Laurent Molez

Influence of recycled sand containing fillers on the rheological and mechanical properties of masonry mortars

In this work, we aim to study experimentally the influence of the fillers (<125 µm) of recycled sand on the properties of masonry mortars, with the same consistency, from the observation of the rheological behavior, slump, plasticity and shear strength and comparison of mechanical strength, compressive, flexural and tensile by splitting at 7 and 28 days. The formulation of the reference mortar based on natural river sand is made with cement CEM I 52.5 (C=506 kg/m3 ), with ratios water/cement = 0.5 and sand/cement = 3.0. The other recycled mortars were shown to have the same plasticity as the reference mortar, and the amount of water added was determined using the weight of the recycled sand. The study was carried out on four series of mortars based on recycled sand with and without superplasticizer, replacing natural sand with recycled sand with and without fillers with different percentages of 0, 15, 30, 40, 50, 75 and 100%. The obtained results show that the recycled sand has relatively low physicochemical properties compared to natural sand due to the heterogeneity and the large percentage of the old hardened mortar contained in the recycled sand, in particular the fractions below 250 µm, a high percentage of fillers greater than 10% and a very high water absorption, seven times higher. The comparative study of different mortar compositions with different percentages of recycled sand with and without fillers showed that fillers require more water, which negatively affects the physical and rheological behavior, but in most cases,the the mechanical performance is better than that of the control mortar, in particular the mortars with admixtures.

Physico-mechanical and Microstructural Characterization of Concretes Ultra High Performance Matrix Fiber.

Abstract This work will be devoted on the one hand to the formulation of an ultra-high performance fiber concrete based on local materials (cement and fine sand) and on the other hand to the study of the effect of the fibers on the physico-mechanical behavior of the concrete. The formulation will be obtained by the search for the optimum percentage of the fibers and by adopting as criterion the workability of the concrete. For the optimal fiber retention, the influence of the fibers on the mechanical behavior of the concrete (compression strength, tensile strength and ductility) will be studied. The results of this study will highlight the impact of the microstructure on the improvement of the physico-mechanical characteristics of concrete.

Characterisation and microstructure of high-performance concretes reinforced with metal fibres ripened in seawater

Abstract High-performance concretes reinforced with metal fibres (SFRHPC) have multiple advantages when they are used in the marine environment. These materials provide high strengths at the young age that permit faster formwork stripping, resistance to hydrostatic thrusts due to the tides, structural elements sections’ reduction, as well as weight reduction of the structure, and the increase of the abrasion resistance to sand or gravel. The maritime works are exposed to specific seawater aggressions. Seawater contains aggressive salts, which damage the concrete and the steel that it may contain. These salts are mainly chlorides and sulphates. This study investigated the ripening of steel fibre-reinforced high-performance concrete, with 15% substitution of cement by blast furnace slag, in Rance (France’s seawater). This experimental study analysed the effect of 6 and 24 months of ripening of the sample, in aggressive water, on the characterisation of the concrete and the microstructure of the cement’s matrix and its fibres. Also, in this study, after two years of concrete conservation, we carried out the chemical and mineralogical composition of the seawater. The results showed that there is no significant alteration of concrete kept in seawater and the steel fibres were not altered. In other words, it stayed passivated even after two years of ripening.

Properties of fibre mortars after exposure to high temperatures

Results obtained by testing mechanical behaviour and microstructure of fibre mortars and standard mortars after exposure to high temperatures are presented in the paper. A flame test using propane gas was developed to enable the best possible simulation of fire conditions. The testing was conducted on three different mortars: standard mortar, steel fibre mortar, and hybrid mortar (with equal proportion of steel fibres and polypropylene fibres). The addition of fibres ensured greater ductility of mortar at temperatures from 400 to 700°C. These observations served as a basis for explaining the loss of strength.