This study determined the elastic properties of “green” concrete with cement partially replaced by oil shale ash (OSA) and reinforced with short basalt integral fibers (BIFs). Commercially available Deutsche Basalt Faser (DBF) GmbH Turbobuild Integral basalt fibers were used. There is currently a high demand both for strengthening concrete and applying ecological approaches with respect to circular economy. Oil shale ash is the byproduct of oil shale combustion. Basalt fiber is produced by melting basalt rock. Both BIF and OSA are used as additives in concrete. Cement replacement by OSA non-linearly changes the concrete’s strength properties, and the addition of BIF improves them. An experimental investigation was conducted using four-point bending tests and cube sample compression tests. Theoretical methods such as Voigt and Reuss boundaries, the Halpin–Tsai method, and the Mori–Tanaka method were used to predict the elastic properties of the fabricated samples. The theoretical models can provide useful information, although they may not fully capture the real properties observed experimentally. The results show that BIFs protect against instant brittle destruction. The experiments demonstrated an optimal OSA concentration for a fixed amount of BIF, resulting in the highest load-bearing capacity of the concrete. The addition of either 15% OSA only or 20% OSA and CBF can increase the stiffness of the concrete. This article provides guidance to the construction sector on using OSA and CBF together.

The fracture and pull-out behaviour of vertically aligned basalt composite fibres embedded in an oil shale ash (OSA)-based cementitious matrix was investigated using the double cantilever beam (DCB) test. OSA replaced cement at 0 %, 10 %, 15 %, and 35 % to reduce carbon emissions and improve the mechanical properties of fibre-reinforced concrete. The basalt fibres were oriented vertically, perpendicular to the fracture plane, and aligned with the loading direction to facilitate accurate assessment of the pull-out mechanisms during crack initiation and propagation. The DCB test involved two notched concrete beams joined by a thin fibre-reinforced layer, which enabled controlled crack opening. Specimens with varying OSA content were evaluated for peak load, fracture energy, interfacial bond strength, and fibre pull-out. The results indicated that vertical fibre alignment enhanced load transfer and inter-facial resistance, resulting in higher pull-out forces and improved crack-bridging compared to random fibre placement. Incorporating a moderate amount of OSA improved fracture performance by strengthening the matrix–fibre interface and promoting more ductile failure. Specifically, 10–15 % OSA produced notable improvements in fracture resistance and fibre–matrix bonding, shifting the failure mode from brittle, matrix-dominated to a more ductile, pull-out–controlled process. On the contrary, 35 % of OSA reduced the strength of the interfacial bond due to matrix dilution. Force–displacement curves demonstrated that optimally modified mixtures dissipated more energy and delayed crack propagation. Post-test examination of fibres and force–displacement data confirmed a transition from brittle fracture to gradual pull-out, primarily attributed to enhanced fibre–matrix adhesion. In general, OSA-modified matrices with vertically aligned basalt fibres demonstrated significant potential for developing durable, high-strength, and crack-resistant cementitious composites.

Modified basalt fibers doped with neutron-absorbing and gamma-attenuating oxides were developed as a multifunctional concrete admixture for nuclear shielding applications. Within the ECOSCREEN project, basalt microfiber compositions were modified by introducing boron-, gadolinium-, hafnium-, and yttrium-bearing oxides, aiming to achieve a uniform, mix-independent distribution of absorbers in concrete while retaining the durability benefits of fiber reinforcement. The fibers were produced under laboratory conditions and characterized by tensile testing, chemical resistance in aggressive media, and SEM/EDS-based microstructural assessment, confirming stable morphology and the presence of absorber elements. Shielding performance was quantified using continuous-energy Monte Carlo transport simulations with three independent codes (Serpent, MCNP6, OpenMC) employing harmonized geometry, sources, detectors, and ENDF/B-VII.1-based nuclear data. A dedicated cross-verification stage demonstrated consistent predictions of neutron, primary-photon, and activation-photon transport, enabling code-averaged spectra to be used for dose rate assessment. A simplified slab model was evaluated for three representative sources: VVER-1000 spent fuel, RBMK-1500 spent fuel, and a DEMO/EuroFusion activated-water source. For 21 concrete mixes (five modified basalt fiber types at 25-100 kg/m3 plus plain concrete), modified basalt fiber addition produced a monotonic reduction of neutron flux (most pronounced in the thermal range) and a measurable improvement in photon shielding for fibers modified with heavy-element oxides. The largest total dose rate reductions behind the shield were obtained for the hafnium-modified basalt fiber concrete at 100 kg/m3 (13.44% for VVER-1000 spent fuel, 14.24% for RBMK-1500 spent fuel, and 4.97% for the DEMO/EuroFusion source relative to plain concrete).