This study investigates the preparation and performance of ultra-high-performance concrete (UHPC) incorporating manufactured sand as a full replacement for quartz sand. The mix design was optimized by integrating the compressible packing model (CPM) with an orthogonal experimental design. The influence of stone powder content in manufactured sand—0, 5, 10, and 15% by mass of fine aggregate—on fresh-state fluidity and 7d-mechanical properties was systematically evaluated. Hydration products and microstructural features were analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM), and mercury intrusion porosimetry (MIP). Results show that the manufactured sand-based UHPC achieved a fresh-state fluidity of 185 mm and a 7-day compressive strength of 152.4 MPa. Both fluidity and compressive strength exhibited a unimodal trend with increasing stone powder content, reaching maxima at 10%. Microstructural analysis revealed intimate interfacial bonding between unhydrated particles and calcium silicate hydrate (C–S–H) gel; notably, the UHPC matrix with 10% stone powder displayed the densest microstructure. MIP results further demonstrated that an optimal stone powder content effectively reduced total porosity, with the lowest overall porosity and the highest volume fractions of harmless (≤20 nm) and less harmful (20–100 nm) pores observed at 10%. These microstructural refinements collectively underpin the superior mechanical performance of manufactured sand-based UHPC.

To address the high construction difficulty and cost resulting from the heavy self-weight of concrete-filled steel tube (CFST) skeletons in the construction of long-span arch bridges, as well as the ineffective utilization of 0–3 mm waste fraction of sintered shale pottery sand —which leads to resource waste and environmental pollution when stockpiled—this study employed an experimental approach combining the close packing and over slurry theories to determine the optimal mix proportion for lightweight ultra-high performance concrete (LUHPC) incorporating 0–3 mm waste fraction of 800/700-grade sintered shale pottery sand. LUHPC exhibited excellent properties. With a volume fraction of 3% straight-round steel fibers, the compressive strength was 147.7 MPa, the tensile strength was 17.4 MPa, and the elastic modulus was 49.9 GPa. All groups achieved a slump flow of at least 220 mm, meeting the requirements for self-compacting. The apparent density ranged from 1.943 to 2.178 g/cm ³ , 22.2%–30.6% lower than that of ultra-high performance concrete (UHPC). Scanning electron microscope (SEM) analysis showed that the waste fraction of 800-grade sintered shale pottery sand provided better internal curing than that of 700-grade sand, thereby improving its mechanical performance. The addition of irregular steel fibers (end-hooked and wavy) enhanced tensile strength, but reduced flow properties and other mechanical properties. Analyses of carbon emissions and economics indicated that LUHPC with the waste fraction of 700- and 800-grade sintered shale pottery sand reduced emissions by 21.0% and 24.1%, and raw material costs by 42.9% and 45.0%, respectively, compared with conventional UHPC. Finally, a method integrating combined weighting and grey relational analysis was proposed to evaluate multiple performance criteria and select the optimal mix proportion, providing decision support for various engineering applications.

The presence of impurities directly affects the properties of α-hemihydrate gypsum (α-HH) prepared from phosphogypsum (PG) as a raw material. However, the effect of soluble fluorine impurities on the properties of α-HH by autoclaving remains insufficiently understood. This study investigated the influence of sodium fluoride on the morphology, hydration, and hardening properties of α-HH, using XRD, XPS, SEM, MIP, and tests of setting time, evolution of hydration temperature increase, and strength. The results showed that during the preparation of α-HH, some F⁻ reacted with Ca²⁺ to form CaF₂, which adhered to the surface of the α-HH crystal, hindering the growth and development of the crystal and resulting in small crystals with rough surfaces. When α-HH hydrated, sodium fluoride caused the early, rapid nucleation of dihydrate gypsum (DH) crystals, accelerating the crystallization process of DH. The introduction of sodium fluoride inhibited the early hydration of α-HH and promoted its later hydration. The increase in sodium fluoride content caused the initial setting time of α-HH hydration to first increase and then decrease, while the final setting time continued to decrease. In the absence of sodium fluoride, the average pore diameter of the hardened paste was approximately 617.99 nm. When the NaF content was 0.2%, the DH crystals were prismatic and densely packed, which resulted in a decrease in the average pore diameter to 449.35 nm. When the NaF content was 0.6%, the DH crystals exhibited a plate-like morphology and were loosely interlocked, leading to an increase in the average pore diameter to 1169.58 nm. Based on these results, the sodium fluoride content in PG should be controlled below 0.2%.

Leaning-type arch bridges are attractive for wide-deck urban applications, but their elastic global buckling mechanisms and parameter sensitivities remain insufficiently quantified. This study investigates a leaning-type steel box arch bridge using a three-dimensional finite element model validated against field-measured arch deflections and hanger forces. Linear elastic eigenvalue buckling analyses examine the structural system, rise-to-span ratio, arch stiffness, leaning-arch inclining angle, and transverse-bracing characteristics, together with the coupled effect of rise-to-span ratio and main-arch stiffness. Within the investigated bridge configuration, the integrated leaning-arch–transverse-bracing system increases the stability coefficient by approximately 71% relative to the unbraced main-arch system. A relatively favorable main-arch rise-to-span ratio of approximately 1/7–1/4.5 is identified. Main-arch bending stiffness has a pronounced influence, and its quantitative effect depends on the rise-to-span ratio. Variations in leaning-arch inclining angle produce relatively limited net changes, while further increases in bracing stiffness yield diminishing improvements. For a fixed bracing quantity, balanced spatial distribution over the arch span is more effective than concentrating bracings within a limited region. These findings provide a quantitative basis for comparative stability assessment and preliminary design of similar bridge systems.

Integral abutment jointless bridges (IAJBs) offer superior structural robustness, seismic performance, and long-term durability owing to the elimination of expansion joints and bearings, making them particularly suitable for mountainous regions. However, when such bridges are constructed on sloping terrain, the abutment-pile system is subjected to asymmetric soil constraints—the so-called "slope effect"—which complicates the soil-abutment-pile interaction (SAPI). To quantify this effect, pseudo-static cyclic tests were conducted on an integral abutment-reinforced concrete (RC) pile system embedded in a layered clay-sand slope, taking the ratio of the distance from the pile side to the slope crest to the pile diameter (b/d) as the key parameter. Two configurations were tested: APSD-1 (b/d = 0.0, level ground) and APSD-2 (b/d = 2.0, 30°slope). The results show that the slope effect significantly weakens the lateral resistance and amplifies the asymmetric response of the system. Compared with the level-ground case, the peak lateral force in the slope-facing direction decreased by 33.1% and the overall system stiffness degraded by 24.8%, while the plastic hinge in the pile developed to a greater depth. The earth pressure behind the abutment exhibited similar distribution patterns in both configurations, but its magnitude in APSD-2 was approximately 4.6% lower at large displacements. The average soil reaction on the pile decreased to 0.932 times that of the level-ground case, with a pronounced asymmetry in the embedment depths of the maximum reaction between the backslope and slope-facing directions. In addition, the equivalent viscous damping ratio in the slope-facing direction was reduced by about 5% on average. These findings clarify the integrated interaction mechanism and asymmetric failure characteristics of the abutment-pile-soil system in sloping terrain and provide essential experimental evidence for the seismic design and performance assessment of IAJBs in mountainous regions.