Salt Attack Research Articles

Effect of polyvinyl alcohol fibers on mechanical properties of nano-SiO2-reinforced geopolymer composites under a complex environment

Abstract Buildings in service are severely affected by the complex environment with multiple coupled factors such as high temperatures, humidity, and inorganic salt attack. In this work, the mechanical properties of nano-SiO2-reinforced geopolymer composites (NSGPC) incorporated with varying dosages of polyvinyl alcohol (PVA) fibers were investigated under a complex environment. A simulated environmental chamber was employed to simulate the complex environment with relative humidity, temperature, and NaCl solution concentration of 100%, 45°C, and 5%, respectively. Fly ash/metakaolin geopolymer composites (GPCs) were fabricated by utilizing 1.5% nano-SiO2 by weight and five various dosages of PVA fibers by volume (0, 0.2, 0.4, 0.6, and 0.8%). The compressive strength, tensile strength, elastic modulus, and impact resistance of NSGPC eroded in a simulated environmental chamber for 60 days were determined. Then, the impact of the PVA fiber dosage on the mechanical properties of NSGPC under complex coupled environments was analyzed. In addition, scanning electron microscopy (SEM) was employed to evaluate and analyze the microstructural behavior of NSGPC under complex environments. Results indicated that the compressive strength, tensile strength, elastic modulus, and impact resistance of NSGPC increased with increasing PVA fiber to 0.6% and then decreased with a continuous increase to 0.8% but remained higher than those of the reference specimen. NSGPC exhibited the best performance at a PVA fiber dosage of 0.6%, which increased by 13.3, 12.0, 17.2, and 522%, respectively. The outcomes of SEM analysis indicated that the usage of PVA fiber and NS remarkably improved the mechanical properties and microstructural behavior of GPC by making the inner structure of GPCs more robust and compact under a complex environment. The outcomes of this work can provide theoretical guidance for buildings serving under a complex environment.

Chloride transportation and electrochemical behavior of concrete containing corrosion-inhibiting admixture and its inhibition mechanism under compound salt and drying-wetting cycles

The purpose of this study is to provide an ecological corrosion-inhibiting admixture (CIA) for retarding the degradation of reinforced concrete under compound salt attack and drying-wetting cycles. The effects of CIA on the mechanical behavior, chloride transportation, and electrochemical behavior of concrete under compound salt and drying-wetting cycles were investigated. The pore contents with different sizes in concrete and the micro-morphology of rebars were analyzed by the bubble spacing coefficient analyzer and the scanning electron microscopy (SEM), respectively. The findings showed that the addition of CIA retarded the deterioration of concrete under compound salt and drying-wetting cycles. After exposure for 150 d, the weight loss rate and average free chloride concentration of concrete containing 5 % CIA decreased by 74.14 % and 51.53 % respectively, and the compressive strength was 1.49 times that of concrete without CIA. Chloride transportation was primarily dominated by diffusion and convection. Additionally, CIA significantly reduced the content of larger pores, prevented the diffusion of chloride and sulfate into the interior concrete, and formed adsorption films through a combination of physical and chemical effects, thus improving the electrochemical performance of rebars. This study is of great significance to provide new perspectives and improvement measures for mitigating the deterioration of reinforced concrete under compound salts and drying-wetting cycles.

Influence of particle size distribution on biocarbonation method produced microbial restoration mortar for conservation of sandstone cultural relics

Biocarbonation of reactive magnesia based on microbially induced carbonate precipitation (MICP) process is a sustainable geotechnical reinforcement technology for strength development and permeability reduction. This method can be used to produce microbial restoration mortar (MRM) for the application of stone cultural relics restoration. In this paper, the influence of particle size distribution on the strength and porosity of MRM was examined. By mixing fine and coarse sandstone powder in various proportions, nine different particle size distributions were obtained to investigate the restoration performance, including the unconfined compressive strength (UCS), porosity, and color difference. The results indicate that the well-graded particle size distribution can lead to the UCS improvement and porosity reduction of MRM. The findings also imply that adding fine sandstone powder to the coarse sandstone powder can provide extra bridging contacts within the soil matrix. These bridging contacts can be easily connected by the precipitated hydrated magnesium carbonates (HMCs) minerals, consequently resulting in more effective bonding and filling within the pore matrix. The microstructural images of MRM confirm the formation of HMCs, which exhibited a dense network structure, filling out the gap and bonding the sandstone powders. Furthermore, the microbial restoration mortar showed a high weather resistance to dry-wet cycles, acid rain, and salt attack, which is attributed to better stability and strength of HMCs than the original calcic cemented minerals in sandstone.

Soil security under salt attack: Protection of the soil against the salinization caused by drying up of Lake Urmia

In recent decades, Lake Urmia (LU), a hypersaline lake in northwestern Iran, has suffered significant water loss due to both human-induced and natural causes. This drought could lead to the emission of millions of tons of saline particulates from its dried bed, resulting in saline dust storms that compromise soil and food security in LU basin as an agricultural region. Despite some restoration programs by the central government and provincial administrations, efforts have not been sufficient to revive LU and mitigate risks. This paper explores the legal dimensions of the impact of LU's drying on soil security and assesses current legal initiatives for LU restoration and soil security along with their challenges. The study concludes that current legal initiatives for soil security against LU drought are inadequate, and without significant changes in sustainable water and soil governance, soil and food security in the region will be impossible. The paper recommends taking more serious actions to prevent LU drying according to the precautionary principle, promoting sustainable and polycentric soil and water governance, shifting economic and agricultural priorities, and protecting the environment and local people against the impacts of this catastrophe.

Performance of Alkali-Activated Slag Concrete Masonry Blocks Subjected to Accelerated Carbonation Curing

This study investigates the effect of accelerated carbonation curing on the carbon sequestration potential, performance, and microstructure of alkali-activated slag mixes representing concrete masonry blocks (CMBs). The carbonation curing process parameters varied, including initial curing duration, carbonation curing duration, and carbonation pressure. Research findings showed that a maximum CO2 uptake of 12.8%, by binder mass, was attained upon exposing concrete to 4 h initial curing and 20 h carbonation curing at a pressure of 5 bars. The compressive strength and water absorption capacity improved with longer initial and carbonation curing durations and higher pressure. Upon subjecting to salt attack, the mass and strength of 28-day concrete samples increased, owing to the formation of Friedel’s salt and Halite. All mixes could be used as non-load-bearing CMB, with a 1-day strength greater than 4.1 MPa. Based on the global warming potential index, the carbon footprint of carbonation-cured, alkali-activated slag concrete masonry units was up to 46% lower than non-carbonation-cured counterparts. Research findings offer valuable information on the production of carbonation-cured, cement-free concrete masonry blocks to replenish natural resources, recycle industrial waste, and mitigate CO2 emissions.

Shelf-life enhancement of bio-inoculants through synergistic effects of encapsulation technology and osmotic protectants

A novel protective capsule for encapsulating microorganism inoculants was developed based on a core/shell structured hydrogel doped with osmotic regulators, with the aim of protecting against salts stress. The resulting capsules showed favorable mechanical toughness, high encapsulated efficiency, low cell leakage and increased resistance against salt attack. Different types of sugar alcohol molecules were selected as the osmoprotectants and their effectiveness in retaining the microbial count of trichoderma harziana under adverse conditions was examined. It was found that by using trehalose-doped core/shell structured hydrogels as the microbial carrier, the survival rate and mycelial growth rate of trichoderma harziana increased during incubation in sodium chloride solution and on sodium chloride-containing solid medium. Furthermore, the shelf-life of the microorganisms demonstrated a significant increase from log 5.72 cfu/g to log 7.30 cfu/g after an incubation period of 180 days in compound fertilizers with 15 % nitrogen‐phosphorus‐potassium (NPK) content. This novel microbial encapsulated system showed remarkable preservation of microorganism inoculants under salt stress from fertilizer nutrients, suggesting a noticeable practical potential in agriculture.

Fracture Behavior of Concrete under Chlorine Salt Attack Exposed to Freeze-Thaw Cycles Environment.

Fracture behavior is one of the key properties to study concrete cracking under sodium chloride attack exposed to the freeze-thaw cycles environment, which is frequently neglected. In this paper, 24 single edge notch beam specimens and 24 cubes were poured. The corresponding freeze-thaw cycles test in sodium chloride solution, standard cube compressive strength of concrete test, and three-point-bending tests were carried out. The research revealed that the fracture toughness, fracture energy, relative dynamic modulus of elasticity, and standard cube compressive strength were decreased by increasing freeze-thaw cycles under sodium chloride attack, and the damage degree of concrete caused by sodium chloride solution was deeper than that of pure water. In particular, there existed good linear correlation between the fracture behavior and imposed freeze-thaw damage for various solution. Accordingly, a more reliable damage model using fracture control parameters as damage factors was proposed.

A multi-phase numerical simulation method for the changing process of expansion products on concrete under sulfate attack

Concrete constructions used in harsh marine environments are commonly destroyed by sulfate ions. In this paper, by modeling aggregates as random convex polygons, to analyze and forecast the deteriorating condition of concrete under salt attack, a finite element method is suggested. The sulfate attack on concrete is studied using the numerical analytical method to examine changes in sulfate ions and expansion products at the mesoscale. Since concrete is a heterogeneous mixture, the diffusion characteristics of phases, such as the aggregate, interfacial transition zone (ITZ), mortar and pore, were considered. The proposed mesoscale numerical analysis method is validated by experiments. It is demonstrated that: (1) the setting of ITZ thickness and pore has negligible effect on concrete damage in sulfate environment; (2) reducing the water-cement ratio can significantly enhance the erosion resistance of concrete; (3) within a certain range of depth, the surface sulfate concentration is positively correlated with the erosion degree; (4) aluminate determines the peak value of ettringite content in concrete.

Mechanical and seepage characteristics of polyvinyl alcohol fiber concrete under stress-seepage coupling

This study presents an experimental investigation of the coupled stress and seepage water pressure loading test conducted on polyvinyl alcohol (PVA) fiber concrete, which had undergone salt attack freeze-thaw (F-T) cycles. This study delves into the influence of the number of salt attack F-T cycles, as well as the magnitude of seepage water pressure, on the triaxial compression seepage mechanical properties and permeability evolution of the specimens. Additionally, the nuclear magnetic resonance (NMR), scanning electron microscope (SEM) and X-ray diffraction (XRD) test results were analyzed, revealing that sodium sulfate solution penetrates the interior of PVA fiber concrete and reacts with cement stone to form ettringite and gypsum, which initially fills and compacts the pore structure. The increased production of such compounds causes pore structure to expand, with the maximum number of mesopores and macropores increasing by 115.5%. Macroscopically, it was observed that the mass and peak strength of the specimens increased at the beginning of the cycle, and the initial permeability decreased. However, the opposite phenomenon occurred after 15 cycles. When seepage water pressure was increased from 1 MPa to 3 MPa, the crack initiation stress, crack damage stress, and peak stress of the specimens decreased by 13.1%, 16.9%, and 15.6% on average, respectively, and the initial permeability increased by 69.3% on average. The deformation process of PVA fiber concrete under stress-seepage coupling loading was divided into five stages, including the initial compaction stage, elastic deformation stage, crack initiation and stable propagation stage, crack unstable propagation stage, and post-peak deformation stage. Correspondingly, the permeability exhibited a rapid decline, followed by a relatively stable phase, a slow rise, a rapid rise, and a continuous increase. Besides, the relationship between permeability and volume strain in compression and expansion stages was clarified.

Review on the durability of eco-friendly engineering cementitious composite (ECC)

A comprehensive manual review of the use of slag and fly ash in engineered cement-based composites (ECBCs) was conducted. The extensive use of supplementary cementitious materials and integrated fibers in engineered cement-based composite (ECBCs) in seawater composite structures can help to enhance the durability of infrastructure in marine environments and minimize the extensive use of cement and CO2 emissions in the construction industry. This paper retrieved journal and review articles on slag/fly ash utilization in ECBCs from the Scopus database, mainly from 2015 to 2022, and performed an analysis using a suitable software tool. It also provided an up-to-date review of the literature on eco-friendly engineered cementitious composites’ (ECC) durability, with in-depth discussions on the effects of temperature fluctuation on ECCs, supplementary cementitious material, frost and salt corrosion resistance, pre-cracking, seawater resistance, and microstructural alteration. The durability of ECCs is closely related to the behaviors of the fiber distribution, matrix, and fiber-matrix interface under various environmental conditions. The main factors causing the deterioration of the engineering cement-based composites are fiber orientation and dispersion, frost resistance, corrosion, and alkaline environment. Fiber dispersion is mainly assumed to be highly homogeneous in theory, but in practice, due to the uneven dispersion of the fibers the property of each composite structure is not uniform. Further, among all issue associated with durability, sulfate salt attack considered as the most significant environmental deterioration process that affect the resilience of hydraulic structure. At last, it is necessary to conduct additional research on the durability of ECC under various environmental conditions to comprehend its behavior in the actual world. The experimental data currently available on the short-term durability of ECC fluctuate over time. Which indicates that the mechanisms for the long-term degradation of ECC under specific environmental conditions remain unknown.

Effect of Metakaolin on the Diffusion Properties of Chloride Ions in Cement Mortar under the Coupling Effect of Multiple Factors in Marine Environment

To address the problem of chloride ion transport in cement concrete in marine environment, this study investigates the effect of metakaolin dosage on the chloride ion diffusion resistance of mortar and its mechanism by testing the chloride ion binding capacity and microstructure of mortar under the coupling effect of chlorine salt-sulfate-carbonation multiple factors. The results show that the coupling of sulfate or carbonation reduces chloride ion transport to some extent compared with single chlorine salt attack, while the three-factor coupled environment promotes free chloride ion diffusion. This is because the products of calcium alumina, gypsum, and calcium carbonate grow together and compete with each other to form more large capillaries; thus, accelerating the diffusion of chloride ions in cement mortar. Metakaolin, due to its higher pozzolanic activity, increases the monocarbon aluminate content in the erosion products, promotes F-salt generation, and increases the Al/Si ratio, which strengthens the binding ability of C-S-H gel to chloride ions, so the free chloride ion concentration inside the specimens doped with metakaolin is lower. In particular, the three-factor coupled environment has less 0.05–10 μm capillary pore content and higher F-salt stability in the specimens, which has the strongest effect on chloride ion curing, and the free chloride ion concentration integral in M-SCCl is reduced by nearly 30% compared with MF-SCCl and F-SCCl.

Development of Self-Passivating, High-Strength Ferritic Alloys for Concentrating Solar Power (CSP) and Thermal Energy Storage (TES) Applications

Concentrating solar power (CSP) and thermal energy storage (TES) based on molten salts still lacks economic feasibility, with the material investment costs being a major drawback. Ferritic stainless steels are a comparatively cheap class of materials that could significantly contribute to cost reductions. The addition of aluminum to ferritic steel can result in self-passivation by forming a compact Al2O3 top layer, which exhibits significantly higher corrosion resistance to solar salt compared to the Cr2O3 surface layers typically formed on expensive structural alloys for CSP and TES, such as austenitic stainless steels and Ni-base super alloys. However, to date, no ferritic stainless steel combining Al2O3 formation and sufficient structural strength is available. For this reason, cyclic salt corrosion tests under flowing synthetic air were carried out on seven Laves phase-forming, ferritic model alloys (17Cr2-14Al0.6-1Nb2.6-4W0.25Si), using “solar salt” (60 wt. % NaNO3 and 40 wt. % KNO3). The Al content was varied to investigate the influence on the precipitation of the mechanically strengthening Laves phase, as well as the impact on the formation of the Al-oxide top layer. The W and Nb contents of the alloys were increased to examine their influence on the precipitation of the Laves phase. The salt corrosion experiments demonstrated that simultaneous self-passivation against a molten salt attack and mechanical strengthening by precipitation of fine Laves phase particles is possible in novel ferritic HiperFerSCR (salt corrosion-resistant) steel. Microstructural examination unveiled the formation of a compact, continuous Al2O3 layer on the surface of the model alloys with Al contents of 5 wt. % and higher. Furthermore, a stable distribution of fine, strengthening Laves phase precipitates was achieved in the metal matrix, resulting in a combination of molten salt corrosion resistance and potentially high mechanical strength by a combination of solid solution and precipitation strengthening. These results show that high-strength ferritic alloys are suitable for use in CSP applications.

CMAS + sea salt corrosion to thermal barrier coatings

In marine environment, sea salt and calcium-magnesium-alumina-silicate (CMAS) coexist largely endangering thermal barrier coatings (TBCs) service safety. In this study, the corrosion behavior of synthetic sea salt and CMAS to TBCs was investigated. Sea salt changed the CMAS structure, thereby decreasing its melting temperature and high-temperature viscosity. At 1200 ℃, CMAS + sea salt completely melted but CMAS did not; at 1250 ℃, both melted while CMAS + sea salt had stronger penetration ability in TBCs than CMAS. Thus, TBCs which have not been or are less affected by CMAS may be damaged due to CMAS + sea salt attack.

Effect of Sulfate Crystallization on Uniaxial Compressive Behavior of Concrete Subjected to Combined Actions of Dry–Wet and Freeze–Thaw Cycles

This study focuses on the influence of salt crystallization from sodium sulfate on uniaxial compressive properties of concrete subjected to the coupling action of dry–wet cycles and freeze–thaw cycles. Eight groups of concrete specimens with different concentrations of sodium sulfate solution (CSSS) and different numbers of drying and wetting cycles (NDWC) were designed. Three groups of specimens with different numbers of freezing and thawing cycles (NFTC) exposed to same dry–wet cycles and same sulfate concentration were prepared to study the effects of combined environmental conditions. Salt crystallization from sodium sulfate was generated under a cyclical dry–wet time ratio of 3:1. Scanning electron microscopy and X-ray diffraction analysis were used to analyze reaction products of sulfate and concrete matrix. The results show that under single sulfate dry–wet cycles, with the increase of CSSS and NDWC, the uniaxial compressive strength of concrete degrades as a parabola and corresponding strain increases as a parabola, except for the linear increase of CSSS strain. Subjected to the combined action of sulfate dry–wet cycles and freeze–thaw cycles, it shows that the uniaxial compressive strength of concrete decreases as a parabola with the increase of NFTC, but corresponding strains have no obvious variation. The sulfate salt attack in advance greatly accelerates the deterioration of specimens after freeze–thaw cycles. The common dimensionless predication model of stress–strain relationship of concrete subjected to the combined action of dry–wet cycles and freeze–thaw cycles has been established.

Application of Biogenic Mineral Formation for the Preservation of Limestone Masonry at the Eski-Kermen Archeological Site

Minimal interference with historical material and maximum preservation is one of the basic principles of the scientific restoration and conservation of monuments of historical and cultural heritage. The creation of nanoscale and microscale inorganic coatings is a promising way to protect limestone and marble cultural heritage objects. We conducted a laboratory testing of a method for stimulating biogenic mineral formation on the surface of limestone-masonry samples from the medieval cave town on the Eski-Kermen plateau (Crimea, Russia). The results showed the formation of a layer of crystallites of 0.4 to 1.3 µm on the surface of the limestone, an increase in the average strength values of the samples by 28% from 12.3 ± 2.8 to 15.8 ± 2.6 MPa, a 42% increase in the specific surface area of limestone, an 86% increase in salt attack resistance, and preservation of the capillary water-absorption level. The obtained results show the potential of using biogenic mineral formation for the conservation and restoration of limestone.

Performance deterioration of asphalt mixture exposed to salt-water-temperature-ultraviolet coupling effect

ABSTRACT The intense ultraviolet radiation and large amount of saline-alkali soil in the Golmud region of Province, China, have deteriorated the performance of asphalt pavement. Given the effect of adverse conditions in this area, this paper investigated the collective and interaction effects of salt chemicals, air temperature, and ultraviolet radiation on asphalt and asphalt mixture through laboratory experiments under controlled conditions. In particular, using different concentrations of Na2SO4 and NaCl solutions, simulated salt chemicals for asphalt and asphalt mixture performance impact. The mechanism of performance deterioration of the asphalt mixture suffered from salt attack was explored. The results show that the original asphalt's storage and loss modulus are higher than the modified asphalt at different temperatures with the multi-factors effect. In addition, the modified asphalt's phase angle is 5%∼10% higher than the original asphalt below −2°C. At the same time, strength loss rates of asphalt mixture increase with the cycles and solution concentration, varying from 20%−40%. Wet-dry cycles and the concentration of salt solution are positively correlated with the deterioration of asphalt mixture strength. This research provides the durability prediction and the more reasonable composition design of the asphalt mixture applied in salt enrichment regions.

Damage characteristics of hybrid fiber reinforced concrete under the freeze-thaw cycles and compound-salt attack

This paper presents an experimental investigation on the damage characteristics and microstructures of hybrid fiber reinforced concrete (HFRC) subjected to the freeze-thaw（F-T）cycles and compound- salt attack. The effect of steel fiber content and steel-polypropylene fiber hybridization on the apparent morphology, mass loss, relative dynamic elastic modulus (RDEM), mechanical strengths in terms of compressive and flexural strengths were studied. The damage mechanism was explored based on an analysis of pore structures of specimens. The results showed that the F-T cycle has adverse effect on the physical and mechanical properties of specimens. The addition of fibers alleviates the damage degree of concrete, and the fiber hybridization shows more pronounced effect. Results from the porosity analysis indicate the pore sizes of 1.2HFRC are mainly distributed within 40 nm and those of OC are within 60 nm. The volume of larger pore size of 1.2HFRC increases less than the others after salt F-T cycles. Finally, based on Weibull distribution function, evolution equations for the salt-frozen damage of HFRC are developed by a combination of strength attenuation and RDEM degradation. The research results provide theoretical basis and reference for the practical application and building maintenance of fiber reinforced concrete.

The deterioration mechanisms of hardened cement paste exposed to combined action of cyclic wetting–drying, salt attack and carbonation

In saline soil or salt lake regions, cement-based materials suffer from combined action of salt attack (SA), carbonation, and cyclic wetting–drying (CWD), and its deterioration mechanism remains an open question. Taking advantage of multiple techniques, this study is dedicated to unveiling the deterioration mechanism of hardened cement paste (HCP) exposed to combined action of SA (sulfate salt or sulfate–chloride salt), carbonation (natural carbonation, 0.035 vol.% CO2 or accelerated carbonation, 20 vol.% CO2) and CWD. The results show that, when exposed to combined action of SA, carbonation and CWD, HCP exhibits distinct deterioration mechanisms depending on the concentration of carbon dioxide: chemical sulfate attack (i.e., formation of ettringite and gypsum) is mainly responsible for the deterioration of HCP in the case of natural carbonation, whereas decomposition of C-S-H and formation of gypsum are both responsible for the deterioration of HCP in the case of accelerated carbonation. The presence of sodium chloride in sulfate–chloride solution inhibits the sulfate attack as well as carbonation attack of HCP.

Performance of magnesium oxysulfate (MOS) cement with granite powders after combined sulfate and chloride attacks

Salt erosion is one of the main factors affecting the durability of cement and concrete. Magnesium oxysulfate (MOS) cement is regarded as a new type of binder with many good features such as lower carbon dioxide emission, excellent fire resistance, etc. However, the salt erosion resistance of MOS cement is rarely studied. This research investigated the performance of MOS cement, with granite powders (GPs) as mineral admixture, soaked in NaCl and Na2SO4 solutions. X-ray diffraction (XRD) and simultaneous comprehensive thermal analyzer (TG-DSC) were used to detect the phase composition and hydration products of MOS cement. Scanning electron microscope (SEM) and mercury porosimeter (MIP) were used to analyze the pore structure and microstructure of MOS cement. The results showed that the value of the salt attack coefficient of MOS cement with 50 % by weight GPs reached 0.58 and 0.57 after immersion in NaCl and Na2SO4 solutions for 230 days, respectively. The compressive strength of MOS cement with 30 % by weight GPs reached the maximum value of 74.1 MPa after standard curing for 28 days by optimizing the pore structure. Both needle-like and plate-like Na2SO4·xH2O crystals were observed in the hydration products. Gypsum and Na2SO4·xH2O grew in the pores and matrix, generated expansion stress and destroyed the matrix structure of MOS cement. During the soaking period, the decomposition of the 5·1·7 phase and MgSO4·nH2O negatively affected the salt resistance of MOS cement. Physical and chemical erosion leads to a decrease in the value of the salt attack coefficient.

The new Samuel De Champlain Bridge, Canada

Opened to traffic on 1 July 2019, the new Samuel De Champlain Bridge represents one of the largest infrastructure projects in North America. The rapidly deteriorating condition of the original Champlain Bridge in Montréal led the Government of Canada to accelerate its replacement and ultimately awarded a contract to the Signature on the Saint Lawrence Group, in 2015, to deliver a new replacement crossing. The project was fast-tracked, with a schedule of only 48 months from design to bridge opening. Due to its geographical location, this lifeline structure faces unique hazards including extreme cold temperatures, ice abrasion, de-icing salt attacks, wind, vessel collision, scour and seismic, while meeting its design life of 125 years. Sustainability and durability are also important project requirements. The 3.4 km long bridge is comprised of three independent structures: the 529 m long, asymmetric cable-stayed bridge (which features a single 169 m high tower), the 762 m long east approach and the 2044 m long west approach. The owner used a public–private partnership procurement model and the project was delivered using the design–build delivery method. An overview of this Can$2.4 billion mega project is provided in this paper, and the design and build solutions to overcome the suite of technical and schedule challenges are discussed.