Construction Materials

Textile-reinforced concrete (TRC) sandwich panels with lightweight cores are a promising solution for sustainable and slender building envelopes. However, their structural performance depends strongly on the shear connection between the outer shells. This study investigates the flexural behavior of TRC sandwich panels with glass fiber-reinforced polymer (GFRP) rod connectors under four-point bending. Three full-scale specimens were manufactured with high-performance concrete (HPC) face layers, an expanded polystyrene (EPS) core, and 12 mm GFRP rods as shear connectors. The panels were tested up to failure, with measurements of load–deflection behavior, crack development, and interlayer slip. Additionally, a linear-elastic finite element model was developed to complement the experimental campaign, capturing the global stiffness of the system and providing complementary insight into the internal stress distribution. The experimental results revealed stable load-bearing behavior with ductile post-cracking response. A degree of composite interaction of γ = 0.33 was obtained, indicating partially composite action. Slip measurements confirmed effective shear transfer by the GFRP connectors, while no brittle failure or connector rupture was observed. The numerical analysis confirmed the elastic response observed in the tests and highlighted the key role of the GFRP connectors in coupling the TRC shells, extending the interpretation beyond experimental results. Overall, the study demonstrates the potential of TRC sandwich panels with mechanical connectors as a safe and reliable structural solution.

The development of sustainable self-compacting concrete (SCC) requires alternative binders that minimise ordinary Portland cement (OPC) consumption while ensuring long-term performance. This study investigates sulfate-activated SCC (SA SCC) incorporating high volumes of industrial by-products, whereby 72% ground granulated blast furnace slag (GGBS) and 18% fly ash (FA) were activated with varying proportions of OPC and gypsum. Quarry dust was used as a fine aggregate, while granite and electric arc furnace (EAF) slag served as coarse aggregates. Among all formulations, the binder containing 72% GGBS, 18% FA, 4% OPC, and 6% gypsum was identified as the optimum composition, providing superior mechanical performance across all curing durations. This mix achieved slump flow within the EFNARC SF2 class (700–725 mm), compressive strength exceeding 50 MPa at 270 days, and flexural strength up to 20% higher than OPC SCC. Drying shrinkage values remained below Eurocode 2 and ASTM C157 limits, while EAF slag increased density, but slightly worsened shrinkage compared to granite mixes. Microstructural analysis (SEM-EDX) confirmed that strength development was governed by discrete C-S-H and C-A-S-H gels surrounding unreacted binder particles, forming a dense interlocked matrix. The results demonstrate that sulfate activation with a 4% OPC + 6% gypsum blend enables the production of high-performance SCC with 94–98% industrial by-products, reducing OPC dependency and environmental impact. This work offers a practical pathway for low-carbon SCC.

Ultra-high-performance concrete (UHPC) delivers outstanding durability and strength but typically relies on high Portland cement content. This study evaluates a 20% cement replacement with limestone powder (LP) in UHPC and benchmarks performance under two curing regimes: moist curing (MC) and warm bath curing at 90 °C (WB). Metrics include workability, compressive and flexural behavior, shrinkage, freeze–thaw resistance, chloride transport (surface resistivity, RCPT), material cost, and embodied CO₂. LP improved fresh behavior: flow increased by 14.3% in plain UHPC and 33% in fiber-reinforced UHPC (FR-UHPC). Compressive strengths remained in the UHPC range at 28–56 days (approximately 142–152 MPa with LP), with modest penalties versus 0%-LP controls (about 2–5% depending on age and curing). Under WB at 56 days, controls reached 154 MPa (plain) and 161 MPa (FR-UHPC), while LP mixes achieved 145.2 MPa (plain) and 152.0 MPa (FR-UHPC). Flexural performance was reduced with LP: for FR-UHPC, 28-day MOR under MC was reduced from 15.5 MPa to 12.7 MPa and under WB from 14.3 MPa to 10.3 MPa; toughness under MC was reduced from 74.4 J to 51.1 J. Durability indicators were maintained or improved despite these moderate strength reductions. After 300 rapid freeze–thaw cycles, all mixtures retained relative dynamic modulus near 100–103%, with negligible MOR losses in LP mixes (plain UHPC: −1.1% with LP versus −4.7% without; FR-UHPC: −3.7% versus −8.1%). Chloride transport resistance improved: at 56 days under MC, surface resistivity increased from 558 to 707 kΩ·cm in plain UHPC and from 252 to 444 kΩ·cm in FR-UHPC; RCPT for LP mixes was 139 C (MC) and 408 C (WB), about 14–23% lower than respective controls. Drying shrinkage was reduced by roughly 23% (plain) and 28% (FR-UHPC). Sustainability and cost outcomes were favorable: embodied CO₂ was reduced by 18.8% (plain) and 15.5% (FR-UHPC), and material cost was reduced by about 4.5% and 2.0%, respectively. The main shortcomings are moderate reductions in compressive and flexural strength and toughness, particularly under WB curing, which should guide application-specific limits and design factors.