bluuebunny/crossref_metadata_2025 huggingface dataset:
Multistate Outbreak ofSalmonellaInfections Associated With Small Turtle Exposure, 2007–2008
Authors: Harris Julie R. , Bergmire-Sweat David , Schlegel Julie H. , Winpisinger Kim A. , Klos Rachel F. , Perry Christopher , Tauxe Robert V. , Sotir Mark J.
Published: October 2009

OBJECTIVE: Turtle-associated salmonellosis was increasingly recognized in the United States during the 1960s, leading to a federal ban in 1975 on the sale of turtles <4 inches in carapace length (small turtles). Although sporadic reports of turtle-associated Salmonella are frequent, outbreaks are rare. In September 2007, several patients with Salmonella enterica serotype Paratyphi B var Java infections reported recent turtle exposure. We conducted an investigation to determine the source and extent of the infections.

PATIENTS AND METHODS: Patients with Salmonella Paratyphi B var Java infections with a specific pulsed-field gel electrophoresis pattern (outbreak strain) and illness onset between May 2007 and January 2008, were compared with healthy controls. Reptile exposure and awareness of a Salmonella-reptile link were assessed. Turtle size and purchase information were collected.

RESULTS: We identified 107 patients with outbreak-strain infections. The median patient age was 7 years; 33% were hospitalized. Forty-seven (60%) of 78 patients interviewed reported exposure to turtles during the week before illness; 41 (87%) were small turtles, and 16 (34%) were purchased in a retail pet store. In the case-control study, 72% of 25 patients reported turtle exposure during the week before illness compared with 4% of 45 controls (matched odds ratio [mOR]: 40.9 [95% confidence interval (CI): 6.9–unbounded]). Seven (32%) of 22 patients versus 11 (28%) of 39 controls reported knowledge of a link between reptile exposure and Salmonella infection (mOR: 1.3 [95% CI: 0.4–4.6]).

CONCLUSIONS: We observed a strong association between turtle exposure and Salmonella infections in this outbreak. Small turtles continue to be sold and pose a health risk, especially to children; many people remain unaware of the link between Salmonella infection and reptile contact.
Secondhand Smoke and Respiratory Symptoms Among Adolescent Current Smokers
Authors: Lai Hak-Kan , Ho Sai-Yin , Wang Man-Ping , Lam Tai-Hing
Published: October 2009

OBJECTIVE: No study has ever reported the association between persistent respiratory symptoms and exposure to secondhand smoke (SHS) in adolescent smokers. The impact of SHS exposure on child health could be largely underestimated by not taking into account such effects. We investigated the association between exposure to SHS and respiratory symptoms among adolescent current smokers.

METHODS: A total of 32506 students aged 11 to 20 years from 85 randomly selected secondary schools in Hong Kong completed a self-administered questionnaire that included persistent respiratory symptoms (for 3 consecutive months in the past 12 months), number of days of SHS exposure per week at home and outside home, smoking status, amount of active smoking, and other basic demographic characteristics and socioeconomic status.

RESULTS: Adolescent current smokers who were exposed to SHS at home 1 to 4 and 5 to 7 days/wk were 50% (95% confidence interval [CI]: 3%–121%) and 77% (95% CI: 5%–199%) more likely, respectively, to report respiratory symptoms compared with those who were unexposed (P = .01 for trend). The corresponding figures for exposure outside home were 41% (95% CI: 3%–94%) and 85% (95% CI: 31%–161%; P = .004 for trend). Such associations were also observed among never-smokers, but they were weaker than those among current smokers (P < .01 for interaction).

CONCLUSIONS: This is the first evidence that SHS exposure is associated with increased risks for persistent respiratory symptoms among adolescent current smokers. Health promotion programs should aim at SHS reduction as well as smoking cessation among adolescent smokers.
Tobacco Use: A Pediatric Disease
Authors:   Committee on Environmental Health, Committee on Substance Abuse, Committee on Adolescence, and Committee on Native American Child Health
Published: October 2009

This Policy Statement was revised. See https://doi.org/10.1542/peds.2015-3109.

Tobacco use and secondhand tobacco-smoke (SHS) exposure are major national and international health concerns. Pediatricians and other clinicians who care for children are uniquely positioned to assist patients and families with tobacco-use prevention and treatment. Understanding the nature and extent of tobacco use and SHS exposure is an essential first step toward the goal of eliminating tobacco use and its consequences in the pediatric population. The next steps include counseling patients and family members to avoid SHS exposures or cease tobacco use; advocacy for policies that protect children from SHS exposure; and elimination of tobacco use in the media, public places, and homes. Three overarching principles of this policy can be identified: (1) there is no safe way to use tobacco; (2) there is no safe level or duration of exposure to SHS; and (3) the financial and political power of individuals, organizations, and government should be used to support tobacco control. Pediatricians are advised not to smoke or use tobacco; to make their homes, cars, and workplaces tobacco free; to consider tobacco control when making personal and professional decisions; to support and advocate for comprehensive tobacco control; and to advise parents and patients not to start using tobacco or to quit if they are already using tobacco. Prohibiting both tobacco advertising and the use of tobacco products in the media is recommended. Recommendations for eliminating SHS exposure and reducing tobacco use include attaining universal (1) smoke-free home, car, school, work, and play environments, both inside and outside, (2) treatment of tobacco use and dependence through employer, insurance, state, and federal supports, (3) implementation and enforcement of evidence-based tobacco-control measures in local, state, national, and international jurisdictions, and (4) financial and systems support for training in and research of effective ways to prevent and treat tobacco use and SHS exposure. Pediatricians, their staff and colleagues, and the American Academy of Pediatrics have key responsibilities in tobacco control to promote the health of children, adolescents, and young adults.
Solution Processed Silver Sulfide Filament Memories
Authors: Yin Shong , Volkman Steven K. , Subramanian Vivek
Published: October 2009

Ionic resistive switches are emerging as a potential successor for flash in non!volatile memory applications. In ionic switches, metal cations migrate through a solid electrolyte forming filaments on an inert cathode that results in an abrupt increase in conductivity. This process is reversible, and the switches may be reverted to a low!conductive state. These switches have low transition voltages and fast read speed. The low switching energy potentially makes them more scalable than many other resistive memories. Silver Sulfide Resistive switches have been fabricated by sulfidizing evaporated silver films in Sulfur solutions. XPS is used to quantify stoichiometry of resultant films. SEM and AFM indicate that surface roughness increases with sulfidation time as the bulk silver film is consumed in forming the silver sulfide. XRD has confirmed presence of the acanthite phase of silver sulfide in the films. The entire process is performed at temperatures below 200C, so the devices are potentially stackable over conventional CMOS substrates in a BEOL process, and are applicable to printable electronics on plastic substrates. Initial characteristics measured on these cells are very promising, exhibiting low energy switching and good programming margins. Write/Erase voltages for cells were about 400mV and !200mV respectively. Ron/Roff ratios range from 10 to as high as 10, 000 depending on process conditions. Impact of bath concentration, bath temperature and post!annealing on the silver sulfide film structure are studied. Ionic switching is demonstrated in the films.
Significance of the Width of Keratinized Mucosa on the Health Status of the Supporting Tissue Around Implants Supporting Overdentures
Authors: Adibrad Mehdi , Shahabuei Mohammad , Sahabi Mahasti
Published: October 2009

Our objective was to determine the association between keratinized mucosa width and the health status of the supporting tissue around implants supporting overdentures. Sixty-six functioning dental implants were examined. Periodontal parameters measured included gingival index, plaque index, bleeding on probing, probing depth, mucosal recession, periodontal attachment level, radiographic bone level, and width of keratinized mucosa. A negative correlation was found between keratinized mucosa width and mucosal recession and periodontal attachment level. When data were dichotomized by keratinized mucosa width, the mean gingival index score, plaque index score, and bleeding on probing were significantly higher for those implants with a narrow zone (<2 mm) of keratinized mucosa. A wider mucosal band (≥2 mm) was associated with less mucosal recession and periodontal attachment loss compared with a narrow (<2 mm) band. The absence of adequate keratinized mucosa around implants supporting overdentures was associated with higher plaque accumulation, gingival inflammation, bleeding on probing, and mucosal recession.
Mechanism for the modification of Portland cement hydration using polyacrylic acid
Authors: Lota J. S. , Kendall K. , Bensted J.
Published: October 2009

Determining ways to increase the dissolution and setting of the calcium silicate phases which make up Portland cement (PC) will be advantageous in producing a dense, strong and ultimately a durable cementitious material. Polymers including polyelectrolytes such as polyacrylic acid (PAA) have been known to modify the dissolution behaviour of PCs. In the present work the hydration of PC paste with PAA is investigated. Considerable changes in microstructure of the hydrated cement pastes were observed in the presence of PAA as compared with the control paste. The physical properties of mortars containing PAA were also studied. The presence of PAA alone in a paste or mortar did not improve the compressive strength. A combination of metakaolin (MK) and PAA significantly improved the properties of the mortar over those of the mortars containing MK only. Furthermore, the combination of MK and PAA much improved the workability of the mortar thus allowing reduction in the water:cement ratio, while aiding its placement and finishing in the moulds as well as considerably increasing the strength developed. The mechanism by which PAA with and without MK alters the hydration of PC is discussed. Possible reasons for the synergistic effect of MK and PAA combination on the cement hydration behaviour are given.
Kinetics and mechanism of the carbonation of ettringite
Authors: Zhou Q. , Glasser F. P.
Published: October 2009

Synthetic, phase pure ettringite has been exposed to a moist CO2 atmosphere at 68 and 88% relative humidity (RH) both at 21–25°C and at 40°C. Physically, the ettringite was carbonated in the form of powders and pellets, pressed to ∼80% theoretical density. Nucleation of decomposition products is a slow process, requiring a definite induction period, the duration of which decreases with both increasing temperature and RH. The surfaces of compacted ettringite pellets, like loose powders, decompose to mixtures of calcium carbonate, calcium sulphate hydrate (both gypsum and hemihydrate), alumina gel and water but the interior of pellets retain water with the result that recrystallization occurs and AFm forms. Pellets more reliably predict the behaviour of industrial ettringite-based cements than loose powders, which are not observed to form AFm
Influence of ultrafine powder on the fluidity and strength of cement paste
Authors: Feng N.-Q. , Shi Y.-X. , Hao T.-Y.
Published: October 2009

The influence of several kinds of ultrafine powders (UFPs) of mineral admixtures on the fluidity and strength of cement paste have been studied. Experiments show that silica fume and UFPs of natural zeolite have a filling effect and little dispersing effect on the fluidity of cement paste; UFPs of phosphorous slag and blastfurnace slag have both a filling effect and a dispersing effect. Both kinds of UFP have a strengthening effect. Adding UFP and superplasticizer simultaneously leads to better filling and dispersing effects in cement paste, because the particles of UFP cannot fill in the cement floc effectively unless the self-coagulation of the UFP is destroyed by adsorbing superplasticizer. The strengthening effect of UFP is due to its densifying effect and chemical activity, as well as its capacity to modify the pore structure.
Stiffening rates of blended-cement pastes in hot climates
Authors: Alshamsi A. M.
Published: October 2009

The influence of microsilica, ground granulated blast-furnace slag (ggbs) and a set-retarding superplasticiser on the setting of pastes at different curing temperatures was studied. The replacement level of ordinary Portland cement (OPC) by microsilica was 10%. Replacement levels of OPC by ggbs were 30, 50 and 70%. In addition to this, three different sources of ggbs from three countries were tested. Ambient temperatures of 25, 35 and 50°C were simulated. The results show that at 25°C, microsilica retarded setting only slightly whereas the ggbs and the set-retarding superplasticiser resulted in significant retardation. At the other two curing temperatures, the retardation effects of the ggbs and the superplasticiser diminished.
Early-age hydration kinetics of steel slags
Authors: Ionescu D. , Meadowcroft T. R. , Barr P. V.
Published: October 2009

Unlike blast-furnace slags, steel-making slag is not a normal admixture for Portland cement. However, recent work has suggested that by adjusting the chemistry and the cooling rate to generate a substantial glassy phase, the potential for hydration and strength development for the granulated product is enhanced. In order to better understand the role of glassy phases in the hydration process, isothermal calorimetry was used to determine the heat release and the rate of hydration within the 25–70°C range. Synthetic slags, of varying glass:crystal ratios, were used along with Portland cement as a reference. The reactivity of the synthetic slags was found to increase with glassy content which is in agreement with the lower activation energies calculated for these slags. Activation energies for slags were found to be greater than for Portland cement.
Time-dependent load-induced deformation of Ca(OH)2
Authors: Tamtsia B. T. , Beaudoin J. J. , Marchand J.
Published: October 2009

Short-term time-dependent strains were monitored on calcium hydroxide compacts having a porosity of 19·7%. The creep experiments were conducted in a controlled environment chamber maintained dry (0% RH) at 22 ± 2°C with nitrogen purging. Prior to loading, the compact specimens were vacuum dried at 105°C for 3 h (equivalent to D-drying). The applied stress for the creep test corresponds to 5% of the compaction pressure (386 MPa). The Ca(OH)2 compact specimens were in the form of T-shaped columns with a minimum thickness value (for the web and flanges) less than 1·2 mm. The AC impedance spectra of loaded and unloaded Ca(OH)2 compact specimens were also monitored in real time. This was achieved by the coupling of the impedance analyser to the creep experiment. An assessment of the relevance of the high frequency arc depression angle obtained from the impedance analysis to an understanding of the load-induced deformation behaviour of the Ca(OH)2 compacts was made.
Recrystallisation of granulated blast-furnace slags and the significance for the hydraulic reactivity
Authors: Wang P. Z. , Trettin R. , Rudert V. , Umlauf R.
Published: October 2009

In this paper the recrystallisation reactions of granulated blast-furnace slags (GBS) with different chemical compositions were studied. The investigations were carried out with X-ray powder method on the chemically modified technical GBS. During the heating merwinite first crystallised at approximately 750°C and converted to melilite with rising temperatures. The concentrations of the crystallised mineral phases merwinite and melilite depend on the CaO content. The merwinite concentration increases and the melilite concentration decreases with rising CaO content. Depending on the chemical composition the structural parameters of the melilite vary in the range between gehlenite and åkmernite. Due to the good correlation between the gehlenite concentration and the reactivity of the GBS the gehlenite concentration can be regarded as an indicator for the reactivity of the GBS.
Heat evolution in composite cements with additions of Sn(II) and Sn(IV) chlorides
Authors: Hill J. , Sharp J. H.
Published: October 2009

The heat evolution in three high-replacement composite cement pastes—that is, Portland cement mixed with 75% and 90% ground granulated blast furnace slag and 75% pulverised fuel ash, alongside a 100% ordinary Portland cement, has been followed using isothermal conduction calorimetry at 35°C. The effects of adding 0·1% and 1% SnCl2.2H2O and SnCl4.5H2O on their heat outputs have also been studied. Results indicate that there is a significant difference between the Portland cement and the three composite cements in terms of their heat output. The addition of tin chlorides also causes complex changes to the setting times and heat output of the various cements.
Chloride diffusivity of volcanic ash blended hardened cement paste
Authors: Hossain K. M. A.
Published: October 2009

This paper reports the results of investigations on the chloride diffusivity of volcanic ash (VA) blended hardened cement pastes with varying curing age of up to one year. The pastes had 0, 20 and 40% VA as cement replacement by mass and water/binder ratios of 0·40, 0·50 and 0·60 by mass. The ACID test was used to calculate the chloride ion diffusion coefficient Di , of pastes using the Nernst–Plank equation for steady state conditions. In addition, electrical resistivity, mercury intrusion porosimetry, and differential scanning calorimetry (DSC) tests were also conducted. Good correlations were found among Di , total pore volume and electrical resistivity of the pastes. The Di of VA blended pastes was within the range of 10−7 and 10−9 cm2/s. It was also found that blending cement with VA significantly reduced the long-term chloride ion diffusion coefficient and hence increased the long-term corrosion resistance of pastes. This fact was also supported by the presence of lower quantity of Ca(OH)2 and higher quantity of Friedel's salt in the VA blended pastes as observed from the DSC tests. Pastes with 40% VA showed better performance in terms of chloride ion diffusivity. W/b ratio was also found to affect the Di at the early ages of curing, but became less important at the later ages of curing.
Effect of activator mix on the hydration and strength behaviour of alkali-activated slag cements
Authors: Fernández-Jiménez A. , Puertas F.
Published: October 2009

This paper examines on the setting time and mechanical strength behaviour of slag cement pastes activated with different alkaline activators. For this purpose three alkaline solutions were used: waterglass solution (27% SiO2, 18 % Na2O and 55% H2O), NaOH and Na2CO3, maintaining always a constant concentration of Na2O (4% by mass of slag). The solutions were prepared with mixes of 0%, 80%/20% and 20%/80%. The activation process was studied at early ages by conduction calorimetric and fourier transform infrared spectroscopy (FTIR). Results show that the initial pH of the alkaline solution plays an important role in the initial slag dissolution. However the factor playing a decisive role in the acceleration or delay of setting times and in the development of mechanical strengths is the nature of the anion present in the solution. [Formula: see text] ions act as an accelerator of the setting time, but [Formula: see text] ions delay the setting time.
Numerical simulation of temperature rise of highstrength concrete incorporating silica fume and superplasticiser
Authors: Swaddiwudhipong S. , Wu H. , Zhang M. H.
Published: October 2009

A numerical model is proposed to predict the process of adiabatic temperature rise of high-strength concrete (HSC) incorporating silica fume (SF) and superplasticisers. On the basis of predicting the exothermic hydration process of plain concrete, the proposed numerical model takes the retardation caused by the superplasticisers and the effect caused by the SF into consideration. The verification of the proposed model is carried out with several groups of experimental data on concrete at different water to cementitious material ratios and initial temperatures. This numerical model is able to predict the adiabatic temperature history of HSC with SF and superplasticiser. The computing model requires the following relevant material parameters, namely, the mineral composition of Portland cement, the amount of SF, the dosage of superplasticiser, mix proportions and initial placing temperature of concrete. The model is useful in the prediction of heat of hydration, temperature distribution in mass concrete providing useful information on de-moulding at early ages and on controlling the potential thermal cracking.
Cementitious materials based on fluidised bed coal combustion ashes
Authors: Havlica J. , Odler I. , Brandsštetr J. , Mikulíková R. , Walther D.
Published: October 2009

This paper summarises work aimed at developing cementitious materials based on fluidised bed coal combustion ashes. It was found that such ashes, unlike most conventional fly ashes, exhibit distinct hydraulic properties and – if mixed with appropriate amounts of water – set and harden spontaneously at ambient temperature, yielding a C—S—H phase and ettringite as main products of hydration. Under hydrothermal conditions the hydrogarnet phase is formed as the main reaction product, together with tobermorite and anhydrite. Depending on the composition of the ashes, the strength of the hardened material can be enhanced by the addition of some other cementitious constituents, particularly blast furnace slag. Due to the favourable strength-to-bulk density ratio, the hardened material may be considered a lightweight cementitious product.
Investigation of the CaO–Al2O3–SiO2–CaSO4–CaCO3–H2O system at 25°C by thermodynamic calculation
Authors: Damidot D. , Barnett S. J. , Glasser F. P. , Macphee D. E.
Published: October 2009

The phase diagram of the CaO–Al2O3–SiO2–CaSO4–CaCO3–H2O system relevant to cement has been calculated at 25°C and 1 bar pressure. It is composed of 331 stable phase assemblages in equilibrium with the aqueous phase and contains 30 invariant points with 15 solids. Thaumasite appears to be a stable phase with a wide stability domain. Compared to ettringite, thaumasite is stable to lower pH and generally demands higher sulphate concentrations to be stable.
Effect of an accelerated chemical degradation on water permeability and pore structure of cementbased materials
Authors: Gallé C. , Peycelon H. , Le Bescop P.
Published: October 2009

In the field of the chemical degradation of cement-based materials, the models currently developed by the CEA are based on local chemical equilibrium and on diffusion as the main transport mechanism. Convective transport is not considered in the modelling approach. In this context, investigations were carried out in order to examine the evolution of water permeability with the degradation state. Accelerated leaching tests with ammonium nitrate were performed on CEM I (OPC) pure hardened paste and concrete. Water permeability was measured and pore structure analysed through MIP. The results showed that the accelerated ammonium nitrate leaching was governed by a diffusion process and was responsible not only for portlandite dissolution but also for CSH decalcification. This degradation generated a large capillary porosity (1–0·1 μm), and was responsible for a significant increase in total porosity. Water permeability for the paste (∼10−20 to 10−18 m2) and concrete (∼10−21 to 10−19 m2) increased by about two orders of magnitude, and was well correlated with the porosity evolution. Dynamic elasticmodulus measurements confirmed the significant impact of this type of degradation on the final physicomechanicalstate of the materials.
Chemical activation of pozzolanic reaction of fluid catalytic cracking catalyst residue (FC3R) in lime pastes: thermal analysis
Authors: Payá J. , Monzó J. , Borrachero M. V. , Velázquez S.
Published: October 2009

In this paper, the role and reactivity of fluid catalytic cracking catalyst residue (FC3R) as a pozzolanic mineral admixture are studied. For that purpose, thermogravimetric (TG) studies of several FC3R/lime pastes, activated by using different chemical compounds (NaOH, gypsum, CaCl2 and Na2SO4), were performed. First, lime fixation and the nature of the hydration products were characterised from TG curves. Second, sodium sulphate was considered as the best chemical activator in the lime fixation process, yielding a 100% of fixed lime for short curing periods. In addition, hydrated gehlenite crystals incorporating sulphate ions were identified, mainly in cured pastes. From these experimental studies, it can be concluded that FC3R is a very good pozzolanic material for inclusion in lime pastes and mortars, and the addition of a small amount of Na2SO4 and CaCl2 enhanced the reactive ability of FC3R with hydrated lime.
Experimental study and modelling approaches for the thermal conductivity evolution of hydrating cement paste
Authors: Mounanga P. , Khelidj A. , Bastian G.
Published: October 2009

Thermal stresses due to hydration heat release within concrete structures can lead to early age cracking particularly in cases of massive structures. In order to prevent, minimise and avoid this, a good knowledge of the evolution of cement-based material heat transfer properties at early stages of hydration is essential. In order to address the problem of the evolution of the thermal conductivity of fresh cement paste, two models developed by the authors are discussed: first, the ‘apparent’ thermal conductivity is calculated, assuming the fresh cement paste to be a multiphase material, which makes it possible to consider the material chemical evolution. The second modelling approach is based on the theory of heat and mass transfer within non-saturated porous media. The second modelling results appear to fit the experimental results better.
Theoretical and experimental research on expansive stress in hardened cement paste
Authors: Shi H. , Yuan L.
Published: October 2009

In this paper, the formation and development of expansive stress in hardened cement paste (HCP) was studied theoretically, based on the principles of chemical thermodynamics and elasticity mechanics. The expansive stress in HCP was measured by a special test. Using both theoretical and experimental results, the disruption produced by the expansive stress caused by the expansive constituent in cement in HCP is discussed. The effects of free lime on the expansion behaviour of HCP were studied at ambient temperatures. It was found that the expansion behaviour of HCP reflects its inner stress match, which is not only relative to the content and the reactivity of expansion constituent, but also to the cohesive stress of HCP.
Resistance heating using electrically conductive cements
Authors: Wang S. , Wen S. , Chung D. D. L.
Published: October 2009

Steel fibre (8 μm diameter, 0·72 vol.%)-reinforced cement was found to be effective for resistance heating. A DC electrical power input of 5·6 W (7·1 V, 0·79 A) resulted in a maximum temperature of 60°C (initial temperature = 19°C) and a time of 6 min to reach half the maximum temperature. Efficiency of energy conversion increased with time of heating, reaching 100% after 50 min. The heat power output per unit area was 750 W/m2 for steel fibre cement, compared with 340 W/m2 for a metal wire with the same resistance. The use of carbon fibres or graphite particles in place of steel fibres resulted in less effective heating, due to the higher resistivity.
Early hydration of ordinary Portland cement with an alkaline shotcrete accelerator
Authors: Xu Q. , Stark J.
Published: October 2009

The early hydration (< 24 h) of ordinary Portland cement (OPC) with an added alkaline shotcrete accelerator was investigated by means of differential calorimetric analysis, an environmental scanning electron microscope, inductively coupled plasma-optical emission spectroscopy and X-ray diffraction analysis. Compared with normal cement paste, the presence of the accelerator first changes the hydration conditions, such as the ion concentrations and the pH value of the liquid phase of the paste directly after mixing. It influences the reactions of cement clinkers and the development of the hydrate phases. A foil-like hydration product composed of calcium aluminate hydrate (CAH) phases, long fibre-like ettringite crystals and tabular monosulphates was detected in the microstructure of the paste with the accelerator. The additional Al(OH)4− from the accelerator takes part in the hydration reactions to form CAH phases. The reactions of the accelerator are dependent on the concentration of Ca2+ ions in the liquid phase of the paste in the early course of hydration.
Hydration process of potassium polysialate (K-PSDS) geopolymer cement
Authors: Zhang Y. S. , Sun W. , Li Z. J.
Published: October 2009

Environmental scanning electron microscope (ESEM) was used to quantitatively study in situ the hydration process of potassium polysialate (K-PSDS) geopolymer cement under an 80% relative humidity environment. An energy dispersion X-ray analysis (EDXA) was also employed to distinguish the chemical composition of the hydration products. The ESEM micrographs showed that metakaolin particles were packed loosely at 10 min after mixing, with many large voids. As hydration proceeded, gels were seen and these precipitated on the surfaces of the particles. At a later stage, the particles were wrapped by thick gel layers, and their interspaces were almost completely engulfed. The corresponding EDXA results showed that the molar ratios of K/Al and Si/Al gradually decreased with the development of hydration. As a result, the molar ratios of K/Al and Si/Al of hydration products after 9 h were 1·28 and 6·54, respectively, and these were close to the theoretical values (K/Al = 1·0, Si/Al = 6·0 for K-PSDS geopolymer cement paste). In addition, no well-developed crystals were found at any age, whereas sponge-like amorphous gels could always be observed.
Tri-dimensional modelling of cementitious materials permeability from polymodal pore size distribution obtained by mercury intrusion porosimetry tests
Authors: Amiri O. , Aït-Mokhtar A. , Sarhani M.
Published: October 2009

An analytical model is developed to predict permeability of cement-based materials. It is based on the geometrical modelling of a porous structure as a tri-dimensional cubic pore network, which contains an association of n types of pores with radii Ri and lengths li. This geometrical configuration gives the model the ability to be applied to all types of pore size distribution. The permeability is expressed in function of porosity, tortuosity, critical pore radius and constrictivity, which depends on pore size distribution. These parameters are obtained from mercury intrusion porosimetry measurements. The predicted permeability values were compared with experimental ones obtained by direct measurements according to Darcy's law. The experimental validation concerns three mortars chosen for their polymodal pore size distribution. Theoretical and experimental results are in the same order of magnitude. However, the model could be improved by a better estimation of the material morphological parameters. This would be possible by using further investigation methods, in addition to mercury intrusion porosimetry tests.
Polycarboxylate superplasticiser admixtures: effect on hydration, microstructure and rheological behaviour in cement pastes
Authors: Puertas F. , Santos H. , Palacios M. , Martínez-Ramírez S.
Published: October 2009

A study was conducted on the effect of a polycarboxylate (PC) admixture on the mechanical, mineralogical, microstructural and rheological behaviour of Portland cement pastes. It was observed that the presence of PC admixture retards the initial cement hydration reactions, although this effect may be offset by possible increased diffusion in later stages. Additionally, the PC admixtures produce a few alterations in the structure and composition of the formed C—S—H gel. The addition of 1% PC admixture in the pastes generates a higher percentage of silicate bridge (Si Q2 units) mainly at 2 days. The admixture used in this study induced microstructural modifications in the pastes which slightly reduced the porosity; however the admixture did not affect the mechanical strength of the pastes at either 2 or 28 days of hydration. Finally, from the results of the rheological studies it was concluded that a low dosage of PC led to a substantial reduction (over 70%) in the yield stress.
Prediction of stress—strain relationship for polyester polymer concrete using recycled polyethylene terephthalate under compression
Authors: Jo B.-W. , Park S.-K. , Lee K.-S.
Published: October 2009

The relationship between stress and strain for polymer concrete under compression was analysed, and the effects of resin content, silane treatment, curing age, and temperature were investigated. These properties are necessary to gain a better understanding of the mechanical behaviour of polymer concrete elements. The polymer concrete cured at an elevated temperature showed a higher rate of compressive strength and elastic modulus gain than that cured at room temperature (20°C). For cylinders that were cured at an elevated temperature (70°C) and silane-treated, both the ascending and descending branches of the compressive stress-strain1 curve became steeper and more linear. A stress-strain model was developed to represent the stress-strain relationship of polymer concrete under compression. This model fitted the experimental data remarkably well and accurately reflected the descending branch of the stress-strain curve and the declining trend in ductility.
Study on early hydration of sulfoaluminate cement using an electrical resistivity method
Authors: Ye Z. M. , Chang J. , Huang S. F. , Lu L. C. , Chen W. , Cheng X.
Published: October 2009

A non-contacting electrical resistivity measurement device was used for measuring the electrical resistivity of early hydration samples of sulfoaluminate cement, a type of rapid-hardening cement. The early hydration process was monitored and the results show that the main early hydration of sulfoaluminate cement was accomplished within the initial 6 h. With the addition of the accelerator to improve the early strength, the hydration process was accelerated as demonstrated by the resistivity—time curve. The agent performed its role in the initial 15 min and reduced the electrical resistivity. The experimental results obtained by means of X-ray diffraction and the hydrated heat instrument were assessed to elucidate the relationship between the hydration process and the electrical resistivity of sulfoaluminate cement.
Transition of Friedel phase to chromate-AFm phase
Authors: Zhou J.-Z. , Qian G.-R. , Cao Y.-L. , Chui P.-C. , Xu Y.-F. , Liu Q.
Published: October 2009

The transition of the Friedel phase to the chromate-AFm phase in chromate solution and the thermal stability of the products was investigated using thermal analysis combined with mass spectrometry, X-ray diffraction and Fourier transform infrared spectrometer. The results indicated that [Formula: see text] easily substituted for Cl in the Friedel phase forming chromate-AFm. The chemical formula of chromate-AFm was characterised as 3CaO·Al2O3·CaCrO4·12H2O. Chromate-AFm gave two steps of dehydration, two steps of dehydroxylation and one step of redox reaction of Cr(VI) in the whole heating process from 40 to 1000°C. The Fourier transform infrared spectra showed different OH-metal binding ways for the Freidel phase and chromate-AFm.
The influence of constrained dilatancy on pullout resistance of strap reinforcement
Authors: Lo S. R.
Published: October 2009

It was observed that the pullout resistance factor of strap-type geosynthetic reinforcement increases with reduction in overburden stress, despite the interface friction angle of these reinforcements being less than that of the surrounding soil. This observation was investigated by examining the influence of three-dimensional constrained dilatancy on the pullout resistance factor for a two-dimensional design equation. An analytical model was developed for predicting the variation of pullout resistance factor with overburden stress. The validity of the prediction model at overburden stresses less than 100 kPa was verified by comparison with test results.
Time-dependent settlement analysis of a geosynthetic-reinforced soil
Authors: Shukla S. K. , Yin J. H.
Published: October 2009

This paper presents a mechanical modelling approach to determining the settlement of a geosynthetic-reinforced engineered granular fill–saturated soft foundation soil system. In this approach, the geosynthetic-reinforced engineered granular fill is represented by a reinforced Timoshenko beam and the saturated soft foundation soil is idealised as a Terzaghi spring–dashpot system. A parametric study has been carried out to observe the settlement response of the reinforced soil system along with the tension in the geosynthetic reinforcement at different stages of consolidation of the saturated soil.
The isochronous strain energy approach applied to the load–strain–time–temperature behaviour of geosynthetics
Authors: McGown A. , Khan A. J. , Kupec J.
Published: October 2009

The load–strain–time–temperature behaviour of geosynthetics can be determined by a variety of strength-testing methodologies. However, to date it has not been possible to directly compare and correlate the data obtained from different testing regimes in a generally applicable manner. In this paper, a strain energy approach to the characterisation of the load–strain–time–temperature of geosynthetics is developed that is intended to deal with this problem. This approach takes account of the changes in the behaviour of geosynthetics that occur with time, and is called the isochronous strain energy (ISE) approach. The background to the ISE approach is set out and used to compare and correlate the data from various strength tests carried out on a wide range of geosynthetics. This shows that the isothermal load–strain–time behaviour of a geosynthetic can be represented in a generally applicable manner within an ISE–time plot and that temperature effects can be represented within ISE–time–temperature plots. It is shown that the ISE absorbed by a geosynthetic comprises two basic components, the immediately recoverable ISE and the locked-in ISE. Representation of the behaviour of geosynthetics using these two ISE components allows the prediction of their response to any loading regime applied over any time period.
Effect of acidic mine drainage on the polymer properties of an HDPE geomembrane
Authors: Gulec S. B. , Edil T. B. , Benson C. H.
Published: October 2009

A laboratory exposure programme was conducted to assess the effects of acidic mine drainage (AMD) from metallic mine wastes on the bulk polymer properties of a 1.5-mm-thick HDPE geomembrane. Coupons of the geomembrane were immersed in tanks containing a synthetic AMD maintained at 20, 40 and 60°C. Two other solutions (acidic water and deionised water at 20, 40, and 60°C) were also used. Specimens were periodically removed from the tanks and tested to determine whether changes were occurring in the melt flow index (MFI), polymer structure (as determined by Fourier transform infrared spectroscopy, or FTIR), and oxidation induction time. Only modest effects of AMD exposure were observed in the MFI and FTIR tests over the 22-month exposure period. The OIT changed appreciably during exposure, and followed a first-order (exponential in time) degradation pattern. Greater depletion rates occurred at higher temperatures and in the chemical solutions. An Arrhenius model was used to estimate the antioxidant depletion time for HDPE geomembranes immersed in AMD. Conservative estimates of the depletion time range from 46 years to 426 years depending on field temperature, initial OIT, and exposure condition.
Viscous deformation of geosynthetic reinforcement under cyclic loading conditions and its model simulation
Authors: Kongkitkul W. , Hirakawa D. , Tatsuoka F. , Uchimura T.
Published: October 2009

To evaluate the deformation characteristics of geosynthetic reinforcement under cyclic loading conditions, a series of tensile loading tests were performed on three types of polymer geogrid and one type of geocomposite using a wide variety of loading histories, including cyclic loading and sustained loading applied during otherwise monotonic loading. In order to separate the loading rate effects due to viscous properties from the rate-independent cyclic loading effects, cyclic loading was applied at five different frequencies for the same total period of cyclic loading at several base loads using two different load amplitudes. It is shown that the residual strain that develops during a given cyclic loading history is controlled essentially by the total period of cyclic loading, whereas it is independent of loading frequency (i.e. independent of the number of loading cycles). That is, the residual strain that develops during a given cyclic loading history is due mostly to the intrinsic viscous properties of the respective geosynthetic reinforcement type. The whole relationship between the tensile load and the tensile strain measured from the start to the end of the respective test, which consisted of monotonic loading and cyclic or sustained loading or both, was successfully simulated by a non-linear three-component rheology model with parameters that do not incorporate any rate-independent cyclic loading effects.
Modelling of beams on a geosynthetic-reinforced granular fill–soft soil system subjected to moving loads
Authors: Maheshwari P. , Chandra S. , Basudhar P. K.
Published: October 2009

This paper presents an analytical method for a geosynthetic-reinforced granular fill–soft soil system subjected to a load, moving at constant velocity, over an infinitely long beam. The upper reinforced granular bed is modelled by a rough membrane embedded in a Pasternak shear layer overlying a series of compressible Winkler springs representing the underlying soft soil. Parametric studies reveal that velocity, load intensity and compressibility of granular fill have significant effects on both the flexural response of the infinite beam and the reinforcement. In contrast, interfacial frictional coefficients, shear modulus of granular layers and coefficient of lateral earth pressure do not affect the response of the beam.
Numerical study of infiltration into a soil–geotextile column
Authors: Iryo T. , Rowe R. K.
Published: October 2009

The hydraulic response to infiltration of geotextiles embedded in a sandy soil is examined. An experiment examining infiltration in a one-dimensional, homogeneous sand column is simulated using the finite element method, and functions for the hydraulic properties of the unsaturated porous media that incorporate hysteresis are examined. The numerical procedure is used to model infiltration into a sand column containing a geotextile layer, and the numerical results are compared with the experimental data. To provide insight into the hydraulic behaviour of these systems, the calibrated model is then used to perform a series of numerical experiments for different soil and boundary conditions. Finally, based on these results, the hydraulic behaviour of a one-dimensional, soil–geotextile layered system during infiltration is discussed.
Evaluation of base-reinforced pavements using a heavy vehicle simulator
Authors: Perkins S. W. , Cortez E. R.
Published: October 2009

Four full-scale flexible pavement test sections were constructed to evaluate pavement performance containing three geosynthetic reinforcement products. The test sections were constructed in an indoor facility and loaded with a heavy vehicle simulator equipped with a dual tire standard truck half axle. Stress and strain sensors were embedded in the pavement test sections, and a surface profiler was used to monitor rutting. A significant improvement in rutting, due to the development of permanent strain in the pavement and soil layers, was observed in all reinforced sections. The order of performance of the reinforced test sections corresponded to that observed in a previous study using a smaller-scale facility where a repeated traffic load was applied to a stationary plate. The benefit values, defined in terms of a traffic benefit ratio, were comparable between the two test facilities, but lower for the moving wheel load. Mechanisms of reinforcement were also seen to be similar between the two facilities. Comparison of benefit values predicted from a design model developed in a previous project showed that the model offered predictions that were consistent in trend yet conservative in magnitude.
Influence of plasticizer molecular weight on plasticizer retention in PVC geomembranes
Authors: Stark T. D. , Choi H. , Diebel P. W.
Published: October 2009

Plasticizers are used to make PVC flexible so it can be used as a geomembrane. Plasticizers can migrate from PVC geomembranes over time because of contact with air, liquid, and/or an absorbent solid material. Plasticizer migration can reduce the flexibility of PVC geomembranes, resulting in brittle behavior. This paper discusses the three mechanisms of plasticizer migration and the factors influencing these mechanisms, such as plasticizer molecular weight and linearity of the plasticizer. Field case histories are used to show how these mechanisms influence plasticizer retention in PVC geomembranes. Finally, it is recommended that a minimum average plasticizer molecular weight of 400 be used to ensure long-term plasticizer retention and adequate field performance of PVC geomembranes. The weighted-average method for calculating the average molecular weight is recommended when two or more plasticizers are used in the PVC geomembrane formulation.
Axisymmetric temperature- and stress-dependent creep response of ‘new’ and ‘old’ HDPE geomembranes
Authors: Merry S. M. , Bray J. D. , Yoshitomi S.
Published: October 2009

In this study, an axisymmetric tension test apparatus that is capable of performing constant-stress creep tests was used to compare the creep response of new and old HDPE geomembranes. Thirty-six-hour constant-stress creep tests were performed on new (about one year old) HDPE using a temperature range of 2–53°C and stresses ranging from 2 to 15 MPa. Excess material was then stored in a laboratory for an additional 7 years, after which time tests on ‘old’ geomembranes were performed. Because the experimental results could not be compared directly, an adaptation of the Singh–Mitchell creep model for soil, which is a rate process equation, was used to characterize the observed stress–strain–time–temperature response from the constant-stress creep tests over four logarithms of time. The model, which was calibrated using results on ‘new’ geomembranes, was used to predict the response of the ‘old’ geomembranes. It is shown that there was essentially no difference in the creep response of the old geomembranes.