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Sempach, Switzerland

Wetzel A.,University of Bern | Wetzel A.,University of Kassel | Herwegh M.,University of Bern | Zurbriggen R.,Elotex AG | Winnefeld F.,Empa - Swiss Federal Laboratories for Materials Science and Technology
Cement and Concrete Research | Year: 2012

Shrinkage and expansion of cementitious materials like tile adhesive mortars depend on the presence of water as well as on the drying and rewetting history. Particularly for large-sized tiles such volumetric changes induce stress concentrations, which may result in cracking. This study focuses on the interplay between water infiltration and cracking, starting at the early curing of the mortar during the first days after application until water transport in the hardened system. Based on laboratory experiments, different events concerning the effect of water transport were induced by variation of the experimental setups in order to provoke cracking. Cracks at the tile-mortar interfaces suggest these domains to reflect zones of mechanical weakness. Along these cracks, water can enter the system inducing precipitation of secondary minerals in cracks and pores already after one wetting cycle. These processes reveal increasing importance during repeated cycles of drying and wetting, i.e. under outdoor conditions and may lead to failures. © 2011 Elsevier Ltd. All rights reserved. Source


Kaufmann J.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Winnefeld F.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Zurbriggen R.,Elotex AG
Cement and Concrete Composites | Year: 2012

The interaction between mineral surfaces and organic polymer dispersions with different monomer base and protective colloids as present in tile adhesive mortar systems was investigated by measuring the ζ-potential and by direct observation by atomic force microscopy (AFM). The charge situation of pure mineral powders and pure polymer dispersions as well as their interaction in presence of different cementitious aqueous solutions was studied. The binding of Ca ++ ions leads to positive ζ-potentials for quartz or ceramic in calcium containing aqueous solutions and acts as a transmitter of attractive forces. However, the adsorption of sulfate ions may disturb such attraction. The interaction between polymer dispersions and ceramic (polished and original tile) or mica surfaces influenced by the presence of artificial cementitious pore solutions was observed by AFM. A flat index (height/diameter of latex particles in contact with these surfaces) was defined to quantify the polymer-mineral interface affinity. The different flat indices for different polymer-substrate combinations are mainly related to two parameters, the glass transition temperature of the copolymer and the stabilization system (steric versus cationic). Furthermore tapping phase imaging revealed significant heterogeneities in the inner structure of the polymer particles and inhomogeneous distribution at their surface probably related to local variations of the protective colloid, especially polyvinyl alcohol. © 2012 Elsevier Ltd. All rights reserved. Source


Winnefeld F.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Kaufmann J.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Hack E.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Harzer S.,Empa - Swiss Federal Laboratories for Materials Science and Technology | And 3 more authors.
Construction and Building Materials | Year: 2012

The durability of tilings is affected by the size and type of ceramic tiles. We therefore performed a study on adhesion and shrinkage mechanisms of large-sized fully vitrified tiles (30 cm × 30 cm), which were applied on a concrete substrate using two different polymer-modified tile adhesive mortars (floor and wall application). The spatial distributions of adhesion strength and mortar hydration degree, as well as the length changes of the composite specimen were determined under various curing conditions. The deformations caused by wetting and drying events are restrained by the stiff tile. Thus, stresses result especially at the edges of the tile, which may cause micro-cracking at the interface of tile and mortar resulting in a reduction of adhesion strength. © 2011 Elsevier Ltd. All rights reserved. Source


Wetzel A.,University of Bern | Zurbriggen R.,Elotex AG | Herwegh M.,University of Bern
Cement and Concrete Composites | Year: 2010

The rising number of failures of porcelain tiles, especially in outdoor applications, is to some extent a consequence of the critical combination of applying tiles of large dimensions and the non-porous nature of these tiles. A special setup allows a reproducible application of large-sized tiles (30 × 30 cm). In analogy to outdoor conditions, samples were stored under dry and wet conditions and have been investigated with different physico-chemical approaches. Under dry storage conditions adhesion strength is significantly lower along the periphery of the tiles compared to their centre. This reduction in adhesion performance is mainly caused by shrinkage of the mortar and substrate (∼0.1 mm/m). In situ observations through glass tiles indicate that the stresses induced by shrinkage are highest in the rim regions of the tiles. Under wet storage conditions, water percolates into the rim regions of the mortar, which leads to swelling of mortar and substrate, accelerating the delamination process. The findings of this study confirm observations on the construction site, where initial failures are often found at the periphery of large-sized tiles. © 2010 Elsevier Ltd. All rights reserved. Source

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