Elhem Ghorbel

Analysis of concrete internal deterioration due to frost action

This study concerns the frost durability of an ordinary concrete without air-entraining agents. The water—cement ratio and the quantity of cement were chosen within the limitations imposed by the French standard. Physical and mechanical characteristics evolutions during freezing—thawing cycles have been followed. The obtained results show that the reduction in the mechanical resistance and the elastic modulus is accompanied by an increase in the intrinsic permeability. The damage is characterized by a scalar parameter, Df, due to frost action with which the resistance reduction as well as the permeability evolution may be described as a function of crack development. The pore liquid phase pressure, generated during ice formation, was also calculated by an inverse poroelastic analysis based on strains recorded during freezing—thawing cycles. A negative pore pressure of 25 MPa at a temperature of -15° C resulting in an effective stress representing 25% of the compressive strength was found.

Characterization of Thermo-Mechanical and Fracture Behaviors of Thermoplastic Polymers

In this paper the effects of the strain rate on the inelastic behavior and the self-heating under load conditions are presented for polymeric materials, such as polymethyl methacrylate (PMMA), polycarbonate (PC), and polyamide (PA66). By a torsion test, it was established that the shear yield stress behavior of PMMA, PC, and PA66 is well-described by the Ree-Eyring theory in the range of the considered strain rates. During the investigation, the surface temperature was monitored using an infrared camera. The heat release appeared at the early stage of the deformation and increased with the strain and strain rate. This suggested that the external work of deformation was dissipated into heat so the torsion tests could not be considered isothermal. Eventually, the effect of the strain rate on the failure modes was analyzed by scanning electron microscopy.

Incorporation of Crushed Sands and Tunisian Desert Sands in the Composition of Self Compacting Concretes Part II

This paper is interested in the incorporation of crushed sand and desert sand in the composition the self compacting concretes (SCC). Desert dune sand, which has a fine extra granulometry, and the crushed sand, which contains an important content of fines, can constitute interesting components for SCC. Part II consists in studying the behaviour of SCC containing various sands with different origins. These sands, with different sizes, consist of several combinations of rolled sand (RS), crushed sand (CS) and desert sand (DS). The study examines the influence of the granular combination of sands on the characteristics in the fresh and the hardened state of SCC. The results of the experimental tests showed an improvement of the workability of the fresh SCC by combining sands of varied granulometry. The addition of the DS to CS or to RS allowed the increase of the mixture viscosity but decreased the mechanical strengths. Furthermore, the CS-RS combinations increased the compressive and the tensile strengths of the studied SCC. The optimized formulations of sands gave the highest performances of the SCC.

Incorporation of CrusHed Sands and Tunisian Desert Sands in the Composition of Self Compacting Concretes Part I: Study of Formulation

This paper examines the incorporation of the crushed sand (CS) and desert sand (DS) in the formation of self compacting concrete (SCC). These sands have been substituted for the rolled sand (RS), which is currently the only sand used in concretes and which is likely to run out in our country. DS, which comes from the Tunisian Sahara in the south, is characterized by a tight distribution of grains size. CS, a by-product of careers containing a significant amount of fines up to 15%, is characterized by a spread out granulometry having a maximum diameter of around 5mm. These two sands are considered as aggregates for the SCC. This first part of the study consists in analyzing the influence of the type of sand on the parameters of composition of the SCC. These sands consist of several combinations of 3 sands (DS, CS and RS). The method of formulation of the adopted SCC is based on the filling of the granular void by the paste. The CS substitution to the RS made it possible, for all the proportions, to decrease the granular voids, to increase the compactness of the mixture and to decrease the water and adding fillers proportioning. These results were also obtained for a moderate substitution of DS/CS (

Influence of Strain Rate on the Yielding Behavior and on the Self Heating of Thermoplastic Polymers Loaded under Tension

The effect of strain rate on the mechanical behavior of thermoplastic polymers (Polymethyl methacrylate, Polycarbonate and Polyamide 66) has been studied. Deformation tests in tension were conducted over the range of strain rate varying between 2.6 10-4s-1 to 1.3 10-1s-1. The Young’s Modulus E and Yield stress σST evolutions have been identified and modelled as a function of the strain rate. It has been established that, in the range of the considered strain rates, the yielding behavior of PMMA and PC is well described by the Eyring theory while for PA66 the Ree-Eyring theory is successfully used to illustrate the yielding behavior. During tensile tests the specimen surface temperatures were monitored using an infrared camera. Results reveal a significant temperature rise at large deformations for PA66 and PC. As the strain rate increases the temperature is steadily increased with deformation due to plastic work. Hence, for PC and PA66, a significant thermal softening is observed after yielding which affects the stress-strain behavior. Thermo-mechanical coupling during polymer deformation can be considered in the modeling of the mechanical behavior of polymers. No self-heating has been detected for PMMA.

Shear Behavior of Reinforced Recycled Aggregate Concrete Beams

The results from an experimental study on the shear behavior of concrete made with natural aggregates (NAC) and 100% recycled aggregates (RAC) are presented in this study. Full scale 200 × 250 × 1900 mm reinforced concrete beams without stirrups were manufactured from two mixtures with C35/45 target class of compressive strength and S4 class of workability. The beams were tested under 4 points bending for a shear span-to-depth ratio (a/d) equal to 1.5 and 3.0. The mechanical properties of two mixtures were characterized in terms of compressive strength, splitting tensile strength, and modulus of elasticity.

Bond and Cracking Behavior of Reinforced Concrete Members Incorporating Recycled Aggregates

The aim of the present work is to investigate the bond strength and cracking properties of recycled aggregate concretes (RAC). For this purpose, six recycled concrete aggregate mixtures and two conventional concrete mixtures with C25/30 and C35/45 target class of compressive strength and S4 class of workability were chosen. For both series, specimens were fabricated with different incorporation ratios of fine and coarse recycled aggregates and only coarse recycled aggregates.

Mechanical Behavior of Recycled Aggregate Concrete under Uniaxial Loading-Unloading Cycles

The paper presents the results of an experimental program related with the damage behavior of Recycled Aggregate Concrete (RAC) under uniaxial loading-unloading cycles. To this purpose, the effect of the percentage of recycled aggregates (RA) on the compressive mechanical properties of concrete was investigated. Eight mixes with C25/30 and C35/45 target class of compressive strength were prepared using normal or recycled coarse aggregates. For both series, a target S4 class of workability has been chosen. Cylindrical specimens were fabricated with different RCA replacement percentages of 0%, 30%, 100% fine and coarse RA and 100% of coarse RA. Uniaxial loading-unloading compression tests were performed using controlled displacement rate of 0.5 mm/min. From the obtained stress-strain curves, the scalar damage is quantified as the variation of the elastic modulus. Based on the experimental results, it was found that the damage depends on the replacement percentage of recycled aggregates and increases when the replacement ratio is high.

Physical and Mechanical Properties of Recycled Demolition Gravels Submitted to Freeze/Thaw in Comparison to Natural Ones

Nowadays, there is a significant increase in researches of concretes based on recycled aggregate. In this study, the recycled aggregates are provided from demolition waste. This work aims to characterize recycled gravels (RG) and to estimate their deterioration after their exposure to freezing and thawing cycles. The main objective is to determine the quality and suitability of RG by comparison to natural ones (NG) in manufacturing concretes dedicated to buildings, in particular when they are exposed to freeze/thaw. For each granular type, sieving, water absorption, porosity (n), Los Angeles (LA) and Micro-Deval (MDE) tests were conducted before and after their exposure to freezing/thawing in water according to European standards. The coefficient of water absorption, WA, was evaluated by three different methods. Results show that the law of mixtures can be used to predict all the studied properties of gravels mixes (natural and recycled gravels) except for MDE. Relationships are established between WA-density, LA-WA and LA-density on the basis on the results of this work and those of literature. Good correlation between the Micro-Deval (MDE) and the WA, as well as between MDE and LA was found. The analysis of the durability performance allowed concluding that, RGs are less resistant to freeze/thaw than NGs but their degradation, estimated through WA, n and MDE, is not significant.