Introduction The increasing environmental impact of conventional concrete production and the seismic vulnerability of reinforced concrete structures in Morocco have encouraged the development of sustainable alternative construction materials. This study evaluates the seismic and thermal performance of reinforced concrete frames incorporating shale powder from the Settat-Khouribga region as a partial replacement for natural sand. Methods Four concrete formulations containing 0%, 5%, 15%, and 25% shale substitution were evaluated using calibrated finite element modeling. Linear elastic analyses were done in SAP2000 as per the Moroccan seismic code RPS 2011. Pushover and Incremental Dynamic Analysis (IDA) analyses were carried out in OpenSees software with 12 spectrum-consistent ground motions. Thermal behavior was determined using steady-state analysis in ANSYS Mechanical. Results The F15 mixture, which consisted of 15% shale substitution, demonstrated the best behavior in terms of structure and thermal stability. Compressive strength was achieved at 22.3 MPa, and the ductility index rose to 3.97. Median capacity for collapse was measured at 1.19 g, and the probability of surpassing the design level of earthquake protection is 9.8%, while in the case of the reference concrete, the same indicator is 12.1%. Discussion The mixture F15, which was made up of 15% shale replacement, showed the best performance in respect of structural properties and thermal stability. Compressive strength was observed to be equal to 22.3 MPa, while the ductility factor increased to 3.97. The median collapse capacity reached 1.19 g, and the possibility of exceeding earthquake protection design levels was calculated to be 9.8%, as compared to 12.1% for reference concrete. Conclusion The addition of 15% shale powder is considered to achieve an optimum combination of seismoprotection, structural flexibility, and energy savings. The obtained results confirm the possibility of using the shale powder as a sustainable construction material for reinforced concrete structures in seismically active areas of Morocco.
Introduction Environmental problems are becoming increasingly prevalent in the construction industry, mainly due to the significant carbon emissions associated with Ordinary Portland Cement (OPC) production and the growing accumulation of non-biodegradable plastic waste. In this context, the present study focuses on the use of discarded Low-Density Polyethylene (LDPE) as a partial replacement for fine aggregate in geopolymer mortars. Methods Three distinct binder systems were considered: fly ash-based Geopolymer Mortar (GPM), blended Fly ash–GGBS Geopolymer Mortar (FG), and traditional OPC mortar, with LDPE replacement levels ranging from 0% to 50%. The experimental investigation was carried out to evaluate compressive strength, thermal properties including thermal conductivity and specific heat capacity, and dynamic thermal parameters such as time lag (φ) and decrement factor (f). Results The results showed that as the LDPE content increased, the thermal performance of all mixtures consistently improved, while the compressive strength gradually decreased. The fly ash–GGBS blended geopolymer mortar with 50% LDPE showed better thermal performance among all the mixtures, with a low thermal conductivity of 0.29 W/m·K, a decrement factor of 0.029, and a time lag of approximately 4.10 hours. Discussion The inclusion of LDPE improved internal porosity, which reduced thermal conductivity and enhanced dynamic thermal performance. This demonstrates the ability of fly ash–GGBS geopolymer mortar to maintain a balance between mechanical strength and thermal insulation. Conclusion These findings suggest that LDPE-incorporated geopolymer mortars, especially fly ash–GGBS-based systems, can serve as energy-efficient and sustainable alternatives for non-structural building envelope applications.
Introduction/Objective The depletion of natural aggregates and accumulation of steel slag waste pose environmental challenges. However, there is limited research on the combined effect of steel fiber and slag aggregate in concrete. This study evaluates the fresh, mechanical, durability, and microstructural properties of Steel Fiber-Reinforced Slag Aggregate Concrete (SFRSAC) to identify the optimum fiber content and slag replacement level for durable, sustainable concrete. Methods Twenty concrete mixes were prepared with varying amounts of steel fiber and slag aggregate replacing coarse aggregate. Fresh properties were assessed via the slump test, and hardened properties via compressive, flexural, and split tensile strength, ultrasonic pulse velocity, abrasion resistance, apparent density, permeable voids, water permeability, acid attack, and chloride penetration. The microstructure was investigated using detailed SEM analysis. Results Steel fiber improved mechanical performance, with the optimum mix achieving a compressive strength of 59 MPa, approximately 27% higher than conventional concrete. Slag aggregate enhanced acid and chloride resistance, and SEM confirmed a denser microstructure with improved interfacial bonding and reduced microcracking. Slag utilization reduced natural resource consumption and material cost. Discussion The interaction between steel fiber and slag aggregate improved mechanical properties, durability, and microstructural integrity, confirming that combining fiber reinforcement with industrial waste aggregate is an effective route to durable, high-performance, sustainable concrete. Conclusion Combined utilization of steel fiber and slag aggregate produces sustainable, high-performance concrete, with 3% steel fiber and 50% slag aggregate replacement giving the optimum overall performance. This mixture is recommended for structural and infrastructure applications requiring enhanced strength, durability, and sustainability.
Introduction/Objective The selection of a reinforced concrete slab system influences structural efficiency, cost, embodied carbon, and serviceability. Six cast-in-place slab systems were compared for a four-story office building in Kuwait with 6- and 9-meter spans to determine which system provides the best overall performance. Methods Twelve CSI ETABS models were developed. Loads were specified in accordance with ASCE 7-16, and reinforced concrete design was in accordance with ACI 318-19. Evaluated parameters included concrete and reinforcement quantities, direct material cost, embodied CO 2 emissions, structural weight, vertical natural frequency, and X-direction seismic displacement. An MCDM method was used to rank the alternatives, with deflection, punching shear, and story drift assessed separately. Results The flat slab with drop panels (Design 5) achieved the highest ranking at both spans, with MCDM scores of 0.989 and 0.993. This system resulted in the lowest cost, embodied CO 2 emissions, structural weight, and X-direction displacement. At a 9-meter span, Design 5 reduced cost and CO 2 emissions by 6.4% and 7.3%, respectively, compared to the next-best alternative. Discussion The results indicate that maximizing stiffness does not always yield the most efficient structural solution. Targeted strengthening at column zones can enhance performance without incurring the material costs associated with continuous beams. Conclusion For similar office buildings in Kuwait, Design 5 provides the optimal balance of economy, sustainability, structural efficiency, and serviceability, pending project-specific verification.
Introduction/Objective Saltwater intrusion can significantly alter the geotechnical properties of coastal soils, with implications for infrastructure stability and environmental management. This study investigated the effects of salinity on the shear strength parameters of coastal soils in Ikot Abasi Local Government Area, Nigeria. Methods Laboratory tests, including triaxial, direct shear, Atterberg limits, and compaction tests, were conducted on soil samples subjected to different salinity levels. Samples were collected from four locations within the coastal zone and designated as Points A, B, C, and D for identification. Results Grain-size analysis classified soils from Points A, B, and C as clayey sand (SC), while Point D was classified as well-graded sand with silt (SW-SM) according to the Unified Soil Classification System (USCS). Accordingly, Points A–C exhibited cohesive behavior, whereas Point D was predominantly non-cohesive. Saltwater intrusion was simulated using NaCl solutions prepared with distilled water. Increasing salinity reduced the liquid limit of Points A–C by 23.2–32.0% and the plastic limit by 7.02–14.6%. Similarly, OMC decreased while MDD increased with increasing salt concentration. Cohesion increased progressively with salinity, from 34% to 48% at Point A, 42% to 58% at Point B, and 17.3% to 26.0% at Point C, whereas the corresponding variations in the angle of internal friction (ϕ) were nonlinear. At Point D, ϕ decreased progressively from 31.34° to 24.86° with increasing salinity. Discussion Increasing salinity reduced the liquid limit and the plasticity index of soils from Points A, B, and C, whereas Point D remained non-plastic. The reduction in PI indicates a narrower plasticity range and reduced susceptibility to shrink–swell behavior. The observed decrease in OMC and increase in MDD with increased salinity may be associated with salinity-induced changes in clay-particle interaction and soil fabric. Triaxial tests further showed that cohesion increased with salinity for the cohesive soils at Points A, B, and C, although the corresponding variations in friction angle (ϕ) were nonlinear. In contrast, Point D exhibited a progressive decline in ϕ, with a reduction of approximately 6.48° between distilled water and 15% saline water. The failure-envelope intercepts (−0.10 to +0.04 kPa) were close to zero, indicating negligible cohesion and confirming that shear strength at Point D was governed mainly by friction. Conclusion The results of this study demonstrate that increasing salinity was associated with the changes observed in the shear strength parameters and mechanical behavior of coastal soils. These findings highlight the need to account for salinity-induced changes in geotechnical design and assessment of coastal infrastructure.
