Effect of cellulose ethers on water retention in freshly-mixed mortars

International audienceCellulose ethers are polymers frequently introduced into mortar formulations in order to improve water retention capacity and workability of the freshly-mixed materials. Physico-chemical parameters of these admixtures (molecular weight, granulometry, substitution degrees, etc) seem to have a strong influence on mortar water retention capacity. In this paper, the influence of cellulose ether molecular weight on mortar water retention and its consistency was studied. Moreover, a new method was used to evaluate mortar consistency, named Consistor Baronnie method. This method was confirmed with rheological measurements

NMR investigations of water retention mechanism by cellulose ethers in cement-based materials

International audienceWe show how nuclear magnetic spin-lattice relaxation dispersion of proton-water (NMRD) can be used to elucidate the effect of cellulose ethers on water retention and hydration delay of freshly-mixed white cement pastes. NMRD is useful to determine the surface diffusion coefficient of water, the specific surface area and the hydration kinetics of the cement-based material. In spite of modifications of the solution's viscosity, we show that the cellulosic derivatives do not modify the surface diffusion coefficient of water. Thus, the mobility of water present inside the medium is not affected by the presence of polymer. However, these admixtures modify significantly the surface fraction of mobile water molecules transiently present at solid surfaces. This quantity measured, for the first time, for all admixed cement pastes is thus relevant to explain the water retention mechanism

Water transport in freshly-mixed mortars containing cellulose ethers

Groupe de travail n°2 : Interactions éther de cellulose-ciment du CEReM (Consortium d'Etudes et de Recherches sur les Mortiers)Polysaccharides are polymers frequently introduced into mortar formulations in order to improve the workability and water retention capacity of the fresh materials [1]. Among all the polysaccharides, cellulose ethers seem to be the most suitable molecules to obtain a mortar with pretty good water retention ability (i.e. higher than 94%). On the other hand, polysaccharides such as starch ethers or starches generally induce a low increase in water retention (i.e. up to 85%). Mortar consistency may contribute to its water retention capacity but this hypothesis should be checked by further investigations. Indeed, cellulose ethers could induce excellent water retention thanks to the possible superposition of two phenomena [2]: - a rheological effect similar to the one caused by other polysaccharides; - an effect that could be specific to cellulose ethers, which remains to be defined. It could be caused by a modification of the porous network in the fresh state, osmotic pressure or the presence of a cellulose ether film playing the role of diffusion barrier. The molar mass distribution of polysaccharides has been determined by size exclusion chromatography. Using such well-known molecules, it should be possible to understand the functioning of three types of cellulose ethers (HEC, HPMC and HEMC) on mortar water retention. Then, the influence of mortar consistency on water retention has been studied in order to verify if there is a relationship between these two parameters. To complete the panel, the impact of starch ethers on water retention and mortar consistency has also been investigated

Influence of Cellulose Ether Particle Size on Water Retention of Freshly-Mixed Mortars

International audienceCellulose ethers are polymers frequently introduced into mortar formulations in order to improve water retention capacity and workability of the freshly-mixed materials. Physico-chemical parameters of these admixtures (molecular weight, granulometry, substitution degrees, etc) seem to have a strong influence on mortar water retention capacity. In this paper, the influence of cellulose ether particle size was studied. Two behaviors were highlighted regarding the particle size effect on mortar water retention. On the one hand, for cellulose ethers providing intermediate water retention, this parameter is fundamental: the thinner the particles, the better the water retention. The increase in water retention was explained by the rate of dissolution of every fraction which was faster for the thinnest particles. On the other hand, for admixtures providing strong water retention, the effect of this parameter was weaker or not relevant. Indeed, a cellulose ether concentration threshold was noticed, justifying this behavior

Cellulose ethers influence on water retention and consistency in cement-based mortars

International audienceCellulose ethers (CE) are commonly used as additives to improve the quality of cement-based materials. As admixtures, they improve the properties of mortars such as water retention, workability, and open time. Also, polysaccharides such as starch derivatives are used to improve the consistency of the fresh material. The properties of cement-based mortars at fresh state were investigated. The effect of CE and their physico-chemical parameters (molecular weight, substitution degrees, etc.) on both water retention and rheological properties of mortars were studied. Moreover, some starch derivatives were also examined in order to better understand the water retention mechanisms. Rheological measurements showed that CE have a thickening effect for a content of 0.27 wt.%. Besides, a fundamental effect of CE molecular weight on mortar consistency and its water retention capability was highlighted. Finally, the comparison with starch ethers proved that, for those admixtures, water retention is not directly linked to mortar's viscosity

Nuclear magnetic relaxation dispersion investigations of water retention mechanism by cellulose ethers in mortars

International audienceWe show how nuclear magnetic spin-lattice relaxation dispersion of proton-water (NMRD) can be used to elucidate the effect of cellulose ethers on water retention and hydration delay of freshly-mixed white cement pastes. NMRD is useful to determine the surface diffusion coefficient of water, the specific area and the hydration kinetics of the cement-based material. In spite of modifications of the solution's viscosity, we show that the cellulosic derivatives do not modify the surface diffusion coefficient of water. Thus, the mobility of water present inside the medium is not affected by the presence of polymer. However, these admixtures modify significantly the surface fraction of mobile water molecules transiently present at solid surfaces. This quantity measured, for the first time, for all admixed cement pastes is thus relevant to explain the water retention mechanism

A pulsed field gradient and NMR imaging investigations of the water retention mechanism by cellulose ethers in mortars

International audienceThe study presented in this paper is devoted to improve the knowledge on the influence of cellulose ethers (CE) on the freshly-mixed mortars water retention. Indeed, this crucial property is the most important imparted by these polysaccharides. One of the assumptions proposed to explain this phenomenon is that CE acts as diffusion barrier to the water. To test this hypothesis, the CE effect on the self-diffusion coefficient of water in solution and on the water mobility between two fresh cement pastes was studied by Nuclear Magnetic Resonance. CE does not significantly modify the water self-diffusion coefficient in CE solution or in admixed cement pastes. Moreover the interdiffusion imaging experiments demonstrated that the water diffusion at the paste/paste interface is not affected by the presence of cellulosic admixture

Reliability of Immunoglobulin G Antitoxoplasma Avidity Test and Effects of Treatment on Avidity Indexes of Infants and Pregnant Women

The immunoglobulin G antitoxoplasma avidity test (Vidas; BioMérieux) is an immunoenzymatic test useful for excluding acute infection after the onset of pregnancy. The avidity index (AI) is the ratio of the signal in a test sample washed with urea, which disrupts low-avidity complexes, to that washed without urea. An AI of >0.3 is taken to mean that infection had occurred more than 4 months ago. The increase of the AI with time and the influence of the different treatments given to pregnant women and their newborns were evaluated. A total of 59 pregnant women (271 sera) and their 60 neonates (199 sera) were tested from 1998 to 2002. There were five groups of women based on the type and duration of treatment given. Thirteen pregnant women (group 1) did not receive any treatment, 15 (group 2), 11 (group 3), and 17 (group 4) women received treatment with spiramycin (9 MIU/day) for 0.5 to 2, 2.5 to 5, and 5.5 to 8 months, respectively, and the last 3 women (group 5) received tritherapy (pyrimethamine-sulfonamide and spiramycin alternatively) for 1.5 to 2.5 months. All of the maternal sera collected in the first 6 months had an AI of <0.30, with a mean of 0.07 (range, 0.01 to 0.21). The increase was slow (0.02/month), and there was no significant difference when comparisons were made between the treatment groups. Neonates with proven maternofetal transmission had an increasing AI, unlike those without transmission. However, long-term therapy with pyrimethamine-sulfonamide, as opposed to treatment with spiramycin alone, was found to slow down the progression of the AI. An AI of >0.2 is sufficient to exclude acute infection in pregnant women. In neonates, it is not of major use to diagnose congenital infection; however, it could be a good indicator of compliance and efficacy of treatment of infected infants

Early skin-to-skin contact and risk of late-onset-sepsis in very and extremely preterm infants

International audienceBackgroundTo evaluate the association between exposure to early skin-to-skin contact (SSC) and incidence of late-onset sepsis (LOS) in extremely and very preterm infants.MethodsObservational study using the national population-based EPIPAGE-2 cohort in 2011. A propensity score for SSC exposure was used to match infants with and without exposure to SSC before day 4 of life and binomial log regression used to estimate risk ratios and CIs in the matched cohort. The primary outcome was at least one episode of LOS during hospitalization. Secondary outcomes were the occurrence of any late-onset neonatal infection (LONI), LOS with Staphylococcus or Staphylococcus aureus, incidence of LOS and LONI per 1000 central venous catheter days.ResultsAmong the 3422 included infants, 919 were exposed to early SSC. The risk ratio (RR) for LOS was 0.86 (95% CI, 0.67–1.10), for LONI was 1.00 (95% CI, 0.83–1.21), and for LOS with Coagulase-negative Staphylococcus or Staphylococcus aureus infection was 0.91 (95% CI, 0.68–1.21) and 0.77 (95% CI, 0.31–1.87). The incidence RR for LOS per-catheter day was 0.87 (95% CI, 0.64–1.18).ConclusionEarly SSC exposure was not associated with LOS or LONI risk. Thus, their prevention should not be a barrier to a wider use of SSC