Influence de la teneur en ciment sur les propriétés thermomécaniques des blocs d’argile comprimée et stabilisée

Ce travail vise à déterminer la résistance à la compression et la conductivité thermique des blocs à base d’argile comprimée et stabilisée au ciment d’une part et à étudier la variation de ces propriétés en fonction de la teneur en ciment d’autre part. Les mesures réalisées indiquent que la résistance des blocs sans ciment est de 3,7 MPa par « voie sèche » pour une conductivité thermique de 0,91 Wm-1K-1 (déterminée à l’aide d’un fluxmètre). L’incorporation de ciment entraine une variation de ces deux propriétés. Ainsi on note d’abord une baisse de la résistance suivie d’une augmentation au delà de 4% de ciment. Toutefois la conductivité thermique des blocs ayant les teneurs en ciment les plus importantes reste proche de celle des blocs sans ciment.Mots-clés: bloc d’argile, ciment portland, stabilisation, résistance en compression, conductivité thermique. Influence of cement content on the thermomechanical properties of compressed and stabilized clay blocks This work aims to determine the compressive strength and the thermal conductivity of clay compressed blocks and stabilized with cement and to study the influence of the cement ratio on these characteristics of the blocks. The resistance of blocks without cement is (determined at dry state) is 3.7 MPa and measurements made with a fluxmeter show that the thermal conductivity of these blocks is 0,91 Wm-1 K-1. The results show also that the thermal conductivity and the compressive strength of the blocks vary according to the cement ratio. However the thermal conductivity of the blocks with high cement ratio is close to that of the blocks without cement.Keywords: clay blocks, Portland cement, stabilization, compressive strength, thermal conductivity

Global temporal changes in the proportion of children with advanced disease at the start of combination antiretroviral therapy in an era of changing criteria for treatment initiation

Introduction: The CD4 cell count and percent at initiation of combination antiretroviral therapy (cART) are measures of advanced HIV disease and thus are important indicators of programme performance for children living with HIV. In particular, World Health Organization (WHO) 2017 guidelines on advanced HIV disease noted that >80% of children aged <5 years started cART with WHO Stage 3 or 4 disease or severe immune suppression. We compared temporal trends in CD4 measures at cART start in children from low-, middle- and high-income countries, and examined the effect of WHO treatment initiation guidelines on reducing the proportion of children initiating cART with advanced disease. Methods: We included children aged <16 years from the International Epidemiology Databases to Evaluate acquired immunodeficiency syndrome (AIDS) (IeDEA) Collaboration (Caribbean, Central and South America, Asia-Pacific, and West, Central, East and Southern Africa), the Collaboration of Observational HIV Epidemiological Research in Europe (COHERE), the North American Pediatric HIV/AIDS Cohort Study (PHACS) and International Maternal Pediatric Adolescent AIDS Clinical Trials (IMPAACT) 219C study. Severe immunodeficiency was defined using WHO guidelines. We used generalized weighted additive mixed effect models to analyse temporal trends in CD4 measurements and piecewise regression to examine the impact of 2006 and 2010 WHO cART initiation guidelines. Results: We included 52,153 children from fourteen low-, eight lower middle-, five upper middle- and five high-income countries. From 2004 to 2013, the estimated percentage of children starting cART with severe immunodeficiency declined from 70% to 42% (low-income), 67% to 64% (lower middle-income) and 61% to 43% (upper middle-income countries). In high-income countries, severe immunodeficiency at cART initiation declined from 45% (1996) to 14% (2012). There were annual decreases in the percentage of children with severe immunodeficiency at cART initiation after the WHO guidelines revisions in 2006 (low-, lower middle- and upper middle-income countries) and 2010 (all countries). Conclusions: By 2013, less than half of children initiating cART had severe immunodeficiency worldwide. WHO treatment initiation guidelines have contributed to reducing the proportion of children and adolescents starting cART with advanced disease. However, considerable global inequity remains, in 2013, >40% of children in low- and middle-income countries started cART with severe immunodeficiency compared to <20% in high-income countries