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See detailCombination of mechanical and optical profilometry techniques for concrete surface roughness characterization
Perez, Fabien; Bissonnette, Benoît; Courard, Luc ULg

in Magazine of Concrete Research (2009), 61(6)

Achieving durable bond between new and old concrete still represents a challenge in concrete repair technology. It has been the subject of a number of investigations, but in most cases, only adhesion ... [more ▼]

Achieving durable bond between new and old concrete still represents a challenge in concrete repair technology. It has been the subject of a number of investigations, but in most cases, only adhesion strength was addressed. To better understand bond mechanisms, in particular those related to surface roughness, two complementary surface characterisation techniques were implemented, providing a multiscale roughness characterisation by means of specific filtering calculations: mechanical profilometry for low-scale roughness and optical profilometry for the upscale roughness. Using these complementary approaches, different types of concrete surface preparation were characterised. The resulting description highlights the complexity of concrete surface topography. Moreover, it shows that the type of surface preparation essentially affects the meso- and macro-roughness levels, microroughness being practically insensitive. Such results will be useful for better understanding the interlocking potential and bond performance of concrete repairs. [less ▲]

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See detailAdhesion of repair systems to concrete: influence of interfacial topography and transport phenomena
Courard, Luc ULg

in Magazine of Concrete Research (2005), 57(5), 273-282

Eight types of cement slurries were applied to concrete substrates. Surface preparation involved mechanical action - sandblasting and polishing - as well as saturation regulation, both dry and saturated ... [more ▼]

Eight types of cement slurries were applied to concrete substrates. Surface preparation involved mechanical action - sandblasting and polishing - as well as saturation regulation, both dry and saturated surface wet. The adhesion strength for the different combinations was measured by direct tensile tests. Multivariate statistical analysis led to the identification of a major effect of surface saturation on the results. Knowledge of the interfacial behaviour was obtained by the discrimination of the effects of partial interaction between slurry and aggregates and slurry and cement mortar respectively. It clearly showed that a third factor has to be taken into account in the explanation of adhesion, namely the interfacial transition zone between cement paste and aggregates, due to its porosity and anchoring effect. This effect was quantified by topographical observation and image analysis. Penetration of cement slurry was also confirmed by observation with binocular and fluorescent microscopy. [less ▲]

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See detailEffect of concrete surface treatment on adhesion in repair systems
Garbacz, A.; Gorka, M.; Courard, Luc ULg

in Magazine of Concrete Research (2005), 57(1), 49-60

Existing concrete surfaces need to be roughened to a profile necessary to achieve mechanical interlocking with any repair material. In this study, different surface treatments (e.g. grinding, sandblasting ... [more ▼]

Existing concrete surfaces need to be roughened to a profile necessary to achieve mechanical interlocking with any repair material. In this study, different surface treatments (e.g. grinding, sandblasting, shotblasting, hand- and mechanical milling) were performed and the quality of the preparation established on the basis of three main parameters: surface geometry, superficial concrete microcracking and adhesion. Surface geometry was characterised on the basis of the measurement of surface profile-profilometry-and the analysis of statistical and amplitude parameters calculated from the waviness (lower frequencies) and the roughness (higher frequencies) profiles of the surface. Investigations were also performed to assess the quality of the superficial zone of concrete and cracks were systematically observed in relation to surface treatment where both scanning electron microscopy and light microscopy were used for analysis. Finally, a repair mortar with or without bond coat, was applied to the concrete substrates in order to measure adhesion. Relationships clearly show the effect of roughness on adhesion in the case where no bond coat was used and also the influence of the power of the surface treatment on the waviness shape of the profile and the presence of microcracks in the near-surface layer related to failure type. [less ▲]

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See detailAlkali-silica reactivity with pessimum content on Devonian aggregates from the Belgian Arden massive
Merriaux, K.; Lecomte, A.; Degeimbre, Robert ULg et al

in Magazine of Concrete Research (2003), 55(5), 429-437

Tests of alkali-silica reactivity were conducted on Devonian aggregates from the Belgian Arden massive. These are 'Bastogne sandstones' of the metamorphosed Mirwart layer consisting of the silica rich ... [more ▼]

Tests of alkali-silica reactivity were conducted on Devonian aggregates from the Belgian Arden massive. These are 'Bastogne sandstones' of the metamorphosed Mirwart layer consisting of the silica rich psammite rock family Petrography analysis reveals the presence of wavy extinction quartz and small size silica elements known to be potentially reactive to the alkalis in the base medium of concretes. Two accelerated tests were conducted according to the RILEM TC-106 and the French Standard NF P 18-590; they confirmed the strong reactive character of the sands,from these materials. The reaction is strongest in the presence of certain percentage of non-reactive sand. For this reason, the aggregates arc, described as being potentially reactive with pessimum content'. Their use in structures concretes must therefore be considered with the particular precaution of using cements that are low in free alkalis, and if necessary, with the addition of slag, fly ash or silica fume, all of which are known to reduce alkali silica reactivity. Verification of the dimensional stability of tat-get formulae must also be conducted on concrete test pieces. [less ▲]

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See detailSurface analysis of mineral substrates for repair works: roughness evaluation by profilometry and surfometry analysis
Courard, Luc ULg; Nélis, Marc

in Magazine of Concrete Research (2003), 55(4), 355-366

Existing concrete surfaces need to be roughened to a profile necessary to achieve mechanical interlock with repair material. Surface mechanical morphometry is based on the measurement of surface profile ... [more ▼]

Existing concrete surfaces need to be roughened to a profile necessary to achieve mechanical interlock with repair material. Surface mechanical morphometry is based on the measurement of surface profile - profilometry - which can be extended to 3D representation with surfometry by means of a stylus registering the profile. Profilometry and surfometry analysis enables the quantification of the profile by means of statistical and amplitude parameters lcalculated from the total profile of the surface (the waviness (lower frequencies) and roughness (higher frequencies) profiles). These parameters have been used to compare sandblasted and polished concrete surfaces. Arithmetic mean of the pro le and flatness coefficient are particularly discriminant. Bearing ratio and Abbott curve observations are also useful for clear and simple characterisation of surface profiles. Moreover, this investigation led to the calculation of the specific length of the profile and the Wenzel's coefficient. [less ▲]

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See detailExperimental research on the determination of the main parameters affecting the behaviour of reinforced concrete columns under fire conditions
Dotreppe, Jean-Claude ULg; Franssen, Jean-Marc ULg; Bruls, Alois et al

in Magazine of Concrete Research (1996), 48(6), 117-127

The design of reinforced concrete columns under fire conditions is generally made on the basis of national and international recommendations. The CEB/FIP recommendations have been used for many years ... [more ▼]

The design of reinforced concrete columns under fire conditions is generally made on the basis of national and international recommendations. The CEB/FIP recommendations have been used for many years. Recently, in the framework of the Eurocodes, the document ENV 1992-1-2 (Eurocode 2-1-2), Structural fire design, has been approved by Commission CEN/TC250/SC2 of the European Committee for Standardization. In the CEB/FIP documents and in Eurocode 2-1-2 the main part is devoted to design from tabulated data containing the dimensions of the cross-sections and values for the concrete cover. The use of simplified calculation methods is not current practice for concrete elements, while they are widely used in the case of steel. The determination of the temperature distribution in the cross-section does not facilitate the development of a simplified method. Furthermore, in columns there is a wide scatter of experimental results. In order to gain additional information, an extensive experimental research programme on the behaviour of reinforced concrete columns under fire conditions, financially supported by the Belgian Funds for Fundamental Collective Research (FRFC-FKFO), has been performed at the Universities of Liege and Ghent. In this article the results of this research are presented and the influence of the main parameters is analysed. [less ▲]

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