Aissa Asroun

Early-age cracking severely limits concrete durability in hot, arid environments due to rapid plastic and drying shrinkage. This study evaluates the cracking sensitivity of cement-based materials incorporating four local supplementary cementitious materials (SCMs): limestone filler from Djebel Béchar, natural pozzolan, silica fume, and gypsum under simulated arid conditions (55 °C, 12% relative humidity, 10 km/h wind). Using a custom climatic chamber, prismatic cement-grout specimens with internal restraints were tested. SCMs were evaluated at substitution rates of 2% to 8%. Limestone was further tested at higher rates (up to 40%) and in binary combinations. Findings were validated using micro-concrete with limestone substitutions (0–35%) combined with 4% natural pozzolan. Cracking sensitivity was assessed using maximum crack width and a cracking index, along with setting times and mechanical strengths. Results indicate that limestone filler demonstrated the most favourable performance. A 4% limestone substitution yielded a single crack with a maximum width of 0.1 mm, while an 8% substitution resulted in five cracks of about 0.2 mm. The optimal cracking index was achieved at a 35% limestone substitution rate, which also successfully extended initial and final setting times. While binary SCM combinations significantly reduced cracking compared to the unsubstituted reference, they did not outperform the optimal 35% single limestone substitution. Furthermore, the 28-day compressive and flexural tensile strengths of the micro-concrete were effectively maintained at up to 35% limestone combined with 4% pozzolan. Overall, these preliminary findings demonstrate that crushed limestone fines from Djebel Béchar are highly promising as partial cement replacements to improve concrete durability in arid climates. Further durability assessments and statistical validation are recommended to confirm these benefits for practical field applications.

This study investigates the influence of curing conditions on mechanical performance, residual strength after high-temperature exposure, and microstructural evolution of geopolymer mortars based on ceramic sanitaryware waste (CSW). Direct and delayed thermal curing regimes were applied at 60 °C and 80 °C for 48 h and 72 h. The fresh mixtures exhibited adequate workability with a flow diameter of 21 cm, indicating suitable consistency for casting. Results show that direct curing consistently enhances compressive strength, reaching 30.97 MPa at 80 °C for 72 h, compared with 15.88 MPa under delayed curing. Increasing curing temperature and duration improved early-age mechanical performance, particularly under direct curing conditions. After exposure to 800 °C, directly cured specimens retained higher residual compressive strength, with an improvement of approximately 6.6% compared with delayed-cured specimens. Microstructural characterization using scanning electron microscopy coupled with energy-dispersive spectroscopy and X-ray diffraction supported the observed mechanical trends under different curing conditions. The findings highlight the role of curing strategy in optimizing CSW-based geopolymer mortars for construction applications where mechanical performance and high-temperature resistance are required.

Scrap tires are abundant and alarming waste. The aggregates resulting from the crushing of the waste tires are more and more used in the field of civil engineering (geotechnical, hydraulic works, light concretes, asphaltic concretes, etc.). Depending on the type of the used tires, dimensions and possible separations and treatment, the physical and mechanical characteristics of these aggregates might change. Some physical, chemical and direct shear tests were performed on three gradation classes of waste tire rubber powder. The tests results were combined with data from previous studies to generate empirical relationships between cohesion, friction angle and particle size of waste tire powder rubber. A cubic (third order) regression model seems to be more appropriate compared to linear and quadratic models.

This paper studies the numerical simulations of retaining walls supporting tire reinforced sand subjected to El Centro earthquake excitation using finite element analysis. For this, four cases are studied: cantilever retaining wall supporting sand under static and dynamical excitation, and cantilever retaining wall supporting waste tire reinforced sand under static and dynamical excitation. Analytical external stability analyses of the selected retaining wall show that, for all four cases, the factors of safety for base sliding and overturning are less than default minimum values. Numerical analyses show that there are no large differences between the case of wall supporting waste tire reinforced sand and the case of wall supporting sand for static loading. Under seismic excitation, the higher value of Von Mises stress for the case of retaining wall supporting waste tire reinforced sand is 3.46 times lower compared to the case of retaining wall supporting sand. The variation of horizontal displacement (U1) and vertical displacement (U2) near the retaining wall, with depth, are also presented.

An experimental programme was undertaken to investigate the effect of scrap tyre rubber on the swelling behaviour of composite clayey soils, using a large mix ratio. Two soils were studied (Ayaida and bentonite soils in the north-west of Algeria) by considering the high compressibility and low water absorption of scrap tyre rubber. Grain size, specific gravity, Atterberg limit analysis, swell-consolidation and loading–unloading tests were performed on the two soils and their mixtures with varying fibre content (10%, 20%, 25% and 50%). The results show that the liquid limits, swell potentials, swelling pressure and time to reach maximum heave decrease gradually when the scrap rubber content increases, and this reduction is significant for the soil with the higher swelling potential. Owing to the high compressibility of scrap tyre rubber, the compression and recompression indexes increase considerably with the content of scrap tyre rubber. It appears from the results that scrap tyre rubber can be used as reinforcement material for the modification of clayey soils, yet with a content that should not greatly affect the mixture compressibility.

La Revue Française de Géotechnique (RFG) est une publication scientifique parrainée par les comités français de mécanique des sols, de mécanique des roches, de géologie de l’ingénieur et des géosynthétiques