Materials

Calcium leaching is a key degradation mechanism governing the long-term durability of cement-based materials, particularly in marine environments where multi-ionic interactions significantly alter dissolution behavior. In this study, the solid–liquid equilibrium of calcium in hardened Portland cement exposed to NaCl solution and artificial seawater was experimentally established. A wide range of equilibrium states was achieved by varying the liquid-to-solid ratio, and the corresponding aqueous chemistry and phase assemblage were characterized using ICP-AES, XRD, and SEM-EDS. The results show that both NaCl solution and seawater substantially increase the equilibrium calcium concentration compared to deionized water, with a much stronger effect observed in seawater. In NaCl solution, the equilibrium relationship follows a classical three-stage decalcification process. In contrast, seawater induces coupled dissolution–precipitation reactions due to the presence of Mg²⁺ and SO₄²⁻, leading to rapid and extensive decalcification within a narrow calcium concentration range. The findings provide important experimental evidence for improving thermodynamic models and predicting the long-term degradation of Portland cement concrete in marine environments.

This study presents a hierarchical conductive-network strategy to overcome the performance trade-off in cement structural supercapacitors (CSSCs). By incorporating one-dimensional carbon nanotubes (CNTs) and two-dimensional graphene oxide (GO) into Portland cement, we simultaneously enhance its electrochemical and mechanical properties. The approach exploits the complementary roles of the two nanomaterials: CNTs establish a three-dimensional percolation network that facilitates electron transport, while GO promotes formation of a denser calcium silicate hydrate (C-S-H) gel and refines the pore structure by complexing with calcium ions, thereby improving ionic pathways. The k12gc sample attains a specific capacitance of 66.8 F g⁻¹ at 0.1 mA cm⁻², a 58.4% rise in conductivity and a 63% reduction in charge-transfer resistance. At the same time, the composite reduces harmful macropores by 27.9% and strengthens the material, with compressive and flexural strengths increasing by 4.8% and 8.3%, respectively. This work establishes a rational design principle based on functional division between CNTs and GO for developing high-performance, multifunctional CSSCs.

Compression testing of high-performance carbon fiber composites remains challenging due to premature failure modes in unidirectional laminates, which can underestimate true material strength. This study investigates the compressive behavior of T800-grade carbon fiber-reinforced polymer (CFRP) cross-ply ([90/0]_2s) and unidirectional ([0]₈) laminates using finite element simulation and experimental testing following the SACMA SRM-1R-94 standard, combined with macroscopic and microscopic failure analysis. The results show that cross-ply laminates consistently exhibit valid mid-gauge failure with lower data dispersion (coefficient of variation: 3.44%), whereas unidirectional laminates are prone to invalid root failures (crushing or shear). The compressive strength derived from cross-ply laminates using the back-out factor (2040 MPa) is 13% higher than that from direct unidirectional testing (1802 MPa), attributed to the in situ effect where adjacent 90-degree plies suppress fiber microbuckling. The cross-ply approach provides a more reliable and practical method for characterizing the true in situ compressive strength of high-performance CFRP composites.