Aeolian sand along the Hojiakueri Railway in the Taklimakan Desert exhibits poor mechanical properties for direct use as a filler for railway subgrades. Although cemented soil reinforced with single fibers can improve mechanical properties, its limited effectiveness and high cement usage pose significant economic and environmental concerns. This study investigated the improvement of splitting tensile strength (STS) in cemented aeolian sand through hybrid fiber reinforcement. An orthogonal test was designed to evaluate four factors-fiber types (pairwise combinations of basalt, polypropylene, and glass fibers), fiber lengths (3, 6, and 9 mm), hybridization ratios (1:1, 1:3, and 3:1), and fiber contents (4 %o, 8 %o, and 12 %o) - along with their interactions. The performance of cemented aeolian sand reinforced with hybrid fiber (CASRHF) was evaluated through STS tests and scanning electron microscopy (SEM). The results identified the optimal combination as a 1:1 mix of 6 mm basalt and polypropylene fibers with a fiber content of 12 %o. The interaction between hybrid fiber type and fiber length was the most critical factor influencing STS, followed by hybrid fiber type, fiber length, and fiber content. SEM analysis further revealed a linear negative correlation between STS and porosity, providing new insights into the microscopic mechanisms. The findings underscore the importance of optimizing hybrid fiber combinations to meet the performance requirements of railway subgrade beds in aeolian sand regions.

Over the last 20 years, the development of electrically conductive composites for removing snow and ice from transportation infrastructure has received exceptional traction. However, these composites need to exhibit stable electrical conductivity and high mechanical properties to be sustainable and cost-effective. Towards this goal, the article investigates the roles of ground granulated blast furnace slag (BFS) and copper slag (CS) content, in addition to hooked-end steel fiber length, on the electrical properties of eco-friendly ultra-high performance hybrid fiber-reinforced self-compacting concrete (HFR-SCC) for the first time in the literature. For this purpose, sixteen eco-friendly electrically conductive ultra-high-performance HFR-SCC were designed based on the variable parameters of four different BFS/total binder ratios (20, 40, 60, and 80 %), a CS/total fine aggregate ratio of 50 %, and two different hooked-end fiber lengths (30 and 60 mm), while all mixes used 1.75 % by volume fraction of steel fibers. After determining the workability properties (slump-flow and T500 values) of all mixes, compressive strength and electrical resistivity/conductivity tests of 90-day specimens were conducted. Additionally, environmental and economic evaluations of all mixes in terms of sustainability were performed in order to clarify the effects of the variable parameters. Taking into account the experimental results obtained, it was observed that all electrically conductive ultra-high performance HFR-SCC mixes demonstrated satisfactory workability properties, while the compressive strength values reached to impressive values of 127 MPa. The optimum BFS/total binder ratio was identified to be 40 % for higher compressive strength and conductivity of ultra-high performance HFR-SCC specimens. On the other hand, the addition of CS to the mixes resulted in an increase of almost 9 % in compressive strength compared to one without CS, while at the same time, a significant increase of approximately 363 % was observed in the electrical conductivity values of the specimens. As for the influence of different lengths of hooked steel fibers, the use of 30 mm length hooked-end steel fibers in HFR-SCC mixes performed better in terms of compressive strength, whereas 60 mm fibers performed better regarding electrical conductivity. In conclusion, this experimental work has evidenced that it is possible to develop an ecofriendly and sustainable electrically conductive ultra-high performance cementitious composite (the optimal mix compressive strength and electrical resistivity values were 127 MPa and 2242 Omega.cm, respectively) by using waste from different industries such as iron and copper. Thus, it will provide important insights for the design and application of future electrically conductive concretes, which can be an important alternative in efficient active deicing and snow-melting applications.

This study investigates the stabilization of silty soil using alkali-activated fly ash and fibers with lengths of 3 mm and 12 mm. The study examines the effects of hybrid fiber length, fiber content, fly ash content, and activator content on the mechanical properties of the geopolymerstabilized samples. The objectives of this paper are 1) to examine the effect of activator content and fly ash content on the UCS, Al/Si ratio, and SiO2/Na2O ratio of the stabilized samples using a statistical approach, 2) to investigate the effect of hybrid fiber length on UCS, secant modulus, flexural strength, toughness, and flexural load-deformation characteristics of the stabilized soil. A statistical approach was employed to investigate the relationship between fly ash content, alkali activator content, and UCS value. Optimal fly ash content and alkali activator content were determined based on the statistical model. The geopolymer structure of the stabilized soil was characterized via SEM, EDS, XRD, and FTIR analyses. The effects of fly ash and alkali activator content on UCS, Al/Si ratio, and SiO2/Na2O ratio were determined using the derived statistical model. The study demonstrated that activator content, a critical factor in compaction, significantly influences the UCS value, as much as the effect of the Si/Al and SiO2/Na2O ratios. Additionally, variations in fly ash content led to an increase in the UCS value of up to 15%. Moreover, changing the activator content resulted in a maximum 12-fold increase in UCS value. Incorporating hybrid fibers for stabilization led to higher secant modulus (up to 30%), flexural strength (up to 6%), and ductility without compromising UCS.