Reed, Hale 1. Slag Cement Concrete for Use in Bridge Decks. August 1, Words (6 Tables = 1500 words)

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1 Reed, Hale Slag Cement Concrete for Use in Bridge Decks August 1, Words (6 Tables = 1500 words) Neil T. Reed, Structural Engineer Marc Barry Engineering, P.C. 300 North 2 nd Street, Suite B Rogers, AR Ph: (479) Fax: (479) ntr@mbe.arcoxmail.com W. Micah Hale, Associate Professor (Corresponding Author) Department of Civil Engineering 4190 Bell, 1 University of Arkansas Fayetteville, AR Office: (479) Fax: (479) micah@uark.edu ABSTRACT This paper documents the development and performance of a high performance bridge (HPC) bridge deck. One of the major challenges in the project was developing a concrete mixture that met the Arkansas State Highway and Transportation (AHTD) provisional HPC specifications. The specifications were designed to ensure a concrete with low permeability coupled with a slow rate of strength gain. The research focused on the performance aspect of HPC and not high strength. AHTD specified a maximum compressive strength of 6000 psi with a maximum chloride ion penetrability of 1500 coulombs at 56 days of age. Several mixtures were developed that contained supplementary cementing materials (SCMs) at replacement rates as high as 75 percent of the total binder content. The laboratory testing determined that slag cement was necessary to meet the specifications. The final mixture used in the bridge deck contained 50 percent slag cement and a total cementitious material content of 518 lb/yd 3. The bridge deck has been in service for approximately four years and when compared to a control bridge deck cast at approximately the same time, there is minimal amount of cracking on the deck.

2 Reed, Hale INTRODUCTION Concrete is widely and effectively used in transportation facilities. However, some concretes exposed to the environment have deteriorated rapidly, requiring expensive corrective measures. Bridge decks are subject to intrusion by water and aggressive solutions that may result in corrosion of the reinforcement and freeze-thaw deterioration. In each case, physical or chemical changes occur within the concrete that cause expansion, leading to stresses higher than concrete can withstand. One very effective method of minimizing these stresses is to reduce the intrusio n of water and aggressive solutions (Ozyildirim, 1998a). Conventional concretes often fail to prevent the ingress of moisture and aggressive ions adequately. The use of blended cements or supplementary cementing materials (SCMs) has been reported to decrease the permeability, thereby increasing the resistance of concrete to deterioration by aggressive chemicals such as chlorides (Khan, 2003). BACKGROUND During the late 1980 s and early 1990 s, the US Congress authorized a five-year research initiative to develop and evaluate technologies to combat the deterioration of the nation s highways and to improve their performance, durability, safety, and efficiency. This Strategic Highway Research Program (SHRP) recommended that the Federal Highway Administration (FHWA) initiate a program to implement the use of high performance concrete (HPC) in bridges (Cox & Pruski, 2002). To demonstrate the suitability of HPC for use in highway structures and to stimulate its use, the FHWA initiated a series of projects in 1993 that includes the complete incorporation of HPC from design to long-term monitoring of the bridges in service. HPC bridges have been constructed in most states. Though some states have leaned more towards the high strength aspect of HPC in the construction of beams and piers, Arkansas is at the present time focusing on reducing the compressive strength of bridge deck concrete while not sacrificing but improving durability. By reducing early age strength gain, AHTD hopes to minimize the early age cracking that often appears in their bridge decks. RESEARCH PROGRAM Scope The project was divided into two phases. The first phase focused on developing a concrete mixture with low permeability and a low strength gain rate which met AHTD s specifications for Class S(HP) concrete. During this phase the compressive strength was measured at 1, 7, 28, and 56 days of age. Permeability (ASTM C1202) was measured at 28 and 56 days of age. Once a mixture was developed, it was then used to cast a HPC bridge deck. At approximately the same time the HPC deck was cast, a control bridge was cast using conventional concrete. Both bridge decks have been monitored for four years. AHTD Specifications AHTD classifies HPC as concrete meeting Class S(HP) specifications. The fresh and hardened concrete requirements for Class S(HP) concrete are shown below in Table 1. Also shown in

3 Reed, Hale Table 1 are the requirements for Class S(AE). Class S(AE) concrete is specified for any airentrained concrete used in structural applications in Arkansas including bridge decks. TABLE 1 Specifications for Class S(HP) and Class S(AE) Concrete Class S(HP) Class S(AE) Maximum 56 day permeability (coulombs) Minimum 28 day compressive strength (psi) Maximum 28 day compressive strength (psi) Minimum 56 day compressive strength (psi) Maximum 56 day compressive strength (psi) Minimum cement content (lb/yd 3 ) Maximum cement content (lb/yd 3 ) Maximum slag cement content (%) Maximum Class C fly ash content (%) Maximum silica fume content (%) 5 5 Maximum SCM content (%) Maximum w/cm Maximum w/cm Slump range (in.) Air concrete range (%) 6 ± 1 6 ± 2 LABORATORY TESTING Materials A locally available Type I cement was used. The Class C fly ash, Gr. 100 slag cement, and a commercially available silica fume were the SCMs included in the study. The composition of the slag cement, portland cement, and fly ash are shown below in Table 2. The fine aggregate was washed river sand and the coarse aggregate was crushed limestone with a nominal maximum size of 1 in.

4 Reed, Hale TABLE 2 Composition of Cementitious Materials Portland Cement Slag Cement Fly Ash Chemical Composition (%) SiO Al 2 O Fe 2 O CaO MgO SO Loss on Ignition Compound Composition (%) C 3 S C 2 S C 3 A C 4 AF Na 2 O K 2 O Blaine Air Fineness Blaine (m 2 /kg) Class S(AE) Concrete Field Sampling Concrete was sampled from five bridge decks that were being constructed throughout Arkansas to determine the hardened properties of typical concrete used in bridge decks. The concrete mixture proportions of the five bridge decks, labeled 1 through 5, and their corresponding fresh and hardened properties are shown below Table 3. As for the mixture proportion, all bridge decks used 611 lb/yd 3 of cementitious material and the w/cm ranged from 0.41 to When comparing these values to the HPC specifications, all five mixtures met the proportioning requirements of no more than 611 lb/yd 3 of cementitious material and a w/cm between 0.40 and The compressive strength for four of the five mixtures also met the minimum and maximum strength requirements. However, at 90 days of age, the permeability all mixtures exceeded the maximum value of 1500 coulombs.

5 Reed, Hale TABLE 3 Mixture Proportions and Properties of Bridge Deck Concrete Materials Bridge Decks Total Cementitious Material (lb/yd 3 ) Portland Cement (%) Slag Cement (%) Fly Ash (%) Silica Fume (%) Coarse Agg. (lb/yd 3 ) Fine Agg. (lb/yd 3 ) Water (lb/yd 3 ) W/CM HRWR (fl oz./cwt) AEA (fl oz./cwt) Fresh Concrete Properties Slump (in.) Air Content (%) Compressive Strength (psi) 1 day days days days Rapid Chloride Ion Penetrability (coulombs) 28 days days Mixture Proportioning Laboratory Study Based on the properties of the concrete sampled from the 5 bridge decks, it was apparent that the permeability needed to be reduced while maintaining approximately the same compressive strength. A laboratory study began to develop a mixture that met the Class S(HP) specifications. The first phase of the study focused on compressive strength only. The permeability was then measured for only the mixtures that met the compressive strength requirements. All specimens cast during the laboratory study were cured at 73 C and 100 percent relative humidity. The mixture proportions for the first set of mixtures are shown below in Table 4. To reduce permeability and maintain strength, the first mixture batched (Mix 6) had a lower w/cm (0.40) and less cement (518 lb/yd 3 ). The cement content was lowered to offset the expected gain in compressive strength due to the lower w/cm. By seven days of age, Mix 6 had exceeded the maximum compressive strength of 6000 psi. To reduce the compressive strength of Mix 6, 50 percent of the cement in Mix 6 was replaced with Gr. 100 slag cement in Mix 7. The 50 percent slag cement content was the maximum allowed by AHTD. As shown in Table X, this substitution decreased one day compressive strength by 3000 psi and 56 day by almost 4000 psi. Mix 7 met the compressive

6 Reed, Hale strength requirements. In Mix 8, 35 percent of the cement was replaced with fly ash which was maximum replacement rate allowed by AHTD. The early age compressive strength of Mix 8 decreased when compared to the control mixture (Mix 6), but by seven days, the compressive strength exceeded the 6000 psi limit. For Mix 9, the fly ash content was increased to 50 percent. This exceeded AHTD requirements, but there were some concerns that the strength requirements were unattainable without increasing the replacement rates. The 50 percent fly ash reduced the one day strength to 500 psi and the seven day strength to 5660 psi, but by 28 days, the compressive strength was too high. For the final mixture in this series, Mix 10, a combination of slag cement (30%) and fly ash (20%) was examined. TABLE 4 Concrete Mixture Proportions and Properties Materials Mix Total Cementitious Material (lb/yd 3 ) Portland Cement (%) Slag Cement (%) Fly Ash (%) Silica Fume (%) Coarse Agg. (lb/yd 3 ) Fine Agg. (lb/yd 3 ) Water (lb/yd 3 ) W/CM HRWR (fl oz./cwt) AEA (fl oz./cwt) Fresh Concrete Properties Slump (in.) Air Content (%) Compressive Strength (psi) 1 day days days days For the next round of mixtures (Table 5), the slag cement and fly ash contents were increased in order to decrease early age compressive strength. In the first mixture, Mix 11, 60 percent of the cement was replaced with slag cement. When compared to the control mixture (Mix 6), compressive strength at all ages decreased but were still too high. However, the permeability at both 28 and 56 days was within specifications. In Mix 12, the slag cement contest was increased to 70 and silica fume was added at a 5 percent replacement rate. Slag cement was increased to slow strength gain and silica fume was added to ensure that the permeability was within limits. Although the slag cement content was too high, the strength and permeability met specifications.

7 Reed, Hale For Mixes 12, 13, and 14, the portland cement content was reduced from 45 percent to 30 percent to further decrease compressive strength. When compared to the control mixture, the compressive strengths were less but exceeded specified limits at 28 and 56 days of age. The final mixture batched was Mix 16. Mix 16 was identical to Mix 7 which met the compressive strength requirements, but the permeability of Mix 7 was not measured. At 56 days of age, the permeability was within specifications, but the compressive strengths were too high. This increase in compressive strength was due to high ambient and concrete temperatures during batching. The one day strength of Mix 16 was approximately 700 psi greater than Mix 6 and this difference was consistent and slightly greater through 56 days. Of the 10 different mixtures developed, only one mixture, Mix 7 met AHTD s specifications for Class S(HP) concrete. The compressive strength and permeability of Mix 12 was also within specified limits, but the slag cement content exceeded the maximum replacement rate of 50 percent. TABLE 5 Concrete Mixture Proportions and Properties Materials Mix Total Cementitious Material (lb/yd 3 ) Portland Cement (%) Slag Cement (%) Fly Ash (%) Silica Fume (%) Coarse Agg. (lb/yd 3 ) Fine Agg. (lb/yd 3 ) Water (lb/yd 3 ) W/CM HRWR (fl oz./cwt) AEA (fl oz./cwt) Fresh Concrete Properties Slump (in.) Air Content (%) Compressive Strength (psi) 1 day days days NA 56 days Rapid Chloride Ion Penetrability (coulombs) 28 days days TEST POUR As required by AHTD the contractor in charge of placing the concrete performed a field placement of the HPC. During the test pour the contractor demonstrated adequate production,

8 Reed, Hale transportation, placement, finishing and curing of the Class S(HP) concrete. The test pour was was 14 yd 3 and was conducted at an offsite location in the immediate proximity of the job site. Mix 7 was used for the test pour with an additional 2.5 gallons of water. The additional water increased the w/cm from 0.40 to 0.44 which was still within specifications. However, the increase in water also increased the permeability to 2070 coulombs at 56 days. The compressive strength at 28 and 56 days was 4740 psi and 5720 psi, respectively, which was within the allowable range. Even though the permeability was too high, Mix 7 was approved for the bridge deck. BRIDGE DECK SPECIFICS AND RESULTS Control Deck The control deck was the Jefferson Avenue Bridge spanning Interstate 30 in Texarkana, AR. The bridge is a two span bridge with five lanes of traffic. The specific details of the control deck were not documented, but deck was built according to standard AHTD methods. The deck was cast using a conventional concrete mixture with 611 lb/yd 3 of cementitious material and a w/cm of The concrete was pumped up to the deck. The deck was fogged using a commercial pressure washer in the area of placement. The concrete was then screeded, floated with a pan attached to the finishing machine, and then manually tined with a rake. Finally, a curing compound was applied and then covered with a plastic/cotton mat. HPC Deck The bridge s location was the Highway 245 interchange over Interstate 30 in Texarkana, AR. The Highway 245 Bridge was a two span bridge, each span being 99-4 long and a total length of The construction was divided into two phases, an East Phase for the eastern most lanes and a West phase for the western most lanes. The East Phase was placed in April of 2007 while the West phase bridge deck was placed in Oct-Nov. of The East Phase was divided into three placements, and the West Phase had two placements. The bridge had five lanes; two northbound lanes, two southbound lanes and one turning lane; this resulted in an out to out bridge width of The bridge deck was an 8 thick concrete slab with reinforcement and metal decking for the stay-in-place forms. An automatic screed was used to aide in concrete placement. The concrete was fogged with water until wet burlap was applied. The burlap was left in place for 7 days. The slab was mechanically tined at a later date. Mix7/16 was used in all placements of the deck. The concrete supplier was allowed to adjust the water content for each batch to ensure a slump of 4 to 6 inches provided the w/cm was less than or equal to Test samples were taken from each placement in order to conduct compression and permeability tests on the concrete. The samples were cured in an environmental chamber at 73 F and 100 percent relative humidity until testing. The concrete properties are shown below in Table 6.

9 Reed, Hale TABLE 6 Concrete Properties from the Bridge Deck Testing Age East Phase West Phase Placement 1 Placement 2 Placement 3 Placement 1 Placement 2 w/cm Compressive Strength (psi) 28 days days Permeability (coulombs) 28 days days At 56 days of age, the compressive strength was near the maximum limit of 6000 psi. For two of the placements, the strength was approximately 5600 psi. For the remaining three placements, the compressive strength was approximately 50 psi greater than the limit. Also at 56 days of age, the permeability exceeded the maximum value of 1500 coulombs for all placements. The differences between the laboratory and field properties of the mixtures can be attributed to variations in the w/cm. Although not documented for Placement 1 of the East Phase and both placements of the West Phase, the w/cm was 0.43 and 0.42 for the Placements 2 and 3 of the East Phase. This increase in w/cm contributed to the increase in permeability. BRIDGE DECK PERFORMANCE Four months after the completion of the East phase of the HPC bridge deck, there were no cracks visible in the bridge deck surface. The Jefferson Ave. Bridge which was used as the control deck was showing cracks within days of placement. Approximately four years after casting, the decks were revisited by AHTD personnel. AHTD located 4 small, transverse hairline cracks and two hairline, longitudinal cracks. The lengths of the cracks range from 5 ft. to 12 ft. in length. When compared to the control deck, AHTD personnel reported that they observed approximately 75 percent less cracking in the HPC deck than the control deck. CONCLUSIONS & RECOMMENDATIONS The findings of the research project are listed below. 1. Slag cement can be used to slow strength gain while lowering permeability. 2. A concrete mixture containing 50 percent slag cement was used to cast the HPC bridge deck. After approximately four years of service, the bridge deck displays approximately 75 percent less cracks than the control bridge deck. 3. Slag cement contents as high as 70 percent can be used to achieve compressive strengths of approximately 4000 psi at seven days of age while achieving a permeability of less than 200 coulombs at 56 days of age. 4. Removing the 56 day compressive strength requirements will allow more concrete mixture proportioning options without increasing early age strength gain. 5. Moving the 56 day permeability requirement to 90 days of age will also more concrete mixture proportioning options without sacrificing long term permeability.

10 Reed, Hale REFERENCES 1. Ozyildirim, C. Fabricating and Testing Low-Permeability Concrete for Transportation Structures (VTRC, 99-R6). Charlottesville, VA: Virginia Transportation Research Council, Khan, M. Permeation of High Performance Concrete. Journal of Materials In Civil Engineering, Vol. 15, No. 1, 2003, pp Cox, W.R., & Pruski, K.R. Austin, TX: Texas Department of Transportation, 2002.