Luc Courard

Durability of mortars modified with metakaolin

Abstract Results of an investigation to determine the effects of metakaolin additions on transport properties of mortars are reported. Comparisons are made to ordinary Portland cement (OPC) to determine the influence of addition and replacement percentage. Cement is replaced on a mass basis of 5–20% for metakaolin. A mixture with natural kaolin is also studied. The transport properties and chemical behaviors are analyzed by means of chloride diffusion tests and sulfate immersion. Observations after more than 100 days are used to prescribe mixtures that reduce the rate of chloride diffusion and sulfate degradation. For metakaolin, the optimum seems to be between 10% and 15% with regard to inhibition effect on chloride diffusion and sulfate attack.

Quality enhancement of dehydrated products through the modification of solar tunnel dryer for continuous operation in rural communities

The aim o f th is study is the experimental characterization of the behaviour o f a mo rtar during convective drying. We focalise on mortar that has a rate water-cement of 0.5. The drying tests are developed in a micro-convective dryer that can use samples weighing fro m 0 to 8g. The advantage of these experiments is to reproduce the natural conditions that can be found during the treatment of the mortar-at mosphere problems. The response of the drying curve or the drying kinetic depends on the applied drying conditions. So, the temperature of the air varies fro m 60℃ to 130℃, the velocity of the air is changed fro m 2 m.s -1 to 5 m. s -1 and the relative hu midity is kept less than 1.7%. The co mparison between the experimental results and the proposed analytical solutions of the equation of diffusion represented by Ficks law, applied for a finite shape, allo ws determination o f the values of the d iffusion coefficient. It has a value of 1.71×10 -10 m 2 .s -1 at 60℃, 13.69×10 -10 m 2 .s -1 at 90℃ and 16.27×10 -10 m 2 .s -1 at 130℃. Calculation of the activation energy and the D0 constant are also possible.

Particle Size Distribution of Limestone Fillers: Granulometry and Specific Surface Area Investigations

Mineral fillers can be defined as “inert materials included in a mix design for some useful purpose” (NF P18-508 Janvier 2012). They can be added to compounds in order to complete a large variety of final properties without increasing costs or to improve specific characteristics like hardness, brittleness, impact strength, compressive strength, softening point, fire resistance, surface texture, electrical conductivity, and so on. In Belgium, locally available limestone fillers are specifically very well adapted for the optimization of particle packing and flow behavior of cementitious pastes in concrete mixes. Limestone fillers may be easily characterized in terms of chemical and mineralogical properties. These properties are fundamental for the study of the behavior of concrete mixes in fresh state and for understanding interactions existing at the level of the interfacial transition zone between aggregates and cement paste. These properties are however insufficiently discriminant and particle size, as well as shape distribution, seem to have a potential influence on physical phenomena which happen during the setting process. The aim of this article is to compare five major techniques used to quantify the size and the shape of limestone fillers particles: laser diffraction scattering, wet sieving, and image analysis for particle size measurement; and BET adsorption and Blaine permeability methods for specific surface area.

Nondestructive detection of delaminations in concrete bridge decks

To detect delaminations in concrete bridge decks, nondestructive techniques (NDT) permit a frequent and large inspection of the slabs without damaging structures. This research was devoted to detect simulated defects in twelve repaired concrete slabs. These were scanned with high frequency ground penetrating radar (GPR) with the common offset (CO) and common midpoint (CMP) methods. The electromagnetic waves speed was determined from CMPs. A 3D visualization program was also created to display the CO measurements. The visibility of the inserted defects revealed to be dependent on their lateral extension, their thickness and their constitutive material.

Perforation strength of geosynthetics and sphericity of coarse grains: a new approach

Abstract Perforation of a geomembrane by the coarse grains in the drainage layer of a composite liner for a landfill would be a serious environmental problem. Therefore, the geomembrane is generally protected against perforation by a geotextile. Several laboratory tests already exist for designing the geotextile. Some of them use coarse grains as penetrators, others replace them by artificial geometrically defined penetrators. The first method has the disadvantage of not being reproducible while the second method lacks any correlation between the morphology of the stones and the form of the penetrators. A method of correlating the form of the penetrators with that of the stones has been established (Antoine, 1995). It is based on the measurement of the angularity and bluntness of the bumps on the stones. These measurements were made by analysing digitised pictures. A probability analysis using the Beta law has been used to define the angles and bluntness characterising a ‘dangerous’ stone and an ‘average’ stone. Then, steel penetrators were manufactured with these characteristics. Puncture tests have been run with these artificial penetrators to compare the efficiency of some protection geotextiles. Other tests using stones as penetrators have then been performed to verify the effectiveness of the simulation of the coarse grains. It seems that the correlation found is valid, but that another parameter, describing the more general form of the stone around the bump, is necessary to explain the differences in behaviour.

Surfology: Concrete Surface Evaluation Prior To Repair

The study of adhesion of repair materials on concrete structures implies a good knowledge of the influence of concrete surface treatment. The effects of surface preparation technique are rarely clearly described and parameterised: it is consequently difficult to point out the real influence of roughness on adhesion results. A large research project has been realized with regards to the influence of concrete substrate strength and preparation technique efficiency. The surface roughness of concrete has been quantified by means of the projection “Moire” technique, which is an interferometrical measurement method. Comparison between polished, scrabbled and hydro-jetted surfaces evaluation is presented.

Churches and concrete in Liège district: history, architecture and pathologies

Reinforced concrete is a key element of the architectural evolution and has been specifically involved in the development of religious architecture. Since its discovery in the nineteenth century, this invented material, economic and fire resistant, however showed its limits: cracks, spalling and disintegration are some of the degradations we may observe today. It therefore seems necessary to worry about the current state of churches: these monuments are indeed the testimony of architectural evolution but also landmarks for the neighborhood. In Liège district, Belgium, nine parish churches have been identified as mainly concrete based. For each church, a visual inspection has been realized: this overview led us to make an assessment of the monument, with regard to concrete and reinforced concrete situation. This inspection is the first step for further investigations included into a restoration or renovation process.

Effect of Misalignment on Pulloff Test Results: Numerical and Experimental Assessments

The successful application of a concrete repair system is often evaluated through pulloff testing. For such in-place quality control (QC) testing, the inherent risk of misalignment might affect the recorded value and eventually make a difference in the acceptance of the work. The issue of eccentricity in pulloff testing has been ignored in field practice because it is seen as an academic issue. This paper presents the results of a project intended to quantify the effect of misalignment on pulloff tensile strength evaluation and provide a basis for improving QC specifications if necessary. The test program consisted first of an analytical evaluation of the problem through two-dimensional finite element modeling simulations and, in a second phase, in laboratory experiments in which the test variables were the misalignment angle (0, 2, and 4 degrees) and the coring depth (15 and 30 mm [0.6 and 1.2 in.]). It was found that calculations provide a conservative, but realistic, lower bound limit for evaluating the influence of misalignment upon pulloff test results: a 2-degree misalignment can be expect to yield a pulloff strength reduction of 7 to 9%, respectively, for 15 and 30 mm (0.6 and 1.2 in.) coring depths, and the corresponding decrease resulting from a 4-degree misalignment reaches between 13 and 16%. From a practical standpoint, the results generated in this study indicate that when specifying a pulloff strength limit in the field, the value should be increased (probable order of magnitude: 15%) to take into account the potential reduction due to testing misalignment.

Static detection of thin layers into concrete with ground penetrating radar

Ground Penetrating Radar (GPR) is a nondestructive technique particularly well adapted to the inspection of concrete structures and can help to determine the structure inner geometry or to detect damaged areas. When the GPR is used on structures containing thin layers, for example, the sealing layer of a concrete bridge deck or the void into a masonry wall, it is important for the radar user to know the minimum thickness required to detect and estimate the thickness of those layers. The theory of thin layer detection is based on a sine wave but, in reality, most commercial GPR systems emit a large frequency band wavelet, which undergoes attenuation into the layer. To analyze the influence of those realistic conditions on the reflection coefficient of a thin layer, the authors combined experimental measurements and numercial FDTD simulations. The experimental results matched the numerical predictions well, presenting a fast attenuation compared to the theoretical predictions. Nevertheless, for thicknesses inferior to lambda 11, the reflection coefficient could still be considered as linearly dependent of the thickness to wavelength ratio. (A)

Shape simulation of granular particles in concrete and applications in DEM

ABSTRACT Aggregate occupies at least three-quarters of the volume of concrete, so its impact on concrete’s properties is large. The sieve curve traditionally defines the aggregate size range. Another essential property is grain shape. Both, size and shape influence workability and the mechanical and durability properties of concrete. On the other hand, the shape of cement particles plays also an important role in the hydration process due to surface dissolution in the hardening process. Additionally, grain dispersion, shape and size govern the pore percolation process that is of crucial importance for concrete durability Discrete element modeling (DEM) is commonly employed for simulation of concrete structure. To be able doing so, the assessed grain shape should be implemented. The approaches for aggregate and cement structure simulation by a concurrent algorithm-based DEM system are discussed in this paper. Both aggregate and cement were experimentally analyzed by X-ray tomography method recently. The results provide a real experimental database, e.g. surface area versus volume distribution, for simulation of particles in concrete technology. Optimum solutions are obtained by different simplified shapes proposed for aggregate and cement, respectively. In this way, reliable concepts for aggregate structure and fresh cement paste can be simulated by a DEM system.