No abstract

Discrete element modelling is commonly used for particle-scale modelling of granular or particulate materials. Developing a DEM model requires the determination of a number of micro-structural parameters, including the particle contact stiffness and the particle-particle friction. These parameters cannot easily be measured in the laboratory or directly related to measurable, physical material parameters. Therefore, a calibration process is typically used to determine the values for use in simulations of physical systems. This paper focuses on how to define the particle stiffness for the discrete element modelling in order to perform realistic simulations of granular materials in the case of linear contact model. For that, laboratory tests and numerical discrete element modelling of triaxial compression tests have been carried out on two different non-cohesive soils i.e. poorly graded fine sand and gap graded coarse sand. The results of experimental tests are used to calibrate the numerical model. It is found that the numerical results are qualitatively and quantitatively in good agreement with the laboratory tests results. Moreover, the results show that the stress dependent of soil behaviour can be reproduced well by assigning the particle stiffness as a function of the particle size particularly for gap graded soil.

Since many years ago, the substitution of cement by other cementitious supplementary elements has being a purpose for many researchers. This is to reduce the impact of producing cement on our environment. In this article, we are interested in the possibility of substituting cement with titanium dioxide and titanium dioxide + fly ash. To achieve this purpose, we have manufactured mortars and cement pastes specimens with different rates of replacement of cement by titanium dioxide (0%, 0.1%, 1%) on the one hand and titanium dioxide + fly ash on the overhand. The flexural and compressive strength of each specimen has been determined.

This study is part of a project to develop a bio-based material meeting the criteria of sustainable development in the field of construction. A study was then made on a cement matrix composite reinforced by aggregates of Borassus aethopium mart (palmyra). For this purpose, studies of cement compatibility with this plant aggregate, the physical, mechanical and thermal behavior of the concrete were performed for two granular compositions. The compatibility study revealed that palmyra aggregrates, although not previously treated, are compatible with Portland-limestone cement. The characterization tests focused on the mechanical properties of three-point flexural tensile strength and compressive strength and thermal properties such as effusivity, conductivity and diffusivity. The results obtained are promising: they have very good mechanical and thermal characteristics, considering its use in construction. The mechanical strengths reach 16.25 MPa for a density less than 1500 kg / m3. The thermal conductivity varies between 0.270 and 0.415. They can be used for the manufacture of panels used in the realization of suspended ceilings and tiles for the realization of roofs.

The research of materials with good properties is one of the important concerns of scientists groups, and more again in region where materials are subjected to freeze and thaw cycles. In the case of this paper, it has been a matter of evaluating of the effect of carbon nanotubes on concrete resistance to freeze and thaw cycles. Thus, it has been manufactured concretes with different rates of addition (0%, 0.1%, 0.5%, 1% bwc) of cement by carbon nanotubes. The durability factor, determined for C30 specimens at 28 days, shows that C005 provides a better resistance to freezing-thawing cycles with a 54.96 as index.