Anyi Chen

The widespread application of fly ash ceramsite as a lightweight aggregate in high-performance concrete is restricted by its inherent defects, including high porosity, high water absorption rate and weak interfacial transition zone (ITZ). In this study, a surface pre-treatment strategy is proposed, in which the ceramsite granules are pre-coated prior to mixing, followed by concrete preparation with the modified aggregates. A pre-coating formulation of micro–nano silica fume and modified acrylate emulsion was applied to improve the interfacial characteristics and mechanical/durability performance. The results show that the coating treatment improved 28-day compressive, flexural–tensile, and axial tensile strengths by 21.2%, 16.0%, and 20.6%, respectively, along with the elastic modulus and ultimate tensile strain. The coated concrete achieved an impermeability grade exceeding W14, retained over 85% of relative dynamic elastic modulus after 150 freeze–thaw cycles, and maintained compressive strength above 90.0% after 20 wetting–drying cycles, with a corresponding relative dynamic elastic modulus of 67.24%. Microstructural observation, pore parameter analysis, and microzone mechanical testing were performed to reveal the underlying mechanisms. The performance improvement is mainly attributed to the strengthening of the traditionally weak interfacial transition zone (ITZ). Additionally, the coating refines the pore structure, stabilizes its distribution, and acts as a physical barrier, further enhancing resistance to freeze–thaw and wetting–drying cycles.

To address the technical bottleneck of the trade-off between fluidity and anti-dispersion performance in traditional underwater anti-dispersion cement pastes, this paper performs composite modification on the paste using polyacrylate (PAE) emulsion and nonionic waterborne epoxy resin (NEP) compounded with silica fume. The results show that both polymer components improve paste fluidity, whereas the silica-fume-free mixtures exhibit pronounced composition-dependent fluctuations in fluidity. Silica fume improves the stability of the paste’s fresh-state behavior but adversely affects its fluidity. Within the investigated dosage ranges, increasing the NEP dosage generally reduced turbidity and improved underwater anti-dispersion performance, whereas increasing the PAE dosage produced the opposite trend; silica fume exhibited a dosage-dependent effect, with an appropriate dosage contributing to lower turbidity. Experiments were conducted based on the Box–Behnken response surface methodology to establish second-order regression prediction models for fluidity and underwater anti-dispersion performance respectively. The RSM analysis identified model-derived candidate dosage ranges of 15–25% PAE solids, 9–15% NEP, and approximately 5–15% silica fume by cement mass. An independent validation batch prepared at the predicted optimum of 15.54% PAE solids, 13.69% NEP, and 4.95% silica fume exhibited a fluidity of 142 mm and a turbidity of 148 NTU. The validation results support the local predictive reliability of the models and confirm that the candidate composition satisfies the predefined fresh-state fluidity and turbidity criteria; its hardened-state and engineering-scale performance remains to be evaluated.

The widespread application of fly ash ceramsite lightweight aggregate in high-performance concrete is restricted by its inherent defects, including high porosity, high water absorption rate and weak interfacial transition zone (ITZ). In this study, a high-performance surface strengthening coating composed of micro-namo silica fume and modified acrylate emulsion was designed and prepared, aiming to modify its macroscopic mechanical and durability properties. The results show that, the coating treatment improved 28‑day compressive, flexural‑tensile, and axial tensile strengths by 21.2%, 16.0%, and 20.6%, respectively, along with the elastic modulus and ultimate tensile strain. The coated concrete achieved an impermeability grade exceeding W14, retained over 85% of relative dynamic elastic modulus after 150 freeze‑thaw cycles, and maintained compressive strength above 90.0% after 20 wetting–drying cycles, with a corresponding relative dynamic elastic modulus of 67.24%. Microstructural observation, pore parameter analysis, and microzone mechanical testing were performed to reveal the underlying mechanisms. The performance improvement is mainly attributed to the strengthening of the traditionally weak interfacial transition zone (ITZ). Additionally, the coating refines the pore structure, stabilizes its distribution, and acts as a physical barrier, further enhancing resistance to freeze‑thaw and wetting–drying cycles.

To elucidate the corrosion behavior of cracked reinforced concrete under pressurized permeation at 0.3 MPa, three exposure conditions were established, namely a low-concentration chloride-sulfate solution, a high-concentration chloride-magnesium sulfate solution, and a high-concentration chloride-magnesium sulfate-carbonate composite solution, and cyclic permeation tests were conducted. Based on the chloride ion (Cl⁻) content distribution, permeation behavior, and steel half-cell potential measurements, together with XRD and SEM microstructural analyses, the results showed that Cl⁻ transport was significantly enhanced. At a depth of 15 mm, the Cl⁻ content increased from 0.011% under unpressurized conditions to 0.211% at 90 d and further to 0.322% at 365 d, while it remained close to zero at depths of 35 mm and below. Under the low-concentration condition, permeation ceased after about 3 months, and the half-cell potential recovered from −550 to −580 at 46 d and stabilized at −250 to −340 in the later stage, indicating a certain self-healing capacity of the cracks. Under the high-concentration and composite conditions, permeation persisted throughout the 12-month period, and the half-cell potential dropped to −800 to −900 at 34–40 d and remained at −580 to −840 in the later stage, indicating that the steel remained in an active corrosion state for a long time. XRD and SEM results further showed that corrosion products such as AFt increased, and the internal concrete structure gradually deteriorated.

To address the durability deficiencies and limited service life of concrete structures exposed to complex service environments such as chloride attack in marine and underground engineering, this study employs fly ash (FA) and ground granulated blast-furnace slag (GGBS), typical eco-friendly materials, as functional mineral admixtures to systematically investigate the effects of their combined incorporation on the mechanical properties, durability, drying shrinkage, and microstructural characteristics of concrete. The objective is to develop a concrete material that achieves high durability while maintaining structural safety and service performance, with the additional benefit of improved resource utilization efficiency. Single-factor tests were first conducted to determine the sensitivity ranges of FA and GGBS within 10–30% for slump, compressive strength, chloride migration coefficient (RCM), and drying shrinkage. Subsequently, response surface methodology (RSM) was employed to establish quadratic regression models using FA and GGBS as independent variables and compressive strength, RCM, and drying shrinkage as response indicators. The models exhibited high fitting accuracy, and their reliability was validated through analysis of variance (ANOVA), residual analysis, and predictive performance indices. Multi-objective optimization based on the desirability function identified the optimal mix proportion as FA = 14.8% and SL = 29.3%, yielding predicted values of 56.2 MPa for 28-day compressive strength, 6.03 × 10⁻¹² m²/s for RCM, and 639 με for 90-day drying shrinkage. Microstructural analysis using SEM and MIP further revealed that the binary-blended system promotes the formation of a dense C–S–H/C–A–S–H gel network, refines pore-size distribution, and reduces pore connectivity, thereby improving long-term mechanical and durability performance. The findings provide quantitative guidance for designing high-durability, environmentally friendly concrete suitable for marine and underground engineering applications.