High Performance Concrete Specifications and Practices for Bridges (2013)

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30 chapter five CASE EXAMPLES OF HIGH PERFORMANCE CONCRETE APPLICATIONS IN BRIDGES strengths were about 4.0 ksi. The establishment of a good working relationship among owners, inspectors, contractors, and concrete suppliers was of prime importance for the suc- cessful construction of an LC-HPC bridge deck. All partici- pants must clearly communicate their expectations and needs to successfully meet the specifications (Browning et al. 2009). Bridge decks constructed with LC-HPC had less than 10% of the cracking found in traditional bridge decks. A second phase of the project is underway to include the use of SCMs, internal curing agents, and shrinkage reducing admixtures. In the survey for this synthesis, KDOT reported that the use of HPC has resulted in better performance compared with conventional concrete because of maximum allow- able permeability, SCMs, optimized aggregate gradations, and a 14-day wet cure. It was noted that the binary mixes (cement plus an SCM) were not as effective as ternary mixes (cement plus two SCMs) in reducing permeability. The pre- dominant admixtures used were Type A—water-reducing admixture and Type F—high range water-reducing admixture. LOUISIANA DEPARTMENT OF TRANSPORTATION AND DEVELOPMENT In 1988, a bridge project in Louisiana was used as an exper- iment to determine if a concrete compressive strength of 8.0 ksi could be obtained on a real project (Bruce et al. 1998). The specifications required a cement content of 800 lb/yd3. However, 2,370 linear ft of girder or 68% of the total length did not achieve the specified strength. In 1992, an experimental 24-in. square pile was cast using a concrete containing 750 lb/yd3 of cement and 95 lb/yd3 of silica fume. Average concrete compressive strengths were 8.5 and 10.5 ksi at 18 hours and 28 days, respectively. In 1993, AASHTO Type IV girders with concrete compressive strengths of 8.4 and 11.2 ksi at 18 hours and 14 days, respec- tively, were produced for a bridge in Shreveport. The Charenton Canal Bridge, completed in 1999 and shown in Figure 14, was Louisiana’s first HPC bridge (Bruce et al. 2001). High-strength concrete with a specified compressive strength of 10.0 ksi was used in the prestressed concrete piles and girders. HPC for durability was used in the CIP bent caps Following completion of the survey, the states of Kansas, Louisiana, New York, Virginia, Washington, and Wisconsin were asked to provide more details about their implementation of HPC and levels of performance. These states were selected based on the extent that they have implemented HPC in CIP or precast construction, and to represent different regions of the United States. Information for these case examples was obtained from the survey responses, follow-up contact by phone and e-mail, and a literature review. KANSAS DEPARTMENT OF TRANSPORTATION In 2003, the Kansas Department of Transportation (KDOT) became the lead state of a pooled fund study with 18 other states and FHWA. The goal of the study was to construct at least 40 low-cracking, high performance concrete (LC-HPC) bridge decks (Browning and Darwin 2007; Browning et al. 2009). The specifications for LC-HPC included the following requirements: • Cementitious materials content of 500 to 540 lb/yd3, • Maximum w/cm of 0.42 (later revised to 0.43 to 0.45), • Air content of 7.0% to 9.0% (later revised to 6.5% to 9.5%), • Compressive strength at 28 days of 3.5 to 5.5 ksi, • Paste content (total volume of water and cement) less than 25%, • Slump of 1.5 to 3.0 in., • Concrete placement temperature of 55°F to 70°F, • Combined aggregate gradation optimized for uniform size distribution, • Wet curing with one layer of burlap starting within 10 minutes of concrete strike off followed by a second layer of burlap within five minutes, • Fourteen days of wet curing followed by application of a curing compound, • A qualification slab with dimensions equal to the bridge width, full depth, and 33 ft long to be cast before bridge deck placement to demonstrate the contractor’s capabilities, • Use of only Type I/II cement, • Maximum aggregate absorption of 0.7%. Two of the primary lessons learned were that these con- crete specifications can be implemented at a reasonable cost and that the low-paste concrete mix is workable, placeable, and finishable in the field (Browning et al. 2009). Concrete

31 and bridge deck. The CIP concrete was required to have a minimum compressive strength of 4.2 ksi at 28 days, a maxi- mum permeability per AASHTO T 277 of 2000 coulombs, a minimum cement content of 658 lb/yd3, and a maximum w/cm of 0.40. An inspection of the bridge deck four years later revealed only transverse cracks in the negative moment region over the intermediate piers (Mokarem et al. 2009). In the survey for this synthesis, the Louisiana Department of Transportation and Development (LaDOTD) reported that HPC has better performance than conventional concrete for CIP decks, precast girders, and precast deck panels. The improved concrete performance resulted from the use of chemical admixtures, fly ash, slag cement, and silica fume. For bridge decks, Class C fly ash and slag cement were reported to be the most frequently used SCM. Water-reducing admixture Type A was the most frequently used chemical admixture. For precast girders and slabs, Class C fly ash was also reported to be the most frequently used SCM and water- reducing admixture Types A and F were the most frequently used chemical admixtures. The LaDOTD Standard Specifications has classes of concrete with specified compressive strengths of 5.0, 6.0, and 7.5 ksi for precast girders. For bridge decks, a minimum cementitious materials content of 560 lb/yd3 and a maximum w/cm ratio of 0.44 are specified, and the use of both Class F and C fly ashes, silica fume, and slag cement is permitted. NEW YORK STATE DEPARTMENT OF TRANSPORTATION The New York State Department of Transportation (NYSDOT) development of HPC began in 1994 in an effort to produce more durable and longer lasting bridge decks (Streeter 1999). The newly developed Class HP concrete was achieved by using pozzolans to reduce the cement content, lowering the water-cementitious materials ratio, and using normal range water-reducing admixtures. A comparison of the Class HP concrete mix criteria with NYSDOT’s Class E and H concretes is shown in Table 13 (Owens and Alampalli 1999). Placement of Class HP concrete on a NYSDOT bridge deck is shown in Figure 15. In addition to modifying the mix proportions, greater attention was paid to construction details. Training sessions were held to highlight the procedures to be followed. The addition of silica fume and water-reducing admixtures was tightly controlled. Concrete placement was limited to 5 to 8 ft ahead of the finishing machine. Wet curing was applied imme- diately after texturing the surface and initially continued for seven days. This was increased to 14 days in November 1999. Performance of Class HP concrete was reported to be good (Streeter 1999). The average compressive strength was 5.4 ksi or about 20% higher than for conventional concrete. Permeabilities in the field averaged 1600 coulombs at 28 days, which was about 30% to 50% of the values for conventional concrete. Cracking was reduced and those cracks that did form were finer. Between 1995 and 1998, 84 bridges had been constructed using Class HP concrete (Alampalli and Owens 2000) and a study was undertaken in 1998 to inspect and FIGURE 14 High performance concrete was used in all components of the Charenton Canal Bridge in Louisiana [Photo courtesy of Louisiana Department of Transportation, Bridge and Structural Design Section]. Property Concrete Class E H HP Cement Content, lb/yd3 647 674 506 Fly Ash Content, lb/yd3 0 0 135 Silica Fume Content, lb/yd3 0 0 42 w/cm Ratio 0.44 0.44 0.40 Sand, % of Total Aggregate 35.8 40.0 40.0 Air Content, % 6.5 Slump Range, in. 3–4 Based on Owens and Alampalli (1999). TABLE 13 MIX CRITERIA FOR NYSDOT CLASS E, H, AND HP CONCRETES FIGURE 15 Placement of Class HP concrete [Photo courtesy of NYSDOT].

32 quantify the enhanced performance of Class HP concrete in those projects indicated that: • 49% had no cracks. • 48% had transverse cracks. • 44% had longitudinal cracks. • 40% of the decks had both transverse and longitudinal cracks. Of the decks with cracks, more than half began cracking within 14 days of concrete placement. Class HP bridge decks were observed to crack with less frequency and exhibited narrower and shorter cracks than their non-HPC counterparts. The average measured length of the transverse cracks was 0.021 ft/ft2 compared with lengths of 0.0 to 0.31 ft/ft2 reported by Browning and Darwin (2007) for conventional concrete bridges. Eighty percent of the Class HP decks were reported to perform as well as or better than Class E and H decks. Based on a statistical analysis, cracking densities were found to be independent of superstructure type, super- structure material, span length, or support conditions. NYSDOT’s first use of high-strength HPC for bridge beams began with the completion of three bridges in 2001 (Royce 2002 and 2006). Initial experience showed that con- crete with a compressive strength of 10 ksi allowed the design of bridge beams for significantly longer span lengths compared with lower strength concretes. Based on the success of the initial applications in 2001 through 2003, NYSDOT specified the following seven performance criteria for high-strength HPC for precast, prestressed concrete beams beginning in 2004: • Compressive strength at 56 days by AASHTO T 22: > 10.15 ksi, • Modulus of elasticity by ASTM C469 at the concrete age when the compressive strength is achieved: ≥ 4350 ksi, • Drying shrinkage after 56 days of drying by AASHTO T 160: < 600 millionths, • Specific creep after 56 days of loading by ASTM C512: ≤ 41 millionths/psi, • Freeze-thaw relative dynamic modulus after 300 cycles by AASHTO T 161 Procedure A: ≥ 80%, • Scaling resistance by ASTM C672 visual rating: ≤ 3, and • Chloride penetration by AASHTO T 259 (modified) increase in chloride ion content by weight: < 0.025% at 1 in. depth. In addition, certain prescriptive requirements were estab- lished for the mixes: 1. Minimum entrained air content of 3%, 2. Minimum silica fume content of 5% by weight of the cementitious materials, 3. Maximum w/cm ratio of 0.40, and 4. Calcium nitrite corrosion inhibitor at a dosage rate of 646 fl oz/yd3. According to Royce (2006), these criteria resulted in a chloride penetration resistance many times higher than for conventional concrete used for bridge beams prior to 2004. The calcium nitrite corrosion inhibitor elevates the corrosion initiation threshold so it takes longer for active corrosion to begin. NYSDOT stated that it is confident that the combination of high strength HPC and corrosion inhibitor will provide a service life of 75 to 100 years. In the survey for this synthesis, NYSDOT reported that the use of HPC has resulted in better performance compared with conventional concrete for both CIP and precast concrete decks. The survey did not solicit a response for the use in girders. The improved performance is attributed to the pre- scriptive mix requirements developed in the 1990s, which provided a lower permeability in the field. At the same time, extending the length of wet curing to 14 days and enhanc- ing placement and consolidation practices were beneficial. Transverse cracks are still observed on many decks although the cracks are fewer and narrower. Autogenous shrinkage has been a concern that has led to consideration of the use of internal curing. NYSDOT reported that silica fume is used in more than two-thirds of its bridge decks. Class F fly ash and slag cement are used on one-third to two-thirds of the decks. The pre- dominant chemical admixtures are Type A—water-reducing admixture, Type B—retarding admixture, and Type D— water-reducing and retarding admixture. Each admixture is used in over two-thirds of the CIP bridge decks. The NYSDOT Standard Specifications requires that the cementitious materials used in Class HP concrete contain 20% pozzolan and 6% silica fume and that a water-reducing admixture and/or a water- reducing and retarding admixture be used. Whereas NYSDOT’s approach to HPC in bridge decks is prescriptive, its approach for precast concrete is mainly based on performance of the proposed mix. The predominant SCM used in precast, prestressed concrete beams and panels is silica fume. The predominant chemical admixtures are Type A— water-reducing admixture and Type F—high range water- reducing admixture. Corrosion inhibitors are also used. The NYSDOT Standard Specifications includes the per- formance criteria listed above for precast, prestressed con- crete beams. In addition, the concrete is required to contain a minimum of 5% silica fume. This is one of the few specifi- cations that include numerous performance requirements in the standard specifications rather than in special provisions. Approval of an HPC mix in the NYSDOT specifications is a two-step process. In the first step, the contractor is required to submit information about the constituent materials, proposed concrete mix proportions, production procedures, and testing procedures. After approval, the contractor is required to per- form tests and to submit test results showing that the proposed mix proportions satisfy all the performance requirements.

33 Once approved, the mix may be used on multiple projects without further testing for each project. VIRGINIA DEPARTMENT OF TRANSPORTATION Standards for HPC use in Virginia have evolved through extensive laboratory research and field testing (Napier 2005). In 1988, the Virginia Department of Transportation (VDOT) added requirements for limiting surface evaporation rates for concrete bridge decks. In 1994, a trial provision requiring seven days of wet curing for low permeability concrete was introduced, which later became a standard requirement. In addition, VDOT requires the use of curing compound follow- ing the seven-day wet curing period. Also in 1994, VDOT introduced a permeability provision for HPC with maximum values of 1500 coulombs for precast, prestressed concrete, 2500 coulombs for deck concrete, and 3500 coulombs for the substructure concrete. These values were selected on the basis that they could be achieved consistently. VDOT also used an accelerated method of curing for the test specimens consisting of one week at 73°F followed by three weeks at 100°F, with permeability testing at 28 days. This curing regime gave similar results at 28 days to those obtained at six months using standard curing (Ozyildirim 1998). This method has been adopted by several other states and is used for all HPC projects in Virginia. In 1992, VDOT began using corrosion inhibitors at low dosage rates in low permeability concrete containing pozzolans or slag cement used in a marine environment (Napier 2005). According to the survey for this synthesis, VDOT no longer uses corrosion inhibitors in CIP bridge decks and uses them in less than one-third of precast girders and deck panels. The VDOT standard specifications now requires the use of 3.5 gallons/yd3 of calcium nitrite in prestressed concrete piles, beams, and slabs unless at least 40% of the cementitious material is slag cement or at least 7% is silica fume. Concrete for structures over tidal waters, beams and slabs within 15 ft of high tide, and exposed piles are also required to contain calcium nitrite. The dosage rate is 2.2 gallons/yd3. Also, in 1992, VDOT began requiring either cement with an alkali content of less than 0.40% or the use of pozzolans or slag cement with cement having an alkali content up to 1% to address the potential for ASR (Napier 2005). In 2008, VDOT started requiring low permeability for all concrete and implemented lower permeability requirements for all elements of bridges over tidal waterways. The speci- fied maximum permeability values are 1500 coulombs for prestressed concrete and overlays and 2000 coulombs for general concrete. Permeabilities are measured at a concrete age of 28 days following accelerated curing. In the survey for this synthesis, VDOT reported that its special provisions for HPC combine performance and pre- scriptive requirements. Both types of specifications address strength, permeability, and workability. In addition, ASR is considered for the prescriptive specifications. To minimize deck cracking, VDOT specifies minimum and maximum concrete temperatures at time of deck place- ment of 40°F and 85°F, respectively; maximum w/cm ratio of 0.45; maximum slump of 4 in.; and use of wind breakers and fogging when evaporation rates are determined to be high according to the ACI surface evaporation nomograph (ACI Committee 305, 1999). Class F fly ash and slag cement are each used in one- to two-thirds of its bridge decks. WASHINGTON STATE DEPARTMENT OF TRANSPORTATION Washington State Department of Transportation (WSDOT) has used HPC in both CIP concrete bridge decks and precast, prestressed concrete girders. The focus for bridge decks has been improved durability through the use of fly ash (Khaleghi and Weigel 2001). Air entrainment is required for all WSDOT concrete decks to provide freeze-thaw resistance. Initially, contractors expressed concerns about the addition of fly ash and the requirement for 14 days’ wet curing. These concerns diminished rapidly because the fly ash improved workability and the wet curing was not the problem originally envisioned. The use of high-strength HPC began with a showcase project in 1997 (Russell et al. 2006a). Specified concrete compressive strengths for the girders were either 7.4 or 5.0 ksi at strand release and either 9.5 ksi at 28 days or 10.0 ksi at 56 days. Subsequent experience gained through design and fabrication of HPC girders showed that specifying a release strength of 7.5 ksi and a design strength of 8.5 ksi at 28 days resulted in optimum design economy (Weigel 2000). In 2004, Weigel reported that WSDOT had been using HPC in all its precast, prestressed concrete bridge girders since 1998— an average of 20 bridges per year. According to WSDOT’s response in the survey, the use of HPC has resulted in better performance of precast, prestressed concrete girders. In the survey for this synthesis, WSDOT reported that the performance of HPC in CIP bridge decks was worse than that of conventional concrete, based on an observed increase in the amount of cracking, which appeared to be associated with the required use of fly ash. The cracking, however, may be caused by the use of girders with wide top flanges. These girders provide more restraint to the differential shrinkage between the deck concrete and the girders. WSDOT reported that none of the strategies that it has tried was effective in minimizing cracking. The use of evaporation retardants was found to be the least effective. WSDOT is evaluating the use of lower cementitious materials contents as a means of reducing the deck concrete drying shrinkage. The WSDOT Standard Specifications for bridge deck concrete specifies a minimum cementitious materials content

34 of 660 lb/yd3, with a fly ash content between 10% and 20% or a slag cement content between 10% and 30%. If both fly ash and slag cement are included, the maximum allowable content is increased to 40%. The use of a water-reducing admixture and a retarding admixture is required. The use of a high range water-reducing admixture is permitted. WISCONSIN DEPARTMENT OF TRANSPORTATION In the mid to late 1990s, the Wisconsin Department of Transportation (WisDOT) introduced a Quality Management Program (QMP) (Parry 2011). The principal motivation for these changes was to improve the quality and durability of concrete and to decrease bridge deck cracking. The QMP incorporated the following specification changes: • Introduced percentage within limits requirements for compressive strength with incentive/disincentive payments, • Reduced the minimum cementitious materials content from 610 to 565 lb/yd3, • Increased maximum nominal size of coarse aggregate from ¾ to 1½ in., and • Required seven-day continuous wet cure with burlap cover. In 1998–99, WisDOT initiated a pilot program that equated HPC with high-strength concrete and low w/cm ratio, using the following requirements: • Minimum compressive strength of 5.0 ksi at 28 days, • High range water-reducing admixture required, and • Maximum w/cm ratio of 0.40. This approach resulted in a large amount of deck cracking on several structures and the specification was removed from several scheduled projects. The second generation of HPC specifications for bridge decks was used first on the Marquette Interchange in Mil- waukee, constructed between 2004 and 2008, and shown in Figure 16. The specifications included the following: • Mandatory use of SCMs, • Cementitious materials content between 565 and 660 lb/yd3, • Minimum compressive strength of 5.0 ksi at 28 days, • Maximum rapid chloride permeability of 2000 coulombs using 28-day standard curing, • Wet burlap placement within 10 minutes of surface finishing, • Continuous wet cure for 10 days, and • Silane sealer applied to the deck after cutting longitudinal grooves in the hardened concrete. After construction of the Marquette Interchange, it was decided to require a minimum compressive strength of 4.0 ksi for future HPC bridge decks. Contractors reported it was difficult to satisfy the 28-day rapid chloride permeability requirement using fly ash as the preferred SCM. The acceler- ated curing method developed by the Virginia Transportation Research Council was adopted (Ozyildirim 1998). These changes were incorporated into the third generation of HPC specifications, along with the following: • Maximum cementitious materials content of 610 lb/yd3, • Maximum rapid chloride permeability of 1500 coulombs at 28 days, and • Continuous wet cure for 14 days. The WisDOT use of HPC has been limited to bridge decks. In the survey for this synthesis, the agency reported that the use of HPC has resulted in better performance compared with conventional concrete. The primary practices leading to the improved performance have been a 14-day wet cure, reduced cementitious materials content, and a reduced w/cm ratio. The survey results show limited use of Class C fly ash and slag cement and no use of Class F fly ash, Class N pozzolan, silica fume, and chemical admixtures. The WisDOT Standard Specifications includes cementi- tious materials contents of 565 and 610 lb/yd3 for bridge deck concrete Grades A and D, respectively. The water content for these concrete grades is equivalent to a w/cm ratio of 0.40. In Grade A concrete, fly ash and slag cement are permitted at 30% of the cementitious materials content. For QMP concrete, Class C fly ash or Grade 100 or 120 slag cement is required. For binary mixes, fly ash is required at 15% to 30% or slag at 20% to 30% of the total cementitious materials content. For ternary mixes, fly ash and slag cement are required in combina- tion at 15% to 30% of the total cementitious materials content. The target w/cm ratio is required to be not greater than 0.45. FIGURE 16 The Marquette Interchange in Milwaukee, Wisconsin, used the second generation of HPC specifications [Photo courtesy of Tony Straseske, Wisconsin Department of Transportation].