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Several strength grades of sulphoaluminate cement concrete were designed, and the mechanical properties with different mix ratios were studied. This paper mainly analyzes the mechanical properties of sulphoaluminate cement concrete with the setting time test, compressive strength test and flexural test. The test results show that the setting time of cement concrete can be controlled by mixing different admixtures. One hand, the initial setting time increases from 34 min to 340 min, and the final setting time increases from 57 min to 580 min when the incorporated borax content changes from 0 to 1.0 %. Other hand, the initial setting time decreased from 34 min to 11 min, and the final setting time increased from 57 min to 18 min, when the incorporated borax content changed from 0 to 0.5 %. Furthermore, the compressive strength can reach 40 MPa, and the flexural strength can reach more than 2.5MPa after 6 hours of curing. The experiment results illustrate that the setting time and the mechanical properties satisfy the needs of the rapid construction requirements under normal temperature conditions.

Lack of hard substrate in the ocean has a negative impact on the marine ecosystems, as habitats, hiding places and feeding grounds have disappeared in past decades. By integrating solutions specifically designed for improving biodiversity, social acceptance and aesthetics, while maintaining structural durability more sustainable solutions for coastal infrastructure can be realized. Concrete provides flexibility for creating diverse surface textures, overall shape and chemical composition of each unit, when compared with other materials, providing advantages when utilized as hard substrate for the creation of marine habitats. With this focus, specifically designed concrete units were installed in Copenhagen harbour in collaboration with the art collective SUPERFLEX. Three mineral admixtures were chosen for this art installation to highlight the reduction of environmental impacts as well as achieving specific colours. Namely, iron oxide, biosilica and chamotte were used with a substitution rate of white Portland cement at 1%, 10% and 15% respectively. XRD, TGA, Titration, indicators and were used to characterize changes in mineralogy. After 4 and 19 months of exposure, similar performances for the three mix-designs were observed. However, the mixture containing biosilica showed tendencies towards an increase in early resistance towards chloride ingress.

The use of supplementary cementitious materials such as fly ash, slag, and silica fume improve reinforced concrete corrosion performance, while decreasing cost and reducing environmental impact compared to ordinary Portland cement. In this study, the corrosion behavior of AISI 1018 carbon steel (CS) and AISI 304 stainless steel (SS) reinforcements was studied for 365 days. Three different concrete mixtures were tested: 100% CPC (composite Portland cement), 80% CPC and 20% silica fume (SF), and 80% CPC and 20% fly ash (FA). The concrete mixtures were designed according to the ACI 211.1 standard. The reinforced concrete specimens were immersed in a 3.5 wt.% NaCl test solution to simulate a marine environment. Corrosion monitoring was evaluated using the corrosion potential (Ecorr) according to ASTM C876 and the linear polarization resistance (LPR) according to ASTM G59. The results show that AISI 304 SS reinforcements yielded the best corrosion behavior, with Ecorr values mainly pertaining to the region of 10% probability of corrosion, and corrosion current density (icorr) values indicating passivity after 105 days of experimentation and low probability of corrosion for the remainder of the test period.

Focusing on promoting the widespread application of crystal self-healing technology in marine concrete engineering and improving the durability of marine concrete, the research on the chloride ion transport behavior and corrosion resistance of concrete with crystal admixtures under the action of seawater is conducted. Ion chelator (CA) as crystalline admixture can obviously improve self-healing of cement-based materials. Results showed that CA improved pore structure of mortar, increased the compactness of matrix, and thus limited the chloride diffusion. After 3 months of erosion by NaCl + Na 2 SO 4 , NaCl + MgCl 2 and NaCl + MgCl 2  + Na 2 SO 4 solutions, compared with control sample, the chloride diffusion coefficient of 100%OPC mortar with CA decreased by 49.3%, 47.4%, 56.5%, and 52.9%, respectively. CA-enhanced chloride binding ability of 100%OPC and 50%BFS mortar. Compared with control sample, the chloride binding efficiency of 100%OPC mortar with CA and 50%BFS mortar with CA increased by 26.1% and 35.5% after 3 months of NaCl solution corrosion, increased by 35.3% and 48.0% after 3 months of NaCl + Na 2 SO 4 solution corrosion, and increased by 46.2% and 61.9% after 3 months of NaCl + MgCl 2 solution corrosion, respectively. SEM analysis showed that CA could significantly improve internal microstructure of mortar under salts erosion. The correlation analysis of pore structure and chloride diffusion coefficient displayed that total porosity of mortar had better correlation with chloride diffusion coefficient than gel pore, transition pore, capillary pore and macropore after salt erosion. Therefore, CA mainly limited chloride diffusion into matrix by reducing total porosity of mortar under salt erosion. The research results of this paper can provide theoretical support and basis for the application of crystal self-healing technology in marine concrete.

Considering the harsh marine environment characterized by dry–wet cycles, freeze–thaw action, chloride penetration, and sulfate attack, four optimized ultra-high-performance concrete (UHPC) mix designs were developed. Durability was assessed via electric flux, dry–wet cycles, and rapid freeze–thaw tests to evaluate the effects of curing methods, aggregate types, and mineral admixtures on key durability indicators, including chloride ion permeability, compressive strength loss, and mass loss. Scanning electron microscopy (SEM) examined microstructural changes under various conditions. Results showed that curing method significantly affected chloride ion permeability and sulfate resistance. High-temperature curing (70 ± 2 °C) reduced 28-day chloride ion electric flux by about 50%, and the compressive strength loss rate of specimens subjected to sulfate attack decreased by 2.7% to 45.7% compared to standard curing. Aggregate type had minimal impact on corrosion resistance, while mineral admixtures improved durability more effectively. Frost resistance was excellent, with mass loss below 0.87% after 500 freeze–thaw cycles. SEM analysis revealed that high-temperature curing decreased free cement particles, and mineral admixtures refined pore structure, enhancing matrix compactness. Among all mixtures, Mix Proportion 4 demonstrated the best overall durability. This study offers valuable insights for UHPC design in aggressive marine conditions.

The permeability of different strength grades of submerged non-dispersible concrete with different granulated slag admixtures in a saline soil environment simulated by different erosion solutions was investigated. The variation patterns of the chloride ion diffusion coefficient and pore characteristics were tested using NEL and MIP. The microscopic morphology of the specimens in different erosion environments and with slag doping was observed using SEM. The results showed that the impermeability of concrete in sulfate and complex salt environments was significantly reduced. The resistance of concrete to chloride ion penetration increased with the increase in strength grade, and the Cl− diffusion coefficient of C35 was 5–30% lower than those of C30 and C25 underwater non-dispersible concrete at 360 d. Meanwhile, the admixture of granulated blast-furnace slag optimized the pore size distribution and improved the matrix compactness and permeability.

Being a widely used building material in marine structure, concrete is susceptible to freeze–thaw (F–T) damage in high-latitude marine conditions, which can easily affect the safety and the lifetime of marine infrastructures. This paper investigates the mechanical properties and frost durability of polyvinyl alcohol (PVA) fiber-reinforced geopolymer composites (PFRGC) with bentonite and fly ash before and after frost damage. The mechanical properties of PFRGC were revealed through cubic compressive, flexural and axial compressive strength. The frost durability of PFRGC was also studied through the relative dynamic modulus of elasticity (RDEM). Furthermore, the acoustic emission (AE) technique was adopted to provide real-time monitoring of the damage progress. Meanwhile, the microstructure was characterized by SEM to illustrate the mechanism of macroscopic property degradation. The results show that the compressive strength continued to decrease with increasing fly ash (FA) incorporation when the bentonite admixture was 0%, while the compressive strength of the concrete reached a maximum when FA/C was 1.8 at higher bentonite admixtures (3% and 6%). At the same time, the mechanical and physical performance of PFRGC decreased with freeze–thaw cycles. The AE characteristics were tightly correlated with the progress of damage and stress–strain curves.

Anti-washout admixtures (AWAs) are a unique component of underwater non-dispersive concrete (UNDC), which gives the concrete the ability to remain undispersed in water. On some special occasions, freshly mixed underwater non-dispersive concrete is exposed to the erosion of moving water, and conventional acrylamide-based AWAs are only suitable for static water or the water flow rate is small. In this study, the inorganic component nanosilica (NS) is modified, treated, and copolymerized with the organic components acrylamide (AM) and acrylic acid (AA) to form an inorganic–organic hybrid polymer with a hyperbranched structure, which changes the linear structure of the original polyacrylamide molecule, and we optimize the synthesis process. The polymers are characterized at the microscopic level and their compatibility with polycarboxylic acid water-reducing agents (SP) is investigated. In addition, the polymers are compared and evaluated with commonly used PAM in terms of their working performance. The experimental results indicated that under specific process conditions, polymers endow cement mortar with good resistance to water erosion. At the same time, the polymers’ three-dimensional network structure is prominent, with good compatibility with SP and better anti-dispersity. The microstructure of the cement paste with added polymers is dense and flat, but its flowability and setting time are slightly worse. This study provides a new development direction for the development of AWAs under a dynamic water environment, which has specific engineering significance.

A comprehensive research project was undertaken to evaluate the effect of styrene butadiene rubber (SBR) latex admixture on washout loss and bond strength of underwater concrete (UWC) designated for repair applications. Three UWC series possessing low to high stability levels that incorporate 5 to 15% SBR, by binder mass, were tested. A 1.5 m (4.93 ft) long specially designed channel was developed to enable the UWC to free fall from the outlet of a V-funnel apparatus, flow along an inclined surface submerged in water, then spread onto a horizontal concrete surface. Results show that underwater casting leads to reduced pulloff strengths caused by washout loss and aggregate segregation that weaken in-place properties. The incorporation of SBR was particularly efficient to reduce washout loss and improve adhesion between the repair overlay and substrate. Regression models enabling the prediction of residual bond strengths from the UWC rheological properties, washout loss, and polymer content are established. Keywords: pulloff strength; rheology; styrene butadiene rubber (SBR) latex; underwater concrete; washout loss.

Air-entrained concrete offers significant durability and performance benefits, and it is commonly specified for outdoor pavements, sidewalks, driveways, and other structures exposed to freezing-and-thawing cycles. It is also used in marine environments, bridge decks, and areas subjected to deicing salts or chemical exposure. Air-entraining admixtures (AEAs) can also provide advantages during construction. For example, air-entrainment improves the performance of mortars used for plastering projects. The selection of appropriate AEAs is crucial to ensure compatibility with the raw materials of concrete mixtures and the service environment. Factors such as desired air content, properties of cement/cementitious materials and aggregates, environmental conditions, and specific application requirements influence the choice and dosage of AEAs. Testing should be conducted to ensure compatibility with other chemical admixtures and materials in the concrete mixture. It is also desirable to determine the optimal addition sequence and employ appropriate mixing methods. Overall, careful consideration of AEAs, compatibility testing, and mixing methods ensures the effectiveness and longevity of air-entrained concrete structures. Specifiers should also consider alternatives to AEAs, such as polymer microspheres, to overcome many of the associated challenges.