The origins of thixotropy of fresh cement pastes

A fast, powerful and stable filter based on combined wavelet and Fourier analysis for the elimination of horizontal or vertical stripes in images is presented and compared with other types of destriping filters. Strict separation between artifacts and original features allowing both, suppression of the unwanted structures and high degree of preservation of the original image information is endeavoured. The results are validated by visual assessments, as well as by quantitative estimation of the image energy loss. The capabilities and the performance of the filter are tested on a number of case studies related to applications in tomographic imaging. The case studies include (i) suppression of waterfall artifacts in electron microscopy images based on focussed ion beam nanotomography, (ii) removal of different types of ring artifacts in synchrotron based X-ray microtomography and (iii) suppression of horizontal stripe artifacts from phase projections in grating interferometry.

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Stripe and ring artifact removal with combined wavelet--Fourier filtering.

Properties and applications of foamed concrete; a review

Impact of admixtures on the hydration kinetics of Portland cement

Steady state flow of cement suspensions: A micromechanical state of the art

The objective of this study is to link the molecular structure of polycarboxylate-ether-type superplasticizers with the performance of cementitious systems in order to develop new products with enhanced properties, e.g. improved water reduction with a wide range of cements or a reduced retardation of cement hydration. Different experimental superplasticizers have been synthesized varying length and density of the polyether chains as well as the molecular weight of the polymer. The influence of these polymers on the properties of cement pastes and mortars was determined using various characterization methods like mortar flow, rheological and calorimetric measurements, adsorption measurements and mortar compressive strength. Characteristic connections between molecular structure of the polycarboxylate-type water reducers, adsorption behaviour, workability and retarding effect have been determined allowing the synthesis of new superplasticizers with improved performance.

Effects of the molecular architecture of comb-shaped superplasticizers on their performance in cementitious systems

Adsorption of polyelectrolytes and its influence on the rheology, zeta potential, and microstructure of various cement and hydrate phases.

This parametric study links the molecular structure of a carboxylate-type of superplasticizer with their performance in cement pastes with different C3A-contents. Beside the variation of the C3A-content, the experimental synthesized superplasticizers have been varied by polyethylene-oxide side chain density and length. The connection between the superplasticizers, their effect on workability properties and retardation phenomenon and the dependency of C3A-content in the cement paste has been investigated.

The characteristic interaction phenomenons between different PCE-architectures and different C3A-contents have been examined by calorimetric, rheological, adsorption, and zeta potential measurements. This study shows that with decreasing side chain density the PCE molecules adsorb stronger and thus, lower the yield stress of a cement paste by steric stabilization. It is also shown that PCE molecules with long side chains delaying the setting of the cement paste to less extend than PCE molecules with shorter side chains. Consequently, in terms of optimization of the molecular architecture, good workability can be achieved by addition of highly charged PCE with long side chains. The latter minimizes undesired retardation phenomena.

Interaction of polycarboxylate-based superplasticizers with cements containing different C3A amounts

The microstructure of dispersed and non-dispersed fresh cement pastes : New insight by cryo-microscopy

The present invention relates to polymers which comprise, as monomeric building blocks, (poly)alkylene oxide-substituted diallylamines, ethylenically unsaturated monomers B, and, if appropriate, one or more further ethylenically unsaturated monomers and, if appropriate, crosslinkers, and to the use thereof as additives in cosmetic preparations.

Stefan Becker

Papers

Effects of the molecular architecture of comb-shaped superplasticizers on their performance in cementitious systems

Adsorption of polyelectrolytes and its influence on the rheology, zeta potential, and microstructure of various cement and hydrate phases.

Interaction of polycarboxylate-based superplasticizers with cements containing different C3A amounts

The microstructure of dispersed and non-dispersed fresh cement pastes : New insight by cryo-microscopy

Polymers comprising diallylamines