Marine Exposure Site Research Articles

A Laboratory and Field Assessment of the Performance of Rebar Coatings.

Deteriorating concrete structures are repaired to restore their load-carrying capacity and enhance their appearance. As part of the repair procedure, the corroded reinforcing steel bars are cleaned by sandblasting, and a protective coating is applied to protect them from further corrosion. Generally, a zin-rich epoxy coating is used for this purpose. However, there have been concerns about the performance of this type of coating in protecting the steel due to the formation of galvanic corrosion, thus necessitating the need for developing a durable steel coating. In this study, the performance of two types of steel coatings, namely a zinc-rich epoxy and cement-based epoxy resin coating, was investigated. The performance of the selected coatings was evaluated by conducting both laboratory and field experiments. In the field studies, the concrete specimens were exposed to a marine exposure site for more than five years. The salt spray and accelerated reinforcement corrosion studies indicated that the performance of the cement-based epoxy coating was better than the zinc-rich epoxy coating. However, there was no visible difference between the performance of the investigated coatings in the reinforced concrete slab specimens placed in the field. It is suggested to use cement-based epoxy coatings as steel primers based on the field and laboratory data developed in this study.

Chloride diffusion models for plain and blended cement concretes exposed to laboratory and atmospheric marine conditions

Chloride-induced corrosion of steel in a reinforced concrete structure compromises its safety and may decrease the designed service-life. The initiation and the rate of reinforcement corrosion mainly depends on the diffusion of chloride ions to the surface of the steel bars. As such, it is important to determine the coefficient of apparent chloride diffusion (Da) for the type of concrete to be used in a structure, which is time-consuming. Therefore, the development of a short-term and simple procedure to predict Da is highly desirable. This study was conducted to develop a correlation between the short-term chloride migration coefficient (Dnssm) and long-term Da for Type I, Type V and pozzolanic cement concretes. Two groups of concrete specimens, each consisting of five concrete mixtures designed with a w/b ratio of 0.4, were prepared. The first group was exposed to a marine exposure site for 10 years and Da was evaluated after 1, 2, 5 and 10 years. The second group was tested according to NT BUILD 492 under laboratory conditions to determine the short-term Dnssm. Correlation models between the field and laboratory results were developed and statistically validated by comparing the predicted values with the measured ones. The predicted Da values are within ±7% of the measured values. Further, the Dnssm of pozzolanic cement concretes is 2.20–4.40 and 3.55 to 7.30 times less than that of Type I and Type V cement concretes, respectively. The developed models can be utilized to assess the long-term Da by determining the short-term Dnssm.

Chloride diffusion models for Type I and fly ash cement concrete exposed to field and laboratory conditions

The exposure temperature significantly affects the diffusion of chloride ions in concrete, and, as such, it must be taken into consideration in the development of service-life prediction models for structures exposed to chloride-bearing environments. Most of the earlier studies have used cement paste to assess the effect of exposure temperature on chloride diffusion. In the reported study, chloride diffusion in Type I and fly ash (20% fly ash) cement concrete was evaluated under field and laboratory conditions. The laboratory concrete specimens were exposed to chloride solution maintained at four temperatures (22, 35, 50 and 60 °C) for 365 days. Beam specimens were exposed in the tidal zone of a marine exposure site, along the Arabian Gulf coast, for up to 10 years to study the chloride diffusion in the field specimens. The coefficient of chloride diffusion (Da) in the concrete specimens exposed to 22 or 35 ᵒC in the laboratory was less than that in the concrete specimens exposed to 50 and 60 ᵒC. The Da for Type I cement concrete specimens increased by 3.6 times as the temperature was increased from 22 to 60 ᵒC while this increase was 2.3 times for the fly ash cement concrete specimens for a similar increase in the temperature. The Da decreased with the period of exposure in the field specimens. The values of activation energy that can be used for predicting the chloride diffusion for exposure temperature within the range of 22–60 °C were developed based on the laboratory data. In addition, mathematical models were developed relating the coefficient of chloride diffusion in the field and laboratory concrete specimens. The developed models can be utilized to ascertain chloride diffusion in field specimens, utilizing the laboratory values, and hence calculate the useful service-life of structures.

Field Validation of Concrete Transport Property Measurement Methods.

Reinforcing steel corrosion, caused by chloride ingress into concrete, is the leading cause of reinforced concrete deterioration. One of the main findings in the literature for reducing chloride ingress is the improvement of the durability characteristics of concrete by the addition of supplementary cementitious materials (SCMs) and/or chemical agents to concrete mixtures. In this study, standard ASTM tests—such as rapid chloride permeability (RCPT), bulk diffusion and sorptivity tests—were used to measure concrete properties such as porosity, sorptivity, salt diffusion, and permeability. Eight different mixtures, prepared with different SCMs and corrosion inhibitors, were tested. Apparent and effective chloride diffusion coefficients were calculated using bound chloride isotherms and time-dependent decrease in diffusion. Diffusion coefficients decreased with time, especially with the addition of SCMs and corrosion inhibitors. The apparent diffusion coefficient calculated using the error function was slightly lower than the effective diffusion coefficient; however, there was a linear trend between the two. The formation factor was found to correlate with the effective diffusion coefficient. The results of the laboratory tests were compared and benchmarked to their counterparts in the marine exposure site in the Arabian Gulf in order to identify laboratory key tests to predict concrete durability. The overall performance of concrete containing SCMs, especially fly ash, were the best among the other mixtures in the laboratory and the field.

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.

Performance of rapid-repair concrete in an aggressive marine environment

Rapid-repair concretes are currently used to repair structures such as bridge decks, substructure elements on bridges (e.g. piers and columns), pavements, and components of buildings. Rapid-repair concretes must not only achieve a high-early strength in a short period of time (e.g. 20MPa in 3h) but must also survive for the remaining life of the structure. One way of achieving high early-age strength is the use of ettringite-based cements; in these cements early strength is attributed to the rapid formation of ettringite by incorporating, in the binder, calcium sulfo-aluminate cement or a combination of calcium aluminate cement and calcium sulfate. Although research has proven that early-strength is achievable, there exist limited published durability data for these systems. This paper presents data on the performance of a number of rapid-repair materials placed at the high-tide level of a marine exposure site (Treat Island, Maine, USA) which experiences approximately 100 freeze-thaw cycles a year making it one of the harshest environments for concrete in the world. A number of concretes were studied including an ordinary Portland cement (PC) and a high-early strength Portland cement (HEPC) as references, PC accelerated by calcium aluminate cement (CAC) with calcium sulfate (C$), PC accelerated by calcium sulfo-aluminate (C$A(2)-PC), and calcium sulfo-aluminate belite (C$A(1)-C2S) cement on its own. Reinforced concrete specimens were monitored on a yearly basis to evaluate the corrosion condition of the steel. After three years of exposure, reinforced concrete beams from each mix were returned to the laboratory to determine chloride profiles, and to conduct X-ray diffraction (XRD) and microstructural investigation using scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDS) analysis.

Lessons Learned from the Treat Island Marine Exposure Site

The marine exposure site on Treat Island near Eastport, Maine, was built more than 75 years ago and during this period a wide range of concrete types have been placed on the site. Treat Island represents a very severe exposure condition with the highest tides in the world, salinity typical of the Atlantic Ocean and approximately 100 freeze-thaw cycles per annum. The various research programs that have used this facility have investigated the effects of numerous parameters including fibre-reinforcement, polymer-impregnation, supplementary cementing materials, sulfur concrete, high-alumina cement, ettringite-based rapid-set binders, w/cm and strength, ultra-high-performance concrete, corrosion-resistant reinforcement, impact of load and cracking, “mechanical air-entrainment”, and use of corrosion-inhibiting admixtures. Performance has been evaluated in a number of ways including visual assessment, pulse velocity, dynamic modulus, chloride profiling, and electro-chemical corrosion monitoring. The paper presents an overview of “lessons learned” with detailed information on factors affecting the rate of chloride ingress.

Development of a New Concrete Marine Exposure Site on the Arabian Gulf-East Coast of Saudi Arabia

A concrete durability site in the Eastern Province of Saudi Arabia that exposes Saudi concrete to harsh marine conditions on the Arabian Gulf and salty air conditions was constructed. The site contains 32 concrete blocks formed from eight different mixtures made with Cement Type I, Cement Type V, Cement Type I with 6% silica Fumes, 25% fly Ash, 70% Ground-granulated blast-furnace slag (GGBFS), Migrate Corrosion Inhibitors (MCI), Calcium Nitrite based inhibitors (CNI) and Caltite. Each mixture formed 4 blocks; 2 were reinforced with black steel and two were plain concrete. The concrete blocks were 1200 mm high, 460 mm wide and 230 mm thick placed vertically. The concrete blocks were placed at three zones to achieve different exposure conditions which are atmospheric, splash or spray zone and tidal zone. Samples will be taken periodically to measure the rate of chloride ingress in each concrete mixture under the different exposure conditions. Embedded steel reinforcement in specimens in atmospheric zone have not recorded corrosion activities at six months of exposure. The steel bars in three zones will be monitored for corrosion activity through linear polarization test. The measured chloride profiles in the exposure site will be compared to the measured concrete transport properties from the companion laboratory specimens. Standard compressive test and bulk diffusion test were conducted for 150x300 mm and 75x150 standard cylinders, respectively. All of the cylinders’ strength exceeded the designed compressive strength of 28 MPa. Whereas for 35 days standard bulk diffusion test, mix contained 100% cement type I had the least chloride concentration, and mix 5 that had 70% GGBFS and 30% cement type I had the highest surface chloride concentration. Overall chloride profiles for all the mixes were within ranges reported in literature. Further tests of chloride binding capacity and bulk diffusion for different intervals will be undertaken.

Developments in Performance Monitoring of Concrete Exposed to Extreme Environments

AbstractThe performance of the surface zone of concrete is acknowledged as a major factor governing the rate of deterioration of reinforced concrete structures because it provides the only barrier to the ingress of water containing dissolved ionic species such as chlorides, which ultimately initiate corrosion of the reinforcement. In situ monitoring of cover-zone concrete is therefore critical in attempting to make realistic predictions as to the in-service performance of the structure. To this end, this paper presents developments in a remote interrogation system to allow for continuous, real-time monitoring of the cover-zone concrete from an office setting. Use is made of a multi electrode array embedded within cover-zone concrete to acquire discretized electrical resistivity and temperature measurements, with both parameters monitored spatially and temporally. On-site instrumentation, which allows for the remote interrogation of concrete samples placed at a marine exposure site, is detailed together wi...

Performance of lightweight aggregate concrete containing slag after 25 years in a harsh marine environment

This paper reports the results of a study on concretes containing lightweight aggregate (LWA) retrieved from the tidal zone of a marine exposure site. In terms of chloride resistance, the LWA concrete performed equivalently to similar concretes of the same age produced with normal density aggregate that were retrieved from the same site 2years earlier. The partial replacement of Portland cement with slag led to substantial reductions in chloride penetration and the chloride diffusion coefficient. However, at w/cm≥0.50, the incorporation of slag resulted in increased surface deterioration (scaling) attributed to freezing and thawing. Concrete with LWA, silica fume and w/cm=0.33, showed better-than-expected performance with regard to resistance to chloride-ion penetration and it is speculated that this may be partly attributed to “internal curing” provided by the LWA which reduces the impact of self desiccation. Further studies are needed to confirm this phenomenon.

Influence of climatic factors in cyclic accelerated corrosion test towards the development of a reliable and repeatable accelerated corrosion test for the automotive industry

AbstractTwo designs of experiments made of nine accelerated tests each were used in order to study the influence of a selection of important climatic parameters such as the concentration of NaCl, the drying level, the basic humidity cycle, the frequency of salt spray and the temperature. The accelerated corrosion tests were all performed using automatic chambers. Different automotive materials were selected in order to study the resistance to cosmetic corrosion, perforation corrosion and bi‐metallic corrosion. For cosmetic materials, coated panels of cold rolled steel (CRS), zinc‐coated steel and aluminium alloys were chosen. Perforation corrosion was investigated using crevice panels of CRS, zinc‐coated steel or different grades of aluminium alloys. From the results, the influence of testing conditions on the cosmetic and perforation corrosion of different automotive materials was obtained. As an example, it was shown that an elevation of the temperature from 35 to 45 °C in the cyclic corrosion test increased the scribe creep on painted CRS and aluminium alloys while it has no significant effects on painted hot dip galvanized (HDG) panels. The results were also compared to that obtained after 2 years of exposure at a marine exposure site and on busses driving in area using de‐icing salt. It was shown that one of the tests performed gives a good correlation to field results.

Performance of pfa concrete in a marine environment––10-year results

Abstract Steel reinforced 100×100×300 mm concrete prisms, with nominal strength grades C25, C35 and C45 and different pfa levels (0–50%), were exposed to various curing treatments during the first 28 days prior to exposure in the tidal zone of the BRE marine exposure site. Chloride concentration profiles and rebar weight losses had previously been measured on specimens exposed for 1, 2 and 4 years and this paper reports the results of similar measurements after 10 years exposure. Chloride profiles were also measured for specimens after 1 and 28 days immersion in seawater under laboratory conditions. Pfa concretes showed substantially increased resistance to the penetration of chlorides compared with control Portland cement (PC) concrete specimens. The improved resistance of the pfa concrete to the penetration of chlorides resulted in reduced corrosion of steel bars imbedded in the concrete. Threshold chloride levels for corrosion, estimated from relationships between steel weight loss and chloride content at the location of the steel, were found to decrease with increasing pfa content. Chloride concentration profiles after 28 days of immersion in seawater showed that considerable chloride penetration occurred during this period due to sorption (capillary suction) of the seawater into the unsaturated specimens. This results in a significant error in diffusion coefficients calculated from the concentration profile using the standard solution to Fick’s second law. The error may be substantial for pfa concretes where chlorides penetrating due to sorption immediately after exposure may outweigh subsequent diffusion during continued seawater exposure. The performance of the concretes, particularly the PC concretes, in this programme is considered in the light of current and new British Standard recommendations for concrete exposed to marine tidal conditions. The adequacy of these recommendations is, however, difficult to assess because the highest concrete quality tested fell a little short of the minimum quality required in the recommendations and cover to reinforcement was also less than required. Nevertheless, the superior performance of concretes containing 30% or more pfa was clearly demonstrated.

Natural marine exposure results for reinforced concrete slabs with corrosion inhibitors

Reinforced concrete slabs were cast with a concrete cover of 20 mm. The water-to-cement ratio was 0.40, and the concrete slabs were either uncracked or precracked. A simulated crack 0.2 or 0.4 mm wide was formed transverse to the axis of the reinforcing bar during the casting. Two types of commercial corrosion inhibitors were added to concrete mixtures for corrosion protection. Slabs were placed about 1 m below high tide at the Treat Island, Maine, USA, natural marine exposure site. The specimens were visually inspected and the corrosion rates were measured annually using the linear polarization technique. Some of the concrete slabs were broken open after 12 months of exposure and corrosion damage was evaluated. Water-soluble chloride content analysis was performed at this time. After three years of exposure, it was found, that both corrosion inhibitors were effective in reducing the corrosion rate for uncracked concrete slabs, but relatively ineffective in preventing localised corrosion of reinforcing steel in the crack area for precracked concrete slabs.

Paint undercutting accelerated test (PUCAT)—test development and mechanistic information

Undercutting is paint film blistering resulting from accelerated corrosion of the metallic coating on painted ZINCALUME ® (55% Al-Zn alloy coating on a steel substrate) or galvanized steel. It is caused by galvanic coupling of the metallic coating and steel substrate at an exposed edge, causing a crevice under the paint film. Once the crevice has formed, undercutting can continue by a crevice corrosion mechanism. This paper describes the development of a laboratory Paint UnderCutting Accelerated Test (PUCAT), in two versions—full immersion and cyclic (wet/dry) PUCAT. The relative importance of galvanic cell and crevice corrosion mechanisms is discussed for these tests, the ASTM standard salt spray test and for an atmospheric severe marine exposure site along with types of paint film blister pattern and corrosion of the metallic coating. It is shown that the salt spray cabinet is the most aggressive, with indications that the crevice corrosion mechanism becomes dominant for ZINCALUME. Full immersion PUCAT and cyclic PUCAT are not as aggressive as the salt spray test, but can be designed to be of similar aggressiveness to each other. Cyclic PUCAT results in a finer paint film blister pattern than either full immersion PUCAT or the salt spray test, and more closely resembles that which occurs at the atmospheric severe marine exposure site. Indications are that the crevice corrosion mechanism operates to a greater extent in full immersion PUCAT than in cyclic PUCAT. Cyclic PUCAT is the most appropriate test for reproducing undercutting in the laboratory.

Marine performance of PFA concrete

Results are presented from a study of the performance of reinforced concrete in a marine environment. Reinforced concrete specimens from three series of concrete mixes of nominal strength grades C25, C35 and C45 and with a range of PFA levels (0–50%) were placed in the tidal zone of the BRE marine exposure site. Measurements of reinforcement weight loss and chloride ion penetration were carried out on the specimens after two years' exposure. The results indicate that chloride ion penetration during early exposure is controlled by sorptivity rather than diffusion, and predictions of diffusion coefficients derived from chloride concentration profiles are not valid. No significant increase in the chloride content at depths below 10 mm were observed between one and two years for concretes containing 30% or more PFA, whereas substantial increases were observed for the OPC control concretes. The PFA concretes were far more resistant to the penetration of chloride ions than the OPC concretes and consequently corrosion of steel reinforcement was reduced in the PFA concrete. It is concluded from results to two years that in marine conditions PFA concrete provides much improved protection to steel reinforcement, compared with OPC concrete of equal strength grade, cementitious content (OPC + PFA) or water–cementitious ratio. Further assessments will be carried out after 5 and 10 years exposure. These results are discussed in the context of current specifications for concrete exposed to marine conditions.

Properties of concretes made with various types of cements

Rapid-repair concretes are currently used to repair structures such as bridge decks, substructure elements on bridges (e.g. piers and columns), pavements, and components of buildings. Rapid-repair concretes must not only achieve a high-early strength in a short period of time (e.g. 20 MPa in 3 h) but must also survive for the remaining life of the structure. One way of achieving high early-age strength is the use of ettringite-based cements; in these cements early strength is attributed to the rapid formation of ettringite by incorporating, in the binder, calcium sulfo-aluminate cement or a combination of calcium aluminate cement and calcium sulfate. Although research has proven that early-strength is achievable, there exist limited published durability data for these systems. This paper presents data on the performance of a number of rapid-repair materials placed at the high-tide level of a marine exposure site (Treat Island, Maine, USA) which experiences approximately 100 freeze-thaw cycles a year making it one of the harshest environments for concrete in the world. A number of concretes were studied including an ordinary Portland cement (PC) and a high-early strength Portland cement (HEPC) as references, PC accelerated by calcium aluminate cement (CAC) with calcium sulfate (C$), PC accelerated by calcium sulfo-aluminate (C$A(2)-PC), and calcium sulfo-aluminate belite (C$A(1)-C2S) cement on its own. Reinforced concrete specimens were monitored on a yearly basis to evaluate the corrosion condition of the steel. After three years of exposure, reinforced concrete beams from each mix were returned to the laboratory to determine chloride profiles, and to conduct X-ray diffraction (XRD) and microstructural investigation using scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDS) analysis.