Study of the Strength and Chloride Corrosion Resistance of Solid Waste-Based Marine Concrete under Combined Conditions

The steel and chemical industries serve as pillar sectors of national economic development, and also as major sources of industrial solid waste generation. The iron and steel industry produces prodigious amounts of solid wastes such as steel slag, granulated blast furnace slag, and desulfurization ash, yet their valorization remains low. Meanwhile, chemical industry residues are often characterized by high toxicity, poor recyclability, and prohibitive end-of-pipe treatment expenses [1], [2], [3]. Traditional approaches to managing these solid wastes are environmentally burdensome and resource-inefficient. Therefore, in integrated steel-chemical industrial parks, coupling technologies must be developed to enable multi-level, cross-industry utilization of steel and chemical wastes, tailored to their specific characteristics. Targeting cleaner production, source reduction, and valorization of industrial solid wastes, these technologies aim to achieve efficient synergistic co-processing and resource utilization of park-scale solid wastes. Chloride ions ingress into concrete via diffusion, permeation, and capillary absorption, reaching the steel reinforcement surface where they disrupt the passive film and initiate corrosion [4], [5], [6], [7]. Research on water-to-binder ratio, mineral additions, curing conditions, and protection strategies confirms that a low w/b ratio and the use of slag, fly ash, and silica fume improve durability by refining the pore structure and increasing chloride binding, thus prolonging structural service life. However, while most studies have focused on cement-based systems, limited attention has been paid to the chloride transport behavior of cement-free all-solid-waste systems under multi-factor coupling conditions [8], [9], [10].

Extensive research worldwide has utilized single or binary solid wastes as partial replacements for cement and aggregates to enhance the workability, mechanical properties, and durability of concrete [11], [12], [13]. Solid wastes such as slag and fly ash undergo secondary hydration to form C-S-H gel, thereby densifying the matrix and enhancing corrosion resistance; meanwhile, recycled aggregates and tailings enable solid waste valorization at the aggregate level [14], [15], [16]. Despite the potential of fully replacing both cement and aggregates with solid wastes, there is a paucity of research on the long-term performance and degradation mechanisms of such materials under coupled marine exposure conditions [17], [18]. Addressing the technical demands of resource utilization, environmental protection, and sustainable industrial development, this study leverages the compositional diversity and complementary roles of iron and steel slags and chemical wastes to develop high-strength, high-performance marine concrete using these residues as primary raw materials. By elucidating the synergistic mechanisms among multiple components and establishing optimization and control strategies, we fabricate all-solid-waste marine concrete with exceptional durability. To investigate the influence of coupled environmental factors on the performance of marine concrete, we designed three combined exposure conditions: artificial seawater coupled with wet-dry cycling, thermal cycling, and carbonation cycling. Concrete specimens prepared using mix proportion S2 were cured for 28 days and then subjected to these environments. The evolution of mechanical properties and chloride resistance was monitored over increasing cycles to elucidate the effects of coupled environments on concrete performance in marine applications.

The primary raw materials employed in this study comprise steel slag, granulated blast furnace slag, desulfurization gypsum, soda residue, and tailings. Steel slag, granulated blast furnace slag, desulfurization gypsum, and soda residue serve as precursors for the all-solid-waste binder system, while tailings are utilized as both fine and coarse aggregates for concrete.

The steel slag used in this study was converter steel slag pellets, supplied by Wuhan Iron and Steel Corporation, exhibiting a blackish-gray color. Its primary chemical composition is presented in Table 1.

The chemical analysis ( Table 1) indicates that the steel slag is predominantly composed of SiO$_2$, Fe$_2$O$_3$, and CaO, constituting nearly 80% of its mass, with considerable proportions of Al$_2$O$_3$ and MgO and only trace amounts of SO$_3$ and other minor oxides. Based on Mason’s basicity criterion, the calculated basicity coefficient of approximately 2.61 classifies this material as high-basicity steel slag. he cementitious activity of steel slag is lower than that of cement and even granulated blast furnace slag, due to its slow cooling process during which most $\beta-\mathrm{C}_2 \mathrm{~S}$ transforms into $\gamma-\mathrm{C}_2 \mathrm{~S}$ with reduced reactivity, and its dense structure resulting from high-temperature formation.

The ground steel slag was subjected to XRD analysis (Figure 1). Characteristic reflections corresponding to Ca(OH)2, C2S, C2F, free CaO, MgO, and RO phase are identified in the raw slag, with C2S and C2F contributing weak hydraulic activity. The detected Ca(OH)2 is attributed to hydration of free CaO upon exposure to ambient moisture. In addition to the distinct crystalline phases mentioned above, the diffraction pattern exhibits a broad hump in the 2$\theta$ range of 5–15°, indicating the presence of a substantial amorphous fraction in the steel slag.

The blast furnace slag used in the experiment is S105-grade slag powder produced by Wuhan Iron and Steel Group. It is grayish-white in appearance, and its main chemical composition is shown in Table 2. The composition of this slag powder complies with the requirements for S105-grade ground granulated blast furnace slag specified in GB/T 18046 “Ground granulated blast furnace slag used for cement, mortar and concrete”. The ground granulated blast furnace slag exhibits 7-day and 28-day activity indices of no less than 95% and 105%, respectively. The chemical composition of blast furnace slag is broadly similar to that of steel slag, albeit with distinct differences in specific oxides. Specifically, the contents of SiO$_2$, Al$_2$O$_3$, and MgO in blast furnace slag are notably higher than those in steel slag, whereas its Fe$_2$O$_3$ content is substantially lower. Calculations yield a quality coefficient of 1.74 and a basicity coefficient of 0.89 for the blast furnace slag used in this study, classifying it as a highly reactive acid slag.

The XRD pattern of the slag powder used in this study is presented in Figure 2. The pattern reveals no distinct crystalline peaks, indicating that the slag powder consists predominantly of amorphous phases and possesses latent hydraulic reactivity. This reactivity can be further enhanced through mechanical grinding or the addition of chemical activators.

Desulfurization gypsum, also referred to as flue gas desulfurization (FGD) gypsum, is a major byproduct of the wet limestone-gypsum desulfurization process in coal-fired power plants. It consists primarily of calcium sulfate dihydrate (CaSO$_4$·2H$_2$O), with a purity exceeding 93%. The desulfurization gypsum used in this study was supplied by Tangshan Thermal Power Co., Ltd. Its chemical composition is presented in Table 3, and the XRD analysis result is shown in Figure 3.

Table 3 reveals that desulfurization gypsum contains substantial amounts of SO$_3$ and CaO, with only minor quantities of other constituents. XRD analysis (Figure 3) shows that the primary mineral phases are calcium sulfate dihydrate (CaSO$_4$·2H$_2$O) and calcium sulfate hemihydrate (CaSO$_4$·0.5H$_4$O), accompanied by trace amounts of other components.

The fine aggregate used in this study was iron tailings sand, derived primarily from metasedimentary iron tailings in ancient metamorphic rocks. Its main chemical composition is presented in Table 4. As shown, the iron tailings consist predominantly of SiO$_2$, Al$_2$O$_3$, Fe$_2$O$_3$, CaO, and MgO.

The iron tailings used as fine aggregate in this study have a particle size range of 0.08 mm to 5 mm. The coarse aggregate consists of iron tailings from the same source, with a particle size range of 2.5 mm to 25 mm, and exhibits similar chemical and mineralogical composition to the fine fraction. Sieve analysis results for both aggregates are presented in Table 5. Calculations yield a fineness modulus of 3.2 for the fine aggregate, classifying it as coarse sand within grading zone I. Accordingly, a higher sand ratio should be adopted in concrete mix design. The particle size distribution of the coarse aggregate complies with the requirements for continuously graded crushed stone aggregate specified in the Chinese standard JGJ 52-2006, “Standard for Quality and Testing Methods of Sand and Crushed Stone for Ordinary Concrete”.

Raw material composition is a critical factor influencing the performance of cementitious materials and concrete. To comprehensively evaluate the effects of mix proportion variations on compressive strength, electric flux, and chloride non-steady-state diffusion coefficient of concrete, this chapter selects the steel slag-to-blast furnace slag ratio, sand ratio, water content, and soda residue-to-gypsum ratio as key experimental variables. Based on the current understanding of solid waste-based concrete from studies worldwide, the experimental mix proportions were designed with varying parameters, as detailed in Table 6. Four steel slag-to-blast furnace slag ratios (1:9, 2:8, 3:7, and 4:6) were designated as S1, S2, S3, and S4, respectively. Three sand ratios (0.45, 0.50, and 0.55) were coded as R1, R2, and R3. Three water contents (130 kg/m$^3$, 140 kg/m$^3$, and 150 kg/m$^3$) were labeled W1, W2, and W3. Four soda residue-to-gypsum ratios (1:3, 2:3, 3:3, and 3:2) were denoted as A1, A2, A3, and A4.

For each mix design, the fine and coarse aggregates were first added to the mixer and blended for 120 s. The all-solid-waste binder materials were then incorporated and mixed for an additional 120 s. Finally, a mixture of superplasticizer and tap water was introduced and mixed for another 120 s. Cubes of 100 mm × 100 mm × 100 mm were prepared for compressive strength testing, while cylinders of $\varphi$100 mm × 50 mm were cast for electric flux and non-steady-state chloride migration tests. All specimens were demolded after 24 h of storage at 20 ± 5 ℃ in accordance with GB/T 50081-2002, “Standard for Test Methods of Mechanical Properties of Ordinary Concrete”, and subsequently cured at 20 ± 2 ℃ with relative humidity $\geq$95\% until reaching ages of 28, 60, and 180 days.

In real-world marine environments, the wet-dry ratio is primarily determined by the position of concrete within the tidal zone. For this preliminary investigation into the effects of artificial seawater coupled with wet-dry cycling on concrete performance, a wet-dry ratio of 2:1 was selected as the test condition. The exposure regime was as follows: with a wet-dry ratio of 2:1 and a cycle period of 2 days, specimens were immersed in concentrated artificial seawater at room temperature for 16 h, then transferred to a constant humidity chamber (43\% RH) for 32 h. This constituted one complete cycle. Compressive strength, electric flux, and chloride concentration profiles were measured after 20, 30, and 40 cycles.

To provide a baseline for comparison, a control group was established in which specimens were not subjected to immersion or wet-dry cycling. Instead, they underwent standard curing conditions for durations corresponding to the exposure cycles, after which compressive strength and electric flux were measured for comparison with the exposed specimens.

Figure 4 illustrates the effect of artificial seawater coupled with wet-dry cycling on the compressive strength of all-solid-waste marine concrete. As the number of cycles increased, the compressive strength of the concrete gradually improved. Under the combined exposure condition, the cycled specimens achieved compressive strengths of 69.1 MPa, 72.3 MPa, and 73.3 MPa after 20, 30, and 40 cycles, respectively-all exceeding 65 MPa. In comparison, the control specimens exhibited compressive strengths of 65.6 MPa, 69.8 MPa, and 71.5 MPa at corresponding curing ages. Compared to standard curing conditions, exposure to artificial seawater coupled with wet-dry cycling significantly enhanced the compressive strength of concrete. The improvements were 3.5 MPa, 2.5 MPa, and 1.8 MPa after 20, 30, and 40 cycles, respectively.

Notably, the magnitude of strength enhancement gradually diminished with increasing cycle number. The initial strength gain after 20 cycles is attributed to Friedel's salt formation induced by chloride ingress, which augmented hydration products and refined pore structure. The subsequent diminishing enhancement with increasing cycles reflects the progressive microstructural refinement of control specimens under extended standard curing, narrowing the strength gap between exposed and control groups. Overall, the compressive strength of the exposed concrete specimens exhibited a progressive increase throughout the 40 cycles regime, indicating that artificial seawater coupled with wet-dry cycling did not adversely affect compressive strength development.

Figure 5 presents the chloride concentration profiles of all-solid-waste marine concrete as a function of depth under artificial seawater coupled with wet-dry cycling. The dashed line indicates the initial chloride content of the concrete. As shown, both the chloride concentration at each depth and the penetration depth increased progressively with increasing number of cycles. After 20 cycles, the chloride concentration near the concrete surface (at 1.5 mm depth) reached approximately 0.40\%, with a penetration depth of about 10 mm. At 30 cycles, the surface chloride concentration remained relatively unchanged, while the penetration depth increased to 12.5 mm. By 40 cycles, the surface chloride concentration had risen to 0.46\%, and the penetration depth had extended to 17.5 mm. This progressive chloride ingress is attributed to the unsaturated state of the concrete interior induced by the drying phase of the wet-dry cycles. During subsequent immersion in artificial seawater, capillary suction driven by surface tension in unsaturated pore networks generates liquid flow to restore pressure equilibrium, enabling rapid chloride ingress into the near-surface zone of concrete. Chloride concentrations within 4.5 mm of the surface consistently exceeded 0.25\%, significantly higher than interior values, indicating that capillary adsorption governed chloride ingress in this near-surface region during wet-dry cycling. Beyond 8 mm depth, chloride concentrations dropped below 0.18\%, suggesting that the refined pore structure of the concrete impeded diffusion in the interior.

Figure 6 illustrates the effect of artificial seawater coupled with wet-dry cycling on the electric flux of all-solid-waste marine concrete. Under this exposure condition, the electric flux of concrete specimens after 20, 30, and 40 cycles was 138 C, 117 C, and 118 C, respectively. In comparison, the control specimens cured under standard conditions for corresponding durations exhibited electric flux values of 133 C, 101 C, and 100 C.

The electric flux of exposed specimens exceeded that of the control group due to chloride ingress induced by artificial seawater and wet-dry cycling. Up to 30 cycles, the progressive formation of hydration products and their reaction with chloride ions led to microstructural refinement, which dominated the enhancement of chloride resistance. Consequently, while the electric flux of exposed specimens gradually decreased, it remained higher than that of the control group. At 40 cycles, the electric flux of control specimens showed minimal change due to diminished hydration product formation at later ages. In contrast, the electric flux of exposed specimens exhibited a slight increase compared to that at 30 cycles, reflecting a balance between the beneficial microstructural refinement from continued hydration and the detrimental effects of chloride ingress. Therefore, within 40 wet-dry cycles, although chloride ingress led to a slight increase in electric flux, the overall trend remained downward, indicating that the exposure did not cause a significant elevation in electric flux.

Based on the aforementioned performance characterization, the concrete exhibited satisfactory mechanical behavior under artificial seawater coupled with wet-dry cycling, with compressive strength slightly enhanced relative to standard curing conditions. Wet-dry cycling facilitated chloride ingress into the surface layer via capillary adsorption, increasing the free chloride content within the concrete and consequently elevating its electric flux. Evaluation of chloride resistance after artificial seawater coupled with wet-dry cycling revealed that the electric flux of concrete remained within the requirements for marine engineering environments throughout the 40-cycle exposure regime.

Temperature variations influence both the hydration kinetics of concrete and the ingress behavior of chloride ions from the environment. Previous studies have demonstrated that ambient temperatures exceeding 40 ℃ substantially increase the chloride diffusion coefficient of concrete. Accordingly, this section investigates the performance of marine concrete under combined artificial seawater and thermal cycling conditions.

The exposure regime for artificial seawater coupled with thermal cycling was established as follows: a high-to-low temperature time ratio of 1:1 with a cycle period of 2 days. Specimens cured to 28 days were immersed in sealed containers filled with concentrated artificial seawater and subjected to 24 h at 50 ℃ followed by 24 h at 20 ℃, constituting one complete cycle. Testing was conducted after 20, 30, and 40 cycles. The 50 ℃ environment was provided by an accelerated concrete curing chamber, while the 20 ℃ condition was maintained in a standard constant temperature and humidity curing chamber. For comparison, a control group was established without immersion or thermal cycling.

The influence of combined artificial seawater exposure and thermal cycling on compressive strength of all-solid-waste marine concrete is presented in Figure 7. As the number of cycles increased, the compressive strength remained relatively stable, reaching 71.4 MPa, 71.0 MPa, and 71.7 MPa after 20, 30, and 40 cycles, respectively. The control specimens cured under standard conditions exhibited compressive strengths of 65.6 MPa, 69.8 MPa, and 71.5 MPa at the corresponding ages.

The primary hydration products of the all-solid-waste binder system are C-S-H gel and ettringite, along with the formation of Friedel’s salt. The generation of these hydration products is endothermic in nature. Within the thermal cycling regime, the elevated temperature phase promotes hydration reactions and increases the yield of hydration products. Consequently, after only 20 cycles, the compressive strength of exposed specimens had already reached the level achieved by control specimens after 108 days of standard curing (corresponding to the age of the 40-cycle exposure group). However, with increasing cycle number, the compressive strength of exposed specimens did not continue to increase, stabilizing at approximately 71 MPa. This plateau is attributed to the uneven distribution of hydration products induced by elevated-temperature curing during thermal cycling. The final strength after 40 cycles remained slightly below that of control specimens after 180 days of standard curing (73.8 MPa), indicating that while thermal cycling enhances early-age strength development, it may compromise long-term strength gain.

Figure 8 presents the chloride concentration profiles of all-solid-waste marine concrete as a function of depth under artificial seawater coupled with thermal cycling. The dashed line indicates the initial chloride content of the concrete. Under this combined exposure condition, the elevated temperature phase promotes chloride diffusion within the concrete. Thus, by 20 cycles, chloride ingress extended to 17.5 mm. Concurrently, the elevated temperature phase promotes reactions between the binder materials and intruded chloride ions, increasing chloride binding capacity and Friedel’s salt formation. The accelerated generation of hydration products refines the concrete microstructure, thereby partially inhibiting further chloride diffusion.

At a depth of 1.5 mm, the chloride concentration reached 0.43\%, which sharply decreased to 0.23\% at 4.5 mm, indicating a significant reduction within the near-surface zone. With increasing cycle number, the chloride penetration depth remained relatively stable at approximately 17.5 mm, while chloride concentrations at each depth exhibited a progressive increase overall. In the surface layer of concrete (1.5 mm depth), chloride concentrations reached 0.46\% and 0.49\% after 30 and 40 cycles, respectively. As depth increased, the magnitude of increase in chloride concentration at each layer gradually diminished. At 40 cycles, the chloride concentration within 4.5 mm of the surface increased by approximately 0.06\%, whereas at depths greater than 8 mm, the increase was reduced to about 0.03\%.

Figure 9 illustrates the effect of artificial seawater coupled with thermal cycling on the electric flux of all-solid-waste marine concrete. Due to the accelerating effect of the high-temperature phase on hydration, the microstructure of thermally cycled concrete was more refined than that of control specimens under standard curing. Consequently, the electric flux of exposed specimens was lower than that of the control group. After 20 cycles, the electric flux of exposed concrete was 88 C, representing a substantial reduction of 45 C compared to the control group (133 C). With increasing cycle number, the microstructural refinement effect induced by combined artificial seawater and thermal cycling diminished. At 30 cycles, the electric flux decreased to 84 C, showing only a marginal reduction relative to the 20-cycle value. In contrast, the control group exhibited a more substantial reduction in electric flux between 20 and 30 cycles, reflecting progressive microstructural refinement under continued standard curing. Consequently, the margin between exposed and control specimens narrowed to 17 C at 30 cycles. By 40 cycles, the electric flux of exposed concrete was 83 C, only 1 C lower than at 30 cycles, indicating that it had essentially stabilized.

Based on the aforementioned performance characterization under artificial seawater coupled with thermal cycling, the concrete exhibited satisfactory mechanical properties and chloride resistance at all tested cycle numbers, fully meeting the requirements for application in marine engineering environments. The high-temperature phase of the cycling regime promoted continued hydration of the binder materials, enhancing the rate of compressive strength gain. Although elevated temperatures also accelerated chloride diffusion into the concrete and increased surface chloride content, the resulting microstructural refinement from hydration products improved the concrete's resistance to chloride ingress.

Carbonation induced by CO$_2$ from seawater or the atmosphere reduces the alkalinity of concrete, thereby compromising its durability. Accordingly, this section investigates the performance of marine concrete subjected to carbonation within a seawater environment.

The exposure regime for artificial seawater coupled with carbonation cycling was established as follows: a carbonation-to-non-carbonation time ratio of 1:1 with a cycle period of 14 days. Specimens were immersed in concentrated artificial seawater for 7 days, then removed, surface-dried, and placed in a carbonation environment for 7 days (during which the CO$_2$ diffusion rate is elevated), constituting one complete cycle. Testing was conducted after 1, 2, 3, and 4 cycles. The carbonation environment for artificial seawater coupled with carbonation cycling was provided by a concrete carbonation test chamber, with temperature maintained at 20 ± 2 ℃, relative humidity at 70 ± 5\%, and CO$_2$ concentration at 20 ± 3\%. Control specimens were kept under standard curing conditions and tested for compressive strength and electric flux at ages corresponding to the carbonation cycles.

The influence of combined artificial seawater and carbonation cycling on compressive strength of all-solid-waste marine concrete is presented in Figure 10. The strength exhibited an initial increase followed by a decline as cycling progressed. The compressive strength reached its maximum value of 74.3 MPa after 2 cycles. At 3 cycles, the strength decreased slightly to 73.1 MPa. By 4 cycles, a significant reduction occurred, with the strength dropping by 7.7 MPa compared to the 3-cycle value, to 65.4 MPa. Under standard curing conditions, the compressive strength of the control specimens exhibited a progressive increase over time, reaching 63.9 MPa, 64.9 MPa, 66.0 MPa, and 69.8 MPa at ages corresponding to 1, 2, 3, and 4 carbonation cycles, respectively.

During early carbonation, intruded CO$_2$ reacts with hydration-derived C-S-H gel, yielding calcium carbonate and amorphous silica Eq. (1):

Although this process consumes C-S-H gel from the hydration products, the resulting calcium carbonate and silica effectively fill concrete pores, exerting only a minor influence on compressive strength. Meanwhile, the steel slag and blast furnace slag within the binder system continue to undergo hydration during carbonation. Consequently, within the first two cycles, the compressive strength of exposed concrete exhibited a progressive increase, remaining higher than that of the control group. With increasing cycles of artificial seawater coupled with carbonation, the progressively formed calcium carbonate reacts with residual calcium sulfate dihydrate and C-S-H gel from hydration to generate thaumasite (Ca$_6$[Si(OH)$_6$]2(CO$_3$)2(SO$_4$)$_2$·24H$_2$O), as shown in Eq. (2):

The formation of thaumasite further consumes the C-S-H gel produced from hydration. Since thaumasite possesses little to no cementitious properties, the compressive strength of concrete gradually decreases with increasing cycle number, ultimately falling below that of the control group.

Figure 11 presents the chloride concentration profiles of all-solid-waste marine concrete as a function of depth under artificial seawater coupled with carbonation cycling. The dashed line indicates the initial chloride content of the concrete. As shown, the chloride penetration depth increased progressively with increasing number of cycles. Chloride penetration advanced from ~8 mm after one cycle to ~12.5 mm with continued cycling, ultimately exceeding 12.5 mm by the fourth cycle. Simultaneously, the chloride concentration at each depth within the concrete also increased with the number of cycles. Surface chloride content (1.5 mm depth) rose progressively with cycling: 0.35% (1 cycle), 0.42% (2 cycles), 0.52% (3 cycles), and 0.54% (4 cycles). The increment between 3 and 4 cycles was marginally lower than in the early cycles.

Figure 12 illustrates the effect of artificial seawater coupled with carbonation cycling on the electric flux of all-solid-waste marine concrete. The number of combined exposure cycles significantly influenced the electric flux of concrete. With increasing cycles, the electric flux initially decreased slightly and then progressively increased, reaching a minimum value of 193 C after 2 cycles and increasing to 248 C after 4 cycles, representing an increase of 55 C compared to the 2-cycle value. In contrast, the electric flux of control specimens gradually decreased with extended curing age, from 277 C to 145 C, 123 C, and 101 C at corresponding ages.

In the early stages of carbonation cycling, the reaction described in Eq. (1), coupled with progressive hydration, led to continuous microstructural refinement of the concrete. Consequently, the electric flux of the exposed concrete was superior (lower) to that of the standard-cured controls. However, as the number of carbonation cycles increased further, the reaction depicted in Eq. (2) was initiated. This resulted in the consumption of additional C-S-H gel, causing the electric flux to increase progressively. Electric flux of carbonation-cycled specimens was 70 C below controls after one cycle, but surpassed controls by 48 C after two cycles. By the second cycle, however, the exposed specimens exhibited significantly higher electric flux than the controls, with a difference of about 48 C. As cycling continued, the electric flux of exposed specimens remained markedly higher than that of the control group, with the gap progressively widening to approximately 147 C. This trend closely parallels the compressive strength behavior observed under combined artificial seawater and carbonation cycling.

In summary, the all-solid-waste marine concrete exhibited excellent mechanical properties and chloride resistance under artificial seawater coupled with carbonation cycling. Although CO2 ingress during carbonation consumes C-S-H gel and accelerates chloride attack-leading to reduced compressive strength and increased electric flux at higher cycle numbers-the concrete continued to meet the requirements for both compressive strength and electric flux even after 4 cycles.

(1) We developed a technology to produce high-performance marine concrete by synergistically combining metallurgical and chemical slags. The resulting concrete, featuring 100\% solid waste content, exhibited superior performance: compressive strength of 71.9 MPa, flexural strength of 7.1 MPa, chloride diffusion coefficient of 0.08 × 10$^{-12}$ m$^2$/s, and electric flux of 51 C. All surpassing standard specifications for conventional cement concrete. This demonstrates a viable technological pathway for the valorization of metallurgical and chemical slags and contributes to ecological environmental.

(2) Exposure to concentrated artificial seawater demonstrated that the compressive strength development of concrete fabricated via this approach paralleled that under standard curing, with enhanced absolute values. Electric flux showed a positive correlation with the soda residue-to-gypsum ratio under immersion, but consistently satisfied marine engineering criteria.

(3) Cyclic exposure tests simulating marine service conditions demonstrated that the concrete exhibited satisfactory mechanical performance under artificial seawater coupled with wet-dry cycling, thermal cycling, and carbonation cycling. In some cases, compressive strength showed slight improvements compared to standard curing conditions. Moreover, the chloride resistance of the concrete consistently met the requirements for marine engineering environments under all three combined exposure regimes.