Durability Of Marine Concrete Research Articles

Durability of Marine Concrete with Nanoparticles under the Joint Effect of Dry–Wet Cycles, Cl− Erosion, and Carbonation

Durability of Marine Concrete with Nanoparticles under the Joint Effect of Dry–Wet Cycles, Cl− Erosion, and Carbonation

Changes in mechanical performance and pore structure of hardened cement paste under the combined effect of calcium leaching and dry/wet cycles

The durability of marine concrete is significantly influenced by the coupled effect of calcium leaching (CL) and dry/wet cycles (DW). This study investigates their combined impact on the Vickers hardness and pore structure of hardened cement paste. The experimental setup includes two groups: Group A (CL followed by DW) and Group B (DW followed by CL), which superimpose the single-factor effects of each factor. Calcium leaching levels were set at 5 %, 10 %, and 15 % loss of sample mass, and dry/wet cycles were varied at 4, 8, and 12 times. A 4 mol/L ammonium nitrate solution was used to accelerate calcium leaching. The results demonstrate that the coupled effect of CL and DW reduces the Vickers hardness by increasing the porosity of the cement paste. Specifically, CL primarily increases the porosity of pores above 200 nm by dissolving calcium hydroxide, and it augments the porosity of 7 ∼ 50 nm pores by removing calcium from C-S-H gels. However, the combined effect of CL and DW on Vickers hardness is less pronounced than the total individual effects. Moreover, Group A exhibits a more substantial impact on the deterioration of mechanical properties in hardened cement paste compared to Group B. In addition, a model is applied for quantitatively predicting mechanical performance based on nominal porosity.

Investigating the chloride ion resistance of cracked concrete through Reverse-seepage and Saturation based Action Anti-corrosion Tech (RS-AAT): Experimental and numerical analysis

This study investigates the chloride ions transport in cracked concrete with the impact of RS-AAT (Reverse-seepage and Saturation based Action Anti-corrosion Tech) in the environment of wet-dry cycling and soaking conditions. With the effect of reverse water pressure, the chloride ions accumulation surrounding the crack on the concrete surface and the chloride ions penetration within the concrete along the cracks are demonstrated by the indoor experiments. A two-dimensional convective diffusion model of chloride ions in cracked concrete is established to simulate the correlation between crack size and the change of reverse water pressure. Four types of cracks with widths of 0 mm, 0.2 mm, 0.4 mm and 1 mm, and a depth of 20 mm were selected. Three types of water pressures with values of 0.2 MPa, 0.3 MPa and 0.4 MPa were used for the technique. The experimental results show that the anti-convection effect induced by the reverse water pressure can inhibit the accumulation of chloride ions around the cracks and effectively limit the intrusion of chloride ions into the concrete protection layer. With the increase of reverse water pressure, the inhibition effect of seepage flow on chloride ions is more obvious. The experimental findings provide valuable references for investigating marine concrete durability and resistance to chloride ion erosion.

Study on Cl− Erosion of Concrete under the Combined Effect of Fatigue Load and Wet–Dry Cycles: A Review

The service environment of concrete in the marine environment is harsh, and demands regarding the durability of marine concrete have increased. Marine concrete in harbor and wharf areas suffers from the combined effect of fatigue load, dry–wet cycles, and Cl− erosion, which can result in spalling of the concrete surface, corrosion of the internal reinforcement, and even concrete damage. This paper reviews recent research results on the durability of concrete and reinforced concrete (RC) under the combined effect of fatigue load, dry–wet cycles, and Cl− erosion. We further assess the variation in Cl− transport properties with fatigue load, the causes behind the reduction in the carrying capacity of RC products under fatigue load, the methods of Cl− erosion on concrete under the pressures imposed by dry–wet cycles, and the damage of the protective layer of concrete due to accelerated Cl− erosion caused by the action of dry–wet cycles. Further studies are needed on the durability of concrete under the action of fatigue load, wet and dry cycles, and Cl− erosion, in addition to the testing of the durability of concrete under the combined effects of the afore-mentioned various factors.

Influences of Friedel's Salt Produced by CaO-Activated Titanium-Extracted Tailing Slag on Chloride Binding.

Titanium-extracted tailing slag (TETS) has high activity, but the content of chloride ions is high. To effectively bind the chloride ions, CaO was used to activate the TETS, and the solidified cementitious material of CaO-activated TETS was prepared. The effects of CaO content and curing age on the strength of solidified samples, chloride binding capacity, and chloride binding mechanism were studied. By means of XRD, FTIR, SEM, and EDS, the hydration reaction products, microstructure, morphology, and micro-components of the solidified sample were characterized. The results show that the chloride ions can be effectively bound by using CaO to activate TETS with higher mechanical strength. When the CaO content is 10 wt%, the strength of the 28-day-cured body can reach more than 20 MPa, the chloride ion binding amount is 38.93 mg/g, and the chloride binding rate is as high as 68%. The new product phases of the solidified sample are mainly Friedel's salt (FS) and calcite, in which the amount of FS production and the degree of crystal development are affected by the CaO content and curing age. The chloride binding ions in the solidified sample are mainly the chemical binding by FS. The FS diffraction peak strength increases with the increase of CaO content and curing age, but the calcite diffraction peak strength is less affected by them. FS mainly accumulates and grows in the pores of the solidified sample. It can optimize the pore structure of the solidified sample and improve the strength of the solidified sample while binding chloride ions. The results can provide useful information for the resource utilization of chlorine-containing TETS, the improvement of durability of Marine concrete, and the application of sea sand in concrete.

Durability of marine concrete doped with nanoparticles under joint action of Cl- erosion and carbonation

Marine concrete is susceptible to seawater erosion and sea tides. Specifically, concrete in tidal areas is influenced by the joint action of Cl- erosion and carbonation, resulting in severe structural corrosion and reduced durability. In this study, nanoconcrete was alternately subject to immersion and carbonization in 5%NaCl to investigate the influence of nanoparticles on the durability of marine concrete under the combined action of Cl- erosion and carbonization. The free Cl- concentration and carbonization depth in concrete were considered as test indexes to evaluate the durability of nanoconcrete under their combined action. The concrete microstructure was analyzed via SEM and XRD. The results demonstrated that the use of nanoconcrete significantly reduced the carbonation depth for the same cycle number. The free Cl- concentration of nanoconcrete at 0–5 mm depth, 56 N cycles, and 2% and 1% nano-SiO2 and nano-ZnO content was 19.3% and 17.6% lower, respectively, than that of normal concrete. Microscopic tests revealed that nanoparticles could optimize the concrete pore structure, generate C-S-H gels, and make the internal structure of concrete dense. Consequently, the addition of nano-SiO2 and nano-ZnO to concrete can significantly improve its resistance against the joint action of Cl- erosion and carbonation, and effectively enhance the durability of marine concrete.

A functional and robust super‐hydrophobic PCC coating based on the induced assembly of modified zirconium phosphate

AbstractImproving the permeability of concrete is one of the important measures to extend the service life of concrete. In addition, for marine engineering, sewerage projects, and so on, mechanical stability and microbial induced corrosion of concrete structures cannot be ignored. We demonstrated a method to prepare high‐performance super‐hydrophobic (SHP) coating using functional zirconium phosphate (ZrP) and polydopamine (PDA) as the primary materials. The micro‐nano rough structures were constructed on the concrete surface by alternating organic–inorganic assembly guided by each other. The coatings' apparent morphology, composition, and structure were analyzed using various surface analysis techniques. Based on the construction of micro‐nano rough structures by the induced assembly of functional ZrP, the silane treatment significantly improved the water contact angle of the coating (WCA = 154° ± 3°), and the coating exhibited relatively high wear resistance, reaching 135° WCA even after 30 friction cycles. The water absorption of the specimens treated with the SHP composite coating was reduced by 79% to treated with silane. Meanwhile, the SHP composite coating showed excellent antimicrobial and anti‐ice properties, due to the role of the functional ZrP and alternating organic–inorganic assembly. It was expected that the composite coating might potentially promote and accelerate applied superhydrophobic anticorrosive coating development for marine concrete durability.

Strength and durability of marine cement-based mortar modified by colloidal nano-silica with epoxy silane for low CO2 emission

The heavy use of marine concrete consumes a large amount of cement increasing CO2 emission. Improving the strength and durability of marine concrete is an effective strategy to reduce CO2 emission. This study aimed to introduce colloidal nano-silica (CNS) and epoxy silane modified colloidal nano-silica (M-CNS) to improve the mechanical performance and durability of High Sulfate Resistance Portland cement. Meanwhile, the CNS and M-CNS were incorporated to marine cement mortar, and the aggregation of CNS, and the hydration mechanism and micro-mechanism of the mortar were investigated. The results indicated that the workability, mechanical properties and durability of marine cement samples were enhanced with M-CNS addition. When adding 1 wt% M-CNS with grafting rate of 15% (M-CNS1), the chloride diffusion coefficient was reduced by 9.49% and the porosity was reduced by 18.84%. In addition, the compressive strength of cement mortar with M-CNS1 increased by 10.42%, 28.71% and 10.49% compared with blank specimens after curing for 3-, 7- and 28-days. The improvements in strength and durability indicate that M-CNS has a promising application for reducing CO2 emissions by marine concrete industry.

Superhydrophobic coatings based on bionic mineralization for improving the durability of marine concrete

Designing a stable superhydrophobic surface has been a current research focus. A functional bionic mineralized layer is introduced into the coating system to enhance the applicability. In the process of bionic mineralization induced by dopamine, silver ions were in situ reduced to nanosilver by dopamine in the interstices of mineralization products, forming a micro-nano composite structure by the mineralized grains and nanosilver microspheres. Then the superhydrophobic (CA = 153°) antibacterial coating was obtained by silane modification. The characterization of the coating shows that it can significantly improve the antibacterial effect, the mineralization layer and the silane molecular network can delay nanosilver loss. Furthermore, the superhydrophobic coating has extreme stability and its wettability hardly changes under abrasion, biological environment and freeze–thaw conditions, obtaining higher superhydrophobic, antibacterial and anti-icing performance. Considering the above properties, this novel superhydrophobic coating is anticipated to be a promising protective material which solves the corrosion, biofouling and freeze–thaw problems confronting marine concrete.

Molecular insights into the adsorption of chloride ions in calcium silicate hydrate gels: The synergistic effect of calcium to silicon ratio and sulfate ion

Corrosion of steel bars by chloride ions is one of the main reasons for determining the service life of marine concrete. In this work, the effects of calcium to silicon (C/S) ratio and SO42− concentration on Cl− adsorption in calcium silicate hydrate (C–S–H) gels were systematically studied by molecular dynamics simulations. Atomic-scale results show that higher C/S ratio induces more Cl− adsorption. The presence of SO42− not only reduces the Cl− adsorption but also buffers the adsorption caused by increasing C/S ratio. The Cl− adsorption is caused by the attraction of interlayer Ca (Cah) and hydroxyl groups in low C/S gel, while in high C/S ratio C–S–H gel is mainly contributed by Cah. More Cl− adsorption at the C–S–H interface ensures less Cl− accumulation in zones surrounding the reinforcement. The insights into ion adsorption behaviour should provide useful information for prolonging the durability of marine concrete by designing appropriate compositions.

Research progress on durability of marine concrete under the combined action of Cl− erosion, carbonation, and dry–wet cycles

Abstract Marine concrete is a kind of construction material which is seeking its growing application in marine engineering. However, the marine concrete structures are exposed to aggressive environment and harmful ions. Therefore, it is crucial to improve the durability of marine concrete. The concrete structure located in the tidal zone is subjected to the dry–wet cycles caused by tidal action, chloride ion (Cl−) erosion in seawater, and CO2 erosion in air. When these factors work together, they cause great damage to the marine concrete structure. In view of the three environmental factors, namely, Cl− erosion, carbonation, and dry–wet cycles, taking fly ash, fibers, and nanomaterials as examples, this article expounds the research status of durability of marine concrete, introduces the latest research progress, the addition of fibers, fly ash, and nanomaterials can improve the Cl− corrosion resistance and dry–wet cycles resistance of marine concrete, while the addition of fly ash is unfavorable for carbonation resistance. And the future development trend of marine concrete is prospected.

Polymer functional coatings modified by ZrP‐based composites: Preparation and applications on marine concrete

AbstractThe development of high‐performance coatings for concrete structures is essential to ensure their durability and service life. However, most of the proposed developed strategies suffer from various limitations, especially regarding the wear and biological‐corrosion resistances of the coatings. This work reports a facile and efficient method to prepare effective composite coatings by nano‐modification, in which the intercalated composites play structural and functional roles in the corrosion, wear, and biological‐corrosion resistances. An in situ assembly synthesis was used to prepare the intercalated composites. The composites exhibited an innovative alternating skateboard structure and a functional composition. The silane‐emulsion modified with the composites was prepared and coated on the mortar surface to systematically study its performance at the concrete interface. The results indicate the good dispersion stability of the innovative α‐ZrP composites in the silane emulsion and their significant enhancement of the silane coatings' ability to improve the durability of marine concrete. The mechanisms of performance improved by the prepared composites through their unique lamellar structure and interlamellar silver‐nanoparticle composition were also examined. The prepared composite coating exhibits a new strategic approach to solve problems associated with concrete applications and provides technical guidance for surface protection of marine concrete structures.

Influence of CaO-based expansive agent on chloride penetration resistance of marine concrete

CaO-based expansive agent (CEA) is a high performance expansive agent, which can well compensate for the shrinkage of concrete. However, due to micro-cracks caused by excessive expansion and poor chemical stability and gelling property of additional Ca(OH)2 (expansion product), durability of marine concrete may deteriorate. Therefore, the application of CEA in marine concrete is controversial. In this study, the autogenous deformation, compressive strength, and chloride penetration resistance of marine concretes containing various dosages of CEA were determined, and the influence mechanism of CEA on the chloride penetration resistance was further explored. The results showed that the addition of CEA increased the expansion deformation, chloride diffusion coefficient, and chloride penetration depth and decreased the compressive strength of marine concrete. In addition, as the dosage of CEA increased, porosity increased and chloride binding capacity decreased. Further discussion indicated that the addition of CEA increased the volume of large capillary pore with diameter between 400 and 5000 nm, and decreased the chloride binding capacity due to the increase in the SO3 content, both of which led to the decrease in chloride penetration resistance of marine concrete. However, when the dosage of CEA was not more than 6%, adding CEA can well compensate for the autogenous shrinkage and improve the crack resistance of marine concrete without a relatively small loss of compressive strength (≤8.7%). In addition, for the marine concretes containing CEA, the chloride diffusion coefficients were very small (<1 × 10-12 m2/s). Therefore, adding no more than 6% CEA, marine concrete had good crack resistance and chloride penetration resistance. Hopefully, the outcomes of this research can provide guidance for the application of CEA in marine concrete.

Effects of Crushed Oyster Shell on Strength and Durability of Marine Concrete Containing Fly Ash and Blastfurnace Slag

A large quantity of oyster shell is generated every year in coastal regions. Instead of being dumped as waste, after crushing or grinding, oyster shell may be recycled for use in concrete. Herein, the use of crushed oyster shell (COS) in conjunction with fly ash (FA) and blastfurnace slag (BS) to produce marine concrete was studied. By varying the COS, FA and BS contents in the marine concrete, the combined effects of COS, FA and BS on the cube compressive strength, water penetration, cyclic wetting-drying chloride attack and long-term seawater attack resistances were evaluated. The results showed that the addition of proper amounts of COS, FA and BS has positive effects on the strength and durability of marine concrete, but excessive COS may have negative effects. Hence, the combined addition of COS, FA and BS up to a certain optimum COS content is a promising way of producing a higher performance and greener marine concrete.

Regression analysis for determination of durability parameter values of marine concrete

The importance of determination of marine concrete durability and lifetime prediction parameters through regression analysis of exposure test results or field measurements is discussed. The parameters considered include the apparent diffusion coefficient, the apparent surface chloride content and the time attenuation coefficient of the apparent diffusion coefficient. According to the analytical expression of Fick's second law, the essential features and the procedure of regression analysis (curve fitting) of chloride profiles are analysed. A new curve-fitting approach for determination of the parameters of marine concrete durability, called the secondary regression analysis method (Sram), is proposed. In this method, the first regression step is to determine the values of the apparent diffusion coefficient and the apparent surface chloride content. Based on the regression results of the vector of different exposure times, the second step is to determine the value of the time attenuation coefficient of the apparent diffusion coefficient and the change of apparent surface chloride content with respect to time. In the first step, the integral transformation method is analysed and used. In the second step, the non-linear equation is transformed into a linear equation. An example calculation shows that the Sram is a new approach for determination of marine concrete durability parameters.

Investigation of pore structure and ITZ of concrete blended with mineral admixtures in a seawater environment

The pore structure and interfacial transition zone (ITZ) in seawater concrete as indicators of marine concrete durability are explored and analysed. Mercury intrusion porosimetry, microhardness tester and scanning electron microscopy are employed to characterise the evolution of the pore structure and ITZ with curing time. Effects of mineral admixtures including slag, silica fume and metakaolin on pore structure and ITZ are also investigated. In addition, the influence of slag, silica fume and metakaolin on the thermodynamic stability of hydrate phases is investigated. The experimental results show that, compared to normal concrete, concrete subjected to simulated seawater conditions at early ages has a higher ratio of fine porosity as well as higher ITZ microhardness, and the ITZ is narrower. However, the microstructure of concrete in the seawater environment degrades up to longer ages. With the addition of mineral admixtures, the pore characteristics of marine concrete are greatly improved. The effect of the mineral admixtures on microstructure is in the sequence: metakaolin &gt; silica fume &gt; slag. Thermodynamic analysis indicates that stable hydration products ettringite (C6AsH32:6CaO·Al2O3·3CaSO4·32H2O) and siliceous hydrogarnet (C3As0·8H4·4:3CaO·Al2O3·0.8SiO2·4.4H2O) form due to pozzolanic reactions to optimise the microstructure and enhance the compressive strength of concrete.

Different Salt Solution on the Deterioration of Marine Engineering Concrete under the Action of Chemical-Mechanical Coupling

The loaded specimens were put in fresh water, 3.5%NaCl solution, 5.0%Na2SO4 solution, and simulated sea water with different concentrations respectively, and then the damage process under wetting and drying cycle was investigated. The ultrasonic non-metal testing technology, X-CT scanned image, free chloride and sulfate ions chemical titration were used to investigate the degradation of the marine concrete under the coupling effect of Chemistry and Mechanics. The effect of solutions, wetting and drying cycle and bending stress to the durability of marine concrete were further studied. The results indicate that different salt solution affects marine concrete at different degrees: sulfate salt is more corrosive than chloride salt, simulated seawater is similar to 5.0%Na2SO4 solution, while five-time simulated seawater is the most corrosive; wetting and drying cycle remarkably accelerates the penetration of corrosive ions, which results in the concrete damage, compared to the corrosive environment, concrete is damaged violently under the coupling effect of Chemistry-Mechanics and tensile stress has greater influence on the damage.

Development of Integrated Experiment Program for Marine Concrete Durability

Traditionally main driving force of chloride penetration in concrete have been regarded as a diffusion, however, large construction such as tunnel elements and foundations for bridges can be placed on large sea water depths where the water pressure is fairly different from the pressure in the splash zone. Moreover, hydrostatic pressure increases in proportional to measured depth from the surface of water because of the increasing weight of water exerting downward force from above. In this study, new experiment method to estimate chloride penetration of concrete under water pressure is introduced. The water pressure has a great influence on the chloride penetration and thereby on the service life of marine concrete.

Exposure of Concrete in Different Marine Environments

The severity of marine environments varies depending on location and has a major bearing on the durability performance of marine structures. A series of concrete specimens was cast, was exposed to four marine environments for two years, and the effect of marine exposure was estimated from chloride ingress levels. Two marine sites in South Africa were chosen, being either sheltered or exposed to severe wave action. At each site, concrete was placed in the tidal and spray zones. Results from this work indicated that concrete in the tidal zone exposed to heavy wave action had significantly higher chloride levels than concrete sheltered from wave action. When predicting the potential durability of marine concrete, allowance must be made for the severity of exposure together with material properties since both factors determine long-term durability performance. The results also have implications for laboratory simulations of marine exposure under relatively stagnant conditions.