parameterresulting in a severe stress test that exposes weaknesses of intrinsicallyless stable catalysts. Furthermore, ECSA values normalized via CO-electrooxidation(ECSACO) and mass activity (MA) before and after the ADTare evaluated using a typical thin-film rotating disc electrode setup(TF-RDE). For the present study, rather harsh ADT conditions wereused in the HT-DE setup that consisted of 5000 cycles in a potentialwindow of 0.4–1.2 VRHE with a scan rate of 1 V s–1. Most importantly, the experiments were run at anelevated temperature of 60 °C to increase the rate of carboncorrosion and also to simulate the real operating temperature of aPEMFC.1 For the present study, the mostimportant parameter used for the assessment of durability was “theability of the catalyst to retain the ECSACO”. Recently,the crucial importance of both the temperature and the potential windowfor evaluation of the stability of the Pt-based carbon-supported catalystshas been clearly demonstrated.36 In thisstudy, however, the initial focus went into the synthesis and preparationof catalyst analogues that are in many aspects as similar as possiblewith the only difference being the type of catalyst’ carbon-basedsupport. In other words, using the same ADT parameters for all theanalogues, the contribution related to the dissolution of metals should,for the most part, be very similar and thus, the main observed differencein retained ECSACO should be related to the differencesin the carbon support. With that in mind, our main hypothesis beforethe durability investigation has been that GD-supported catalystsshould exhibit a better ability to retain ECSACO with respectto the CB-supported analogues due to the increased content of sp2 carbon and fewer carbon structural defects.To adequately assess the durability of the synthesized GD-supportedcatalysts, an in-house designed high-temperature disc electrode (HT-DE)setup was used . For additional comparison and validationof durability, also a state-of-the-art commercial PtCo/CB benchmarkfrom Umicore (Elyst Pt30 0690) denoted in CO after the performed ADT when comparedto their respective CB analogues . Moreover, the PtCo/rGO samples with an ECSACO retentionof 86.0% exhibited the highest durability among all the tested samples,including the commercial benchmark. Additionally, it can be observedthat PtCu analogues retained less ECSACO than the PtCoanalogues. The differences between both groups of Pt-alloys couldbe attributed to the better stability of the more Pt-rich PtM crystalstructure in the case of PtCo analogues with respect to the PtM3 structure of the PtCu analogues (see Table S1).37 On the other hand,the intrinsic differences between PtCu and PtCo alloys or the intermetallicphase itself  could play an important role aswell.40 The durability comparison should thus only be madewithin the PtCu group or PtCo group of analogues, respectively. Theorigin of better catalyst durability should arise from differencesbetween GD and CB carbon supports. Namely, the contents of structuraldefects measured with Raman spectroscopy (sp2 carbonderived from XPS C (KLL) Auger spectra . It can be observed that similarly to ECSACO retention, the GD-supported catalysts also retained a higher MAafter the ADT in comparison to CB-supported analogues. Moreover, thePtCo/rGO sample with a MA retention of 55.7% exhibited the highestvalue among all the tested samples, including the commercial benchmarkwhich retained only 41.5% of the original MA. Additionally, it canalso be observed that the MA retention values for the PtCo group ofelectrocatalysts are substantially higher than for the PtCu analogues.This is also in agreement with the XRD data that show a more dominantpresence of a less stable ordered PtCu3 intermetallic phasein comparison to the more stable ordered PtCo intermetallic phasepresent in the PtCo line of materials.40 In general, for bothgroups of materials, it can be concluded that the ECSACO and the MA retention show on average higher values for GD-supportedelectrocatalysts when compared to the values of CB-supported analogues.The origin of the higher durability could, in principle, also be attributedto the different metal–support interaction (MSI) between theNPs and the carbon. A higher sp2 carboncontent and fewer structural defects (lower ID/IG ratio) of GD materials couldprovide for different MSI that favors better ECSACO aswell as MA retention after the ADT. Although the exact correlationof MSI and its effect on the durability of the PEMFC catalysts isnot yet well understood and defined, the results within this studysuggest that this parameter could play an important role in understandingthe origin of better catalyst durability and should therefore be furtheraddressed in upcoming studies.4244 This method has been proposed as a suitabletool to bridge the gap between the fundamental electrochemical catalystevaluation using rotating disk electrode half-cell methods and theapplied fuel cell research in single cells.48 Here, for additional validationof the catalysts’ performance, similarly to the previous chapter,a comparison with a commercial state-of-the-art PtCo/CB benchmarkfrom Umicore (Elyst Pt30 0690) marked as “Umicore” in Pt cm–2 was used for all measurements, which is in accordance with Departmentof Energy (DoE) 2025 targets.49 Furthermore,the catalyst ink composition used in this study was based on the procedureoptimized as part of the prior work.43 Namely,the ionomer-to-catalyst weight ratio was kept constant for all fivecatalysts evaluated in the GDE within this study. Thus, no furtherink optimization was performed to obtain the results presented incontinuation.The other historicallydifficult challenge is related to the performanceof GD-supported Pt-based catalysts at PEM-FC relevant high currentdensities, especially for graphene-derived materials. To assess thisin the present work, the gas-diffusion electrode (GDE) half-cell approachwas used.CO values measured in the GDE half-cell.The values are comparable within the individual group of samples (PtCuand PtCo) and correlate well with the data obtained using the RDE. It can also be noted thatthe values of ECSACO for samples prepared within this studyexceed the values of the commercial benchmark (Elyst Pt30 0690). Additionally,the ECSACO values for PtCu samples are higher than thosefor the PtCo samples, which is also in strong agreement with the factthat PtCu samples possess different intermetallic phases (PtM3) in comparison to PtCo analogues (PtM) resulting in a higherECSACO due to a lower Pt content in the core of NPs. RHE. It can be observed that the GD analogues possess a higher MA thanthe commercial benchmark (Elyst Pt30 0690). Similarly, as with ECSACO data, the higher values in MA for PtCu catalysts can beattributed to different intermetallic phases (PtM3 vs PtM)due to the more pronounced crystal lattice strain effect.56 Furthermore, by looking at the Tafel plots  the worst performance. With increasingcurrent density, the differences in the performance also increase.At a current density of 1.0 A cm–2 still the PtCu/rGOremains the best performing catalyst, whereas PtCo/rGO exhibits theworst performance. At current densities of 1.5 A cm–2, the difference in the performance becomes even more pronounced.Both CB analogues appear to slightly outperform their respective GDanalogues. Nevertheless, at this point, it should be stressed onceagain that no catalyst ink optimization has been performed for GD-supportedcatalysts. This means that there could be room for improvement inhigh current density performance by optimizing the catalyst ink andconsequently the catalyst layer alone. Hence, as a starting point,it seems that PtM/GD catalysts with a sufficiently high ECSA and themetal loading can reach high currents if appropriately utilized. Thevalues of peak power density performance of GD-supported materialsderived from already published work are collected in Pt cm–2 was used which is alreadymeeting the automotive DoE 2025 targets49 and is on average 3–4 times smaller than used in the otherpublications. For instance, the best prior studies in the literature55 showcased peak power density performances of 0.81 and 0.88 W cm–2 for their GD-supported materials, respectively, whichis still lower than the value of 1.04 W cm–2 reachedin this work. However, whereas those previous studies reported Ptloadings of 0.4 mgPt cm–2, we used avery low loading of 0.1 mgPt cm–2 inthe present work. Thus, the compared normalized values are expectedto be even much more in favor of the present work. Namely, it is knownthat with increasing Pt loading on the cathode, the differences inthe increased catalyst layer thickness start to affect the performance,increasing the mass transport resistance, which could hinder the catalyst’sperformance.57 However, it has to be mentionedthat here MEA single-cell results from the literature are comparedto data obtained in a GDE half-cell. Hence, several parameters suchas operating temperature, back pressure, and humidification can vary.Additionally, the effect of the hydrogen oxidation reaction at theanode (which can be considered minor in the PEMFC) is not includedin GDE half-cell measurements. Nevertheless, a crucial barrier inthe performance of the GD-supported materials in realistic catalystlayers has been overcome within this work.The ORR polarization curvesshown in sp2 carbon and the decrease of structural defects present in the rGOcarbon support. Moreover, these differences could lead to an alteredMSI, which could affect improved durability as well as the performanceof the GD-supported catalysts. To evaluate the high current densityperformance, activity was measured in a GDE half-cell. On average,both electrocatalysts based on the rGO exhibited excellent kineticperformance as well as high current density performance, relevantfor industrial application. Moreover, the peak power density valuesof the rGO-supported materials prepared in this work overpass thevalues from prior publications and the state-of-the-art commercialPt-Co benchmark from Umicore (Elyst Pt30 0690). This makes rGO-basedmaterials if utilized appropriately, a very promising candidate fora potential industrial application as carbon catalyst supports andshould spark further investigation in this direction. In additionto real fuel cell tests and tuning of the catalyst layer’smass transport, future optimizations of GD-derived materials couldbe achieved based on a deeper fundamental understanding of the originsof superior kinetic activity and stability.In conclusion, the applicability of GDsas an advanced supportfor Pt-based fuel cell electrocatalysts has been critically evaluated.Two groups of electrocatalysts, one based on PtCu and the other onthe PtCo intermetallic catalyst, were prepared using the PC synthesisin combination with the double passivation with galvanic displacementmethod. This innovative and scalable synthesis approach allowed thepreparation of very high loadings (up to 60 wt %) of uniformly dispersedmetal NPs on GDs. Accelerated degradation testing using a high-temperatureliquid electrolyte disc electrode showed that the rGO-supported catalystsexhibited enhanced electrochemical stability in both the ECSA andthe mass activity retention compared to their CB-supported analogues,including the commercial benchmark (Elyst Pt30 0690). The XPS andRaman results indicate that the improved electrocatalyst durabilityis related to the increased content of


Colored masks of various construction were handed out free of charge, accompanied by a range of mask-wearing promotional activities inspired by marketing research. Using a grassroots network of volunteers to help conduct the study and gather data, the authors discovered that mask wearing averaged 13.3% in villages where no interventions took place but increased to 42.3% in villages where in-person interventions were introduced. Villages where in-person reinforcement of mask wearing occurred also showed a reduction in reporting COVID-like illness, particularly in high-risk individuals. —CAEven in places where it is obligatory, people tend to optimistically overstate their compliance for mask wearing. How then can we persuade more of the population at large to act for the greater good? Abaluck  Endorsing mask wearing and informing people about its importance encouraged rural Bangladeshis to take the pandemic more seriously. Mask usage remains low across many parts of the world during the COVID-19 pandemic, and strategies to increase mask-wearing remain untested. Our objectives were to identify strategies that can persistently increase mask-wearing and assess the impact of increasing mask-wearing on symptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections.N = 600 villages, N = 342,183 adults). We cross-randomized mask promotion strategies at the village and household level, including cloth versus surgical masks. All intervention arms received free masks, information on the importance of masking, role modeling by community leaders, and in-person reminders for 8 weeks. The control group did not receive any interventions. Participants and surveillance staff were not informed of treatment assignments, but project materials were clearly visible. Outcomes included symptomatic SARS-CoV-2 seroprevalence (primary) and prevalence of proper mask-wearing, physical distancing, social distancing, and symptoms consistent with COVID-19 illness (secondary). Mask-wearing and distancing were assessed through direct observation at least weekly at mosques, markets, the main entrance roads to villages, and tea stalls. Individuals were coded as physically distanced if they were at least one arm’s length from the nearest adult; social distancing was measured using the total number of adults observed in public areas. At 5- and 9-week follow-ups, we surveyed all reachable participants about COVID-19–related symptoms. Blood samples collected at 10- to 12-week follow-ups for symptomatic individuals were analyzed for SARS-CoV-2 immunoglobulin G (IgG) antibodies.We conducted a cluster-randomized trial of community-level mask promotion in rural Bangladesh from November 2020 to April 2021  to 42.3% in treatment villages  . This tripling of mask usage was sustained during the intervention period and for 2 weeks after. Physical distancing increased from 24.1% in control villages to 29.2% in treatment villages . We saw no change in social distancing. After 5 months, the impact of the intervention on mask-wearing waned, but mask-wearing remained 10 percentage points higher in the intervention group. Beyond the core intervention of free distribution and promotion at households, mosques, and markets; leader endorsements; and periodic monitoring and reminders, several elements had no additional effect on mask-wearing, including text reminders, public signage commitments, monetary or nonmonetary incentives, and altruistic messaging or verbal commitments.There were 178,322 individuals in the intervention group and 163,861 individuals in the control group. The intervention increased proper mask-wearing from 13.3% in control villages  in the intervention arm and 8.60%  in the control arm, an estimated 11.6% reduction after controlling for baseline covariates. Blood samples were collected from consenting, symptomatic adults . Adjusting for baseline covariates, the intervention reduced symptomatic seroprevalence by 9.5% . We find that surgical masks are particularly effective in reducing symptomatic seroprevalence of SARS-CoV-2. In villages randomized to surgical masks (N = 200), the relative reduction was 11.1% overall . The effect of the intervention is most concentrated among the elderly population; in surgical mask villages, we observe a 35.3% reduction in symptomatic seroprevalence among individuals ≥60 years old . We see larger reductions in symptoms and symptomatic seropositivity in villages that experienced larger increases in mask use. No adverse events were reported.The proportion of individuals with COVID-19–like symptoms was 7.63% . We cross-randomized mask type  and promotion strategies at the village and household level. Proper mask-wearing increased from 13.3% in the control group to 42.3% in the intervention arm . The intervention reduced symptomatic seroprevalence , especially among adults ≥60 years old in villages where surgical masks were distributed . Mask distribution with promotion was a scalable and effective method to reduce symptomatic SARS-CoV-2 infections.We conducted a cluster-randomized trial to measure the effect of community-level mask distribution and promotion on symptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in rural Bangladesh from November 2020 to April 2021 ( As of September 2021, the COVID-19 pandemic has taken the lives of more than 4.7 million people. Inspired by the growing body of scientific evidence that face masks have the potential to slow the spread of the disease and save lives  declined to recommend mask adoption until June 2020, citing the lack of evidence from community-based randomized-controlled trials as well as concerns that mask-wearing would create a false sense of security  the goal of public health policy is ultimately to prevent symptomatic infections  and (ii) symptomatic individuals are far more likely to be seropositive so powering for this outcome required conducting an order of magnitude fewer costly blood tests. As secondary outcomes, we also report the effects of our intervention on WHO-defined symptoms for probable COVID-19 infection and mask-wearing.Bangladesh is a densely populated country with 165 million inhabitants; reported infections reached 15,000 per day during our study period, but reported cases and deaths are likely underestimated by one to two orders of magnitude (https://osf.io/vzdh6/) except where indicated. Our primary outcome was symptomatic seroprevalence for SARS-CoV-2. We also analyzed the impact of our intervention on mask-wearing, physical distancing, social distancing, and COVID-19–like symptoms. No adverse events were reported during the study period.Our analysis followed our preregistered analysis plan (p = 0.24). We show in table S3 that consent rates are about 40% across men and women and among adults of different age groups in both treatment and control villages.The unions where we conducted our intervention are geographically dispersed throughout rural Bangladesh, as shown in N = 10,085), of whom 339 had COVID-19–like symptoms. We use these to check balance with respect to baseline symptomatic seropositivity (as well as baseline symptomatic status).As such, the sample of individuals for whom we have symptom data is much larger than the sample for whom we have serology data. We tested 9512 (88.2%) of the collected blood samples to determine seroprevalence for SARS-CoV-2 immunoglobulin G (IgG) antibodies. Untested samples (<12%) either lacked sufficient quantity for our test or could not be matched to individuals from our sample because of a barcode scanning error. In our primary outcome analysis, we drop individuals for whom we are missing symptom data or who did not consent to blood sample collection. For the analyses where symptomatic status is the outcome, we report results using both this smaller sample as well as the larger sample of all individuals who provided symptom data. In the baseline, we collected blood samples from a random sample of individuals  because we did not observe them in the baseline period before the intervention and one village and its pair for lack of observational data throughout the intervention period, for a total analysis sample of 572 villages.Although our stratification procedure should have achieved balance with respect to variables observed at the time of randomization, given the many possible opportunities for errors in implementation, we confirm in appendix L that our control and treatment villages are balanced with respect to our primary outcome variables. This assessment was not preregistered. We investigated several other covariates and found a few small imbalances. We checked whether these affect the main results that we report in this paper. For example, we found more 18- to 30-year-olds in the treatment group than in the control group, perhaps because households reported teenagers as 18 years old to receive more masks; our results are robust to dropping this age range.The first column in the top panel of Contrary to concerns that mask-wearing would promote risk compensation, we did not find evidence that our intervention undermines distancing behavior. In the bottom panel of Physical distancing increased 5.1 percentage points overall, but there was substantial heterogeneity across locations. In markets, individuals were 7.4 percentage points more likely to physically distance. By contrast, there was no physical distancing practiced in any mosque, in either treatment or control villages, probably as a result of the strong religious norm of standing shoulder-to-shoulder when praying.It is possible that physical distancing increases because our intervention results in fewer total people being present in public spaces. If socializing increased in the intervention group, but only among risk-conscious people, then we might see physical distancing increase despite people engaging in overall riskier behavior. To assess this, as well as to assess directly if the intervention increased socializing, we studied the effects of our intervention on the total number of people observed at public locations. Although surveillance staff were not able to count everyone in busy public areas, the total number of people they were able to observe gives some indication of the crowd size. We found no difference in the number of people observed in public areas between the treatment and control groups overall (table S6). The social distancing analysis was not preregistered, although the specification exactly parallels our analysis of physical distancing.N = 13,853; 8.6%) compared with participants in the intervention villages . More than one-third (39.7%) of symptomatic participants agreed to blood collection. After omitting symptomatic participants who did not consent to blood collection, symptomatic seroprevalence was 0.76% in control villages and 0.68% in the intervention villages. Because the fractions we are reporting omit nonconsenters from the numerator but not the denominator, it is likely that the true rates of symptomatic seroprevalence are substantially higher .Among the 336,010 participants who completed symptom surveys, 27,160 (8.1%) reported experiencing COVID-19–like illnesses during the study period. More participants in the control villages reported incident COVID-19–like illnesses  for a 29 percentage point increase in mask-wearing over 8 weeks. In the second column of In appendix N, we investigate the robustness of these results to alternative methods of dealing with missing data from nonconsenters. In the main text, following our prespecified analysis plan, we drop nonconsenting symptomatic individuals. If we instead impute seropositivity for symptomatic nonconsenters based on the population average seropositivity among symptomatic individuals, our pooled estimate of the impact of masking becomes larger and more precise. Notably, with this alternative imputation, we find effects for both cloth and surgical masks on symptomatic seroprevalence.Not all symptomatic seroprevalence is necessarily a result of infections occurring during our intervention; individuals may have had preexisting SARS-CoV-2 infections and then became symptomatic (perhaps caused by an infection other than SARS-CoV-2). In appendix I, we show that if either (i) masks have the same proportional impact on COVID and non-COVID symptoms or (ii) all symptomatic seropositivity is caused by infections during our intervention, then the percentage decline in symptomatic seroprevalence will exactly equal the decline in symptomatic seroconversions. More generally, the relationship between the two quantities depends on whether masks have a greater impact on COVID or non-COVID symptoms, as well as the proportion of symptomatic seropositivity that is a result of infections preexisting at baseline.In 1) Fever and cough.2) Any three of the following: fever; cough; general weakness and/or fatigue; headache; muscle aches; sore throat; coryza ; dyspnoea (shortness of breath or difficulty breathing); anorexia (loss of appetite), nausea, and/or vomiting; diarrhea; or altered mental status.3) Anosmia (loss of smell) and ageusia (loss of taste).p = 0.000 for surgical; p = 0.066 for cloth), but the effect size in surgical mask villages was 30 to 80% larger depending on the specification. In table S9, we run the same specifications using the smaller sample used in our symptomatic seroprevalence regression . In this sample, we continue to find an effect overall and an effect for surgical masks but see no statistically significant effect for cloth masks.We find clear evidence that the intervention reduced symptoms: We estimate a reduction of 11.6% . Additionally, when we look separately by cloth and surgical masks, we find that the intervention led to a reduction in COVID-19–like symptoms under either mask type , and in cloth mask villages, red masks were more likely to be observed than purple masks . Text message reminders, incentives for village-leaders, or explicit commitment signals explain little of the observed increase in mask-wearing. Compared with self-protection messaging alone, altruistic messaging had no greater impact on mask-wearing, and twice-weekly text messages and a verbal commitment had no significant effects. We saw no significant difference in the rates of mask-wearing in the village-level randomization of surgical versus cloth masks.We do find nonexperimental evidence that in-person mask promotion and reinforcement is a crucial part of our intervention. Our first pilot study contained all elements of our intervention except in-person reinforcement. Our second pilot study (1 week later) and the full intervention  added in-person reinforcement. Under the assumption that treatment effects would otherwise be constant over time, we find that in-person reinforcement accounts for 19.2 percentage points of our effect , or 65% of the total effect size. In table S10, we show that this difference is statistically significant whether or not we include baseline controls. This was not a prespecified analysis.In appendix M, we present results on mask-wearing after our intervention ended. Even though the door-to-door free mask distribution occurred in the first week only, there was almost no attenuation of mask-wearing over the initial 10 weeks of surveillance. Notably, mask-wearing remained comparably increased in the treatment group during the 2 weeks we continued surveillance after the end of all intervention activities in the village. Three to 4 months later, mask-wearing waned but remained 10 percentage points higher in treatment regions.In table S11, we analyze the impact of our intervention on mask-wearing and physical distancing separately by gender, as well as by whether baseline mask-wearing was above or below the median. Gender was recorded in 65% of observations; age was not recorded during the direct observation surveillance of mask-wearing in public places, and thus we do not conduct an age-stratified assessment. This observed sample is representative of the rural Bangladeshi population that is present in crowded public places during the day; this population is largely composed of men, who have more social contacts outside the home than women. In the gender results, we drop surveillance observations for mosques because in rural Bangladesh it is rare for women to attend mosque. We found that the intervention increased mask-wearing by 27.1 percentage points for men  and 22.5 percentage points for women . Although we do not have the variation to test this, the gendered difference in effect size may be because our mask promoters were predominantly men or because the mask-wearing rate in control villages was so much higher for women (31% for women versus 12% for men). We intentionally hired predominantly men because most staff interactions would be with men. Men constituted 88.2% of all observed adults. We also found a larger increase in mask-wearing in villages with below-median baseline mask-wearing (where mask-wearing increased from 8.7 to 41.9% at endline) than in those with above-median baseline mask-wearing (where the increase was from 17.5 to 42.6%).p = 0.000) . For cloth masks, we find an insignificant (5%) reduction overall but some evidence of a reduction in symptomatic seroprevalence among 40- to 49-year-olds; we investigate more deeply in appendix N and find that the age gradient appears to be sensitive to how we deal with missing values. In the bottom panel of In In tables S13 and S14 (the latter being our preregistered specification), we perform the same analysis using the larger sample of individuals who reported symptom information. In this sample, we continue to find larger effects at older ages, although the differences are not as stark as those for the symptomatic seroprevalence outcome. In table S15, we show that the age gradient is steeper for surgical masks.In appendix N and table S28, we show results for symptoms and symptomatic seropositivity by gender. We see a similar pattern to the cloth and surgical mask results: We see significant effects for both genders for symptoms and symptomatic seroposivity when we impute seropositivity at the average value for nonconsenters. If we instead drop nonconsenters, the symptomatic seropositivity estimates for men become less precise and are no longer significantly different from zero, whereas the estimates for women remain unchanged.In appendix P, we discuss additional preregistered specifications that are not reported in the text, either because they were substantially underpowered given the available data or because data on required variables were unavailable. We also discuss ways in which trial implementation deviated from our preregistered protocol, such as switching from exclusively phone surveys to household visits at weeks 5 and 9 to increase response rates.In appendix Q, we assess the costs of implementing our intervention relative to the health benefits, specifically focusing on our ongoing efforts to implement this same intervention at scale in Bangladesh. We consider a range of possible estimates for excess deaths from COVID-19 from 1 May to 1 September 2021, and we assume that our age-specific impacts on symptomatic seroprevalence will lead to proportional reductions in mortality. We estimate that a scaled version of our intervention being implemented in Bangladesh will cost about $1.50 per person, and between $10,000 and $52,000 per life saved, depending on which estimate we use for excess deaths.We present results from a cluster-randomized controlled trial of a scalable intervention designed to increase mask-wearing and reduce COVID-19 symptomatic infections. Our estimates suggest that mask-wearing increased by 28.8 percentage points, corresponding to an estimated 51,357 additional adults wearing masks in intervention villages, and this effect was persistent even after active mask promotion was discontinued. The intervention led to a 9.5% reduction in symptomatic SARS-CoV-2 seroprevalence (which corresponds to 105 fewer symptomatic seropositives) and an 11.6% reduction in the prevalence of COVID-19–like symptoms, corresponding to 1541 fewer people reporting these symptoms. If we assume that nonconsenting symptomatic individuals were seropositive at the same rate as consenting symptomatic individuals, the total estimated symptomatic seropositives prevented would be 354. The effects were substantially larger (and more precisely estimated) in communities where we distributed surgical masks, consistent with their greater filtration efficiency as measured in the laboratory (manuscript forthcoming). In villages randomized to receive surgical masks, the relative reduction in symptomatic seroprevalence was 11% overall, 23% among individuals aged 50 to 59 years, and 35% among those ≥60 years of age in preferred specifications.We found clear evidence that surgical masks are effective in reducing symptomatic seroprevalence of SARS-CoV-2. Although cloth masks clearly reduce symptoms, we find less clear evidence of their impact on symptomatic SARS-CoV-2 infections, with the statistical significance depending on whether we impute missing values for nonconsenting adults. The number of cloth mask villages (100) was half that for surgical masks (200), meaning that our results tend to be less precise. Additionally, we found evidence that surgical masks were no less likely to be adopted than cloth masks. Surgical masks have higher filtration efficiency, are cheaper, are consistently worn, and are better supported by our evidence as tools to reduce COVID-19 cases.Our results should not be taken to imply that mask-wearing can prevent only 10% of COVID-19 cases, let alone 10% of COVID-19 mortality. Our intervention induced 29 more people out of every 100 to wear masks, with 42% of people wearing masks in total. The total impact with near-universal masking—perhaps achievable with alternative strategies or stricter enforcement—may be several times larger than our 10% estimate. Additionally, the intervention reduced symptomatic seroprevalence more when surgical masks were used and even more for the highest-risk individuals in our sample (23% for ages 50 to 59 years and 35% for ages ≥60 years). These numbers likely give a better sense of the impact of our intervention on severe morbidity and mortality, because most of the disease burden of the COVID-19 pandemic is borne by the elderly. Where achievable, universal mask adoption is likely to have still larger impacts.There are several possible theories for why we might observe a larger reduction in COVID-19 cases for older adults. We did not directly measure age during surveillance, but mask-wearing could have increased more for older adults. A second theory is that older adults are more susceptible to infections at viral loads that are preventable by masks. A third theory is that older adults have fewer social connections, so that reducing transmission through any one connection is more likely to prevent infection by severing all transmissible routes. A fourth theory is that people exercised more care and were more likely to wear masks when proximate to the elderly.We identified a combination of core intervention elements that were effective in increasing mask-wearing in rural Bangladesh: Mask distribution and role-modeling, combined with mask promotion, lead to large and sustained increases in mask use. Results from our pilot studies suggest that combining mask distribution, role-modeling, and active mask promotion—rather than mask distribution and role-modeling alone—seems critical to achieving the full effect. Our trial results also highlight many factors that appear inessential: We find no evidence that public commitments, village-level incentives, text messages, altruistic messaging, or verbal commitments change mask-wearing behavior. The null results on our cross-randomizations do not necessarily imply that these approaches are not worth trying in other contexts, but they teach us that large, persistent increases in mask-wearing are possible without these elements.Prediction studies that we conducted with policy-makers and public health experts at the WHO and the World Bank before presentations of the study results suggest that our results are informative for policy design. Most of the respondents in the prediction studies anticipated that text messages, verbal commitments, and incentives would increase mask-wearing, when in reality, we estimated fairly precise null effects, and poll respondents believed that in-person mask promotion would have no additional effect, whereas the evidence from our pilot studies suggests that it is essential .Our intervention design is immediately relevant for Bangladesh’s plans for larger-scale distribution of masks across all rural areas. The Bangladesh Directorate General of Health has assigned the study team and the nongovernmental organization Bangladesh Rural Advancement Committee (BRAC) the responsibility to scale up the strategies that were proven most effective in this trial to reach 81 million people  or by reducing new infections. We selected the WHO case definition of COVID-19 for its sensitivity, though its limited specificity may imply that the impact of masks on symptoms comes partly from non–SARS-CoV-2 respiratory infections. If masks reduce COVID-19 by reducing symptoms (for a given number of infections), they could help ease the morbidity and mortality resulting from a given number of SARS-CoV-2 infections. If masks reduce infections, they may reduce the total number of infections over the long-term by buying more time to increase the fraction of the population that is vaccinated. At the time of the study, the predominant circulating SARS-CoV-2 strain was B.1.1.7 (Alpha)  staff traveled to many villages that had low mask uptake in the first 5 weeks of the study and found that in these villages, local leaders were not very engaged in supporting mask promotion. Hence, we retrained mask-promotion staff partway through the intervention to work more closely with local leaders and set specific milestones for that partnership.Our primary outcome was symptomatic seroprevalence of SARS-CoV-2. Our secondary outcomes were prevalence of proper mask-wearing, physical distancing, and symptoms consistent with COVID-19. For COVID-19 symptoms, we used the symptoms that correspond to the WHO case definition of probable COVID-19 given epidemiological risk factors: (i) fever and cough; (ii) three or more of the following symptoms ; or (iii) loss of taste or smell. Seropositivity was defined by having detectable IgG antibodies against SARS-CoV-2.https://osf.io/23mws/).Our entire intervention was designed to be easily adopted by other nongovernmental organizations or government agencies and required minimal monitoring. We have made the materials public in multiple languages to ease widespread adoption and replication by other implementers  = 1%]; this is substantially higher than the filtration efficiency of the cloth masks we designed, which had a filtration efficiency of 37% (SD = 6%). These cloth masks had substantially higher filtration than common commercial three-ply cotton masks but lower filtration than hybrid masks that use materials not commonly available for community members in low-resource settings  One-time mask distribution and information provision (about masks) at households.2) Mask distribution in markets for 3 to 6 days per week during all 8 weeks of the intervention.3) Mask distribution at mosques on three Fridays during the first 4 weeks of the intervention.4) Mask promotion in public spaces and markets where non–mask wearers were encouraged to wear masks (weekly or biweekly).5) Role modeling and advocacy by local leaders, including imams discussing the importance of mask-wearing at Friday prayers using a scripted speech provided by the research team.Participants and mask surveillance staff were not told which villages were in which intervention arm, but the intervention materials were clearly visible. The prespecified analyses and sample exclusions were made by analysts blinded to the treatment assignment.Within the intervention arm, we cross-randomized villages to four village-level and four household-level treatments to test the impact of a range of social and behavior change communication strategies on mask-wearing. All intervention villages were assigned to either the treatment or the control group of each of these four randomizations. These village-level randomizations were as follows:1) Randomization of treated villages to either cloth or surgical masks.2. Randomization of treated villages to public commitment (providing households signage and asking them to place signage on doors that declares they are a mask-wearing household) or not. The signage was meant to encourage formation of social norms through public signaling.3. Randomization of treated villages to no incentive, nonmonetary incentive, or monetary incentive of $190 given to the village leader for a project benefitting the public. We announced that the monetary reward or the certificate would be awarded if village-level mask-wearing among adults exceeded 75% at 8 weeks after the intervention started.4. Randomization of treated villages to 0 or 100% of households receiving twice-weekly text message reminders about the importance of mask-wearing.We had three household-level cross-randomizations. In any single village, only one of these household randomizations was operative. Because our data collection protocols relied on passive observation at the village level, we could not record the mask-wearing behavior of individual households. To infer the effect of the household-level treatments, we therefore varied the color of the masks distributed to the household based on its cross-randomization status and had surveillance staff record the mask color of observed individuals. In surgical mask villages, a household received blue or green masks and promoters distributed an equal number of blue and green masks in public settings. In cloth mask villages, households received violet or red masks and promoters distributed blue masks in public settings. To avoid conflating the effect of the household-specific treatment with the effect of the mask color, we randomized which color corresponded to which treatment status across villages (this way a specific color was not fully coincident with a specific treatment). The household-level randomizations, described in further detail in appendix D and visualized in fig. S1, were as follows:1) Households were randomized to receive messages emphasizing either altruism or self-protection.2) Households were randomized to making a verbal commitment to be a mask-wearing household  or not. This experiment was conducted in a third set of villages where there was no public signage commitment.3) Households were randomized to receive twice-weekly text reminders or not. As mentioned above, the text message saturation was randomly varied to 0, 50, or 100% of all households receiving texts, and in the 50% villages, the specific households that received the texts was also random.We selected intervention elements that had a reasonable chance of persuading rural Bangladeshis to wear masks by consulting literature in public health, development and behavioral economics, and marketing to identify some of the most promising strategies. An extensive literature identifies price and access as key deterrents to the adoption of welfare-improving products, and especially of technologies that produce positive health externalities, such as face masks , and how the mask was worn. We defined proper mask-wearing as wearing either a project mask or an alternative face-covering over the mouth and nose and improper mask-wearing as wearing a mask in any way that did not fully cover the mouth and nose. Surveillance staff observed a single individual and recorded that person as practicing physical distancing if he or she was at least one arm’s length away from all other people. Additional details are available in appendix G.The owner of the household’s primary phone completed surveys by phone or in-person at weeks 5 and 9 after the start of the intervention. They were asked to report symptoms experienced by any household member that occurred in the previous week and over the previous month. COVID-19–like symptoms were defined by whether they were consistent with the WHO COVID-19 case definition for suspected or probable cases with an epidemiological link . Blood samples were transported on ice and stored at −20°C until testing.Blood samples were tested for the presence of IgG antibodies against SARS-CoV-2 using the SCoV-2 Detect IgG ELISA kit . This assay detects IgG antibodies against the spike protein subunit (S1) of SARS-CoV-2. The assays were performed according to the manufacturer’s instructions. Additional details are presented in appendix H.i in village j is symptomatic seropositive. To assess seropositivity, we tested all individuals who were symptomatic in either our 5- or 9-week household survey.Our primary outcome is symptomatic seropositivity. As noted above, individuals are symptomatic if they (i) meet the WHO surveillance definition of probable COVID-19 illness and (ii) are seropositive in our blood test at endline. If either of these conditions fail to hold, Our goal is to estimate the impact of the intervention on symptomatic seropositivity, defined as In our preregistered specification, we estimate this parameter by ordinary least squares, clustering at the village level using the approach in (20211202-1Click here for additional data file.


Immunocompromised patients commonly present prolonged viral shedding of the novel coronavirus SARS-CoV-2, detected through reverse transcriptase-polymerase chain reaction (RT-PCR) in nasopharyngeal or oropharyngeal swabs. The detection and estimation of the viral load in patients with COVID-19 is of utmost importance, not only for the effective isolation of the patient but also from a therapeutic point of view. In the current study, we present the case of an immunocompromised patient receiving rituximab infusions for the treatment of multiple sclerosis who exhibited COVID-19 clinical symptomatology for an extended period of time along with prolonged viral shedding while at the same time being unable to organize sufficient humoral immunity. Despite being fully vaccinated and having suffered symptomatic SARS-CoV-2 infections, antibodies against the virus remained undetected. Clinical relapse of his symptoms led to the trialing of a multitude of therapeutic interventions in order to combat the disease, with an extended remdesivir regimen proving the most efficacious in the alleviation of his symptoms. This case demonstrates how immunocompromised COVID-19 patients should be regarded under a different scope when it comes to the diagnosis, management, and resolution of their SARS-CoV-2 infection. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) novel coronavirus has affected the globe for three years now and was first described in Wuhan, China, in late 2019 . Viral sA 49-year-old male with a personal history of multiple sclerosis on a therapeutic regimen of infusions of 700 mg rituximab once every six months presented to the emergency department (ED) of our hospital due to fever for the preceding two days, along with dry cough, arthralgias, and general malaise. Apart from his neurological disease, the patient had no other medical conditions, and he denied using tobacco, alcohol, or recreational drugs. He received his last rituximab infusion approximately one month ago. Apart from rituximab, he was receiving mirtazapine and a vitamin D supplement. The patient was fully vaccinated against SARS-CoV-2 with three Pfizer vaccine doses, the last of which had taken place approximately four months prior to his ED presentation. At presentation, his vital signs showed a fever of 38.1°C, a respiratory rate (RR) of 16 breaths per minute for oxygen saturation (SaO2) of 97% on room air, a blood pressure (BP) of 150/95 mmHg, and a heart rate of 91 beats per minute (bpm). A rapid antigen test and a nasopharyngeal PCR SARS-CoV-2 test were performed upon his arrival, both of which were positive. Blood was drawn for a complete blood count, biochemical profile, and arterial blood gases, with the results being depicted in Table The patient was admitted to the infectious diseases unit of our hospital, where he was placed on a remdesivir regimen of 200 mg on day one and 100 mg on subsequent days, intravenous dexamethasone 6 mg, and empirical antibiotic treatment with piperacillin-tazobactam 4.5 g three times daily and vancomycin 1 g twice daily. On the fifth day after his admission, the patient remained febrile, and various sets of aerobic and anaerobic blood cultures had been drawn without any pathogens being cultured. Due to concerns for hospital-acquired pneumonia (HAP), his antibiotic regimen was empirically adjusted with the addition of trimethoprim-sulfamethoxazole and caspofungin for pneumocystis carinii pneumonia (PCP) and fungal pathogen coverage, respectively. Although the patient remained afebrile for 24 hours, his fever came back, and all antibiotics were discontinued, with the patient receiving only remdesivir and cortisone therapy. At the same time, on the tenth day after his initial ED presentation, a quantitative measurement of the patient’s SARS-CoV-2 antibodies was negative . Cortisone therapy was changed to higher doses of methylprednisolone (40 mg twice daily) with a plan to taper over the next few weeks, and the patient remained afebrile for the next 48 hours with inflammatory markers subsiding. He was discharged on the 12th day, only to come back two days later with a new onset of pyrexia and worsening respiratory status, as depicted in Table Laboratory examinations revealed elevated ferritin and lactate dehydrogenase (LDH) without other adverse prognostic factors . A computed tomography (CT) scan of the chest showed bilateral ground glass opacities compatible with COVID-19 pneumonia Figure . RemdesiNasopharyngeal swab specimens were collected for PCR testing every 14 days thereafter, with the patient expressing positivity for more than 120 days before finally becoming negative on day 127 after his initial presentation to the hospital. A third and final quantitative SARS-CoV-2 antibody test was negative, and the patient opted for a fourth vaccine dose, which was administered a few weeks later.Prolonged SARS-CoV-2 viral shedding has recently been described in the literature in immunocompromised hosts, including patients on rituximab regimens. Individuals in this case presented with a varying degree of waxing and waning of their symptoms, while their disease commonly relapsed, leading to the administration of various therapeutic schemes to combat the disease , 13-15. Furthermore, the use of high corticosteroid doses in the management of the present case needs to be highlighted. Dexamethasone use reduces mortality rates in hospitalized patients with severe COVID-19 who require supplemental oxygen support , but conWhat remains of utmost importance though is the fact that isolation protocols need to be adjusted accordingly for the group of immunocompromised patients. Effective isolation of affected individuals is mandatory not only for closer observation of their symptoms but also to ensure prophylaxis of their surrounding persons, carers, and even other immunocompromised patients that may exist in their environment. Given that there have been reports of extremely prolonged viral shedding times among immunocompromised individuals, even those experiencing milder clinical complaints , the CenConcluding, our case regards an immunocompromised multiple sclerosis patient under a rituximab treatment regimen whose COVID-19 presented with prolonged clinical symptomatology along with extended persistence of viral shedding, as proven by repeated viral RT-PCR on nasopharyngeal specimen swabs. At the same time, the patient was incapable of eliciting protective SARS-CoV-2 antibodies even after completing a full vaccination series and suffering from the clinical syndrome. This case adds to the literature on COVID-19 disease in immunocompromised patients, especially the rituximab-treated population, highlighting the need for further research when it comes to these individuals’ hospitalization and drug regimens, isolation, and general management.


This paper presents a numerical study to evaluate the fire resistance of concrete beams and slabs incorporating natural fiber-reinforced polymers (FRP). A validated finite element model was applied to carry out a series of numerical studies on fire-exposed reinforced concrete (RC) beams and slabs strengthened with conventional and bio-based FRP composites. The model calculates the temperature-dependent moment–curvature relationship for various segments of the member at each time step, which are then used to calculate the moment capacity and deflection of the member. The variables in the beams and slabs include different strengthening techniques , different fiber composites, and fire insulation schemes (uninsulated and insulated). The results from the study indicate that the bio-based FRP-strengthened RC members undergo a faster degradation in moment capacity and also experience higher deflections under fire exposure. This leads to a lower fire resistance in RC members with bio-based FRP composites compared to beams and slabs with conventional FRP-strengthened concrete members. The addition of fire insulation to the bio-based FRP-strengthened members can enhance their fire performance and help achieve the required fire resistance ratings for use in building applications. In this study, the NSM CFRP-strengthened RC beams were found to have a fire resistance of 3 h without any fire insulation; however, the bio-based FRP-strengthened beams required a layer of vermiculite–gypsum-based fire insulation material (of about 25 mm) to achieve similar fire resistance. In recent years, there has been a growing interest to use natural (or bio-based) fiber-reinforced polymer composites in structural applications due to the increasing awareness of the use of renewable, environmentally friendly, and sustainable materials. Different types of natural fibers can be used in the fabrication of FRP composites, namely, animal-based fibers, mineral fibers, and plant-based fibers. Animal-based fibers include silk, wool, hair, and feather. Mineral fibers are obtained from mineral ores and commonly used fibers include asbestos and basalt. Plant-based fibers are obtained from agricultural crops or stubble (waste) and include sisal, flax, ramie, cotton, banana, and hemp.2) emissions and increased energy savings. Furthermore, plant-based fibers offer numerous advantages over conventional synthetic fibers (such as carbon and glass) such as low-cost, eco-friendly, relatively lightweight, and appreciable strength and stiffness properties [Natural fiber-based composites that are derived from locally available raw materials such as agricultural waste or stubble form a sustainable alternative to conventional synthetic fiber-reinforced polymer (FRP) composites and their usage in the construction sector can result in the reduction of carbon dioxide . Currently, there is very limited information on the fire performance of concrete members that incorporate bio-based FRP composites ,11,12. FThis paper presents the fire resistance evaluation of bio-based FRP-strengthened concrete beams and slabs subjected a combination of structural and fire loading. A validated numerical model, originally developed for evaluating the fire resistance of conventional FRP-strengthened members, was extended to evaluate the fire performance of bio-based FRP-strengthened members. Numerical studies were carried out on different bio-based FRP-strengthened concrete members with varying strengthening techniques and insulation schemes. The fire performance of the bio-based FRP composite members was compared with conventional FRP-strengthened concrete members. Practical implications and future research needs for enhancing the fire performance of bio-based FRPs for use in building applications are discussed.g of the resin. For instance, a recent study by Mazzuca et al. [For strengthening and retrofitting of concrete structures, fiber-reinforced polymer (FRP) composites offer several advantages over conventional construction materials such as concrete and steel . Howevera et al.  found tha et al. . This stFurther, the interfacial bond strength of FRP composites also degraded drastically at elevated temperatures and this can affect the force transfer between the FRP and concrete. The study by Yu and Kodur  showed tMuch like conventional FRP composites, bio-based FRP composites also undergo flaming, charring, material degradation, and rapid loss of strength and stiffness properties when exposed to elevated temperatures ,11,12. SSeveral experimental and numerical studies have been carried out in the past to evaluate the fire resistance of strengthened concrete beams, slabs, and columns incorporating conventional FRP composites ,25,26,27In the numerical studies, macroscopic or microscopic finite element-based models were used to predict the performance of FRP-strengthened concrete members under fire conditions. Hawileh et al.  developeDai et al.  developeFor evaluating the fire resistance of FRP-strengthened members, not many empirical relationships or design charts are available ,30, and To assess the fire resistance of reinforced concrete (RC) members with natural fiber-reinforced polymers, a previously developed macroscopic finite element-based model was utilized. The selected numerical model was originally developed by Kodur and Ahmed  using thThe numerical model for tracing the fire response of the FRP-strengthened RC beams and slabs follows a sequential procedure, starting with a thermal analysis followed by a structural analysis. 2K as per Eurocode 1–2 provisions [For the fire resistance calculations, the FRP-strengthened member was discretized into several segments along the span of the member, and the cross-section at the center of each segment is divided into several rectangular elements. The temperature rise in each element, at a given cross-section, was calculated by carrying out a 2-D heat transfer analysis. The transfer of heat from the fire zone to the boundaries of the concrete member (or insulation) was modeled using convection and radiation boundary conditions. The transfer of heat within the cross-section of the concrete member is mainly through conduction. The emissivity coefficient was taken as 0.8 as per Eurocode 1–2 provisions  while spovisions  for the The structural analysis was carried out in incremental time steps. At each time increment, moment–curvature relations are generated for the various segments of the member by applying the conditions for force equilibrium and strain compatibility. These time-dependent moment–curvature relationships were used to carry out a stiffness analysis to obtain the moment and deflection at different segments in the FRP-strengthened member. The temperature-dependent mechanical properties of concrete, steel rebar, and FRP were supplied as input to the structural model. The bond–slip between the FRP reinforcement and concrete was not accounted for in the numerical analysis. Owing to the lower strength and stiffness of bio-based FRP composites compared to conventional FRP composites, as well as more rapid degradation of these properties with temperature, the bio-based FRP-strengthened member fails at earlier times due to loss of capacity before significant slip occurs. Moreover, accounting for the bond–slip of FRP reinforcement requires detailed information on the variation of bond properties of bio-based FRP composites with temperature, which is not available in the current literature. For these reasons, the present study neglects any bond–slip between the FRP reinforcement and concrete.At each time step, different output parameters including cross-sectional temperatures, stresses and strains, moment capacity of the strengthened member, and mid-span deflection are obtained from the analysis. These response parameters were compared with the failure limits prescribed in ASTM E119  to deterFor evaluating the fire resistance of natural FRP-strengthened members, the thermal and mechanical properties of the constituent materials, i.e., concrete, steel reinforcement, FRP, and fire insulation along with the variation of these properties with temperature are required. For the thermal analysis, the properties of interest include density, specific heat, and thermal conductivity. For concrete and steel rebar, the temperature-dependent thermal property variations were obtained from Eurocode 2 . HoweverFor carrying out the structural analysis, high-temperature stress–strain relationships of concrete and steel rebar specified in Eurocode 2  were useAdditionally, a linear elastic stress–strain behavior was assumed for the FRP material at room and elevated temperatures, and this is as per the trends shown in previous tests. Further, the thermal expansion coefficient for concrete and reinforcing steel was taken from Eurocode 2 . For biogligible . Since tFor the generation of moment–curvature relationships, plane sections were assumed to remain plane before and after bending.Only the flexural limit state was considered while evaluating the failure of the beam (or slab) and the shear limit state was ignored.The bond–slip between the steel reinforcement and concrete and that between the FRP reinforcement and concrete were not considered in the model.The FRP reinforcement was considered to exhibit a linear stress–strain response at elevated temperatures up to failure.The thermal properties of the bio-based FRP reinforcement were considered to be the same as those of conventional FRP reinforcement.In the numerical model, the following assumptions were made for evaluating the fire resistance of FRP-strengthened RC members:The numerical model described in the previous section was applied to evaluate the fire resistance of FRP-strengthened RC flexural members (beams and slabs) with different types of fibers , strengthening types (NSM and EB), and fire protection schemes (with and without insulation). The members with conventional FRP strengthening were used as the base case and the fire performance of the natural fiber-reinforced RC members was compared against the conventional ones.The numerical studies are presented for two broad cases: members with NSM FRP reinforcement and members with externally bonded (EB) FRP reinforcement. Beams B1 and B2 were provided with two NSM CFRP strips with a cross-sectional size of 13.5 mm × 4.5 mm, whereas beams B3 and B4 were provided with five NSM bio-based FRP strips 20 mm × 10 mm in size each. Additionally, beams B1 and B3 were uninsulated, whereas beams B2 and B4 were provided with 25 mm U-shaped SFRM-type fire insulation . SimilarThe NSM FRP reinforcement was selected to achieve an increase in moment capacity of 50% in CFRP-strengthened members, whereas only a 15% increase in moment capacity was achieved in bio-based FRP-strengthened members. This is because of the limited space available between the steel reinforcement and the bottom surface of the concrete member that hinders the placement of additional (or larger) bio-based FRP strips, which in turn limits the potential to increase the moment capacity of the bio-based FRP-strengthened members beyond a certain extent.For members with EB FRP reinforcement, the FRP type and insulation scheme were varied similar to the NSM FRP beams and slabs as shown in Each beam and slab were divided into 20 segments along the length of the member. The cross-section of each beam was discretized into 10 mm × 10 mm elements, whereas the cross-section of each slab was discretized into 10 mm × 5 mm elements. For structural members strengthened with EB FRP reinforcement, the CFRP strips were discretized into 10 mm × 1 mm elements, whereas the bio-based FRP strips were discretized into 10 mm × 10 mm elements. The mesh used in the structural analysis was the same as that used in the thermal analysis.For the numerical analyses, the tensile strength and elastic modulus were set as 2.51 GPa and 139.6 GPa, respectively, for the NSM CFRP strips (62% by volume of carbon fiber in epoxy matrix)  and as 1The fire response of the T-beams and slabs strengthened with either conventional or bio-based NSM FRP reinforcement  FRP reinforcements, eight different configurations of beams and slabs were analyzed. The temperatures obtained from the thermal analysis for concrete (at mid-depth), steel rebar, and FRP are plotted for the different flexural members in From The structural response was evaluated through the degradation in moment capacity and mid-span deflections of the EB FRP-strengthened RC members, which are plotted in When fire insulation was applied to the flexural members, the fire performance of both beams and slabs improved significantly. The FRP-strengthened RC members  experienced a slower degradation in moment capacity and a gradual increase in mid-span deflections as seen in It should be noted that the results obtained from the numerical analyses were mainly qualitative and some differences are expected due to the differences between the actual temperature dependencies of the material properties of the FRP reinforcement and those considered in the numerical model. Further, the results obtained are influenced by not considering the appropriate bond stress–slip relations.This study primarily focused on evaluating the fire resistance of bio-based FRP-strengthened concrete members. FRP materials, as discussed before, have numerous advantages that make them attractive for structural applications; however, the main drawbacks of using these materials in buildings are their high flammability, large smoke development, and poor fire resistance properties. Bio-based FRP composites also face the same issues. Further, natural fibers have lower initial strength and stiffness as compared to synthetic fibers, and therefore the fire resistance of bio-based FRP composite members is even lower than the conventional FRP-strengthened members. From the numerical studies, it can be inferred that the fire resistance of the FRP-strengthened members significantly depends on the material properties of the FRP at elevated temperatures. However, there is a lack of reliable material property data for bio-based FRP under room and elevated temperature conditions. This stems from the limited work that has been carried out in this area and the lack of standardized test methods and procedures to characterize the high-temperature properties of these FRP materials. Further research is needed to develop temperature-dependent property data and material models for bio-based FRP composites. The numerical model presented in this study can then be updated with the available material property data to evaluate the required FRP reinforcement, member sizes, cover thicknesses, and fire insulation to achieve the necessary fire resistance ratings for structural applications.Bio-based FRP were intended to be developed as a retrofitting material for applications with low (or moderate) strengthening requirements such as rural infrastructure. In such applications, locally sourced raw materials  can be utilized in developing the FRP material which can lead to cost savings as well as reduced carbon emissions in the construction sector. From the numerical studies carried out in this paper, it is inferred that to achieve reasonable strengthening levels in the flexural members, a larger thickness (or a higher number) of bio-based FRP reinforcement is required in comparison to the conventional CFRP reinforcement. In addition, the insulation thickness required in the case of bio-based FRP-strengthened members for achieving similar fire performance as that of conventional FRP members is higher. This can result in practical challenges such as the need for larger cover thickness, placement of FRP reinforcement, debonding of FRP and insulation, etc. Further research is needed to overcome these challenges in realizing the potential application of bio-based FRP composites in buildings. Further, fire resistance tests of bio-based FRP composite members need to be carried out to generate more test data to validate the predictions from the numerical model.The fire performance of bio-based FRP-strengthened concrete members was lower than that of a conventional CFRP-strengthened member with similar design parameters. This is due to the lower initial strength and stiffness properties of the bio-based FRP and the faster degradation of its mechanical properties with a rise in temperature.Uninsulated NSM bio-based FRP-strengthened members experienced higher deflections and a faster degradation in moment capacity as compared to the conventional CFRP counterparts. While the NSM CFRP-strengthened RC beams can achieve up to 3 h of fire resistance without any fire insulation, the bio-based FRP-strengthened beams required a layer of fire insulation (of about 25 mm) to achieve similar fire resistance.Uninsulated EB bio-based FRP-strengthened RC members undergo severe performance degradation under fire conditions due to direct exposure of the FRP reinforcement to fire. Hence, fire insulation is always needed when the bio-based FRP reinforcement is to be externally applied to an RC member to achieve the required fire resistance ratings as specified in building codes.This study evaluated the fire performance of bio-based FRP-strengthened RC flexural members under the combined effects of structural and fire loading. A set of numerical analyses was carried out on FRP-strengthened beams and slabs with varying strengthening techniques and insulation schemes. The fire resistance of the bio-based FRP composite members was compared with conventional FRP-strengthened concrete members. The results obtained from the numerical studies led to the following conclusions on the fire performance of natural fiber-reinforced polymer (FRP) composite beams and slabs: