Effect of compaction water content on the strength of cement-stabilized rammed earth materials

Current guidelines suggest that stabilized rammed earth materials be compacted at their optimum water content to achieve their maximum strength. Although this is true for traditional rammed earth, there is no evidence that this procedure should also be used for cement-stabilized rammed earth. Furthermore, the water content used at compaction is usually difficult to control on a construction site, so that material might be compacted at water contents other than the optimum. In this paper, a novel experimental programme is presented in which the effect of compaction water content on the unconfined compressive strength of crushed limestone stabilized to 5% Portland cement content is investigated for a range of curing periods. Freeze drying of specimens was used to arrest cement hydration to determine the evolution of hydrated cement content. Scanning electron microscope (SEM) analysis was used to identify differences between the final material microstructures. Results are discussed demonstrating the intimate link between the amount of hydrated cement, material microstructure, and compressive strength. </jats:p

Notched mini round determinate panel test to calculate tensile strength and fracture energy of fibre reinforced cement-stabilised rammed earth

The use of natural fibres (like hemp or bamboo) to improve the mechanical performances of rammed earth structures is not new in construction practice in many parts of the world. However, little scientific investigation has been carried out so far to better understand the real improvement obtained by the addition of fibres. In a recent publication [1], the feasibility of notched mini Round Determinate Panels (mRDP) has been investigated with the aim of deriving a procedure to estimate the intrinsic material properties of Fibre Reinforced Shotcrete (FRS). It was found that it was possible to recover the tensile strength and the fracture energy of the material using an inverse analysis of the experimental data and the well-known Olesen constitutive model [2]. In this paper, the use of the notched mini round determinate panel test to characterise the post-cracking performances of Cement Stabilised Rammed Earth (CSRE) was investigated. For quality control issues, in this study the soil mix consisted of crushed limestone stabilised with 8% cement by soil mass and compacted at its optimum water content (11%). Three specimens were made of CSRE alone and three samples were made of fibre-reinforced CSRE. The fibres used in this experimental campaign were unbundled synthetic copolymer fibres, 54 mm long and 0.3 mm thick. This paper discusses the applicability of a laboratory test conceived for concrete samples to rammed earth specimens. It also presents the comparison between the performances of CSRE materials with and without fibres

Strengthening mechanisms in cement-stabilised rammed earth

There is currently little scientific understanding of stabilised rammed earth (RE) and the re- lationship between water-cement ratio and compressive strength. For traditional (unstabilised) RE materials, it is standard practice to compact the soil mix at its optimum water content to achieve maximum dry density and hence maximum strength. However, this may not also apply to cement-stabilised rammed earth (CSRE). A recent investigation (Beckett and Ciancio 2014) showed that CSRE samples stabilised with 5% cement and compacted at a water content lower than optimum performed better than samples compacted at optimum or higher. This seems to be in agreement with the well-known effect in concrete materials, according to which the lower the water-cement ratio, the stronger the cementitious products hence the higher the compressive strength. This paper investigates the effect of water cement ratio in CSRE samples. Results of an experimental programme are presented and used to discuss the appropriateness of the water-cement ratio for RE materials

Materiales educativos accesibles sobre paleontología: experiencia de un equipo de extensión multidisciplinario de la UNLP

“Caminando sobre gliptodontes y tigres dientes de sable” es un colectivo extensionista de la UNLP en actividad desde el 2009, que entre sus objetivos incluye la producción de recursos educativos accesibles en temáticas paleontológicas, conjugando saberes de la ciencia y el arte. Compartimos nuestra propuesta para el abordaje de uno de los procesos biológicos más importantes de nuestra región, denominado Gran Intercambio Biótico Americano (GIBA). Consideramos que el trabajo desde una perspectiva regional o local, habilita a la construcción de una identidad de la comunidad con el espacio natural del cual forma parte, favoreciendo así la protección del patrimonio paleontológico.Facultad de Ciencias Naturales y MuseoFacultad de Arte

Estimates of Pandemic Influenza Vaccine Effectiveness in Europe, 2009–2010: Results of Influenza Monitoring Vaccine Effectiveness in Europe (I-MOVE) Multicentre Case-Control Study

Results from a European multicentre case-control study reported by Marta Valenciano and colleagues suggest good protection by the pandemic monovalent H1N1 vaccine against pH1N1 and no effect of the 2009–2010 seasonal influenza vaccine on H1N1

I-MOVE Multi-Centre Case Control Study 2010-11: Overall and Stratified Estimates of Influenza Vaccine Effectiveness in Europe

BACKGROUND: In the third season of I-MOVE (Influenza Monitoring Vaccine Effectiveness in Europe), we undertook a multicentre case-control study based on sentinel practitioner surveillance networks in eight European Union (EU) member states to estimate 2010/11 influenza vaccine effectiveness (VE) against medically-attended influenza-like illness (ILI) laboratory-confirmed as influenza. METHODS: Using systematic sampling, practitioners swabbed ILI/ARI patients within seven days of symptom onset. We compared influenza-positive to influenza laboratory-negative patients among those meeting the EU ILI case definition. A valid vaccination corresponded to > 14 days between receiving a dose of vaccine and symptom onset. We used multiple imputation with chained equations to estimate missing values. Using logistic regression with study as fixed effect we calculated influenza VE adjusting for potential confounders. We estimated influenza VE overall, by influenza type, age group and among the target group for vaccination. RESULTS: We included 2019 cases and 2391 controls in the analysis. Adjusted VE was 52% (95% CI 30-67) overall (N = 4410), 55% (95% CI 29-72) against A(H1N1) and 50% (95% CI 14-71) against influenza B. Adjusted VE against all influenza subtypes was 66% (95% CI 15-86), 41% (95% CI -3-66) and 60% (95% CI 17-81) among those aged 0-14, 15-59 and ≥60 respectively. Among target groups for vaccination (N = 1004), VE was 56% (95% CI 34-71) overall, 59% (95% CI 32-75) against A(H1N1) and 63% (95% CI 31-81) against influenza B. CONCLUSIONS: Results suggest moderate protection from 2010-11 trivalent influenza vaccines against medically-attended ILI laboratory-confirmed as influenza across Europe. Adjusted and stratified influenza VE estimates are possible with the large sample size of this multi-centre case-control. I-MOVE shows how a network can provide precise summary VE measures across Europe