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Lesage K.,Catholic University of Leuven | Cizer O.,Catholic University of Leuven | De Schutter G.,Ghent University | De Schutter G.,Magnel Laboratory for Concrete Research | And 3 more authors.
American Concrete Institute, ACI Special Publication | Year: 2012

Calcium nitrate (CN) has been used as a cement hydration accelerator in varying dosages in order to explore its potential to compensate hydration retardation caused by a polycarboxylic ether (PCE) superplasticizer. The initial setting time, obtained from Vicat needle penetration tests, was found to decrease for increasing CN dosage until 4 percent of the cement mass was added. For dosages beyond this amount, the initial setting time slightly increased. The detected alite and aluminate hydration products appeared to have an influence on the structure evolution during setting. It is assumed that the AFt needles destruct the C-S-H network, which could lead to lower needle penetration resistance. Source

Ramirez A.M.,Magnel Laboratory for Concrete Research | Demeestere K.,Research Group EnVOC | De Belie N.,Magnel Laboratory for Concrete Research | Mantyla T.,Tampere University of Technology | Levanen E.,Tampere University of Technology
Building and Environment | Year: 2010

This work presents promising results for air purification by heterogeneous photocatalysis on new titanium dioxide loaded cementitious materials. A set of eight concretes and plasters is enriched with TiO2 photocatalyst by dip-coating and/or sol-gel methods. First, the macro-structural features of the cementitious materials have been studied in terms of porosity and roughness. The first parameter has been determined using mercury intrusion porosimetry or by vacuum saturation, and ranged between 9 and 75%, with the highest values obtained for autoclaved aerated white concrete. Surface roughness, determined by laser profilometry, has been characterized by the Ra factor. This expresses the mean deviation of the profile from the centre line and ranged between 0.7 and 252 μm, with the highest value obtained for conventional grey concrete finished with surface brush. Secondly, the weathering resistance of the TiO2 coatings has been determined by exposing them to different abrasive conditions and by performing SEM-Edax analyses to measure quantitatively the coating's titanium content. Hereby, it is shown that high porosity and roughness are favourable for TiO2 particles retention. Finally, the preliminary air purification potential of both dip-coated and sol-gel coated TiO2 enriched concrete samples has been investigated on lab-scale using toluene as a model pollutant. High removal efficiencies (up to 86%) were obtained with the dip-coated samples, indicating their attractive photocatalytic properties for future application as air purifying building materials. © 2009 Elsevier Ltd. All rights reserved. Source

Yuan Q.,Central South University | Yuan Q.,Magnel Laboratory for Concrete Research | Shi C.,Hunan University | De Schutter G.,Magnel Laboratory for Concrete Research | And 2 more authors.
Journal of Materials in Civil Engineering | Year: 2011

Chloride-induced corrosion is the most important durability issue in a reinforced-concrete structure. In this paper, the multispecies model was used to describe the chloride transport in saturated concrete. The model was solved by using the finite-difference method by inputting parameters such as porosity, density, chemical composition of pore solution, diffusion coefficient, and chloride-binding isotherm. A depth-dependent diffusion coefficient, instead of a fixed diffusion coefficient, was used in this model. The chloride-binding isotherm was directly obtained from the diffusion test. Finally, the numerical simulation results were validated with experimental results. It was found that the numerical simulation results were in good agreement with the experimental results. © 2011 American Society of Civil Engineers. Source

Annerel E.,Magnel Laboratory for Concrete Research | Taerwe L.,Magnel Laboratory for Concrete Research
Concrc - Proceedings of Concrete Solutions, 4th International Conference on Concrete Repair | Year: 2012

Generally, concrete structures behave very well during a fire. After a fire, it could be of economical interest to reuse the structure after appropriate repair based on reliable assessment of the strength properties. This paper demonstrates how the strength may be assessed from drilled cores by measuring the weight increase of the concrete after water immersion. Furthermore, the effect on the remaining strength of a change of heating rate, duration at target temperature, water cooling and post-cooling storage is studied. Considering the effect of the storage period, a stress/strain model is developed for both traditional and self-compacting concrete. © 2012 Taylor & Francis Group. Source

Gruyaert E.,Magnel Laboratory for Concrete Research | De Belie N.,Magnel Laboratory for Concrete Research
Concrete Repair, Rehabilitation and Retrofitting III - Proceedings of the 3rd International Conference on Concrete Repair, Rehabilitation and Retrofitting, ICCRRR 2012 | Year: 2012

Concrete containing Supplementary Cementitious Materials (SCMs) such as Fly-Ash (FA) or Blast-Furnace Slag (BFS) shows a slower development of its microstructure when compared to mixes with Ordinary Portland Cement (OPC). However, concrete properties are mostly evaluated at the age of 28 days and also accelerated durability tests may start at that age. Therefore, it may be questioned whether the durability of concrete with SCMs is not underestimated when the attack in an accelerated test is concentrated in the initial stage of its lifetime, when its properties have not yet fully developed. On the other hand, when tests are started at later age, e.g. 6 months, one may criticize that in reality the concrete may undergo some degradation already before that age. Therefore, an alternative approach is suggested, in which degradation curves from accelerated tests starting at various ages are first converted to those corresponding with a real environment. Then, the degradation kinetics at different ages are combined into one final degradation curve. This principle is illustrated with data from accelerated carbonation tests in a 10 vol% CO 2 atmosphere, carried out after 1, 3, 6 or 18 months of curing. The results are used to judge whether carbonation-initiated corrosion is a risk for the structure within its life span. In another approach to compare concrete with SCMs to OPC concrete, some researchers have attempted to determine k-values for fly ash, silica fume and slag with regard to different degradation mechanisms (mainly chloride ingress and carbonation). These k-values may also be time-dependent. An attempt was made to calculate k-values for slag with regard to chloride migration based on experimental test results using a graphical method. The obtained k-values are critically discussed. © 2012 Taylor & Francis Group. Source

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