Creep failure of two historical masonry towers: analysis from material to structure

Abstract: The collapse of several historical masonry towers has been attributed to gradually increasing mechanical damage, such as creep cracking which occurs under constant stress levels. This paper reviews theoretical, experimental and numerical methods for analysing compressive creep in historical masonry. The investigations focus on creep behaviour in ferruginous sandstone, as results are applied to understand the collapse of two historical towers in Belgium that were both constructed in local sandstone. At the level of the material, cracking, creep strains and acoustic emissions are studied in small-to-medium scale sandstone samples under dry and saturated conditions. Results indicate an acceleration of the degradation process when water absorption takes place during the secondary creep phase. At the structural level, numerical macro modelling is performed to investigate the effect of stress redistributions on creep behaviour of three-leaf masonry. Finally, experimental and numerical results are related to the collapse of two historical towers.status: publishe

Polymer film formation in mortars modified with water-soluble polymers

©2015 Elsevier Ltd. All rights reserved. The modification of cement mortars with small amounts of water-soluble polymers (polyvinyl alcohol-acetate, methylcellulose and hydroxyethylcellulose) is studied. During hardening, two processes can take place, i.e. cement hydration and polymer film or bridge formation. Due to the very low polymer contents, the formation of polymer films is generally not considered. In this paper, evidence is given of the presence of polymer films or bridges in mortars modified with 1% of polyvinyl alcohol-acetate or methylcellulose. A contribution to the flexural strength of these mortars is found. By means of SEM investigation, polymer bridges are detected between the layered Ca(OH)2 crystals. Additional bonds are created which strengthen the preferential cleavage sites. Furthermore, polymer films or bridges are intergrown within the cement matrix on a submicron scale.publisher: Elsevier articletitle: Polymer film formation in cement mortars modified with water-soluble polymers journaltitle: Cement and Concrete Composites articlelink: http://dx.doi.org/10.1016/j.cemconcomp.2014.11.015 content_type: article copyright: Copyright © 2015 Elsevier Ltd. All rights reserved.status: publishe

Civil engineering - Ongoing Technical Research. Part I

status: publishe

Merging cement concrete, concrete-polymezr composites and inorganic polymer technologies for sustainability in construction and restoration

status: publishe

Assessing the safety of existing structures: Reliability based assessment framework, examples and application

Safety, reliability and risk are key issues in the preservation of our built, cultural heritage. Several structural collapses make us aware of the vulnerability of our technical and natural environment and demand an adequate engineering response. In the analysis phase, an objective way to assess the safety of the structure is essential. The present raises the need for a reliability based assessment framework for existing masonry structures. Although this field of research is relatively young, different techniques have been proposed and optimised. These permit to calculate the global probability of failure of complex structures, relying on deterministic techniques able to calculate the stability state for a prescribed set of parameters. This paper illustrates how these techniques can be a valid tool to evaluate the bearing capacity of existing structures. Focus is on reliability methods based on simulation procedures (Monte Carlo, Directional Sampling), combined with an adaptive meta‐model (Response Surface, Splines, Neural Networks). Several benchmark examples demonstrate the applicability of the methodology. The mutual efficiency of the different reliability algorithms is discussed. The application focuses on the assessment of an existing masonry structure. The overall stability of a Romanesque city wall of Leuven (B) is studied in detail. The analysis treats the present safety of the city wall, regarding the uncertainties in load, geometry and resistance. Because of the low degree of safety of several parts of the wall, consolidation measures and strengthening techniques are proposed. First Published Online: 14 Oct 201

Modeling lime mortar carbonation

The carbonation process in lime mortar is influenced by the diffusion of carbon dioxide into the mortar pore system, by the kinetics of the lime carbonation reaction, and by the drying and wetting process in the mortar. All these phenomena depend on the presence of water in the mortar. Water is present in liquid form as well as vapour. Physical models and their mathematical basis are given for the factors influencing carbonation. The mathematical description of the carbonation process in lime mortar completes the information necessary to model the simulation of carbonation in conjunction with the drying process. Simulations at different carbon dioxide concentrations showed a good correlation between experiment and mathematical prediction.status: publishe

Multi-scale approaches for the assessment of time-dependent mechanical damage in masonry. (keynote)

© 2016 Taylor & Francis Group, London. Time-dependent mechanical damage, such as creep phenomena, can lead to changes in material properties and cause gradual deterioration of structural components or even collapse of structures. While historic masonry structures are generally expected to have relatively lowstress levels with little consequence on their longterm performance, increasing age and structural alterations can result in increasing stress levels and accelerated long-term deterioration. This contribution presents experimental and numerical methods which are applied to understand and analyze compressive creep behavior of masonry at different scales: at the micro scale, crack initiation and growth is visualized by means of X-ray microfocus Computed Tomography (microCT); at the meso level, creep tests are performed on samples at the scale of building blocks; at the macro level, numerical modelling is performed to investigate creep effects at the scale of a multi-leaf masonry wall and at the scale of the whole structure. The discussion will be related to a case study, a medieval church tower constructed in 3-leaf sandstone masonry, which collapsed in 2006. New insight has recently been acquired with respect to the cause of collapse during the analysis of the debris and during the archeological investigations which preceded the erection of a new tower.status: publishe

Restauratie en revalorisatie van de ’s Hertogenmolens te Aarschot, 2006-2010

De watermolen werd gebouwd in 1505-1507 door Guillaume de Croy, heer van Aarschot. Naast molen, was het gebouw ook één van de belangrijkste versterkte punten van de verdediging van de stad: met de sluizen kon het Kempens deel (noordelijk deel) van het (niet omwalde) stadsdeel onder water worden gezet. Deze banmolens (molens waar de naburige boeren hun graan verplicht moesten laten malen), eigendom van de hertog van Aarschot, werden in1795 onteigend en tot nationaal eigendom van de Franse staat gemaakt. In 1795 werden de Oostenrijkse Nederlanden immers officieel ingelijfd bij Frankrijk. In 1812 verkoopt de overheid de molens aan de familie Ectors. In 1910 werd de molen in openbare verkoop aangekocht door de Belgische Staat. Nog in de jaren 1960 werd de molen gebruikt als pletmolen voor glas. Het poeder werd o.a. gebruikt bij de fabricage van schuurpapier. Eenmaal verlaten, trad het verval vlug in. Na een brand in 1970, werd een zijvleugel gesloopt. In 1986 volgde de bescherming als monument. In het kader van een Belgische staatshervorming werd de molen overgedragen aan het Vlaams Gewest. In 2004 ging nogmaals een eigendomsoverdracht door naar de stad Aarschot. Al sinds de jaren 1980 werden restauratieplannen opgemaakt. De uitvoering ervan werd dringend, aangezien één van de westgevels instortte in 1986. Pas na de overdracht aan het Vlaams Gewest en na de opname van de 's Hertogenmolens in een stadsvernieuwingsproject kwam het dossier in een stroomversnelling. De onderbouw, waar het water van de Demer doorstroomt, werd gerestaureerd door de dienst Waterwegen en Zeekanaal nv. De bovenbouw werd via een privaat-publieke samenwerking (pps) gerevaloriseerd als hotel. In het weekend van 12 en 13 juni 2010 werden de gerenoveerde 's Hertogenmolens officieel geopend. In 2011 werden de 's Hertogenmolens bekroond met de Provinciale Architectuurprijs Vlaams-Brabant en met de Europa Nostra Award.status: publishe

Combining mineral and polymer binder material science for sustainability in construction and restoration

The study of microstructure formation in polymer-cement concrete provides opportunities to exploit synergetic actions between cement and polymer, leading to performance improvement and to a wide range of new and innovative properties and applications. Polymers can reduce the impact of construction industry on environment, by decreasing the carbon footprint of cement and concrete production. Renovation and restoration, largely figuring in the concept of sustainable construction development, thank their growing share in construction activity to the input of polymers in repair and binder materials and in rehabilitation procedures. The study of ancient binders and mortars reveals aspects of the origins of the observed long lasting durability of those ancient mortars. It also reveals the interaction mechanisms between carbonation of air hardening components and hydration of hydraulic components, which in turn helps to develop chemical activation methods (i.e. alkaline activation) to improve the hydraulic properties of pozzolans and industrial residues to develop inorganic polymers (i.e. geopolymers) for eventually full replacement of cement in binders.status: publishe

Durable restoration of reinforced concrete grillage roof shell of Ensor Gallery in Ostend (B)

status: publishe