Marine Exposure Conditions Research Articles

Performance of cementitious systems containing calcined clay in a chloride-rich environment: a review by TC-282 CCL

In this review by TC- 282 CCL, a comprehensive examination of various facets of chloride ingress in calcined clay-based concrete in aggressive chloride-rich environments is presented due to its significance in making reinforced concrete structures susceptible to chloride-induced corrosion damages. The review presents a summary of available literature focusing on materials characteristics influencing the chloride resistance of calcined clay-based concrete, such as different clay purity, kaolinite content and other clay minerals, underscoring the significance of pore refinement, pore solution composition, and chloride binding mechanisms. Further, the studies dealing with the performance at the concrete scale, with a particular emphasis on transport properties, curing methods, and mix design, are highlighted. Benchmarking calcined clay mixes with fly ash or slag-based concrete mixes that are widely used in aggressive chloride conditions instead of OPC is recommended. Such comparison could extend the usage of calcined clay as a performance-enhancing mineral admixture in the form of calcined clay or LC2 (limestone-calcined clay). The chloride diffusion coefficient in calcined clay concrete is reported to be significantly lower (about 5–10 times in most literature available so far) compared to OPC, and even lower compared to fly ash and slag-based concrete at early curing ages reported across recent literature made with different types of cements and concrete mixes. Limited studies dealing with reinforcement corrosion point out that calcined clay delays corrosion initiation and reduces corrosion rates despite the reduction in critical chloride threshold. Most of these results on corrosion performance are mainly from laboratory studies and warrant field evaluation in future. Finally, two case studies demonstrating the application of calcined clay-based concrete in real-world marine exposure conditions are discussed to showcase the promising potential of employing low-purity calcined clay-based concrete for reducing carbon footprint and improving durability performance in chloride exposure.

Improvement on Strength, Durability, and Crack Closure Behavior of Bacteria Concrete under Marine Soil Exposures

Abstract In the concrete industry, bacteria-precipitated calcium carbonate (CaCO3) can be used to repair cracks. If cracks in concrete are not repaired in a timely manner, other durability problems arise, necessitating expensive crack repair methods. Bacteria can be isolated from an appropriate physical environment so that they continue to function effectively in concrete. In this study, suitable self-healing bacteria are isolated from a concrete dump yard and incorporated into concrete specimens. After 3 days of normal curing, the specimens were pre-cracked and kept in marine exposure conditions for a period of 56 days. Strength and durability properties such as compressive strength regain, ultrasonic pulse velocity (UPV), and dynamic Young’s modulus were studied, and a water absorption test was carried out for cubes exposed in marine soil conditions. Marine soil treated with a bacteria and nutrient solution (1:9) exhibited improved crack-healing behavior as well as increased strength and durability. Compressive strength regain of 45.98 %, an increased modulus of 54.04 %, and crack healing of 83.05 % were reached with a 60 % reduction in water absorption and 32.49 % increment in UPV values. A microstructure study demonstrates the presence of CaCO3 compounds in healed crack surfaces and treated marine soil, which is primarily due to bacterial action under marine exposures conditions.

An experimental investigation on mitigating cracks and augmenting the endurance of concrete structures in marine environment by bio-mortar immobilised with halophilic bacteria

In coastal areas, built structures encounter hostile conditions and forces that can cause them to deteriorate over time owing to saltwater exposure, tidal forces, reinforcement corrosion, and freeze–thaw cycles. Early age cracks in such structures accelerate the rate of deterioration, and the current research focuses on alleviating such threats. This paper evaluates the performance of a self-healing mortar made by encapsulating expanded perlite with the bacterium Halobacillus Halophilus MCC2188. Mortar cube specimens of size 70.6 mm × 70.6 mm× 70.6 mm were prepared with cement: fine aggregate in 1:3 ratios. A 10% volume of the fine aggregate fraction was substituted with the expanded perlite immobilised with bacterial spores and nutrients. The expanded perlite aggregates were coated with sodium silicate and cement solution to protect the spores from the nonconducive environment. The specimens were subjected to fully and partially submerged marine water curing. The mechanical properties and self-healing potential were evaluated, and the precipitated polymorphs in completely healed cracks were identified and examined by characterisation techniques such as XRD, FEGSEM, FTIR, and TGA-DTG. The marine bacterium under investigation can tolerate the high salt concentrations commonly found in seawater and saline marshy soil and produce calcite through the metabolism of organic compounds, making it a suitable microorganism for self-healing applications. Crack widths of up to 0.84 mm and 92.79% average strength recovery were achieved in 56 days post-cracking, and the pace of healing was quicker in partially submerged curing conditions. The results showed improved self-healing, strength regain and mechanical strength and proved to be an efficient tool for enhancing the endurance of biomortar in severe marine exposure conditions.

Gowanus Canal Superfund Site. V: Evaluation of ISS Cylinder Sample Crusts Formed During EPA 1315M Testing

The main purpose of treatability testing is to tailor a proposed remedial approach and related testing to site-specific conditions to ensure the maximum possible applicability of the bench-scale results at the full scale, and thus the success of the approach. One such adaption involves the use of modified (“M”) EPA 1315 tests to assess the leaching of volatile organic compounds (VOCs) under simulated brackish-water conditions to provide insights into the mass transfer rates that result from the in situ stabilization/solidification (ISS) of sediments at coastal sites heavily impacted by nonaqueous-phase liquids (NAPLs). As shown in this study, the use of saltwater (SW) baths during EPA 1315M testing can result in the formation of surface crusts on ISS samples and mass-transfer reductions in naphthalene, this effect being very pronounced in Gowanus Canal sediments. At the same time, the pH of the SW bath can drop from greater than 11 for a corresponding deionized water (DIW) bath to approximately 8, thus enabling biological activity. The newly formed ISS sample crusts (primarily aragonite and brucite) were similar in many respects to crusts that form on concrete under marine exposure conditions, based on mineralogical and x-ray-based analyses. However, surprisingly, while some SW baths were shown to be biologically active based on gene-probing analyses, petroleum hydrocarbon degraders, when present, did not necessarily reduce the observed leaching rates. The authors concluded that, while the surface crusts do appear to be associated with mass-transfer reductions, to varying degrees, remedial design should conservatively proceed on the basis of EPA 1315M tests utilizing DIW baths only, and any crusts potentially occurring under field conditions constitute an inherent benefit.

Enhanced corrosion resistance of CPC coatings modified with rice husk ash for rebar applications in marine environment

This work investigated the anti-corrosive properties of cement polymer composite coatings modified with fly ash and rice husk ash over steel rebars in a marine environment. So far there are no reports of supplementing rice husk ash in cement polymer coatings and hence, in this research work we attempt to develop a corrosion resistant cementitious composite coating over carbon steel reinforcements embedded in concrete structures in a marine environment. Four types of coatings were synthesized and designated as OC (100 wt% Ordinary Portland Cement), PC (100 wt% Portland Pozzolana Cement), OPF (OC replaced with 20 wt% fly ash), OPR (OC replaced with 20 wt% rice husk ash). The coatings were prepared with a commercially available polymer solution and applied on to the steel rebars in triplicate. Electrochemical studies like open circuit potential measurements, electrochemical impedance spectroscopy and potentiodynamic polarization measurements were carried out on all the coated rebars and compared with uncoated rebars under marine exposure conditions. Optical microscopy and Field Emission Scanning Electron Microscopy were used for understanding the morphology of coated surfaces. The results indicated that addition of rice husk ash improved the corrosion performance of CPC coatings as compared to others. The significantly lower Icorr value of 8.92e-08 μA (a order of magnitude less than reinforcements without coating) and the highest impedance value and polarization resistance, implied more corrosion resistance for OPR coated rebars than others. The characterization of the surfaces revealed the smooth morphology of the OPR coating. Our results highlight the significant benefits of using supplementary cementious materials in cement polymer composite coatings for improving the anti-corrosive properties of rebars and the findings will definitely throw light on a new direction of research towards development of eco-friendly coatings with improved corrosion resistance and durability to enhance the life of reinforced concrete structures.

Assessment of Durability Indicators for Service Life Prediction of Portland Limestone Cementitious Systems Produced with Permeability-Reducing Admixtures

Supplementary cementing materials (SCMs) and the challenges associated with admixture compatibility and durability performance are continuous challenges for the construction industry. Utilizing SCMs has apparent benefits in reducing the carbon footprint and improving the durability performance of concrete structures. This work investigates the performance of mortars composed of Portland limestone cement, calcium carbonate, butyl stearate, and oleic acid. The effort focuses on transport properties using electrical resistivity, chloride migration, porosity, and water permeability measurements. Then, various methods based on the last parameters are compared to assess the changes in the effective chloride diffusion coefficient and the intrinsic liquid water permeability. Measurements for drying shrinkage, thermal expansion, and compressive strength are conducted to verify durability and mechanical performance. The effect of the admixture addition on the service life of a structure fully submerged in marine exposure conditions is then evaluated using Fick’s second law of diffusion and the approach described by FIB model code 34. The results indicate that incorporating calcium carbonate, butyl stearate, and oleic acid in mortar mixtures provides enhanced durability compared to plain Portland limestone cement mortars.

Oxygen Availability and Corrosion Propagation in RC Structures in the Marine Environment—Inferences from Field and Laboratory Studies

The splash and spray and tidal zones are generally assumed to be the most severe marine exposure environments with respect to steel reinforcement corrosion in concrete structures. However, it has been observed in several aged marine structures along the Southern African coastlines, that there is usually relatively insignificant reinforcement corrosion damage in the tidal zone, despite very high (above-threshold) chloride contents. To develop a full understanding of the severity of marine exposure conditions with regard to the actual deterioration, it is imperative that other factors that directly affect corrosion, such as oxygen availability at the steel surface (which is influenced by concrete quality, cover thickness and moisture condition), are carefully considered. The laboratory experimental work in the study presented in this paper comprised of different cover depths (10, 20 and 30 mm) and w/b ratios (0.5 and 0.8) and simulated marine tidal, splash and submerged environments. The results show that for any give exposure environment, the relative influence of each of the various factors considered should be considered in conjunction with the other factors; this finding can be generalized to include all relevant factors that can affect corrosion in a given exposure environment including ambient temperature. For example, a cover depth of 30 mm in the tidal zone with a simulated intertidal duration of 6 h effectively resulted in similar corrosion behavior to that in the submerged zone. The paper concludes that engineers should consider these factors when applying standard exposure classes in the design for durability of marine structures.

New service limit state criteria for reinforced concrete in chloride environments

Abstract In chloride environments, reinforcement stress limits, intended to control flexural cracking, are one of the most important requirements for service limit state (SLS) design. However, concrete damage at the steel-concrete interface between bending cracks, so called cover-controlled cracking, is always correlated to areas of severe steel reinforcement corrosion. Based on the assumption that cover-controlled cracking should be limited, a model has been developed to provide alternative reinforcement stress limits in marine exposure conditions such as concrete in sea water, including permanently submerged, spray zone and tidal/splash zone, as well as coastal constructions located within 1 km of the shoreline. In this paper, the new reinforcement stress limitation is compared to the Australian Standards AS3600 concrete building code and AS5100.5 concrete bridge code provisions. Analysis shows that the new model is very sensitive to the reinforcement percentage of the cross-section. As a result, the existing AS3600 and AS5100.5 code provisions are more conservative than the new limitation for lightly to normally reinforced concrete cross-section. In this case, crack width control governs the SLS design. However, for normally to heavily reinforced concrete cross-section, the new model provides more conservative results suggesting that cover-controlled cracking governs the SLS design.

Field evaluation of corrosion mitigation on reinforced concrete in marine exposure conditions

The Arabian Gulf is one of the most unfriendly environments for concrete structures due to the harsh chloride attack to reinforcing steel. Durability of concrete is improved by the addition of Supplementary Cementitious Materials (SCMs) and/or chemical agents to concrete mixtures. A marine exposure site was constructed on the west coast of the Gulf in order to study the influence of SCMs and chemical admixtures on corrosion activities in reinforced concrete. Plain and reinforced concrete blocks made from eight mixes, containing cement Type I and Type V with different SCMs and corrosion inhibitors (MCI, CNI, and Caltite), were subjected to natural marine weathering process in exposure zones; tidal, splash and atmospheric for twelve months. Eight blocks, four plain and four reinforced with four black steel bars with various cover depth, were made from each mix. The blocks were monitored and their performance were evaluated in terms of chloride ingress and steel corrosion activity. Corrosion inhibitors showed better effectiveness with cover depth increase. Fly ash and slag cement showed the best performance of corrosion mitigation. Caltite showed marginal reductions in chloride concentrations and a slight improvement in corrosion rates compared to control blocks. The atmospheric-exposed samples showed marginal increase in chloride surface concentration unlike the tidal-exposed ones. The results illustrate the importance of ensuring adequate cover depth for achieving a long service life in harsh environment.

Study on performance of waterborne anticorrosive coatings on steel rebars

Durability of reinforced cement concrete structures is mainly affected by corrosion of steel reinforcements. In order to protect the reinforcing bars from corrosion and to enhance the lifetime of reinforced cement concrete structural members, anticorrosive treatment to steel is of prime importance. Conventional coatings are solvent based. In this study, water based Latex was used to formulate anticorrosive coating. Latex is applied to steel specimen substrates such as plates and rods and their mechanical properties such as flexibility, abrasion, bendability, adhesive strength, impact resistance, etc. were studied. It was inferred that coating containing latex, micro silica, zinc phosphate, ferric oxide, aluminum oxide, titanium oxide and silica fume was found to possess more corrosion resistance under marine exposure conditions.

Long-term corrosion performance of blended cement concrete in the marine environment – A real-time study

Blended cement is widely used in critical structures mainly because of its enhanced corrosion resistance concerning its durability. This paper presents the long term corrosion performance of blended cements namely; Portland pozzolana cement (PPC) and Portland slag cement (PSC) concrete under the three marine exposure conditions such as, atmospheric zone (AZ), immersion zone (IZ) and splash zone (SZ). Offshore Platform Marine Electrochemistry Center (OPMEC), Tuticorin, Tamil Nadu, India was selected as an exposure station. The concrete cubes were exposed over the period of 10years and their physicochemical properties such as compressive strength, alkalinity, free chloride content and sulphate content, bio-fouling attachment and electrochemical properties like, AC-impedance and potentiodynamic polarization were carried out and the results obtained were compared with Ordinary Portland Cement (OPC) concrete. XRD and SEM studies were also carried out for both OPC, PPC and PSC concrete samples exposed under various zones. It was observed that the strength and alkalinity of the blended cement concretes were relatively equal to that of OPC concrete. In addition, the pH values of the blended cement concretes are above the threshold limit recommended for depassivation. Furthermore, the resistance to chloride ion penetration was significantly reduced for blended cement concretes than that of OPC concrete and also exhibited very high amount of bio-fouling attachment. The electrochemical studies revealed that the blended cement concretes are having higher corrosion resistance in all three exposure zones than that of OPC concrete. From the results it is observed that the blended cement concretes are technically viable from the durability point of view and highly recommended for aggressive marine environments rather than OPC concrete.

Parametric Study of Shear Strength of Concrete Beams Reinforced with FRP Bars

Fibre Reinforced Polymer (FRP) bars are being widely used as internal reinforcement in structural elements in the last decade. The corrosion resistance of FRP bars qualifies its use in severe and marine exposure conditions in structures. A total of eight concrete beams longitudinally reinforced with FRP bars were cast and tested over shear span to depth ratio of 0.5 and 1.75. The shear strength test data of 188 beams published in various literatures were also used. The model originally proposed by Indian Standard Code of practice for the prediction of shear strength of concrete beams reinforced with steel bars IS:456 (Plain and reinforced concrete, code of practice, fourth revision. Bureau of Indian Standards, New Delhi, 2000) is considered and a modification to account for the influence of the FRP bars is proposed based on regression analysis. Out of the 196 test data, 110 test data is used for the regression analysis and 86 test data is used for the validation of the model. In addition, the shear strength of 86 test data accounted for the validation is assessed using eleven models proposed by various researchers. The proposed model accounts for compressive strength of concrete (fck), modulus of elasticity of FRP rebar (Ef), longitudinal reinforcement ratio (ρf), shear span to depth ratio (a/d) and size effect of beams. The predicted shear strength of beams using the proposed model and 11 models proposed by other researchers is compared with the corresponding experimental results. The mean of predicted shear strength to the experimental shear strength for the 86 beams accounted for the validation of the proposed model is found to be 0.93. The result of the statistical analysis indicates that the prediction based on the proposed model corroborates with the corresponding experimental data.

Investigations for structural safety assessment of corroded cast iron bridge piers

Cast iron bridge piers, often more than 100 years old, are still in service in rail and road bridges in many parts of Australia. Increasingly, the effect of corrosion on their present and future structural safety is of interest. Field investigations and observations to assess corrosion losses and pitting of the cast iron piers of four different operational railway bridges located in tidal marine exposure conditions are described, noting that direct visual examination usually is rendered difficult by immersion, marine growth and the presence of the graphitised layer. Measured corrosion losses and pit depths showed considerable variability between piers and between bridges. Evidence was found for the influence of microbiological corrosion, fostered by nitrogenous pollution. Implications for structural safety assessment are discussed and an example given of the estimation of likely future rate of (long-term) corrosion, necessary for assessment of remaining structural safe life.

Service-Life Assessment of Existing Precast Concrete Structure Exposed to Severe Marine Conditions

The overall performance of a concrete structure is considered to be a key issue when determining its service life. The widespread use of precast concrete and consideration of durability as a design parameter in most of the international codes have the goal of achieving concrete structures with better durability. Nevertheless, the early deterioration of concrete is still common in a large number of concrete structures, which reduces the service life. This paper presents a case study of an existing precast concrete cooling tower for a thermal power station subjected to severe marine exposure conditions, which showed symptoms of serious deterioration after operating for three years. The main goal of this study was to clarify the origin of the accelerated deterioration of the structure. Wetting-drying cycles were identified as the main cause of the early deterioration of the structure. Furthermore, estimations on its remaining service life were made considering the accelerating effect of the wetting-drying cycles. Finally, the variation in the safety factor of the main structural elements was evaluated.

A study of the degradation of marine concrete under the coupled effect of wetting–drying cycles and bending loads

Marine concrete with excellent salt corrosion resistance was cast, followed by ultrasonic testing technology, chemical analysis of free chloride ion and calculation of the chloride ion diffusion coefficient to investigate the degradation of the marine concretes subjected to wetting–drying cycles and bending loads during their exposure to a marine environment. Additionally, an indoor accelerated corrosion test was conducted. The effects of the water-to-binder ratio, mineral admixtures, bending loads and other factors on the durability of the marine concrete were investigated, and initial primary correlation between marine exposure conditions and the indoor accelerated corrosion test was established based on the diffusion coefficient of chloride ions.

Degradability of organic-inorganic cellulose acetate butyrate hybrids in sea water

Degradability of organic-inorganic cellulose acetate butyrate hybrids in sea water Environmental degradability of novel organic-inorganic cellulose acetate butyrate hybrids obtained via solgel process was investigated. The degradation of hybrids was studied under marine exposure conditions in the Baltic Sea for a period of 25 weeks. The influence of characteristic parameters of sea water on the degree of degradation monitored by changes of weight and optical microscopy was discussed. The degraded samples were also examined by FT-IR spectroscopy. It has been established that the CAB/silica hybrids are more susceptible to biodegradation in sea water environment than pure cellulose acetate butyrate.

Chromium(III) and Chromium(VI) Surface Treated Galvanized Steel for Outdoor Constructions: Environmental Aspects

The long-term degradation of chromium(III) (Zn-Cr(III)) and chromium(VI)-based (Zn-Cr(VI)) surface treatments on galvanized steel and their capacities to hinder the release of zinc induced by atmospheric corrosion at nonsheltered urban and marine exposure conditions for 2 years are investigated. Compared to bare zinc sheet, both surface treatments revealed high corrosion protection abilities and capacities to hinder the release of zinc, still evident after 2 years of exposure. The zinc barrier properties of the thinner Zn-Cr(VI) (10 nm) treatment were during the first 100 days of urban exposure slightly improved compared with Zn-Cr(III) (35 nm). However, their long-term protection capacities were inverse. Released concentrations of total chromium correspond to annual release rates less than 0.000032 (Zn-Cr(III)) and 0.00014 g Cr m(-2) yr(-1) (Zn-Cr(VI)) after 1 year of urban exposure. Aging by indoor storage of the surface treatments prior to outdoor exposure reduced the released Cr concentrations from the surface treatments. No Cr(VI) was released from the aged surfaces but from the freshly exposed Zn-Cr(VI). Marine exposure conditions resulted in a faster reduction of chromate to chromium(III)oxide compared with urban conditions, and a significantly lower amount of both chromium(III) and chromium(VI) released from Zn-Cr(VI) at the marine site compared with the urban site.

Environmental Degradation of Blends of Atactic Poly[(R,S)-3-hydroxybutyrate] with Natural PHBV in Baltic Sea Water and Compost with Activated Sludge

Degradation of atactic poly[(R,S)-3-hydroxybutyrate] (a-PHB) binary blends with natural poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV, 12 mol% of 3HV units), has been investigated and compared with plain PHBV in the compost containing activated sludge and under marine exposure conditions in the dynamic water of the Baltic Sea. Characteristic parameters of compost and the Baltic Sea water were monitored during the incubation period (6 weeks) and their influence on the degree of biodegradation is discussed. After specified degradation times of the experiments the weight loss of the samples, surface changes, changes in molecular weight and polydispersity as well as changes of the composition and thermo-mechanical properties of the blends have been evaluated. Macroscopic observations of the samples were accompanied by investigations using optical microscopy, size-exclusion chromatography (SEC), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and tensile testing. The degree of degradation of blends of a-PHB with PHBV depends on the blend composition and environmental conditions. In both environments studied the weight loss of plain PHBV was more significant than changes the molecular weight. In both environments only enzymatic degradation of the blends, which proceeds via surface erosion mechanisms, was observed during the incubation period.

Long-term strength and durability parameters of lightweight concrete in hot regime: importance of initial curing

The paper presents results on strength development and durability of 35 and 50 MPa total lightweight concretes exposed to hot marine exposure conditions for a period of 7 years. An initial water curing of 7 days and subsequent seaside exposure was found more beneficial for the strength development of lightweight concrete. One day of initial curing and subsequent seaside exposure was not very conducive for the strength development. A marginal degradation in both the stiffness and the modulus of rupture of the concretes over the exposure period was observed. Likewise, the water penetrability of the two mixtures, for all the three initial curing regimes, increased over a period of 7 years. This establishes that the compressive strength of concrete is not synonymous with its durability. Overall, 3–7 days of initial water curing seems most desirable to enhance the durability of concrete exposed to hot salty marine exposure conditions.

Field studies of surface cleaning and salt retention on openly exposed metal plates

The paper describes a number of studies relating to the retention of marine salts on atmospheric corrosion test plates and the cleaning of such salts in field exposures. Data from three separate field studies are presented. In each study, instrumented zinc plates were openly exposed to the atmosphere. Plates were exposed in tropical, subtropical and temperate regions of Australia in severe marine, marine, urban and inland exposure conditions. Plates were washed at various times during exposure and, in some cases, they were ultrasonically cleaned after exposure. Ion chromatographic analysis was undertaken to determine the ion contents of the wash-off and ultrasonic cleaning solutions, and thus the salts present on the exposed plates. Sites and plates were also instrumented with rain gauges, salt candles, relative humidity sensors, surface temperature sensors and surface wetness sensors. Changes in the relative humidity at which the surfaces became wet were determined and used as a guide to infer the presence of salts on the surfaces. The effect of rainfall on the presence of salt was then determined. The factors controlling salt retention on surfaces are discussed, including the possibility that the ability of a surface to retain salt changes with time, and that sources of chloride other than crystalline salt may exist. The relevance of the study to atmospheric corrosion is discussed.