Rebound surface hardness of concrete: Introduction of an empirical constitutive model

Surface hardness testing of concrete is a long established NDT method for in situ strength estimation. Nowadays, the rebound hammer is the surface hardness testing device for concrete of the most widespread use. Based on a comprehensive literature review it was realized that no general theory was developed in the last more than 50 years that could describe the relationship between surface hardness and compressive strength of concrete. The diversity of the numerous empirical proposals that can be found in the technical literature needs to be explained. It can be even found in some publications that the method is suitable only for assessing the uniformity of concrete. There is long a time need for a model that can clarify the rebound surface hardness of concrete. Present paper introduces a phenomenological constitutive model (SBZ-model) that can be formulated for the surface hardness of concrete as a time dependent material property. The generating functions of the model are based on the time dependent development of the capillary pore system of the hardened cement paste in concretes that is characterised by the water–cement ratio as a practical simplification. The modelling assumptions and the use of the model would add to the fundamental understanding of the rebound surface hardness of concrete. An extensive experimental verification study clearly demonstrated the reasonable application possibilities of the SBZ-model.     

Micro- and macrostructural characterization of polyvinylpirrolidone rotary-spun fibers

The application of high-speed rotary spinning can offer a useful mean for either preparation of fibrous intermediate for conventional dosage forms or drug delivery systems. Polyvinylpyrrolidone (PVP) and poly(vinylpyrrolidone-vinylacetate) (PVP VA) micro- and nanofibers of different polymer concentrations and solvent ratios were prepared with a high-speed rotary spinning technique. In order to study the influence of parameters that enable successful fiber production from polymeric viscous solutions, a complex micro- and macrostructural screening method was implemented. The obtained fiber mats were subjected to detailed morphological analysis using scanning electron microscope (SEM), and rheological measurements while the microstructural changes of fiber samples, based on the free volume changes, was analyzed by positron annihilation lifetime spectroscopy (PALS) and compared with their mechanical characteristics. The plasticizing effect of water tracked by ortho-positronium lifetime changes in relation to the mechanical properties of fibers. A concentration range of polyvinylpyrrolidone solutions was defined for the preparation of fibers of optimum fiber morphology and mechanical properties. The method enabled fiber formulation of advantageous functionality-related properties for further formulation of solid dosage forms.     

Neutral spherical inhomogeneities in a twisted circular cylindrical bar

We consider the torsion problem of a circular cylindrical bar which is filled up with composite spherical inclusions. The composite inclusions consist of a core and coating both of which are spherically orthotropic with the volume fractions of the core being the same in every composite inclusion. The center points of the spherical inhomogeneities are on the axis of revolution of the circular cylinder. The neutral inhomogeneity in the considered problem of elastic equilibrium is defined as a foreign body (inclusion) which can be introduced in a host body without disturbing the elastic field (displacements, stresses) in it. The conditions of the neutral inhomogeneity for the twisted circular cylindrical bar are derived, and some special cases of inhomogeneity are analyzed. The present paper gives a new example for neutral inhomogeneity in the field of elasticity.     

Electrochemical template synthesis of protein-imprinted magnetic polymer microrods

A novel method for the electrochemical template synthesis of surface-imprinted magnetic polymer microrods for protein recognition is proposed. The polymer was electrodeposited into sacrificial cylindrical microreactors, the internal walls of which were previously modified with a target model protein, avidin, by simple physisorption. The electropolymerization was performed from a mixture of 3,4-ethylenedioxythiophene, poly(styrenesulfonate) (PSS), and PSS-coated superparamagnetic nanoparticles resulting in the formation of inherently electroconductive polymers confined to the volume of the microreactor. Here we show that: (i) the template synthesis within cylindrical microreactors results in polymer rods with dimensions matching that of the reactor, (ii) the incorporation of superparamagnetic particles induces magnetic properties that allow for efficient collection and manipulation of the microrods released from the microreactors in magnetic field even from dilute solution, and (iii) the protein coating on the internal walls of the microreactors is shown to generate molecular imprints on the surface of the polymeric rods. This latter property was demonstrated by comparative binding experiments of a fluorescent avidin derivative to the surface-imprinted and non-imprinted magnetic polymer microrods.     

Composition and characterization of in situ usable light cured dental drug delivery hydrogel system

Biodegradable polymers are compatible, permeable and nontoxic, thus they can provide a useful tool for drug delivery or tissue engineering. These polymers can form hydrogels, which are suitable vehicles for different types of materials e.g. drugs, bioactive molecules or cells. In the case of dentistry, photopolymerization is an obvious method to obtain in situ useable devices which can provide a more efficient way of tailoring drug release. A hydrogel system was developed based on poly-gamma-glutamic acid that was modified with methacryloyl groups to achieve this purpose. The resulting new reactive structure was proved by NMR spectroscopy. The swelling ratio of this type of hydrogel has been found remarkable, over 300 % after 24 h, and it can release 5 ng/mm² metronidazole. The prepared hydrogels were nontoxic as viability, cytotoxicity tests and cell morphology investigations proved it. These results render this model system an excellent candidate for use as an in situ curing local drug delivery device. The new photoactive system can be utilized in the treatment of periodontal diseases or raising the effectiveness of drugs used only in the minimal effective dose.     

Improved absorption characteristics of thermally modified beech veneer produced by plasma treatment

In this study the effect of an atmospheric pressure plasma treatment by a dielectric barrier discharge (DBD) on the wettability and absorption characteristics of thermally modified beech veneer is investigated. A common immersion test using water and melamine solution has been conducted and showed improved wettability and liquid uptake after plasma treatment. Determination of the weight percent gain (WPG) confirmed increased melamine content after plasma treatment.     

"Nanoarmoured" droplets of different shapes formed by interfacial self-assembly and crosslinking of metal nanoparticles

Films comprising metal nanoparticles are assembled on the surfaces of liquid droplets of different shapes and macroscopic dimensions. These films are reinforced by dithiol crosslinks and are mechanically rugged yet permeable to the diffusion of small molecules.     

Preparation, Characterisation and Some Reactions of Organocatalysts Immobilised Between the Layers of a CaFe-Layered Double Hydroxide

Five- and six-membered cyclic ??-amino acid anions with secondary nitrogen in the ring (l-prolinate and dl-pipecolinate) were immobilised in Ca₃Fe-L(ayered)D(ouble)H(ydroxide) by the dehydration-rehydration method. The resulting organic?Cinorganic hybrids were characterised by various instrumental methods (powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray fluorescence with elemental mapping, and analytical techniques for determining the iron as well as the organic contents) and molecular modelling. The immobilised organocatalysts were tested in the cross-aldol dimerization-condensation reaction between benzaldehyde and acetone and found to be active and enantioselectivity in the dimerization was also observed.