Materials

This study investigated the use of calcined seashell ash (CSA) as a Ca-rich modifier to enhance the mechanical performance and CO₂ mineralization of high-calcium fly ash-based alkali-activated mortar. CSA was incorporated at 0–20% replacement levels, while liquid-to-binder (L/B) ratios of 0.35, 0.40, and 0.45 were investigated. Fresh and mechanical properties were evaluated through spread flow, initial setting time, compressive strength, and flexural strength tests. Mineral carbonation was assessed using accelerated carbonation depth, X-ray diffraction (XRD), and thermogravimetric/derivative thermogravimetric (TG/DTG) analyses. Increasing CSA content generally reduced flowability and shortened initial setting time, while 15% CSA produced the highest mean 28-day mechanical strengths. At this level, the 28-day compressive strength increased by 11.5–38.8%, depending on the L/B ratio, while the 28-day flexural strength increased by approximately 102–107% relative to the corresponding mixtures without CSA. Carbonation behavior was strongly influenced by the L/B ratio. At 20% CSA replacement, the carbonation-depth enhancement factor (CEF_x) relative to the corresponding mixture without CSA increased from only 1.2% at L/B = 0.35 to 13.2% and 16.6% at L/B = 0.40 and 0.45, respectively. XRD revealed substantially increased calcite-related diffraction features following accelerated carbonation, particularly in the CSA-containing mixtures, while TG/DTG showed a stronger carbonation-associated thermal response for the mixture containing 20% CSA at L/B = 0.45 than for the corresponding mixture without CSA. Together with the carbonation-depth results, these complementary observations consistently indicate that CSA enhanced CO₂ mineralization through increased carbonate formation under accelerated CO₂ exposure. However, the absolute amount of chemically bound CO₂ was not directly quantified in the present study. Overall, CSA can function as both a partial fly ash replacement and a Ca-rich modifier, with its mineral carbonation response governed by the balance between the availability of Ca-bearing phases and CO₂ accessibility within the hardened matrix.

This paper presents a study of thermal-insulating dry-mix mortars containing shell limestone, shell limestone extraction waste, and hollow microspheres. The effects of shell limestone and fillers on physical, mechanical, and thermal properties were investigated. The microstructure of shell limestone was examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) using a JEOL JSM-7000F scanning electron microscope. The elemental mass fractions confirmed the carbonate nature of the shell limestone raw material (wt.%: O, 50.3–43.7; Ca, 34.1–44.2; C, 15.6–12.1). Finely dispersed fillers, hollow glass microspheres, and amorphous aluminosilicates were found to be suitable for producing a low-density thermal-insulating lime–shell limestone–cement composition. The particle size of the shell limestone powder was 5.67 × 10⁻⁶ m, with calcium carbonate (CaCO₃) and silica (SiO₂) contents of 71.0% and 22.5%, respectively. The shell limestone and microsphere proportions in the binder substantially affected thermal conductivity (0.090–0.113 W/(m·°C)), compressive strength (3.25–4.05 MPa), adhesion strength to the substrate (0.8–1.2 MPa), flexural tensile strength (2.0–2.5 MPa), and water absorption coefficient (0.3–0.5%). The optimum thermal-insulating dry-mix formulation contained, by mass: lime, 25–40%; shell limestone, 15–20%; glass microspheres, 15–20%; amorphous aluminosilicates, 5–10%; diatomite, 2–10%; and cement, 0.5–4.0%.

To reveal the synergistic effect of chopped fibers and basalt fiber textile in different failure stages of concrete, this study investigated the hybrid effects of chopped basalt fibers, polypropylene fibers, and end-hooked steel fibers and basalt fiber textile on concrete at the stages of initial cracking, crack propagation, and post-peak softening. The four-point bending test results show that the basalt fiber textile has limited effect on the initial crack strength but can increase the ultimate load by 19.98% and the ultimate deflection by 175.94% compared with plain concrete by inhibiting macroscopic crack propagation. There is a complex synergistic effect between chopped fibers and fiber textile. Chopped fibers can compensate for the insufficient reinforcement of the textile in the initial cracking stage, while the textile dominates the toughness maintenance in the later stage of crack development. The hybrid system of chopped fibers and textile can enhance the flexural bearing capacity of textile-reinforced concrete. The mixture of polypropylene fibers or basalt fibers with fiber textile exhibits a post-peak embrittlement trend, while the ternary system of basalt fibers, end-hooked steel fibers, and fiber textile can achieve synergistic optimization of strength and toughness. Its peak load, bending toughness index of I20, and peak load deflection increased by 44.30%, 50.71%, and 13.76%, respectively, compared with the control group. This study provides theoretical support for the material design of high-performance basalt fiber textile-reinforced concrete and its application in thin-walled, prefabricated, and seismic strengthening engineering.