Résumé: The susceptibility of concrete to elevated temperatures is a paramount concern in civil engineering, especially in fire-related scenarios. This material often suffers mechanical weaknesses such as fracturing and reduced durability under high temperatures. Despite its ubiquitous use, concrete’s vulnerability to thermal stress presents significant challenges for maintaining structural integrity and safety. The novelty of this work lies in its innovative approach to addressing these challenges by proposing the utilization of waste plastic fibers, which are readily available due to the extensive use of various plastic products. This approach not only enhances the mechanical resilience of concrete but also contributes to mitigating environmental and health impacts associated with plastic waste. The research focuses on the effects of high temperatures on the mechanical properties of sand concrete reinforced with fibrous materials. Concrete specimens were prepared with different lengths (1 cm and 2 cm) of packing tape fibers at concentrations of 1% and 2%. These specimens underwent controlled thermal treatments ranging from 100 °C to 700 °C with a heating rate of 1 °C/min, following a 90-day water immersion curing period. The evaluation encompassed various tests including visual inspection, residual weight measurement, residual compressive and tensile strength assessments, and ultrasonic pulse velocity (UPV) testing. The analysis revealed a notable improvement in mechanical strength for concrete reinforced with 1% fibers at 300 °C. However, exposure to higher temperatures (500 °C and 700 °C) led to a significant decline in strength across all samples due to the evaporation of fibers, resulting in the formation of voids and conduits within the concrete’s structure. While previous research has extensively investigated the effectiveness of polypropylene fibers in crack mitigation during fire incidents, limited attention has been given to the potential of plastic waste as a reinforcement material. Thus, this study’s novelty contributes to expanding the scientific understanding of using waste plastic fibers to enhance concrete’s resilience to high temperatures, thereby filling a crucial gap in existing literature.

Résumé: At ambient temperature, concrete exhibits excellent mechanical properties. However, understanding the behavior of concrete under high-temperature conditions is crucial, especially for civil engineering applications during fire incidents. The growing use of plastic-based products has led to a significant increase in polymer waste, posing environmental challenges. The valorization of this plastic waste in the form of fibers presents both economic and environmental advantages. This study focuses on the study of the behavior of sand concrete incorporating polyethylene terephthalate (PET) fibers with percentages of 1% and 2% at high temperatures (100, 300, 500 and 700 °C). Specimens are tested for residual mass loss, residual compressive and tensile strength. A complementary analysis of SEM makes it possible to confirm and better clarify the morphology of the concretes of sand before and after the rise in temperature. The results obtained from this study indicate that the residual resistance is reduced with the rise in temperature for all the concretes studied, except in the temperature range of 300 °C, in which a slight improvement in resistance is noticed. The incorporation of PET fibers in the test concretes does not enhance their residual behavior significantly. However, it does serve as an effective solution by reducing the susceptibility to spalling, by preventing cracking and by fulfilling a similar role to that of polypropylene fibers. Keywords: sand concrete; PET fibers; high temperature; mass loss; mechanical resistance

Résumé: This research focuses on the optimization of formulation, characterization, and damage analysis of plant fiber-reinforced polyester resin composites (jute and date palm). To better understand the characteristics and mechanical behavior of these materials, this study investigates the influence of resin content and plant fibers on the physico-mechanical behavior of the resin composites. Resinous composites consisting of polyester resin and raw earth were studied using a novel formulation based on an empirical method that follows the principle of earth saturation with polyester resin. Saturation was achieved with a 28% content of polyester resin, which appeared to be an optimal blend for the earth–resin composite. Plant fibers were randomly incorporated as reinforcement in the composites at various percentages (1%, 2%, and 3%) and lengths (0.5 cm, 1 cm, and 1.5 cm). Mechanical tests including bending, compression, and indentation were conducted to evaluate the mechanical properties of the composites. Analysis of fracture morphology revealed that the deformation and rupture mechanisms in bending, compression, and indentation of these composites differ from those of traditional concrete and cement mortar. The obtained results indicate that the composites exhibit acceptable performance and could be favorably employed in the rehabilitation of historic buildings.

Résumé: The valorization of local by-products in the manufacture of a new range of sand concrete and the improvement of their properties, will lead to seek an arrangement between performance and cost in order to achieve a resistant material. Waste recycling affects two very important affect namely the environmental impact and the economic impact. The main objective of our work is to contribute to optimize the formulation of sand concrete as part of the recovery of waste, which is harmful to the environment given its bulky and unattractive nature, it is waste plastic. Most PET bottles become waste after use, causing environmental problems. To solve this problem, a method for recycling PET bottles as fibers to strengthen concrete is proposed. Two types of plastic waste are added to sand concrete; the first concerns the recycling of post-consumer bottles in PET, in the form of polyester fiber supplied by the company RET-PLAST and the second type concerns the packaging belts made of polyethylene terephthalate (PET). The properties in the fresh state (workability and density) and in the hardened state (compressive strength, tensile strength and water absorption) of the various produced concretes are analyzed and compared against their respective controls. From the experimental results, it can be concluded that the reinforcement of the cement matrix with PET fibers with a rate of 1% improves the mechanical properties of sand concrete as well as a remarkable decrease in its water absorption capacity.

Résumé: This paper is concerned with investigating of the plastic behaviour on gap K-joints of truss girders, made from thin-walled rectangular hollow section members. An experimental study was carried out on a full-scale girder under a concentrated load on two central nodes. A numerical analysis was carried out using ABAQUS in order to clearly see the behaviour of this type of joint and to make a comparison with the experimentation. This study will make it possible to examine attentively and to define the analytical model for this type of joint. The results obtained in this paper have shown that the sections with very thin-walled present different behaviours compared to the thin or more or less thick sections. As a result, the tested truss made it possible to observe the failure mode of this type of section, follow-up of a comparative study on the determination of the joint capacity by Eurocode 3 and CIDECT.

Résumé: The reuse of concrete waste as a secondary aggregate could be an efficient solution for sustainable development and long-term environmental protection. However, the variable quality of waste concrete, especially with various compressive strengths, can have a negative effect on the final compressive strength of recycled concrete. In this approach, the major goal of this research is to study the effect of parent concrete qualities on the performance of recycled concrete. To accomplish this task, three grades of different compressive strengths (10 to 15) MPa, (20 to 25) MPa, and (30 to 40) MPa have been analyzed in an experimental test program, in which an unknown compressive strength is introduced as well. The experimental mix use 40% of secondary aggregates (both course and fine) and 60% of natural aggregates. This led to the decreasing of the compressive strength of the test concrete between 14% and 23.7% compared to the normal concrete. This loss was improved by adding an amount of cement equivalent to 4% of the weight of the recycled aggregate used. The achieved results prove that the strength properties of the parent concrete have a limited effect on the compressive strength of the recycled concrete. Additionally, low compressive strength parent concrete, when crushed, generates a high amount of fine aggregate and large percentage of recycled coarse aggregates with less attached mortar, and presents the same compressive strength as an excellent parent concrete.

Résumé: The reuse of concrete waste as a secondary aggregate could be an efficient solution for sustainable development and long-term environmental protection. However, the variable quality of waste concrete, especially with various compressive strengths, can have a negative effect on the final compressive strength of recycled concrete. In this approach, the major goal of this research is to study the effect of parent concrete qualities on the performance of recycled concrete. To accomplish this task, three grades of different compressive strengths (10 to 15) MPa, (20 to 25) MPa, and (30 to 40) MPa have been analyzed in an experimental test program, in which an unknown compressive strength is introduced as well. The experimental mix use 40% of secondary aggregates (both course and fine) and 60% of natural aggregates. This led to the decreasing of the compressive strength of the test concrete between 14% and 23.7% compared to the normal concrete. This loss was improved by adding an amount of cement equivalent to 4% of the weight of the recycled aggregate used. The achieved results prove that the strength properties of the parent concrete have a limited effect on the compressive strength of the recycled concrete. Additionally, low compressive strength parent concrete, when crushed, generates a high amount of fine aggregate and large percentage of recycled coarse aggregates with less attached mortar, and presents the same compressive strength as an excellent parent concrete.

Résumé: The service life of reinforced concrete structures is conditioned by the response to physical and chemical attacks from the environment, as well as by the capacity of the constituent materials to protect themselves against these attacks. Carbonation is one of the pathologies of concrete that represents a risk for reinforced concrete structures, it corresponds to a chemical phenomenon manifested when CO2 reacts with the hydrate of lime present in the concrete. This work is a study of the art concerning this phenomenon, process, consequences and characterizations. The conclusion is that carbonation generates a slow modification of the structure of the material and a change in its behavior. The conclusion is that carbonation generates a slow modification of the structure of the material and a change in its behavior. Certainly it has a harmful effect by reducing the chemical protection of the reinforcements, but it is also beneficial aggressive by improving the mechanical resistance and the resistance to water

Résumé: é - Le béton est un matériau relativement durable, c’est le matériau le plus utilisé aujourd'hui dans le domaine des travaux publics BTP. Mais les constructions en béton sont enclines aux risques des attaques chimiques lors de leurs fonctionnements, ce qui reflète sur sa durée de vie, et éventuellement la minimise. La prédiction des divers signes d’endommagement ainsi que le temps d’apparition de ces désordres sont l’objectif de nombreuses recherches dans le domaine de conception. D’où, la seule démarche disponible pour analyser le cycle de vie des ouvrages d’art et estimer le degré d’endommagement au cours du temps se limite uniquement à la simulation numérique et expérimentale. Dans ce contexte, cette recherche porte sur une validation des résultats numériques par une simulation expérimentale faite au sein du laboratoire de génie civil à l’université d’Annaba. Un modèle numérique macroscopique de Baghdadi et ces collègues est programmé par le logiciel Matlab (version 2014), en simulant l’effort de compression dans des éprouvettes (Ø11 ; h22) cm. Et cela en cas des attaques chimiques sous un impact environnemental hyperbasique d’un béton à base de granulats fortement réactifs apportés d’une carrière Algérienne de Guelma (Bouhachana). Les résultats montrent une bonne fiabilité de ce modèle numérique par rapport à d’autres modèles existants, car les écarts calculés de déformation étaient assez faibles d’environ 0.08 au maximum.