Background The extent to which very young children contribute to the transmission of SARS-CoV-2 is unclear. We aimed to estimate the seroprevalence of antibodies against SARS-CoV-2 in daycare centres that remained open for key workers' children during a nationwide lockdown in France. Methods Children and staff who attended one of 22 daycare centres during a nationwide lockdown in France (between March 15 and May 9, 2020) were included in this cross-sectional, multicentre, seroprevalence study. Hospital staff not occupationally exposed to patients with COVID-19, or to children, were enrolled in a comparator group. The primary outcome was SARS-CoV-2 seroprevalence in children, daycare centre staff, and the comparator group. The presence of antibodies against SARS-CoV-2 in capillary whole blood was measured with a rapid chromatographic immunoassay. We computed raw prevalence as the percentage of individuals with a positive IgG or IgM test, and used Bayesian smoothing to account for imperfect sensitivity and specificity of the assay. This study is registered with ClinicalTrials.gov, NCT04413968. Findings Between June 4 and July 3, 2020, we enrolled 327 children (mean age 1•9 [SD 0•9] years; range 5 months to 4•4 years), 197 daycare centre staff (mean age 40 [12] years), and 164 adults in the comparator group (42 [12] years). Positive serological tests were observed for 14 children (raw seroprevalence 4•3%; 95% CI 2•6-7•1) and 14 daycare centre staff (7•7%; 4•2-11•6). After accounting for imperfect sensitivity and specificity of the assay, we estimated that 3•7% (95% credible interval [95% CrI] 1•3-6•8) of the children and 6•8% (3•2-11•5) of daycare centre staff had SARS-CoV-2 infection. The comparator group fared similarly to the daycare centre staff; nine participants had a positive serological test (raw seroprevalence 5•5%; 95% CI 2•9-10•1), leading to a seroprevalence of 5•0% (95% CrI 1•6-9•8) after accounting for assay characteristics. An exploratory analysis suggested that seropositive children were more likely than seronegative children to have been exposed to an adult household member with laboratory-confirmed COVID-19 (six [43%] of 14 vs 19 [6%] of 307; relative risk 7•1 [95% CI 2•2-22•4]). Interpretation According to serological test results, the proportion of young children in our sample with SARS-CoV-2 infection was low. Intrafamily transmission seemed more plausible than transmission within daycare centres. Further epidemiological studies are needed to confirm this exploratory hypothesis.

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This study introduces the results of an experimental investigation on the behavior of the circular columns of concrete under a load of axial compression, confined by an envelope of composite materials (carbon fiber and glass fiber). The composite used is a FRP glued in surface with epoxy resin. The specific objectives of this study are: verifying the applicability of this method of reinforcement of the columns to improve the behavior of concrete from the point of view strength and ductility, seeing the influence of composite materials type used, and confronting the experimental results acquired with different models developed on one hand and on the other hand with empirical formulas developed by other researches. Two models were developed to represent the structural behavior of the tested samples based on the calibration of the experimental results and criterion of Mohr—Coulomb failure. The validity of the results acquired numerically is based on a comparison with experimental results as well as with empirical formulas developed.

The aim of this study is to explore the possibility of recycling a waste material that is now produced in large quantities, while achieving an improvement of the mechanical properties and durability of the mortar. This study examines the mechanical properties and the durability parameters of mortars incorporating plastics bag wastes (PBW) as fine aggregate by substitution of a variable percentage of sand (10, 20, 30 and 40 %). The influence of the PBW on the, compressive and flexural strength, drying shrinkage, fire resistance, sulfuric acid attack and chloride diffusion coefficient of the different mortars, has been investigated and analyzed in comparison to the control mortar. The results showed that the use of PBW enabled to reduce by 18-23 % the compressive strength of mortars containing 10 and 20 % of waste respectively, which remains always close to the reference mortar (made without waste). The replacement of sand by PBW in mortar slows down the penetration of chloride ions, improves the behavior of mortars in acidic medium and improves the sensitivity to cracking. The results of this investigation consolidate the idea of the use of PBW in the field of construction.

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