Effect of Nanosilica on Rheology, Fresh Properties, and Strength of Cement-Based Grouts

The effect of colloidal nanosilica on the fresh and rheological parameters, plastic shrinkage, heat of hydration, and compressive strength of cement-based grouts is investigated in this paper. The fresh and rheological properties were evaluated by the minislump flow, Marsh cone flow time, Lombardi plate cohesion meter, yield value, and plastic viscosity. The key parameters investigated were the dosages of nanosilica and superplasticizer and temperature of mixing water. Statistical models and isoresponse curves were developed to capture the significant trends. The dosage of nanosilica had a significant effect on the results. The increase in the dosage of nanosilica led to increasing the values of flow time, plate cohesion meter, yield stress, plastic viscosity, heat of hydration at 1 day and 3 days, and compressive strength at 1 day, while reducing the minislump, plastic shrinkage up 24 h, and compressive strength at 3, 7, and 28 days. Conversely, the increase in the dosage of superplasticizer led to decreasing the values of flow time, plate cohesion meter, yield stress, plastic viscosity, heat of hydration at 1 day and 3 days, and compressive strength at 1 day, while increasing the minislump, plastic shrinkage, and compressive strength at 3 and 7 days. Increasing the temperature of mixing water led to a notable increase in the results of minislump, flow time, plastic viscosity, heat of hydration at 3 days, and compressive strength at 1 day, while it reduced the plate cohesion, compressive strength at 3, 7, and 28 days. The statistical models developed in this study can facilitate optimizing the mixture proportions of grouts for target performance by reducing the number of trial batches needed.

Influence of rheology on the quality of surface finish of cement-based mortars

Aesthetics of concrete structures is directly related to the quality of their surface finish. The objective of this investigation was to examine the effect of rheological properties of cement-based mortars on the quality of their surface finish. The study was divided into two phases. Firstly, the influence of the mix composition of mortars, viz. the water to cement (w/c) ratio, the sand content and the superplasticiser (SP) dosage on their rheology was evaluated. Secondly, the surface finish quality was characterised and related to the rheology of the studied systems. Rheology of these materials, i.e. the yield value, was measured using a vane viscometer. The quality of the surface finish was assessed by quantification of the surface air voids by analysing digital photographs of the mould finished sample surfaces. It was found that an increase in the w/c ratio and the SP content decreased the yield value, whilst the increase in the sand content had an opposite effect. When the surface quality is concerned, an increase in the yield value was found to increase the total content of the surface air voids and especially those with size smaller than 1 mm in diameter. Moreover, the analysis of the location of the surface air voids along the height of the sample revealed that with the increase in the yield value their concentration was higher in the bottom section of the analysed samples.

Influence of mix proprtions on rheolgy of cement grouts containing limestone powder

In this paper the parameters of cement grout affecting rheological behaviour and compressive strength are investigated. Factorial experimental design was adopted in this investigation to assess the combined effects of the following factors on fluidity, rheological properties, induced bleeding and compressive strength: water/binder ratio (W/B), dosage of superplasticiser (SP), dosage of viscosity agent (VA), and proportion of limestone powder as replacement of cement (LSP). Mini-slump test, Marsh cone, Lombardi plate cohesion meter, induced bleeding test, coaxial rotating cylinder viscometer were used to evaluate the rheology of the cement grout and the compressive strengths at 7 and 28 days were measured. A two-level fractional factorial statistical model was used to model the influence of key parameters on properties affecting the fluidity, the rheology and compressive strength. The models are valid for mixes with 0.35-0.42 W/B, 0.3-1.2% SP, 0.02-0.7% VA (percentage of binder) and 12-45% LSP as replacement of cement. The influences of W/B, SP, VA and LSP were characterised and analysed using polynomial regression which can identify the primary factors and their interactions on the measured properties. Mathematical polynomials were developed for mini-slump, plate cohesion meter, inducing bleeding, yield value, plastic viscosity and compressive strength as function of W/B, SP, VA and proportion of LSP. The statistical approach used highlighted the limestone powder effect and the dosage of SP and VA on the various rheological characteristics of cement grout

Rheological characterization of thermoresponsive semisolids for vaginal HIV vaccine delivery

Purpose. To manufacture and characterize, through oscillatory rheology, thermoresponsive rheologically structured vehicles
(RSV’s) capable of enhanced retention times within the vagina for the purposes of HIV vaccine delivery.
Methods. Pluronics F127, F108 and F68 were investigated and RSV’s were prepared by dissolving sorbic acid (0.1% w/w)
and mucoadhesive component (Gantrez SBF97 or Noveon AA1, 3% w/w) in the required amount of H2O and NaOH.
Pluronic (10% w/w) was added via mixing in an ice-bath followed by hydroxyethylcellulose (5%) and subsequently
poly(vinylpyrollidone) (4%w/w). Oscillatory temperature sweeps between 10-38°C were preformed within the linear
viscoelastic region of the formulations on an AR2000 rheometer (T.A. Instruments, Surrey, England) with a 2cm diameter
parallel plate geometry and a plate gap of 1000µm at 1Hz.

Characterisation of the Interaction of Lactate Dehydrogenase With Tween-20 Using Isothermal Titration Calorimetry, Interfacial Rheometry and Surface Tension Measurements

In this study the nature of the interaction between Tween-20 and lactate dehydrogenase (LDH) was investigated using isothermal titration calorimetry (ITC). In addition the effects of the protein and surfactant on the interfacial properties were followed with interfacial rheology and surface tension measurements in order to understand the mechanism by which the surfactant prevents protein adsorption to the air– water interface. Comparisons were made with Tween-40 and Tween-80 in order to further investigate the mechanism. ITC measurements indicated a weak, probably hydrophobic, interaction between Tween-20 and LDH. Prevention of LDH adsorption to the air–water interface by the Tween surfactants was correlated with surface energy rather than surfactant CMC. While surface pressure appears to be the main driving force for the displacement of LDH from the air–water interface by Tween-20 a solubilisation mechanism may exist for other protein molecules. More generally the results of this study highlight the value of the use of ITC and interfacial measurements in characterising the surface behaviour of mixed surfactant and protein systems.

Rheological Evaluation of the Isothermal Cure Characteristics of Medical Grade Silicone Elastomers

Silicone elastomer systems have been shown to offer potential for the fabrication of medical devices and sustained release drug delivery devices comprising low molecular weight drugs and protein therapeutics. For drug delivery systems in particular, there is often no clear rationale for selection of the silicone elastomer grade, particularly in respect of optimizing the manufacturing conditions to ensure thermal stability of the active agent and short cycle times. In this study, the cure characteristics of a range of addition-cure and condensation-cure, low-consistency, implant-grade silicone elastomers, either as supplied or loaded with the model protein bovine serum albumin (BSA) and the model hydrophilic excipient glycine, were investigated using oscillatory rheology with a view to better understanding the isothermal cure characteristics. The results demonstrate the influence of elastomer type, cure temperature, protein loading, and glycine loading on isothermal cure properties. By measuring the cure time required to achieve tan delta values representative of early and late-stage cure conditions, a ratio t(1)/t(2) was defined that allowed the cure characteristics of the various systems to be compared. Sustained in vitro release of BSA from glycine-loaded silicone elastomer covered rod devices was also demonstrated over 14 days. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2320-2327, 2010

Effect of MWCNT addition on the thermal and rheological properties of polymethyl methacrylate bone cement

Multi-walled carbon nanotube (MWCNT)/polymethyl methacrylate (PMMA) composites with loadings ranging from 0.1 to 1.0 wt.% were prepared for use as bone cement. Unfunctionalised, carboxyl and amine functionalised MWCNT were used. Thermal properties were characterised in accordance with the International Standard for acrylic cements, ISO 5833:2002. The rate of reaction exotherm generated and thermal necrosis index (TNI) values were calculated. Polymerisation kinetics were characterised using parallel plate rheology and the exotherm during polymerisation was reduced by ˜4–34%, as a consequence of the MWCNT thermal conductivity. The rate of reaction was significantly altered, such that the setting times of the cements were extended (˜3–24%). Consequently, significant decreases in TNI values (ranging from 3% to 99%) were recorded, which could reduce the exothermic temperatures experienced in vivo and therefore prevent the likelihood of polymerising PMMA cement causing thermally-induced bone tissue necrosis. Thermal data was supported by the rheological characterisation results. Onset of polymerisation for PMMA cement exhibited a strong linear increase as a function of MWCNT loading, however, polymer gelation was not affected to the same degree. It is proposed that the chemically functionalised MWCNT altered PMMA bone cement polymerisation kinetics, reducing the rate of polymerisation, and hence, the reaction exotherm.

Rheological, mechanical and membrane penetration properties of novel dual drug systems for percutaneous delivery

In this study it has been demonstrated that mixtures of two solid drugs, ibuprofen and methyl nicotinate, with different but complementary pharmacological activities and which exist as a single liquid phase over a wide composition range at skin temperature, can be formulated as o/w emulsions without the use of an additional hydrophobic carrier. These novel dual drug systems provided significantly enhanced in vitro penetration rates through a model lipophilic barrier membrane compared to conventional individual formulations of each active. Thus, for ibuprofen, drug penetration flux enhancements of three- and 10-fold were observed when compared to an aqueous ibuprofen suspension and a commercial alcohol-based ibuprofen formulation, respectively. Methyl nicotinate penetration rates were shown to be similar for aqueous gels and emulsified systems. Mechanisms explaining these observations are proposed. Novel dual drug formulations of ibuprofen and methyl nicotinate, formulated within the liquid range at skin temperature, were investigated by oscillatory rheology and texture profile analysis. demonstrating the effects of drug and viscosity enhancer concentrations, and disperse phase type upon the rheological, mechanical and drug penetration properties of these systems. (C) 2000 Elsevier Science B.V. All rights reserved.

Physical characterisation and component release of poly(vinyl alcohol)-tetrahydroxyborate hydrogels and their applicability as potential topical drug delivery systems

Poly(vinyl alcohol)-tetrahydroxyborate (PVA-THB) hydrogels are dilatant formulations with potential for topical wound management. To support this contention, the physical properties, rheological behaviour and component release of candidate formulations were investigated. Oscillatory rheometry and texture profile analysis were used at room temperature and 37 °C. Results showed that it was possible to control the rheological and textural properties by altering component concentration and modifying the type of PVA polymer used. Hydrogels made using PVA grades with higher degrees of hydrolysis displayed favourable characteristics from a wound healing perspective. In vitro release of borate and PVA were assessed in order to evaluate potential clinical dosing of free species originating from the hydrogel structure. Component diffusion was influenced by both concentration and molecular weight, where relevant, with up to 5% free PVA cumulative release observed after 30 min. The results of this study demonstrated the importance of poly(vinyl alcohol) selection for ensuring appropriate gel formation in PVA-THB hydrogels. The benefits of higher degrees of hydrolysis, in particular, included lower excipient release and reduced bioadhesion. The unique physical characteristics of these hydrogels make them an appealing delivery vehicle for chronic and acute wound management purposes.