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Bridge deck cracking: A field study on concrete placement, curing, and performanceSteve W. Peytona, Chris L. Sandersb, Emerson E. Johnc, W. Micah Halec,aArkansas State Highway and Transportation Department, Little Rock, AR 72203, USAbAPAC-Central, Inc., Tulsa, OK 74146, USAcUniversity of Arkansas, 4190 Bell Engineering Center, Fayetteville, AR 72703, USAa r t i c l ei n f oArticle history:Received 2 November 2011Received in revised form 13 January 2012Accepted 25 February 2012Keywords:Concrete curingBridge deck crackingCompressive strengthPermeabilitya b s t r a c tThe concrete properties, curing regimens, and crack density of the five bridge decks were measured. Con-crete was sampled from two or three locations in the bridge decks, and the fresh and hardened concreteproperties were measured. Curing regimens for the bridge decks were also documented. After construc-tion, the research team returned to each bridge to investigate and measure the amount of cracking. Fac-tors that led to cracking included low 1 day compressive strengths, delayed curing, and improper curingcompound dosages. The research team also determined that the concrete properties, both fresh and hard-ened, varied significantly within some bridge decks.? 2012 Elsevier Ltd. All rights reserved.1. IntroductionMany factors contribute to cracking in concrete bridge decks.Some of these factors include structural design, material proper-ties, mixture proportioning, and construction and curing practices.During the summer of 2005, five bridge decks that were under con-struction were examined to determine which of these factors con-tributed to bridge deck cracking. The research focused on theconstruction practices, curing regimens, and concrete properties.1.1. BackgroundPermeability, durability, and compressive strength are threeconcrete properties that play a significant role in the overall bridgedeck performance. All three of these properties are affected by con-crete mixture proportioning and construction practices. These con-crete properties have been proven as good indicators of bridgedeck concrete performance.Permeability is the ability of concrete to resist penetration bywater or other substances. Inspection of concrete bridge decks overthe years indicates that chloride penetration is a major concern 1.In order to lower the permeability of concrete, the water to cemen-titious materials (w/cm) ratio is generally reduced. This approachhas been verified by an a number of researchers who have founda direct correlation between w/cm and permeability. Low perme-ability concrete provides greater protection against reinforcementcorrosion 2. Decks that have high permeability tend to alsoexperience severe cracking; therefore, permeability is an indicatorfor predicting the cracking potential of concrete bridge decks 3.The National Cooperative Highway Research Program (NCHRP)Synthesis 333 recommends bridge deck concrete to have perme-ability, per American Association of State Highway TransportationOfficials (AASHTO T 277), in the range of 1500 and 2500 C toenhance the performance of bridge deck concrete 1.Concrete durability is the ability to resist weathering action,chemical attack, abrasion, and any other process of deterioration.ACI Committee 201 (Guide to Durable Concrete) recommends thatbridge decks exposed to deicing salts have a maximum w/cm of0.45 and an average air content of 6% for a nominal maximumsize aggregate (NMSA) of 25.4 mm (1 in.) 2. National CooperativeHighway Research Program Synthesis 333 recommends the use ofconcrete with w/cm between 0.40 and 0.45 to enhance the bridgedeck performance 1.As compressive strength increases, creep decreases at a higherrate than the rate of increase of tensile strength. This is one ofthe reasons why high strength concretes, which have higher tensilestrengths than regular concrete, experience more cracking 3,4.Cracking tends to increase with compressive strengths, which isa result of increased cementitious materials content and hence,an increase in paste volume. Schmitt and Darwin 5 show thatthere is a direct relationship between the amount of paste in agiven concrete and the amount of cracks in bridge decks that arecast with the same material. Many agencies have suggested thatthe trend of increasing 28-day compressive strengths has led to in-creased cracking. Some specified mixtures can achieve 28-daystrengths in three to 7 days. Compressive strengths for bridgedecks should be based on later age compressive strengths, such0950-0618/$ - see front matter ? 2012 Elsevier Ltd. All rights reserved.doi:10.1016/j.conbuildmat.2012.02.065Corresponding author.E-mail address: micah (W. Micah Hale).Construction and Building Materials 34 (2012) 7076Contents lists available at SciVerse ScienceDirectConstruction and Building Materialsjournal homepage: /locate/conbuildmatas 56- or 90-day compressive strength in order to permit the use oflow heat of hydration cement and supplementary cementing mate-rials (SCMs) in bridge deck concretes without violating strengthrequirements 6. In order to avoid early bridge deck cracking, earlyage strengths of concrete should be controlled 7. Finer moderncements typically have 1-day compressive strengths near 45% ofthe 28-day strengths. Cement manufactured in the mid-1940shad 1-day compressive strengths of only 11% of the 28-daystrength 6. The American Association of State Highway Transpor-tation Officials and Arkansas Highway Transportation Department(AHTD) require a minimum 28-day compressive strength of28 MPa (4 ksi) for bridge deck concrete 8,9.2. Testing programThe research team sampled concrete from five bridge decks in the state ofArkansas from June 2005 to September 2005. The quantity of concrete placed atthe bridge decks ranged from approximately 92306 m3(120400 yd3). The freshconcrete tests performed were slump (AASHTO T 119), unit weight (AASHTO T121), air content (AASHTO T 152), and concrete temperature (AASHTO T 309).For the first three decks, the research team performed all the fresh concretetests at three different locations (beginning, middle, and end regions) on the bridgedeck and cast 100 ? 200 mm (4 ? 8 in.) cylinders for compressive strength tests atthose same locations. At the middle sampling location, eight 100 ? 200 mm (4 ? 8)cylinders (for rapid chloride ion penetrability (RCIP) tests), four freezethaw spec-imens 76 ? 76 ? 406 mm (3 ? 3 ? 16 in.), and four unrestrained shrinkage speci-mens 100 ? 100 ? 286 mm (4 ? 4 ? 11-1/4 in.) were cast in addition to thecompressive strength cylinders. The last two decks were much smaller, and there-fore the research team performed the fresh concrete tests at only two locations onthe bridge decks. Compressive strength cylinders were also cast at two locations onthe smaller decks.The compressive strength cylinders (AASHTO T 22), freeze/thaw specimens(AASHTO T 161A), and unrestrained specimens (AASHTO T 160) cast at the firstbridge deck were transported the morning after the deck placement, therefore com-plying with AASHTO T 23. However, for the four other bridge decks, the majority ofthe samples were transported before the 8 h minimum time limit. These sampleswere transported in the back of a full-size truck in containers that were placedon approximately three inches of soft foam to reduce vibration.After the initial 24 h, the molds were removed and all specimens were air curedin an environmental chamber at 23 ?C (73 ?F) and approximately 50% relativehumidity. The research team measured compressive strength at 1, 7, 28, and56 days of age. Three cylinders were tested on each of these days. Length changesof shrinkage specimens were measured at 1, 4, 7, 28, 56, and 112 days of age, RapidChloride Iron penetration (RCIP) tests at 28 and 90 days of age, and freezing andthawing testing began at 14 days of age.2.1. Manual crack mappingThe process used to assess bridge deck cracking was similar to that used byAHTD Research Section personnel in a previous bridge deck study. The first stepin the mapping process is typically an initial examination of the entire bridge deckto locate the areas most affected by cracking. This is then the survey area. It is gen-erally limited to 30.5 m (100 ft.) in length unless the additional length would betterrepresent the distress level of the deck as a whole. Traffic control was provided bytwo AHTD personnel using a simple flagged lane closure with traffic cones along thecenterline to keep motorists out of the survey area.The actual mapping of distress in the survey section began with team memberslaying out a 30.5 m (100 ft.) tape measure along the lane edge. This provided longi-tudinal stationing for the map. A 7.6 m (25 ft.) tape measure was used to measuretransversely from the lane edges. Cracks were then visually located and docu-mented. The length and location of the cracks were measured and recorded, alongwith their orientation and approximate widths, on a prepared form with a grid rep-resenting the survey section. The widths of the cracks were measured with a crackcomparator card.2.2. AHTD specifications for Class S(AE) concreteConcrete used in bridge decks in Arkansas are classified as Class S(AE) concrete(AE for air entrained). For Class S(AE) concrete, AHTD requires a minimum 28-daycompressive strength of 28 MPa (4 ksi), a slump of 25100 mm (14 in.), and an aircontent of 6 (2%. The Arkansas Highway and Transportation Department also re-quires Class S(AE) concrete mixtures to have a maximum w/cm of 0.44, a minimumtotal cementitious material content of 362 kg/m3(611 lbs/yd3), and a coarse aggre-gate meeting either the AHTD Standard Gradation or the AASHTO M43 #57Gradation.The Arkansas Highway and Transportation Department allows the use of fly ashand slag cement in bridge decks. Fly ash can either be Class C or F, with no mixing ofthe two. The maximum fly ash replacement rate is 20% by weight, and the maxi-mum slag replacement rate is 25% by weight. If both materials are used, the max-imum replacement rate is 20%, by weight, for both materials. The limits on totalcementitious materials content and the use of supplementary cementitious materi-als (SCMs), such as fly ash, are employed to guarantee achieving the 28-day com-pressive strength outlined in the specifications and to ensure that the amount ofSCM used in the concrete mixture does not significantly retard strength gain.The Arkansas Highway and Transportation Departments specifications allowthe use of several different materials for concrete curing. Burlappolyethylenesheeting, polyethylene sheeting, copolymer/synthetic blanket, membrane curingcompounds, and other materials that meet AASHTO M 171 are allowed. The Arkan-sas Highway and Transportation Departments specifications require that the bridgedeck be covered immediately after finishing and that it remains covered for at least7 days. During these 7 days, the curing materials must be kept wet (except formembrane curing).Contractors are permitted by AHTD to place concrete bridge decks with contin-uous pours. If the contractors choose this option, the concrete must remain plasticduring the entire length of the pour. Rather than casting the negative moment re-gions of the bridge deck first then followed by the positive moment regions, mostcontractors are choosing continuous casting or pours to speed up the constructionprocess. In this research program, all five bridge decks were continuously poured.2.3. Concrete mixture proportionsThe concrete mixture proportions for the five bridge decks are shown below inTable 1. As previously stated, AHTD requires a maximum w/cm of 0.44, a totalcementitious material content of 362 kg/m3(611 lbs/yd3), and an air content of6 2% for bridge deck concrete. All contractors chose to use the least amount ofcementitious material required (362 kg/m3) and three contractors chose to use flyash, the only SCM, at replacement rates ranging from 9% to 12% by weight. Fourof the five concrete mixtures had the maximum w/cm of 0.44, and the lowest w/cm used was 0.41. A high range water reducer (HRWR) was used in the third bridgedeck, which had the lowest w/cm. The coarse aggregate content was different for allbut two of the decks primarily because AHTD does not specify a coarse aggregatecontent.3. Bridge specificsAs previously stated the research team sampled concrete fromfive bridge decks from June 2005 to September 2005. In additionto concrete properties, the researchers also documented the curingprocedures and measured the cracking in each bridge deck. EachTable 1Concrete mixture proportions.MaterialsBridge decks123a45Cement (kg/m3)308308290362362Fly ash (kg/m3)55557200Fly ash (%)991200Coarse agg. (kg/m3)990990115010211037Coarse aggregate typeLimestoneLimestoneRiver Gr.LimestoneRiver Gr.Fine aggregate (kg/m3)767767580755659Water (kg/m3)160160149160160w/cm0.440.440.410.440.44AEA dosage (L/m3)40.120.15aHigh range water reducer (HRWR) was used to improve workability.S.W. Peyton et al./Construction and Building Materials 34 (2012) 707671bridge deck is discussed in more detail in the following paragraphs.The air temperature, relative humidity, and curing procedures aresummarized for all decks and shown in Table 2. Typically, concreteplacement is scheduled for the late evening or early mornings. Ide-ally, the placement should commence in the evening and extendinto the night when the temperature has dropped and the relativehumidity is high. The time duration for the placement of each deckis summarized in Table 2.3.1. Bridge deck 1The first bridge deck visited is an interstate overpass. The bridgedeck was cast in the middle of June, and concrete placement beganat 5:45 AM. The bridge is a two-span plate girder bridge with spansof 45.4 and 37.5 m (149 and 123 ft.) and 13 m (43 ft.) wide. The to-tal quantity of concrete used was 253 m3(331 yd3), pouredcontinuously.Like most bridge decks visited, the concrete was pumped up tothe deck. One construction worker with a commercial pressurewasher fogged the concrete in the area of placement. The concretewas then screeded, floated with a pan attached to the finishing ma-chine, and then manually tined with a rake. Finally, a curing com-pound was applied and then covered with a plastic/cotton mat.3.2. Bridge deck 2The second bridge deck visited was also an interstate bridgeoverpass. The deck was cast in the middle of July and concreteplacement began at 9:00 PM. The overpass is 100 m (330 ft.) long,comprising of four spans of curved plate girder units, and 10 m(32 ft. 6 in.) wide. The total quantity of concrete used was 252 m3(330 yd3), continuously poured.The concrete was pumped up to the deck. One constructionworker fogged the concrete at the surface near the finishing ma-chine (prior to floating). The concrete was screeded and pan floatedby a device which was attached to the finishing machine. The con-crete was then bull floated with a 3.05 m (10 ft.) rounded float, andthen manually tined with a rake. The concrete was then sprayedwith a curing compound and later covered with burlappolyethyl-ene sheeting for final cure.3.3. Bridge deck 3The third deck was a large city bridge that spanned a river. Theplacement consisted of 305 m3(400 yd3) of concrete and was acontinuous pour. The deck was cast in late August at 3:15 AM.The plate girder bridge spans 112 m (367 ft.) with spans of 34.5,43, and 34.5 m (113, 141 and 113 ft.). The bridge deck is 13 m(42.6 ft.) wide.The concrete was pumped, screeded with the finishing machine,floated with a pan attached to the finishing machine, bull floated,and then tined with a finned float. Like the previous decks, oneconstruction worker fogged the concrete near the finishing ma-chine using a pressure washer. The concrete was then sprayed withcuring compound and later covered with burlappolyethylenesheeting.3.4. Bridge deck 4The fourth bridge deck was a state highway bridge that spanneda drainage ditch. The bridge was placed in early September. Thethree-span bridge was a steel girder (w-section) bridge with spansof 11.6, 14.6, and 11.6 m (38, 48 and 38 ft.). The bridge deck was10 m (32.8 ft.) wide. The placement consisted of 89 m3(117 yd3)of continuously poured concrete.The concrete was pumped, screeded with the finishing machine,floated with a pan and dragged with burlap that were both at-tached to the finishing machine. It was then tined with a rake,sprayed with curing compound, and later covered with burlappolyethylene sheeting.3.5. Bridge deck 5The final bridge deck is a US highway spanning a small creek.The bridge deck was placed in late September. The deck was a131 m3(171 yd3) continuous pour placement. The concrete waspumped, screeded with the finishing machine and floated with apan attached to the finishing machine. The deck was bull floatedwith a 3.05 m (10 ft.) rounded float, and then manually draggedwith burlap. It was then tined with a rake, sprayed with curingcompound, and later covered with burlappolyethylene sheeting.4. Results and discussion4.1. Crack mappingAfter the bridge decks were sampled, each deck was revisited toassess cracking. For Bridge Deck 1, cracks were mapped on 04/05/06 (10 months after placement) after the bridge was open to trafficand after the contractor had sealed larger cracks at some time priorto opening. Crack density represents crack length per unit area. Theresearchers attempted to map all cracks in 3.7 ? 30.5 m (12 by100 ft.) section of south bound lane, but after measuring 12 m(40 ft.) of the 3.7 (12 ft.) wide section, cracking became too smalland random to effectively map. A 3 ? 3.7 m (10 by 12 ft.) sub-areawas measured as a representative sample. From visual estimation,the density was approximately the same as the representativesample for the remainder of original 30.5 m (100 ft.) section,Table 2Summary of observations for all decks.BridgedeckTime ofplacementSize of placement(m3)Air temp. range(?C)Ave. R.H(%)Time to curing compoundapplication (h)Time to final curea(h)Amount of cracking(m/m2)15:45 AM12:20 PM2532035570.5115.51.0329:05 PM3:05 AM22132287237.000.0433:15 AM12:20 PM30624356963.500.3746:00 AM10:15 AM8919345335.750.0257:05 AM10:40 AM1312236532.55.000.17aTimes are from the end of the placement.72S.W. Peyton et al./Construction and Building Materials 34 (2012) 7076although it lessened some in the last 4.6 m (15 ft.). The cracks ran-ged from 100 mm (4 in.) to 14.6 m (48 ft.) in length and from lessthan 0.127 mm to 0.61 mm (0.0050.024 in.) in width. The crackswere a network of transverse and longitudinal cracks with diagonalcracks connecting them. Long lines of cracking in the wheel path ofthe lanes were observed. Also, cracks were concentrated over thecenter support (near the middle sampling location) of the deck.This could possibly be due to a combination of vibrations from traf-fic passing under the bridge (which were noticeable) and low com-pressive strengths (at least up to 7 days) at this section.Bridge Deck 2 was revisited on 08/01/05, 1 year after place-ment. The visible cracks were measured for the entire length andwidth of the bridge. The cracks ranged from 76 mm to 5 m (3 in.16.4 ft.) in length and 0.05 mm to 0.40 mm (0.0020.016 in.) inwidth. The cracks were mostly transverse and heavily concentratedin the positive moment section. The flexural cracks were locatedmainly near the piers and the plastic shrinkage cracks were locatednear the low gutter (the downhill side of the deck). Large amountsof paste were brought down to this side during construction usinga highway screed. This increase in the amount of paste could havecontributed to increased shrinkage in that area.Bridge Deck 3 was revisited on 01/27/06, 5 months after place-ment. The research team measured the cracking in a 3.7 by 30.5 m(12 by 100 ft.) section of the west bound lane. The cracks rangedfrom 0.9 to 3.7 m (312 ft.) in length and were less than0.18 mm (0.007 in.) wide. The cracks were almost exclusivelytransverse cracks that started and stopped at similar points inthe cross section (near beam lines).Bridge Deck 4 was revisited on 02/09/06, 6 months after place-ment. The research team measured cracking in a 3.7 by 30.5 m (12by 100 ft.) section of the deck. There was very little cracking in thedeck. The cracks ranged from 152 mm to 1.2 m (3.2 in. to 4 ft.) inlength and 0.05 to 0.25 mm (0.0020.01 in.) in width.Bridge Deck 5 was mapped on 02/10/06, 5 months after place-ment. The cracks were measured over a 3.7 by 20 m (12 by66 ft.) section. The cracks were 0.601.50 m (25 ft.) in lengthand were 0.050.18 mm (0.0020.007 in.) wide. There were somecracks that were 0.601.50 m (25 ft.) long and were at 45? anglesto the intermediate bents.4.2. Fresh concrete dataAs stated in the Testing Program, the fresh concrete propertieswere measured in two or three random locations (determined byAHTD) for each bridge deck. If the bridge deck was large enough,the sampling locations were typically at the beginning, middle,and ends of the bridge deck. The results of all the fresh concretetests, the amount of cracking and the AHTD specifications for eachproperty are shown in Table 3.From Table 3, one can see that four of the five bridge decks hadslumps that exceeded AHTD specifications in at least one location.Bridge Deck 1 was the only deck where all slumps fell within the25100 mm (14 in.) specification. For the air content, three ofthe five bridge decks had measured air contents that did not meetAHTD specifications. Only two bridge decks had fresh concretetemperatures that were greater than that allowed by AHTD.The final fresh concrete properties shown in Table 3 are the cal-culated and measured unit weights. The calculated unit weightsare based on the concrete mixture proportion used by the concretesupplier and assuming a fresh concrete air content of 6%. The dif-ferences between calculated and measured unit weights rangedfrom a low of 16.02 kg/m3(1 lb/ft3) to a high of 144.2 kg/m3(9 lb/ft3). These differences between calculated and measured unitweights could be attributed to the addition of extra mixing waterand/or to higher or lower than expected air contents.In an attempt to determine if there were any relationships be-tween the fresh concrete properties and crack density, the averageslump, air content, differences between measured and calculatedunit weights, and concrete temperature were plotted versus thecrack density. Each bridge deck was ranked by each concrete prop-erty and assigned a ranking. For example, Bridge Deck 1 had anaverage slump of 80.5 mm (3.17 in.) which was the lowest averageTable 3Fresh concrete properties.Bridge deckSlump (mm)Air content (%)Calculated unit wt. (kg/m3)Measured unit wt. (kg/m3)Concrete temp. (?C)Amount of cracking (m/m2)1895.822442292281.03836.3226032704.9a3221143.822442372350.041843.5234033642.223883531593.222442308330.37894.61281275.023243542109.222602180230.021528.722122751525.722282260270.17894.8230830AHTD Specifications2510048NoneNone432?aUnit weight samples were not taken.0123450.000.200.400.600.801.001.20Crack Density (m/m2)Ranking (5 = Greatest & 1 = Least)SlumpAir ContentUnit Wt. Diff.Concrete Temp.Fig. 1. Fresh concrete properties and crack density.S.W. Peyton et al./Construction and Building Materials 34 (2012) 707673slump of the five decks, and therefore it received a ranking of 1.Likewise, Bridge Deck 4 had the greatest average slump, 181 mm(just over 7 in.), and received a ranking of 5. Shown in Fig. 1are the rankings for each fresh concrete property and crack density.The graph shows that Bridge Deck 1, which had the highest crackdensity of 1.03 m/m2(0.315 ft./ft2), did not have the greatest valuefor any of the fresh concrete properties. Bridge Deck 1 had the sec-ond highest air content, third highest concrete temperature, fourthhighest unit weight, and was ranked last in unit weight differenceand slump. For the concrete properties measured and bridge deckssamples, there was no correlation between fresh concrete proper-ties and crack density.To further support this conclusion, a statistical comparison ofthe measured properties based on a 90% confidence interval indi-cates the following:1. There were no significant difference between the measuredslumps of the five decks and the true mean slump values fallwithin the specified limits of 25100 mm (14 in.). However,a comparison of the crack density for the five decks indicatesa wide scatter, which confirms a lack of trend between slumpand crack density.2. The true mean values of air content for the five decks meet thespecified limits of 6 2% (Fig. 2). However, Bridge Decks 2 and 4have the highest and lowest values of air content respectively,and similar values for crack density.3. There is no trend between unit weight and crack density.4. There is no significant difference between the concrete temper-atures of the five decks and therefore, the level of cracking mea-sured on either of the decks cannot be directly attributed tovariations in concrete temperature.4.3. Hardened concrete propertiesThe results from the compressive strength tests are shown inTable 4. Three cylinders for compressive strength testing were castfrom either two or three random locations (as determined byAHTD) in each bridge deck. The amount of cracking is also shownfor each bridge deck in Table 4. For all decks, the contractors optedto pour each deck continuous, which by AHTD specifications, re-quires that all the concrete remain in a plastic state until concreteplacement is finished. For this reason, a set retarder was used in alldecks.The first bridge deck that was visited (Bridge Deck 1) had thelowest 1 day strengths. The first and last sampling location had a1 day compressive strength of approximately 2 MPa (300 psi)while the middle sampling location had a 1 day compressivestrength of 0.42 MPa (60 psi). At 2 days of age, cylinders that weresampled from the first and middle locations of the bridge deckwere tested. These tests showed that the first location had gainedover 14 MPa (2 ksi) in 24 h, but the middle section was still muchlower (a compressive strength of 0.90 MPa (130 psi). By 28 daysand 56 days of age, the middle section had reached similarstrengths as the first and last sections of the bridge. However,the research team did observe several transverse cracks in the cen-ter section of the Bridge Deck 1. These cracks could be the result ofthe low compressive strengths of the middle location and the cor-responding higher compressive strengths of the surrounding re-gions, but one cannot be certain due to the limited number ofsampling locations. Statistical comparison of the measured 7-daycompressive strengths does indicate a significant difference be-tween Bridge Decks 2 and 3 (Fig. 3) and a corresponding differencebetween the crack densities. The 28-day compressive strengthsresult shows a significant difference between Bridge Decks 1 and3 (Fig. 4). Bridge Deck 1 has the highest value of compressivestrength and the highest degree of cracking. The level of crackingon Bridge Deck 3 (compressive strengths more than 10 MPa(1.4 ksi) less than Deck 1) is three times that of Deck 1. Also, the28-day compressive strength of Bridge Deck 1 exceeds the speci-fied compressive strength by a minimum of 12 MPa (1.7 ksi), indi-cating that higher compressive strengths could contribute tohigher levels of cracking.02468101212345Air Content (%)Bridge DecksFig. 2. Statistical comparison of measured air content.Table 4Compressive strength results (MPa).aBridge deck1 Day2 Day7 Day28 Day56 DayAmount of cracking (m/m2)12.317.846.047.21.030.40.943.948.22.239.652.054.8223.635.134.940.20.0436.224.639.840.247.7310.225.330.332.00.3714.724.728.931.213.426.432.534.1416.226.034.034.30.0219.730.538.038.332.662.8520.427.6725.030.436.739.3aFor each deck, each row represents one sampling location.74S.W. Peyton et al./Construction and Building Materials 34 (2012) 7076The only other bridge deck to have large variations in compres-sive strength was Bridge Deck 4. This deck was a smaller pour anddue to time constraints only a limited number of cylinders weresampled from the last portion of the deck. As seen in Table 4, thecompressive strengths at one and 28 days of age for the last sectionof the deck were much higher than the first two sections (over14 MPa (2 ksi) at 1 day and over 28 MPa (4 ksi) at 28 days). How-ever, unlike the Bridge Deck 1, the large variation in compressivestrength did not appear to contribute to bridge deck cracking. Forthis particular bridge deck, the concrete supplier was having prob-lems with the air content. For the first two sections the air contentswere at or near 9%, and efforts were being made to lower the aircontents. The researchers believe that the air content was indeedlower for the last section, which resulted in the higher compressivestrengths.The remaining hardened concrete properties are shown in Table5. These properties include permeability, durability factors, and112 day drying shrinkage. The permeability (measured by the RCIPtest) was measured at 28 and 90 days of age. ASTM and AASHTOclassify bridge decks with passing between 2000 and 4000 C ashaving moderate permeability. By 90 days of age, four of the fivedecks would be classified as having moderate permeability.The durability factor was determined by AASHTO T161A. Mostresearchers recommend a durability factor of at least 60 to provideadequate freezing and thawing resistance. Four of the five bridgedecks had durability factors that were greater than 60. Bridge Deck5 had a durability factor of only 47 which is indicative of poorfreezing and thawing resistance. Most likely the aggregate source(river gravel) was the cause of the poor durability, since the aircontents were near 5% and the specimens experienced crackingnear and around the coarse aggregate. The final hardened concreteproperty measured was drying shrinkage. Problems with thelength change comparator were encountered for the specimensfrom Bridge Deck 1. The remaining shrinkage values ranged from339 to 467 microstrains at 112 days of age for specimens castsfrom Bridge Decks 2 through 5.As with the fresh concrete properties, the hardened concreteproperties were ranked and plotted versus the cracking density(Fig. 5) to determine if there were any relationships between thehardened properties and cracking for the decks in this study. Eachhardened property was ranked from 1 to 5 and the rankings wereplotted. Like the fresh concrete data, there were few if any correla-tions between the hardened properties and cracking. Bridge Deck 1did have the greatest 7 and 28 day compressive strength and themost cracking, but Bridge Deck 3 which had the second highest le-vel of crack density also had the lowest compressive strength at 7and 28 days of age.4.4. CuringAs stated previously, AHTD specifications allow the use of sev-eral different materials for concrete curing. All the materials usedto cure the five decks met the specifications. AHTDs specificationsalso require that the bridge deck be covered immediately after fin-ishing and that it remains covered for at least 7 days. During these7 days, the curing materials must be kept wet (except for mem-brane curing). All bridge decks were moist cured for the 7 days,but there were differences among the contractors as to whenimmediately after finishing curing began. The application of final05101520253035404512345Compressive Strength (MPa)Bridge DecksFig. 3. Statistical comparison of measured 7-day compressive strengths.0102030405060708012345Compressive Strength (MPa)Bridge DecksFig. 4. Statistical comparison of measured 28-day compressive strengths.Table 5Hardened concrete properties.aBridgedeckRCIPb(C)DurabilityfactorUnrestrainedshrinkage(microstrains)Amount ofcracking(m/m2)28 Day90 Day12807255199NAc1.032401928981014510.04353004072864470.374255230471054670.02524242429473390.17aPermeabilities, durabilities, and shrinkage are averages of four specimens.bValues are at 112 days.cLength change difficulties.0123450.000.200.400.600.801.001.20Crack Density (m/m2)Ranking (5 = Greatest & 1 = Least)7 day fc28 day fc28 day RCPT90 RCPTDF112 day ShrinkageFig. 5. Hardened concrete properties and crack density.S.W. Peyton et al./Construction and Building Materials 34 (2012) 707675cure ranged from 3.5 h to 15.5 h after final placement of the deck.Also, there were significant differences among the contractorsregarding application of the curing compound. Curing compoundapplication ranged from 30 min to 6 h after the deck was tined.As with the fresh and hardened properties, the curing times andcrack density were plotted in Fig. 6. Similar to the fresh and hard-ened properties, there were no correlations or trends observed forall the decks. However, the two bridge decks with the greatestamount of cracking, Bridge Decks 1 and 3 had the longest time tofinal cure and the longest time to the application of the curingcompound, respectively.5. ConclusionsThe res