Richard E. Weyers

Probabilistic model for the chloride-induced corrosion service life of bridge decks

Abstract A statistical model to determine the time to first repair and subsequent rehabilitation of concrete bridge decks exposed to chloride deicer salts that incorporates the statistical nature of factors affecting the corrosion process is developed. The model expands on an existing deterministic model using statistical resampling techniques. Emphasis was placed on the diffusion portion of the diffusion-cracking model. Data collected for the time for corrosion deterioration after corrosion initiation can be readily incorporated into the model. Data for the surface chloride concentration, apparent diffusion coefficient and clear cover depth were collected from 10 bridge decks built in Virginia. Several ranges of the chloride corrosion initiation concentration, as determined from the available literature, were investigated. The resampling techniques known as the simple and parametric bootstrap were used to predict time to first repair and rehabilitation based on the observed field data. The two methods provide results that substantially agree for all decks investigated.

Impact of specification changes on chloride-induced corrosion service life of bridge decks

Abstract A model was developed to determine the time to first repair and to subsequently rehabilitate concrete bridge decks exposed to chloride deicer salts. Said model incorporates the statistical nature of factors affecting the corrosion process. The time to first repair and rehabilitate was predicted for 10 bridge decks built in Virginia between 1981 and 1994. The model was validated using historical service life data for 129 bridge decks built in Virginia between 1968 and 1972. The time for rehabilitation predicted for the newer set of bridge decks was approximately 13 years longer than the normalized time for rehabilitation projected for the older bridge decks. The increase in time for rehabilitation for the newer set of bridge decks was attributed to a reduction in the specified maximum water/cement ratio and increase in clear cover depth. The probabilistic model is shown to be an advancement over the deterministic model currently in use.

ESTIMATING THE SERVICE LIFE OF EPOXY-COATED REINFORCING STEEL

Corrosion protection performance of fusion bonded epoxy-coated reinforcing steel (FBECR) was evaluated in chloride doped simulated concrete pore water solutions and field structures. Results demonstrate that a different corrosion protection failure mode exists in the field than in short-term laboratory studies. In laboratory studies, the chloride is at the bar surface area immediately and the degree of corrosion protection is a function of the quality of the coating. In field structures, the epoxy coating debonds from the steel in moist-wet concrete. The rate of epoxy debondment and the chloride increase at the bar depth determine if the chloride corrosion threshold limit is reached before or after the epoxy debonds. If the coating is debonded when the chlorides reach the corrosion threshold limit, corrosion takes place under the coating in an acidic environment and the corrosion protection of FBECR is nil. In Virginia, FBECR may provide protection for approximately 5% of the bridge decks and thus FBECR is not a cost-effective corrosion protection system for Virginia bridges.

Field Investigation of Corrosion-Protection Performance of Bridge Decks Constructed with Epoxy-Coated Reinforcing Steel in Virginia

The corrosion-protection performance of epoxy-coated reinforcing steel (ECR) in three 17-year-old bridge decks in Virginia was assessed. The decks had an upper mat of ECR and a lower mat of bare steel. Surface cracking in the right traffic lane was visually surveyed and 12 cores randomly located in the lowest 12th percentile cover depth in each deck were drilled. The concrete core and the extract ECR were visually inspected. In the concrete moisture content, absorption, percent saturation, carbonation depth, and the effective chloride diffusion constant were measured. In the ECR physical damage, coating thickness, adhesion loss and corrosion at damaged sites, and undercoating corrosion at adhesion test sites were measured. The chloride content of the concrete and carbonation of the ECR trace were determined. Significant coating adhesion loss occurred before the chloride arrived at the bar depth. The debonding of the epoxy is wet debonding, which is predicted by the negative thermodynamic work of adhesion. ECR will extend the service life of only 5 percent of the bridge decks in Virginia. Thus, its use is not cost-effective. Additional decks should be evaluated to confirm the results of this and other studies.

Chemical Treatment of Corroding Steel Reinforcement After Removal of Chloride-Contaminated Concrete

Abstract The increasing use of deicing salts on bridge decks has accelerated their deterioration due to chloride-induced corrosion of steel reinforcement, which causes cracking and spalling. One method being considered as a possible corrosion abatement measure is the removal of chloride-contaminated concrete followed by chemical treatment of the partially exposed rebar through ponding and/or placement of chemically treated mortar. Several commercial and experimental corrosion inhibitors were evaluated in order to determine the most effective corrosion treatment when applied in conjunction with removal of chloride-contaminated concrete. The performances of the inhibitors were evaluated in an accelerated test program. Based on post-treatment electrochemical measurements, calcium-nitrite-based corrosion inhibitor was most effective when applied as a ponding and when placed in backfilled mortar. Several other inhibitors were also sufficiently effective and were recommended for further evaluation in large-scal...

EFFECT OF CORROSION-INHIBITING ADMIXTURES ON MATERIAL PROPERTIES OF CONCRETE

Several commercially available admixtures have been introduced to inhibit the onset of chloride-induced corrosion of concrete reinforcement. Properties such as workability, set time, strength gain, permeability, and interaction with other admixtures are of concern to ensure proper placement and long-term durability. This paper examines the influence on placement and material properties of a series of commercially corrosion-inhibiting admixtures under laboratory evaluation. Admixture performance was assessed within concrete specimens, relative to the potential for positive or negative effects on characteristic concrete properties. Such properties include slump, air content, heat of hydration, compressive strength, and electrical indication of chloride ion permeability, as well as measured chloride diffusion. The performance of each admixture is discussed, relative to the interrelationships between observed test results.

Comparison of guarded and unguarded linear polarization CCD devices with weight loss measurements

Abstract Two types of linear polarization devices may be used to measure the corrosion current density (CCD) to assess the degree of active corrosion in concrete structures. The devices, with and without a guard electrode, provide significantly different CCD values for the same conditions. The 5-year study reported herein presents a comparison of the two devices over a range of CCD values from passive to highly active corrosion conditions for outdoor exposure slabs. The results demonstrate that both devices are able to qualitatively rank the instantaneous corrosion conditions in structures. The guarded electrode device measurements were less quantitatively precise than the unguarded electrode device. The guarded electrode device underestimated the amount of metal loss by a factor of 4–6. The unguarded electrode device overestimate the metal loss by a factor of about 1.5 when compared to weight loss measurements and adjusted for concrete temperature and resistance.

Validation of Probability-Based Chloride-Induced Corrosion Service-Life Model

The deterioration of bridge decks due to chloride-induced corrosion is a major problem in North America. Chlorides are primarily the result of deicing salt applications on the bridge deck surface. The ingress of chlorides into concrete is typically modeled using Ficks second law of diffusion. Previous service-life models have taken a deterministic approach to estimating chloride diffusion. A recent project, however, developed a service-life model that incorporates the probabilistic nature of the diffusion parameters by using Monte Carlo statistical resampling techniques. This paper validates the probabilistic service-life model using data gathered from 10 bare steel bridge decks constructed in Virginia between 1965 and 1968.

Corrosion inhibiting repair and rehabilitation treatment process for reinforced concrete structures

A repair and rehabilitation treatment process for reinforced concrete structures involves the removal of concrete from above rebar or other metal reinforcement material in the concrete structure. After removal of concrete, the metal reinforcement materials are saturated with corrosion inhibiting agents. Saturation is best achieved by multiple spray applications of the corrosion inhibitor. The cavity in the concrete structure with the treated rebar or other metal reinforcement materials is then backfilled and/or overlaid with repair concrete. Preferably, the repair concrete includes corrosion inhibitors which will diffuse to the rebar over time or is a low permeability concrete that reduces the rate of diffusion of chloride corrosion causing agents to the rebar. The repair and rehabilitation process significantly increases the concrete structures service life.

Modeling the Measured Time to Corrosion Cracking

The deterioration models for reinforced concrete structures include a period for time to corrosion cracking: time from initiation of corrosion to first cracking. Theoretical equations for determining the time to corrosioncracking have been presented but never validated. This paper reports on a study which was initiated to validate or modify a set of theoretical equations for field linear polarization, unguarded and guarded, corrosion rate devices. The test variables included six corrosion rates, two concrete cover depths, two reinforcing steel bar diameters and spacings, two exposure conditions (indoors and outdoors), and one design concrete strength (water to cement ratio). Influence of temperature and chloride content on the measured corrosion rates are presented. Corrosion rates increase with increasing chloride content and corrosion rates vary significantly with annual changes in temperature, highest in the spring and lowest in the winter. Measured metal loss measurements were compared with the calculated metal loss based on monthly corrosion rate measurements for both devices. The 3LP device significantly over-estimated the amount of metal loss and the Geocor 3 device significantly under-estimated the amount of metal loss based on average monthly measurements. The theoretical time to corrosion cracking equations significantly under-estimated the time to corrosion cracking using a uniform corrosion rate based on the measured metal loss.