Influence des composants des interfaces béton - agent démoulant - coffrage sur l'aspect des parements en béton

audience: researcher, professiona

Patch-Scale Movement Dynamics in the Iowa Grassland Butterflies \u3ci\u3eSpeyeria Cybele\u3c/i\u3e and \u3ci\u3eMegisto Cymela\u3c/i\u3e (Lepidoptera: Nymphalidae)

An understanding of the movement dynamics of invertebrates can be critical to their conservation, especially when managing relatively small, isolated habitats. Most studies of butterfly movement have focused on metapopulation dynamics at relatively large spatial scales, and the results from these studies may not translate well for patchy populations within a single nature preserve. In this work we use individual mark and recapture (IMR) methods to follow the movements of two species of butterfly, Megisto cymela (Cramer) and Speyeria cybele F. (Lepidoptera: Nymphalidae) within a 240 hectare forest and grassland preserve in central Iowa, USA. Significant redistribution was seen in both species, with 55.7% of S. cybele and 31.1% of M. cymela undergoing interpatch movement. Median movement rates during the study were 105 m/day for S. cybele and 38 m/day for M. cymela, with the top decile moving at a rate of over five times these values. This movement did not appear to be random. S. cybele exhibited directed movement towards patches with high nectaring potential, although not all such patches were selected. M. cymela aggregated in particular prairie patches, especially those with high edge to area ratios, although the reason for aggregation is not clear

Fixation du CO2 dans les blocs de béton à base de granulats recyclés

A l’heure où l’industrie cimentière est majoritairement responsable de la production de CO2 dans le secteur de la construction, il s’avère utile de compenser cette production par un phénomène inverse: la captation du CO2. Ce processus d’absorption de CO2, appelé carbonatation, améliore certaines propriétés du béton lors de la conversion du dioxyde de carbone CO2 en carbonate de calcium CaCO3. Les préoccupations environnementales actuelles motivent l’étude de la carbonatation dans le but de maximiser l'absorption du dioxyde de carbone. Les granulats recyclés, produits à base de déchets de béton concassés mécaniquement, peuvent prendre place dans de nouvelles applications en béton. Ils peuvent remplacer les granulats naturels en tout ou en partie, épargnant ainsi l’extraction des matières premières naturelles. La combinaison des deux approches vise à élaborer un produit dont l’impact environnemental est réduit au minimum

Effect of concrete surface treatment on adhesion in repair systems

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

Influence of physico-chemical characteristics of limestone fillers on fresch and hardened mortar performances

peer reviewedIn order to meet the specific requirements for fresh Self-Compacting Concrete (SCC), i.e. a high workability together with a good resistance to segregation, the amount of coarse aggregates has to be reduced and replaced by fine material. Since cement is quite expensive and can develop a high heat of hydration with possible problems for thermal cracks in massive concrete, mineral fillers are usually used. In Belgium, local available materials are limestone fillers; they are very well-adapted for the optimisation of particle packing and flow behaviour of cementitious paste in SCC mixes. These by-products are issued from different sectors, such as the aggregate and lime production industry (quarrying operations) and the ornamental stones industry (sawing operations). The suitability of these fillers for use in SCC or conventional concrete production was investigated. This paper reports the effect of the nature and the substitution rate of the fillers on the properties of mortars. Some relationship between the physico-chemical properties of the fillers and the properties of mortars were brought forward

Detection of near-field, low permittivity layers with Ground Penetrating Radar: analytical estimation of the reflection coefficient

peer reviewedThe reflection coefficient of GPR waves encountering embedded thin layers is commonly estimated using a plane wave, far field approximation. But when the thin layer is situated in the near field of the antenna, the spherical nature of the waves and the possible propagation of a lateral wave into the layer may have a strong influence on the measured reflected amplitude. In this work, we studied through 2D FDTD simulations the behavior of a radar wave interacting with thin layers of different thicknesses. The snapshots and radargrams showed a large influence of the layer thickness on the wave propagation. For the very thin layers, the evanescent wave plays a major role and the plane wave approximation gives a good estimation of the reflection coefficient. For thicker layers, the specific inclination of each multiple reflection has to be taken into account, as well as the lateral wave propagation. On the basis of these observations, we determined which analytical method should be used for the analytical prediction of the reflection coefficient, as a function of the layer thickness

Effet de l’empilement et de la forme des additions sur les propriétés des liants à matrice cimentaire

Mélanger le ciment avec des additions minérales, en particulier avec des sous-produits industriels, permet de réduire efficacement la consommation de ciment et de réduire son impact environnemental. Récemment, un concept novateur a été proposé en vue de remplacer les plus gros grains de ciment par les charges inertes, en vue du développement d’un ciment durable. En tant que mécanisme de base, l’empilement des particules joue un rôle important dans le remplacement ou le mélange. Dans la première partie de l'étude, l’empilement des grains de ciment, de filler calcaire (LF) et de ciment mélangé est abordé. Une nouvelle méthode, basée sur l’empilement en phase humide, est comparée à une méthode d'empilement à sec. La distribution de taille des particules (PSD) et la forme des particules des différentes poudres sont caractérisées sur base d’un système d'analyse d'image avancée. Le document présente les résultats des tests d’empilement avec l’influence du paramètre PSD, de la forme des particules, du type de ciment, de l’énergie de vibration, du mélange et du superplastifiant (Sp). Les avantages et les limites des deux méthodes sont également discutés

Patch repair: compatibility issues

peer reviewedRepair of any concrete structure results in formation of complex, at least two-component repair systems. Compatibility approach is treated as a basic requirement during selection of repair material. Recently, the understanding for compatibility requirements in repair systems approach is demonstrated in many papers. The aim of this paper is analyzing the compatibility between repair materials and concrete substrate in the case of patch repair. The compatibility issues were discussed in light of the various requirements which determine the mathematical space of loads, including chemical, mechanical and other physical (mainly thermal) loads. N-dimensional compatibility space is created, taking into account selected patch material control parameters. The requirements for good compatibility between repair material and concrete substrate can be formulated by using mathematical inequalities, where the variables are the material control parameters. The effects of properties of the both repair material and concrete substrate were analyzed using computer system ANCOMP developed at Warsaw University of Technology. Usability of this approach was demonstrated using selected case study as an example

On the evaluation of interface quality in concrete repair system by means of impact-echo signal analysis

According to Concrete Repair Manual as well as ACI 562-16 and European EN 1504-10 standards, a bond strength as a measure of adhesion is one the main feature of repair system necessary to be assessed. The most common laboratory and engineering method for bond strength evaluation is pull-off test. This is however a semi-destructive method that needs a repair in a place of measurement. Recently, the great interest in nondestructive techniques (NDT) development is noted. Impact-Echo (IE) is considered as one of the most promising methods for this purpose. In this paper, the study on the usability the IE test based on frequency spectrum analysis for bond strength evaluation is analyzed. Both Finite Element Method (FEM) simulation and experimental tests were performed in order to obtain potential relations between IE frequency spectrum and parameters characterizing concrete substrate quality that may affect the final bond strength and the real value of pull-off bond strength measured on samples as well. It was concluded that the IE method can be a useful tool for interface quality and bond strength evaluations in concrete repair system. However, more complex signal analysis, e.g. wavelet analysis, should be considered in the future.Peer reviewe