Gérard Ballivy

The use of marine sediments as a pavement base material

The management of marine sediments after dredging has become increasingly complex. In the context of sustainable development, traditional solutions such as immersion will be increasingly regulated. More than ever, with the shortage of aggregates from quarries, dredged material could constitute a new source of materials. In this study of the potential of using dredged marine sediments in road construction, the first objective is to determine the physical and mechanical characteristics of fine sediments dredged from a harbour in the north of France. The impacts of these materials on the environment are also explored. In the second stage, the characteristics of the fine sediment are enhanced for use as a road material. At this stage, the treatment used is compatible with industrial constraints. To decrease the water content of the fine sediments, natural decantation is employed; in addition, dredged sand is added to enhance the granular distribution and to reinforce the granular skeleton. Finally, the characteristics of the mix are enhanced by incorporating binders (cement and/or lime). The mechanical characteristics measured on the mixes are compatible with their use as a base course material. Moreover, the obtained results demonstrate the effectiveness of lime in the mixes. In terms of environmental impacts, on the basis of leaching tests and according to available thresholds developed for the use of municipal solid waste incineration (MSWI) bottom ash in road construction, the designed dredged mixes satisfy the prescribed thresholds.

Contribution to the formation mechanism of the transition zone between rock-cement paste

A number of microstructural and mineralogical models for the rock-paste interface can be found in the literature. Similarly, there are also a few hypotheses relating to the mechanisms responsible for the formation of the interface zone. This paper addresses both of these questions. Based on results from various analysis techniques, it has been shown that a single model is insufficient to describe interface microstructure and mineralogy, since they depend on the type of cement used. The mechanisms responsible for the formation of the interface appear related to differential ion diffusion caused by the zones higher porosity, resulting from the arrangement of the cement grains in contact with the rock. Furthermore, the findings reveal that these mechanisms also govern the concentration of alkalis in contact with the rock.

Effect of concrete moisture on radar signal amplitude

The moisture content of concrete is a critical parameter for most of the physicochemical pathologies, such as steel reinforcement corrosion, alkali-aggregate reaction, and freezing-and-thawing cycles. Therefore, the detection of moisture is important for the diagnosis of concrete structures at early stages of deterioration. The present study was undertaken to assess the effect of the degree of saturation, water-cement ratio (w/c), and volumetric water content on the amplitude variation of direct and reflected radar waves. Four concretes with w/c of 0.5, 0.6, 0.7, and 0.78 were evaluated. Radar measurements were carried out on 72 samples saturated at 0, 20, 40, 60, 80, and 100%. Test results show that an increase in the degree of saturation leads to significant decrease in the amplitude of both direct and reflected waves. This is mainly attributed to the increase in complex permittivity related to the polarization and conduction mechanisms occurring in concrete. Generally, the radar measurements showed good repeatability, which was evaluated using the coefficient of variation, and the statistical dispersion of the direct wave amplitude was lower than that of the reflected wave. For dry and wet concrete, w/c did not appear as an influent parameter regarding the experimental results. A good correlation was found between the amplitude of direct and reflected waves for each degree of saturation. This suggests that the direct and reflected wave amplitudes provide similar information regarding the concrete moisture. Irrespectively of w/c and the depth of reflector, an empirical relationship between signal amplitude of direct wave and volumetric water content was established that can be used to estimate concrete moisture.

Laboratory Investigation of the Control of Acid Mine Drainage Using Alkaline Paper Mill Waste

A great deal of research effort has been undertaken to find an effective solution to the problem of acid mine drainage. Indeed, Canadian legislation requires mining companies to respect environmental regulations by providing a rehabilitation plan with a financial guarantee. In order that the Canadian mining industry remains competitive, the proposed solutions have to be not only efficient but also economic, that is why the use of another waste material is attractive. The main objective of this study was to investigate the technical and environmental feasibility of stabilizing acid mine residues using alkaline paper mill waste produced by the pulp and paper industry as a basic source. The mineralogical characterization of the alkaline paper mill shows that calcite is the dominant mineral with hydrated lime (portlandite) present at a low content.The mineralogical characterization of the mining residues shows a polyphasic system where silica dominates the oxidized zone. On the other hand, a high pyrite content is present in the non-oxidized zone.The essential observations that emerge from the leaching tests undertaken in the laboratory can be summarized by the efficiency of the incorporation of the alkaline paper mill waste (1/3 waste and 2/3 mining residue) on the production of acid mine drainage. In fact, it can be observed that there is a reduction of the high toxicity elements like heavy metals. The increase in pH permits the reduction of catalytic bacterial activity and reduces the rate of oxidation in the mining residue.

Characterization of the ASR rim: Application to the Potsdam sandstone

Abstract Chemical properties of the reaction rim associated with alkali–silica reaction (ASR) were investigated using microprobe and scanning electron microscope (SEM). The studied aggregate is the Potsdam sandstone, a Cambrian siliceous sandstone well known for its reactivity. This particular rock is composed of well-crystallized quartz grains surrounded by a poorly crystallized siliceous cement that is considered to be the reactive constituent. Research was conducted on laboratory concrete specimens having reached various expansion levels and on some samples taken from an ASR-affected dam. Results indicate that the dark rim surrounding reactive particles is mainly composed of silica. This suggests that the reaction rim is formed by the precipitation of dissolved silica. Some alkalis and calcium were detected inside the thin intergranular joints in concentration ranging from 1% to 10%. These ions come from the cement paste and play a major role in dissolving original reactive silica.

Alkali mass balance during the accelerated concrete prism test for alkali–aggregate reactivity

The alkali mass balance was calculated in concrete specimens submitted to the storage conditions of the Canadian standard CSA A23.2-14A concrete prism test for expansion because of alkali-aggregate reaction (AAR). The alkali concentration of both the concrete pore solution expressed under high pressure and the water below specimens in storage pails (bottom water) was measured. Measurements were conducted over a 1-year period that corresponds to the length of the above test. Two reactive aggregates were testes [Potsdam sandstone (PO) and Spratt limestone (SP)]. Each aggregate was incorporated in two concrete mixtures (mass concrete and structural concrete), for a total of four batches. Significant alkali leaching occurred at 38 degrees centigrade while performing tests in high moisture storage conditions even though prisms were covered with plastic sleeves. After 52 weeks, the alkali loss ranged from 12% to 25% of the original Na(2)O(e) content of the concrete, depending on the mixture proportioning and the aggregate type. After estimation of the proportion of alkalis fixed in cement hydrates, it appears that about 23% to 39% of the original alkalis released by the cement are quickly sorbed on aggregate surfaces or have rapidly migrated inside aggregate particles, which may have been incorporated with time in the AAR product. After 52 weeks at 38 degrees centigrade, the pore solution alkalinity expressed from mass concrete made with PO was 250 mmol/l, whereas the alkalinity was 270 mmol/l in mass concrete incorporating SP. Since prisms of both mixtures were still expanding at 1 year, these alkalinity values are above the thresholds required for sustaining AAR in these concrete mixtures.

Detection of Cracking Levels in Brittle Rocks by Parametric Analysis of the Acoustic Emission Signals

Determination of the cracking levels during the crack propagation is one of the key challenges in the field of fracture mechanics of rocks. Acoustic emission (AE) is a technique that has been used to detect cracks as they occur across the specimen. Parametric analysis of AE signals and correlating these parameters (e.g., hits and energy) to stress–strain plots of rocks let us detect cracking levels properly. The number of AE hits is related to the number of cracks, and the AE energy is related to magnitude of the cracking event. For a full understanding of the fracture process in brittle rocks, prismatic specimens of granite containing pre-existing flaws have been tested in uniaxial compression tests, and their cracking process was monitored with both AE and high-speed video imaging. In this paper, the characteristics of the AE parameters and the evolution of cracking sequences are analyzed for every cracking level. Based on micro- and macro-crack damage, a classification of cracking levels is introduced. This classification contains eight stages (1) crack closure, (2) linear elastic deformation, (3) micro-crack initiation (white patch initiation), (4) micro-crack growth (stable crack growth), (5) micro-crack coalescence (macro-crack initiation), (6) macro-crack growth (unstable crack growth), (7) macro-crack coalescence and (8) failure.

Design and Calibration of a Large Open-Ended Coaxial Probe for the Measurement of the Dielectric Properties of Concrete

The subject of this paper is the design and calibration of an open-ended coaxial probe for the nondestructive measurement of the dielectric properties of concrete. Measurements are made between 100-900 MHz, frequencies which are often used in geophysics and civil engineering for ground penetrating radar inspection. The probe is calibrated using measurements on saline solutions in conjunction with three different mathematical techniques for comparative study. Measurements of mortar and concrete specimens having different water/cement ratios were made in order to observe the standard deviations due to their heterogeneous nature. Similar to the case of relatively homogeneous rock specimens (limestone and granite), the standard deviation for heterogeneous concrete samples do not exceed 5%. In addition, the effect of the concretes porosity on its dielectric properties was clearly observed: measured permittivity between 4-4.5 at 900 MHz for porous concrete, and between 6.5-7.5 at 900 MHz for dense concrete.

Application of Jonscher model for the characterization of the dielectric permittivity of concrete

The study of electromagnetic waves propagating in concrete is a complex problem. Understanding the phenomenon of interaction between the wave and the matter is related to the knowledge of the variation process of concretes electromagnetic properties in terms of its physical characteristics. In particular, dielectric permittivity of concrete is affected by moisture content and change in the frequency of the electromagnetic field applied. In this study, we apply the three-parameter Jonscher model (n, χr, e∞) to show the dispersive aspect of the concrete. The validation of this model is carried out through tests on mortar and concrete at the laboratory, on the one hand, and by comparison of the results with data obtained previously by other researchers, on the other hand. The Jonscher model matches very well the experimental measurements of the concrete. At different moisture levels, heterogeneities and porosities, the results obtained are very good. This shows that this model is very effective and very suitable to represent the dielectric properties of concrete.

The Damage Rating Index Method for ASR Affected Concrete—A Critical Review of Petrographic Features of Deterioration and Evaluation Criteria

The Damage Rating Index method has recently been used with success in several cases of damage evaluation in structures affected by alkali-silica reaction in Canada and in Brazil. Although this petrographic method is starting to be widely used and is in the process of becoming integrated as a Canadian standard, it has not been modified yet from the original design. An evaluation of the method is presented in this paper. According to data obtained from many petrographic examinations, the number of cracks in coarse aggregates (filled or not with silica gel) seemed to show to best correlation with the expansion measured on laboratory concrete specimens made with Spratt limestone. The reaction rim is not a real “damage” feature and should not be considered as one but as a “degree of reaction” feature. In an attempt to improve the DRI method for assessing damage related to ASR, a new parameter should be introduced, which takes into account cracks running from aggregate particles to cement paste. The geological nature of the rock used as concrete aggregate may influence the reaction mechanism as well as the petrographic features related to ASR. Comparing concrete specimens subjected to ASR, which incorporate different aggregate types may, in some instances, be influenced by the type of reaction produced by the various reactive rocks and minerals in each aggregate.