François Buyle-Bodin

Efficiency of polypropylene and metallic fibres on control of shrinkage and cracking of recycled aggregate mortars

The use of recycled aggregates in mortar and concrete induces a large shrinkage due to the capacity of these aggregates to absorb a great quantity of water. The influence of polypropylene and metallic fibres (Fibraflex) has been studied in different proportioning to reduce shrinkage and cracking. The efficiency of polypropylene and metallic fibres to reduce restrained shrinkage cracking is evaluated by using a ring mortar cast around a stiff steel ring. By using fibres, the crack width decreases significantly. Free shrinkage results are equally investigated. Finally, crack width in reinforced fibre mortars is calculated analytically by using the model of Grzybowski and Shah. Results are compared with experimental values. The study demonstrates that theoretical values of crack widths correspond reasonably to experimental values.

PROMOTING THE URBAN UTILITIES TUNNEL TECHNIQUE USING A DECISION-MAKING APPROACH

Abstract Urban development and the need for new facilities have led to an increase in the use of urban utilities. These various utilities are generally located under the public highway. Therefore, underground space is limited by the width of the public highway. Because of the increase in urban utilities, the need for maintenance of these utilities and the lack of space, the underground is now very often saturated. Sometimes, the situation is so inextricable and so anarchic that the implementation of a new urban network becomes hardly possible. In addition, trench digging due to work on existing networks or on the addition of a new network generates much traffic interruption. To solve this problem, an urban utilities tunnel can be used. In this case, all the urban utilities are located in a single tunnel. Thus, saturation of the underground space decreases, there are fewer errors in the zone plan used, maintenance is easier, there is no traffic interruption and it is possible to add a new urban network without disrupting the public highway. However, the urban utilities tunnel is expensive compared to classical solutions. Because decision-makers only work based on economic criteria, this solution is rarely chosen. Therefore, to promote the urban utilities tunnel in France, a national research project was created. One of its goals is to develop a multicriteria method integrating the following criteria: safety, sustainable development, economy, maintenance, risk analysis, development facilities… Moreover, the sewer network seems to induce most of the constraints. Thus, another goal is to study the influence of the drainage network location (inside or outside the tunnel) on the general cost of the urban utilities tunnel. This paper details both problems.

Artificial neural network for predicting creep of concrete

The concrete is today the building material by excellence. Drying accompanies the hardening of concrete and leads to significant dimensional changes that appear as cracks. These cracks influence the durability of the concrete works. Deforming a concrete element subjected to long-term loading is the sum of said instantaneous and delayed deformation due to creep deformation. Concrete creep is the continuous process of deformation of an element, which exerts a constant or variable load. It depends in particular on the characteristics of concrete, age during loading, the thickness of the element of the environmental humidity, and time. Creep is a complex phenomenon, recognized but poorly understood. It is related to the effects of migration of water into the pores and capillaries of the matrix and to a process of reorganization of the structure of hydrated binder crystals. Applying a nonparametric approach called artificial neural network (ANN) to effectively predict the dimensional changes due to creep drying is the subject of this research. Using this approach allows to develop models for predicting creep. These models use a multilayer backpropagation. They depend on a very large database of experimental results issued from the literature (RILEM Data Bank) and on appropriate choice of architectures and learning processes. These models take into account the different parameters of concrete preservation and making, which affect drying creep of concrete as relative humidity, cure period, water-to-cement ratio (W/C), volume-to-surface area ratio (V/S), and fine aggregate-to-total aggregate ratio, or fine aggregate-to-total aggregate ratio. To validate these models, they are compared with parametric models as B3, ACI 209, CEB, and GL2000. In these comparisons, it appears that ANN approach describes correctly the evolution with time of drying creep. A parametric study is also conducted to quantify the degree of influence of some of the different parameters used in the developed neural network model.

Auscultation non destructive du chevetre du pont de la Marque (59) : Combinaison de techniques

ABSTRACT This article was the result of a series of measurements on a bridge wall near Lille carried out by the various teams of a national project supported by the RGC&U, entitled “evaluation of the degradation of cover concrete and assistance to the diagnosis and the repair of the works” which the goal is to try to quantify what kind of improvement can be expected from the combination of non-destructive techniques in order to assess the structural state of existing reinforced concrete structures. Three techniques were employed: radar, resistivity and ultrasonic. The various teams implied in the project have tested the aptitude of each technique to detect the alkali-aggregate reaction but also to qualify the state of deterioration of the concrete by the combination of the results obtained by these various techniques.

ASSESSMENT OF DETERIORATED CONCRETE COVER

ABSTRACT Many reinforced concrete structures are suffering from deterioration occurring earlier than their expected service life. The first barrier against attacks of external environmental agents is the concrete cover. The damage mechanisms depend on the microstructure of the cover concrete. This microstructure can be assessed with various measurements. In the present research, concrete and mortar were artificially deteriorated by acid attack. Samples were attacked during different time inducing different depth of deterioration. Different parameters were measured: deterioration depth, velocity and attenuation of compressive, shear and surface high frequency waves, porosity, elastic modulus, compressive strength, water absorption. These measures are conducted on deteriorated layer, or sound layer, or on a combination of the both layers. The depth of deterioration is well correlated with the acoustic velocities decrease for the three types of waves. The high-frequency ultrasonic wave is thus able to detect changes in the micro-structure of the concrete cover. The surface wave seems to be the most appealing for concrete cover evaluation. The correlations between ultrasonic parameters, and civil engineering parameters like porosity or elastic modulus or compressive strength are evaluated in order to perform the correct interpretation of ultrasonic measurement. The distinctive characteristics of each layer must be deduced from homogenized values measured on multi-layer samples. For that series or parallel models have been successfully used.

Mise en conformité de systèmes d'assainissement eaux usées. Aide au choix de solutions

ABSTRACT The general obligation of a successful sewerage on any communal territory currently reaches its conclusion (December 31 2005). But in the case of waste water sewerage, previous programmes of modest size communities (less than 10 000 inhabitants) are still based on a methodology which takes into account neither the interactions between the different infrastructures, nor those with their environment. In order to make the decision process more rational and coherent, we propose in this article a methodological tool providing a decision-making aid support for choices of solutions. Its principle is based on an alternative reasoning with the current approach. This tool integrates concepts borrowed from the expert systems and from the multicriteria analysis.

Influence des fibres sur les caractéristiques mécaniques du mortier de sable recyclé au très jeune âge

ABSTRACT Concrete characteristics are changing with hydration of cement. It is difficult to measure these ones on green concrete. Nevertheless, they are very important for shrinkage prediction and proportioning optimisation. We study natural aggregate mortar and recycled aggregate mortar with different hydration kinetics. We lead Casagrande shear measurements, compressive tests and splitting tests on mortars with different fibre proportioning. Fibres are polypropylene or metallic ones.