Performance of Multiple Corrosion Protection Systems for Reinforced Concrete Bridge Decks

The performance of corrosion protection systems for reinforcing steel in concrete is evaluated. In addition to conventional and conventional epoxy-coated reinforcement, the corrosion protection systems tested include epoxy coatings with improved adhesion to the underlying steel, conventional and conventional epoxy-coated reinforcement used in conjunction with concrete containing one of three corrosion inhibitors, DCI-S, Rheocrete 222+, or Hycrete, epoxy-coated reinforcement with a microencapsulated calcium nitrite primer, multiple-coated reinforcement with a layer of zinc between the epoxy and steel, and pickled 2205 duplex stainless steel. The systems are evaluated using bench-scale and field tests. Two bridges in Kansas, cast with 2205 stainless steel, are monitored using corrosion potential mapping. Epoxy-coated and multiple-coated bars are evaluated to determine the effect of corrosion loss and time on the disbondment of the epoxy coating. Conventional, galvanized, and epoxy-coated reinforcement are evaluated using impressed current to determine the corrosion loss required to crack concrete for each system. A finite element model is developed to represent general and localized corrosion, and the results are used to develop a relationship between concrete cover, bar diameter, and area of bar corroding, and the corrosion loss required to crack concrete. An analysis of pore solutions expressed from cement pastes containing corrosion inhibitors is performed, with pH and selected ion concentrations measured from solutions collected one and seven days after casting. The results obtained from bench-scale and field test specimens are used to estimate cost effectiveness for each system under a 75-year service life. The results show epoxy coatings significantly reduce the corrosion rate compared to conventional reinforcement. Corrosion inhibitors significantly reduce corrosion rates in uncracked concrete. In cracked concrete, corrosion inhibitors also reduce corrosion rates, but their relative effectiveness is reduced. Specimens containing Hycrete exhibit the lowest corrosion rates; however, field specimens containing Hycrete also show signs of scaling. Epoxies with improved adhesion exhibit no improvement over conventional epoxy-coated reinforcement in terms of corrosion rate or disbondment of the epoxy coating. Multiple-coated reinforcement exhibits significantly less disbondment than epoxy-coated reinforcement. Pickled 2205 reinforcement exhibits the least corrosion among all systems tested. Testing of conventional and galvanized reinforcement indicates galvanized reinforcement requires more than twice as much corrosion loss to crack the surrounding concrete compared to conventional reinforcement. An analysis of pore solution extracted from cement pastes containing inhibitors indicates an elevated sulfate content in pore solution collected from specimens containing Hycrete. Increased sulfate levels may explain the reduced strength and critical chloride corrosion threshold observed in concrete containing Hycrete. Elevated sulfate levels are also observed in pore solutions collected 7 days after casting from cement paste containing Rheocrete. An economic analysis of a 0.216-m (8.5-in.) thick bridge deck over a 75-year design life indicates that corrosion protection systems using either coated or stainless steel reinforcement are significantly more cost-effective than any of the systems containing conventional reinforcement.

Rapid Macrocell Tests of 2304 and XM-28 Reinforcing Bars

The corrosion resistance of 2304 and XM-28 stainless steel bars, produced by a single mill and supplied by a single supplier, was evaluated using the rapid macrocell test outlined in Annexes A1 and A2 of ASTM A955-12. Bars were tested both before and after undergoing mechanical straightening. Based on the test results, the stainless steel bars satisfy the requirements of ASTM A955-12. The straightening process allowed corrosion to initiate on the bars, but had limited to no effect on the macrocell corrosion rate

Rapid Macrocell Tests of 2205 and XM-28 Reinforcing Bars

The corrosion resistance of 2205 and XM-28 stainless steel bars from two producers and provided by a single supplier was tested in accordance with Annexes A1 and A2 of ASTM 955-12. Three heats of stainless steel were tested: XM-28 stainless steel from producer A, 2205 stainless steel from producer B, and XM-28 stainless steel, also from producer B. The bars from producer A were supplied in two conditions, as cut from the coil and after having been straightened, while the bars supplied by producer B were rolled straight. The XM-28 stainless steel bars satisfied the requirements specified in Annexes A1 and A2 of ASTM 955. The 2205 stainless steel bars did not satisfy the requirements specified in Annexes A1 and A2 of ASTM 955, exhibiting individual corrosion rates greater than 0.50 μm/yr and an average corrosion rate greater than 0.25 μm/yr. The process of straightening coiled stainless steel reinforcement damages the transverse deformations of the bars and can leave deposits, either of which can serve as initiation sites for corrosion

Graffiti Resistance of Wax-based and Epoxy-based Coatings on Steel and Concrete Substrates

The graffiti resistance of two coatings developed by MicroCor Technologies, Inc. – MicroCor-300 and MicroCor-500 – was analyzed on steel and concrete substrates. The coatings were tested in accordance with ASTM D6578 Standard Practice for Determination of Graffiti Resistance and ASTM D7089 Standard Practice for Determination of the Effectiveness of Anti-Graffiti Coating for Use on Concrete. Masonry and Natural Stone Surfaces by Pressure Washing. In addition, the coatings were evaluated for time of set (ASTM D1640) and chemical resistance (ASTM D1308). Of the two coatings, MicroCor-300 demonstrated better overall graffiti resistant qualities on both steel and concrete surfaces but was not as durable as MicroCor-500. Therefore, MicroCor-300 should be reapplied after each cleaning cycle for its graffiti resistant qualities to remain effective.Research was sponsored by MicroCor Technologies, Inc

Durability, Construction, and Early Evaluation of Low-Cracking High-Performance Concrete (LC-HPC) Bridge Decks

Laboratory evaluations of concrete mixtures based on specifications for low-cracking high-performance concrete (LC-HPC) incorporating internal curing (IC) and supplementary cementitious materials (SCMs) are described. In addition, the development, construction, and evaluation of four IC-LC-HPC bridge decks with IC provided by pre-wetted fine lightweight aggregate (FLWA) in conjunction with a partial replacement of portland cement with slag cement are described along with the evaluation of two Control decks without IC constructed in accordance with standard high-performance concrete (HPC) specifications in Minnesota. Bridge decks containing IC provided by pre-wetted FLWA and SCMs are also evaluated, including two bridge decks in Utah with a partial replacement of portland cement with Class F fly ash and six bridge decks in Indiana, four with IC and a partial replacement of portland cement with silica fume and either slag cement or Class C fly ash constructed in accordance with Indiana HPC specifications (IN-IC-HPC), one with IC and portland cement as the only binder, and one Control without IC. The laboratory evaluations were performed on three groups of concrete mixtures, one for each for the first three years of IC-LC-HPC bridge deck construction in Minnesota. Variations in IC-LC-HPC mixture proportions include the amount of IC water (contents ranging from 0 to 14.1% by total weight of binder), total absorbed water content (IC water from the FLWA plus water absorbed by the normalweight coarse and fine aggregates ranging from 2.9 to 17.7% by total weight of binder), water-to-cementitious material (w/cm) ratios ranging from 0.39 to 0.45, and binder compositions examining the effects of using only portland cement, a 35% Class F fly ash replacement of portland cement, 27 to 30% slag cement replacements of portland cement, and a 2% addition of silica fume of cement for the mixtures containing 27 to 28% slag cement, all by total weight of binder. Tests for scaling resistance, freeze-thaw durability, rapid chloride permeability (RCP), and surface resistivity measurements (SRMs) were completed. The scaling resistance of the IC-LC-HPC mixtures was affected most by the air content, with mixtures having an air content below 7% exhibiting more mass loss than similar mixtures with more than 7% air. Including IC and slag cement did not negatively affect scaling resistance. Freeze-thaw durability was affected most by the total absorbed water content, with increases in absorbed water leading to a decrease in freeze-thaw durability. RCP and SRM results were affected most by the binder composition (specifically, including a partial replacement of portland cement with slag cement). Experiences and lessons learned during the construction of the first four IC-LC-HPC bridge decks along with the failed placement of one deck indicate that the primary aspects of successfully implementing IC with LC-HPC include determining the moisture content of the FLWA shortly before batching and adjusting mixture proportions to maintain the target quantity of IC water (based on the FLWA absorption). Evaluation of the IC-LC-HPC decks and IN-IC-HPC decks demonstrate that low cracking can be achieved for concrete containing IC and SCMs as long as the paste content (volume of cementitious materials and water) is kept below 26%. An overlay with a paste content of 34.3% on one of the IC-LC-HPC decks exhibited high cracking within the first two years after placement. The two IC decks in Utah and one IC deck in Indiana with paste contents of 28% and 27.6%, respectively, also had high cracking. Durability issues in the form of scaling and aggregate popouts were observed during surveys of the IN-IC-HPC decks; the decks had higher IC water contents than planned (leading to a high total absorbed water content), lower air contents than the IC-LC-HPC decks, and late-season placement dates that provided minimal time for the concrete to dry prior to being exposed to freezing conditions.ACI FoundationCONSTRUCTION OF LOW-CRACKING HIGH-PERFORMANCE BRIDGE DECKS INCORPORATING NEW TECHNOLOGY TRANSPORTATION POOLED-FUND PROGRAM PROJECT NO. TPF-5(336

Corrosion Performance of Plain and Epoxy-Coated MMFX Bars

The corrosion resistance of ASTM A1035 Type CL (2% Cr), CM (4% Cr), and CS (9% Cr) steel bars produced by MMFX Technologies were evaluated in both cracked and uncracked concrete as well as in the rapid macrocell test. Uncoated bars with 4% and 9% chromium were tested both in the condition received and after pickling at the University of Kansas; coated bars with 2% and 4% chromium were also evaluated after simulating damage typical to that which would occur during normal handling and placement at a construction site. Bars were compared to the performance of conventional (ASTM A615) and epoxy-coated (ASTM A775) reinforcement from previous studies, and a life-cycle cost analysis over a 75-year design life was performed. The uncoated MMFX bars with 4% and 9% chromium exhibited approximately three times the chloride threshold and between 30-66% of the corrosion rate of uncoated conventional reinforcement, with the 9% chromium bars exhibiting better performance than the 4% chromium bars. Pickling of 9% chromium bars significantly improved its corrosion resistance, while pickling the 4% chromium bars provided only mild benefit. Both epoxy-coated bars tested (2% and 4% chromium) exhibited reduced disbondment of the coating at the end of testing compared to conventional epoxy-coated reinforcement. The 4% chromium coated bars also exhibited significantly lower corrosion rates relative to conventional epoxy-coated reinforcement, with corrosion rates between 15 and 30% of that of conventional ECR. Coated bars with 2% chromium performed comparably or slightly better than conventional epoxy-coated reinforcement (depending on the test method), but the differences were not statistically significant. The life-cycle cost analysis found that epoxy-coated MMFX with 4% chromium was the most cost-effective reinforcement of the bars in this study.MMFX Technologies, Inc

Anchorage Strength of Standard Hooked Bars in Simulated Exterior Beam-Column Joints

The current ACI hooked bar design provisions are based on test results of 38 simulated beam-column joints containing two hooked bars. The provisions address the effects of hooked bar surface condition, concrete cover, amount of confining reinforcement confining the hooks, and type of concrete (normalweight or lightweight). This study uses results of 338 simulated beamcolumn joint specimen tests at the University of Kansas, including two, three, or four No. 5, 8, or 11 (No. 16, 25, or 36) hooked bars with 90° or 180° hooks, along with 61 tests by others to investigate the effects of hooked bar spacing, anchoring the hooked bars outside the column core or halfway through the column depth, concrete tail cover to 90° hooks, and the effect of tail kickout at failure on hooked bar anchorage strength. In the tests performed at the University of Kansas, the center-to-center spacing between hooked bars ranged from 3 to 12 bar diameters, hooked bars were placed inside or outside column core, and hooked bars were extended to the far side of the column core or extended halfway through the column depth. Hooked bars had nominal embedment lengths ranging from 2.5 to 25.2 in. (64 to 640 mm), nominal concrete side cover ranging from 1.5 to 4 in. (38 to 100 mm) in simulated beam-column joints and 11.3 to 24.6 in. (287 to 625 mm) in walls, and nominal concrete tail cover to the hook ranging from 2 to 18 in. (50 to 460 mm). Concrete compressive strength ranged from 4,300 to 16,510 psi (30 to 114 MPa) in simulated beam-column joints and 2,400 to 5,450 psi (17 to 38 MPa) in walls, and bar stresses at anchorage failure ranged from 27,100 to 141,000 psi (187 to 972 MPa) in simulated beam-column joints and 14,200 to 60,000 psi (98 to 420 MPa) in walls. The results show that the center-to-center spacing between hooked bars plays a role in anchorage strength up to a spacing of seven bar diameters. The closer the bars, the lower the anchorage strength per bar, in contrast with the total anchorage strength, which remains constant or increases moderately as the number of hooked bars in a joint increases. The presence of confining reinforcement mitigates the effect of close spacing but does not eliminate it. Hooked bars placed outside the column core or anchored halfway through the column depth exhibit low anchorage strength when compared to hooked bars placed inside the column core or extended to the far side of the column. The reduction in anchorage strength ranges from 4 to 34%, producing an average anchorage strength equal to about 84% of the average strength of hooked bars placed inside the column core or extended to the far side of the column. For hooked bars with a 90° hook, concrete cover to the tail as low as 0.75 in. (29 mm) or tail kickout at failure do not affect the anchorage strength. The likelihood of tail kickout increases with increasing bar size and for hooks with tail cover less than 2 in. (50 mm) and no confining reinforcement. The results from the current analyses were used to modify a previously derived descriptive expression for hooked bar anchorage strength and a design expression for hooked bar development length. These modifications expand the applicability of the descriptive and design expressions to include the effects of hooked bar spacing, placing the hooked bar outside column core, and not extending the bar to the back of the column. Design provisions for ACI 318 are proposed.Electric Power Research Institute, Concrete Steel Reinforcing Institute Education and Research , Foundation, University of Kansas Transportation Research Institute, Charles Pankow Foundation, Commercial Metals Company, Gerdau Corporation , Nucor Corporation , and MMFX Technologies Corporatio

Effects of Total Internal Water Content on Freeze-Thaw Durability and Scaling Resistance of Internally-Cured Concrete

The effects of total internal (TI) water, provided by normalweight coarse and fine aggregates and pre-wetted fine lightweight aggregate (LWA), in the range of 6.8 to 17.3%, corresponding to internal curing (IC) water in the LWA ranging from 0 to 15.1%, by weight of cementitious materials, on the freeze-thaw durability and scaling resistance of 12 concrete mixtures are evaluated. Cementitious materials consist of portland cement only or portland cement with a 30% weight replacement by slag cement. The coarse aggregate consists of limestone (with an oven-dry absorption of 1.8%) or granite (with an oven-dry absorption of 0.6%), which provide 5.5 to 5.6% or 1.9% internal curing water by the weight of cementitious materials, respectively. All of the mixtures with the limestone coarse aggregate failed the test, with the average dynamic modulus of elasticity (EDYN) dropping below 95% of the initial value well before the 660 freeze-thaw cycles specified by the Kansas Department of Transportation, demonstrating that the limestone itself is susceptible to freeze-thaw damage. The mixtures containing granite coarse aggregate had an average relative EDYN above 95% of the initial value at 660 freezethaw cycles in the test of freeze-thaw durability at TI water contents up to 15.7% (corresponding to an IC water content of 13.4% from the LWA) by the weight of cementitious materials. The only mixture with granite coarse aggregate that failed the test had a 30% weight replacement of portland cement with slag cement and a TI water content of 17.3% by weight of the cementitious materials (corresponding to 15.1% IC water from LWA). This result indicates that it is possible to have too much internal curing water. In the scaling test, the mixtures with granite coarse aggregate, all of which contained LWA, had lower mass losses than mixtures with limestone coarse aggregate, although all but one of the 12 mixtures passed the test with a cumulative 56-day mass loss below 0.1 lb/ft2. For concrete with granite coarse aggregate, the mass loss increased slightly with increased TI water content when portland iv cement was used as the only cementitious material. When a 30% weight replacement of portland cement with slag cement was used, the mass loss increased for a TI water content above 12.5% (corresponding to 9.9% IC water from LWA), but remained below the failure limit, suggesting no benefits for a TI water content above 12.5% by the weight of cementitious materials. The mixtures with portland cement as the only cementitious material had lower mass losses than the mixtures with a 30% weight replacement of portland cement with slag cement for the same coarse aggregate. Pre-wetted fine lightweight aggregate (LWA) for internal curing (IC) should equal 7 to 8% by weight of cementitious materials. The results provide no evidence that it would be advantageous to stray much above these values and demonstrate that high TI/ IC water contents can be deleterious

Performance Evaluation of Corrosion Protection Systems for Reinforced Concrete

In this study the performance of corrosion protection systems for reinforced concrete is evaluated. Conventional bare and epoxy-coated reinforcement are compared with alternative forms of reinforcement–galvanized steel, MMFX steel containing 9% and 4% chromium (ASTM A1035 Type CS and CM steel), and epoxy-coated MMFX steel containing 4% and 2% chromium (epoxycoated ASTM A1035 Type CM and CL steel). Furthermore, corrosion performance of reinforced concrete with partial replacement of cement by 20% fly ash, 40% fly ash, 5% silica fume, 10% silica fume, 20% slag cement, and 40% slag cement in bridge decks containing uncoated conventional steel as well as 40% fly ash, 10% silica fume, and 40% slag cement in bridge decks containing conventional epoxy-coated reinforcement are compared with the concrete bridge decks containing only portland cement along with epoxy-coated and uncoated reinforcement. The corrosion performance of systems are evaluated using bench-scale specimens (Southern Exposure, cracked beam, and beam specimens) and rapid macrocell tests. Macrocell corrosion rates, corrosion potential, and total corrosion rates, which are measured by Linear Polarization Resistance test, are used to monitor the corrosion performance of specimens. Critical corrosion loss required to crack concrete cover in specimens containing galvanized bars and conventional steel are investigated and compared with the results of predictive equations introduced in the literature. The critical chloride threshold of conventional reinforcement in concrete containing different supplementary cementitious materials (fly ash, silica fume, and slag cement) are compared. The chloride contents are measured based on the free chloride content (water soluble chloride) of concrete samples at the level of bar. The life-expectancy and cost effectiveness of a bridge deck constructed with each system are estimated for a 75-year design period based on the obtained results. Results show that galvanized steel exhibits better performance than conventional bars against corrosion; galvanized steel requires over twice the corrosion loss and has an expected-life about three times as long as conventional steel. The average critical corrosion loss to crack concrete with 1-in. cover is found to be approximately 25 µm, very close to the value obtained by O’Reilly’s (2011) predictive equation. While MMFX bare bars show higher corrosion resistance than conventional bars, those with 9% chromium exhibit better corrosion performance than MMFX bars containing 4% chromium; however, critical chloride threshold of both MMFX bars are about three times of that for conventional steel. Although use of galvanized steel and uncoated MMFX bars are more cost effective than conventional steel, they are not as cost effective as epoxy-coated bars. Epoxy-coated MMFX bars containing 2% chromium do not show significant better performance against corrosion compared to conventional epoxy-coated bars; however, those with 4% chromium have an appreciably higher corrosion resistance and life-expectancy than conventional ECR. Using supplementary cementitious materials in concrete enhances the corrosion resistance of the systems; with increasing the amount of SCM, the time to initiation increased and the corrosion rates decreased. Chloride ingress rate is significantly lower in concrete containing SCM compared to those without it, with the lowest rate in concrete with silica fume. Most specimens containing 40% fly ash, 20% slag, 40% slag, and 10% silica fume repassivate after initiation, with corrosion re-initiating at a higher chloride threshold. The initial critical chloride thresholds for slag cement and 40% fly ash specimens are similar to that for 100% ordinary portland cement, but the secondary CCCT values are significantly higher. For 10% silica fume specimens, the initial CCCT value is lower, but the secondary CCCT value is similar to the critical chloride threshold of conventional steel in specimens with 100% portland cement. While using epoxy-coated reinforcement and supplementary cementitious materials separately, increases the life-expectancy and cost effectiveness of a corrosion protection system, using them together exponentially increases the effects

Corrosion Performance of Epoxy-Coated MMFX Bars

The corrosion resistance of coated ASTM A1035 Type CL (2% Cr) and CM (4% Cr) steel bars produced by MMFX Technologies were evaluated in both cracked and uncracked concrete as well as in the rapid macrocell test. Coated bars were evaluated after simulating damage typical to that which would occur during normal handling and placement at a construction site. Bars were compared to the performance of epoxy-coated (ASTM A775) reinforcement from previous studies, and a life-cycle cost analysis over a 75-year design life was performed. Both epoxy-coated bars tested (2% and 4% chromium) exhibited reduced disbondment of the coating at the end of testing compared to conventional epoxy-coated reinforcement. The 4% chromium coated bars also exhibited significantly lower corrosion rates relative to conventional epoxy-coated reinforcement, with corrosion rates between 15 and 30% of that of conventional ECR. Coated bars with 2% chromium performed comparably or slightly better than conventional epoxy-coated reinforcement (depending on the test method), but the differences were not statistically significant. The life-cycle cost analysis found that epoxy-coated MMFX with 4% chromium was the most cost-effective reinforcement of the bars in this study.MMFX Technologies, Inc