Siham Kamali-Bernard

Physical and mechanical properties of mortars containing PET and PC waste aggregates.

Non-biodegradable plastic aggregates made of polycarbonate (PC) and polyethylene terephthalate (PET) waste are used as partial replacement of natural aggregates in mortar. Various volume fractions of sand 3%, 10%, 20% and 50% are replaced by the same volume of plastic. This paper investigates the physical and mechanical properties of the obtained composites. The main results of this study show the feasibility of the reuse of PC and PET waste aggregates materials as partial volume substitutes for natural aggregates in cementitious materials. Despite of some drawbacks like a decrease in compressive strength, the use of PC and PET waste aggregates presents various advantages. A reduction of the specific weight of the cementitious materials and a significant improvement of their post-peak flexural behaviour are observed. The calculated flexural toughness factors increase significantly with increasing volume fraction of PET and PC-aggregates. Thus, addition of PC and PET plastic aggregates in cementitious materials seems to give good energy absorbing materials which is very interesting for several civil engineering applications like structures subjected to dynamic or impact efforts. The present study has shown quite encouraging results and opened new way for the recycling of PC waste aggregate in cement and concrete composites.

Assessment of the elastic properties of amorphous calcium silicates hydrates (I) and (II) structures by molecular dynamics simulation

Abstract Based on Hamid model of 11Å tobermorite, amorphous calcium silicates hydrates (or C-S-H) structures (Ca4Si6O14(OH)4•2H2O as the C-S-H(I) and (CaO)1.67(SiO2)(H2O)1.75 as the C-S-H(II)) with the Ca/Si ratio of 0.67 and 1.7 are concerned. Then, as the representative ‘globule’ C-S-H, two amorphous C-S-H structures with the size of 5.352 × 4.434 × 4.556 nm3 during the stretch process are simulated at a certain strain rate of 10−3 ps−1 by LAMMPS program for molecular dynamics simulation, using ClayFF force field. The tensile stress–strain curves are obtained and analysed. Besides, elastic modulus of the ‘globule’ C-S-H is calculated to assess the elastic modulus of C-S-H phases (the low-density C-S-H – LD C-S-H – and the high-density C-S-H – HD C-S-H), where the porosity is a critical factor for explaining the relationship between ‘globule’ C-S-H at nanoscale and C-S-H phases at microscale. Results show that: (1) The C-S-H(I) structure has transformed from crystalline to amorphous during the annealing process, Young’s moduli in x, y and z directions are almost the same. Besides, the extent of aggregation and aggregation path for water molecules in the structure is different in three directions. (2) Young’s modulus of both amorphous C-S-H(I) and C-S-H(II) structures with a size of about 5 nm under strain rate of 10−3 ps−1 at 300 K in three directions is averaged to be equal, of which C-S-H(II) structure is about 60.95 GPa thus can be seen as the elastic modulus of the ‘globule’ C-S-H. (3) Based on the ‘globule’ C-S-H, the LD C-S-H and HD C-S-H can be assessed by using the Self-Consistent Scheme (separately 18.11 and 31.45 GPa) and using the Mori–Tanaka scheme (29.78 and 37.71 GPa), which are close to the nanoindentation experiments by Constantinides et al. (21.7 and 29.4 GPa).

Modélisation tridimensionnelle et multi-échelle du comportement des matériaux cimentaires: Application à la lixiviation

ABSTRACT 3D multi-scale and multi-physics modeling of cement based materials is developed. Two numerical tools are combined to predict the mechanical behavior of these materials CEMHYD3D and ABAQUS. The outcomes of the simulation at the micro-scale are used at the meso-level modeling. This approach is then applied to investigate the mechanical behavior of a mortar with water-to-cement ration equal to 0.4. The effect of the leaching phenomenon is studied. The numerical results of the modeling are consistent with the experimental ones.

Ground Granulated Blast-Furnace Slag

Since the discovery of the latent hydraulic reactivity of ground granulated blast-furnace slag (ggbfs) by Emil Langen at the end of the 19th century, this material has been used successfully as cement and concrete addition. This chapter includes all relevant information about this valuable material—from production and processing to the effect, which ggbfs additions have on the concrete performance. In this context, light is shed on decisive performance parameters of ggbfs. Of special interest nowadays is certainly also the information given about trace element contents in ggbfs and their leachability. Here and throughout the entire chapter, the latest insights from research and development work are included. Last but not least, the chapter contains very practical information when it comes to the use of ggbfs in concrete, including insights on rheological effects, concrete color and “greening”, and adequate curing. Moreover, an overview about relevant norms and standards on ggbfs as concrete addition is given.

Multiscale modelling approach to determine the specific heat of cementitious materials

Abstract A hierarchical multi-scale modelling of cement-based materials devoted here to the determination of the mechanical properties and specific heat of this kind of materials is presented in this paper. This multiscale modelling approach is used to study cementitious materials from nanoscale to mesoscale. Despite the tremendous increase in the multi-scale investigations of cement-based materials, the physical origins of their thermal properties at the nanoscale and their upscaling to the macroscopic properties are still little studied. In this paper, through the investigation of the vibrational states of the unit cells of the various phases of the Hardened Cement Paste as well as their energy phonons using the Debye model, we determine the specific heat of these phases. Then the use of the composite spheres assemblage model enables us to calculate this property for a w/c = 0.45 cement paste and the corresponding mortar (870 J/kg/K for the well-hydrated cement paste, and 742 J/kg/K for the mortar).