(asce)cf.1943-5509.0000504

Chloride Penetration Resistance of a Ternary BlendLightweight Concrete Bridge DeckRyan Ankabrandt 1and Edwin Burdette,F.ASCE 2Abstract:In 2010,the Tennessee Department of Transportation (TDOT)launched a bridge rehabilitation project to rerate all truss bridges with gusset plate connections due to the federal mandate after the Minneapolis bridge collapse in 2005.One bridge that needed to be renovated was the Hurricane Bridge in Dekalb County,Tennessee.To provide a durable bridge deck and meet the latest highway loading specifications,TDOT used a Class L ternary (sand-lightweight ternary)mix instead of their standard Class D (normal weight nonternary)bridge deck mix.While placing a section of the deck,TDOT would cast cylinders to send to the University of Tennessee for rapid chloride penetration (RCP),surface resistivity (SR),and compressive strength testing.Previous RCP and SR testing of the TDOT Class D mix found that the mix provides poor to moderate chloride ion penetration resistance.Research reported herein supports the use of the TDOT Class L ternary mix as an alternative to the TDOT Class D mix in order to increase bridge deck durability.The results of the Class L ternary mix cylinder testing show a decrease in chloride ion penetration,an increase in surface resistivity,higher compressive strengths,and a higher correlation between SR and RCP than Class D cylinders.DOI:10.1061/(ASCE)CF.1943-5509.0000504.©2014American Society of Civil Engineers.Author keywords:Ternary blend;Durability;Bridge deck;Surface resistivity;Chloride ion penetration.IntroductionThe Tennessee Department of Transportation (TDOT)regularly uses a Class D normal weight (NW)concrete mix for highway and inter-state bridge decks throughout the state.For proportioning and qual-ity assurance,the mix requires 27.6MPa (4,000psi)minimum 28-day compressive strength,368kg =m 3(620lbs =yd 3)of cementi-tious material,0.40maximum water-to-cement ratio,6.0–8.5%air (for pumpability),and a 203.2-mm (8-in.)maximum slump [76.2-mm (3-in.)maximum before addition of high-range water-reducing admixture (HRWRA)](TDOT 2006).During the past decade,a study has been ongoing at the Uni-versity of Tennessee (UT)dealing with the durability of the Class D mix.The emphasis of the study was to determine the resistance to chloride ion penetration of the mix using the surface resistivity (SR)test and the rapid chloride penetration (RCP)test.For the past 3years,UT has been performing SR and RCP tests on Class D mix cylinders from various bridge deck placements across Tennes-see.From the studies performed at UT,the majority of Class D mix bridge decks were found to be,at best,mediocre in terms of resisting the penetration of chloride ions into the concrete.Despite there being no requirements on the use of mineral admixtures in the Class D mix,most of the mixes were found to contain 100%port-land cement or,more commonly,portland cement with a relatively small amount of Class F fly ash.While work done by UT both in the laboratory and in cooperation with a local ready-mix supplier showed clearly that the use of a ternary blend mixture containing cement,fly ash,and ground granulated blast furnace slag (GGBFS)(herein referred to as slag cement)was better in terms of resistance to chloride ions,TDOT has never implemented such a mixture on an entire bridge deck.Recently,the need for a high-performance lightweight concrete (HPLWC)bridge deck arose with TDOT ’s rehabilitation of the Hurricane Bridge.To ensure greater durability with lower chloride ion penetration,TDOT decided that the Hurricane Bridge deck would consist of a lightweight (LW)ternary mix incorporating portland cement,fly ash,and slag cement (TDOT 2010)instead of the typical 100%portland cement or binary Class D mix.This decision led to the work presented in this paper.Hurricane BridgeIn the fall of 1947,the construction of the Hurricane Bridge started as a means to carry relocated State Route 56over the Caney Fork River in northern Dekalb County,Tennessee,in order to accommo-date the closure of the newly constructed Center Hill Dam and subsequent impoundment of the river.Two years later construction of the bridge was finished and the bridge opened to traffic (Fig.1).Designed by the Nashville District of the U.S.Army Corps of Engineers,the 544.4-m (1,786-ft)–long Hurricane Bridge resided 82.9m (272ft)above the river bed and consisted of two 235.0-m (771-ft)–long continuous Warren deck trusses spaced 7.3m (24ft)on centers and a 18.6-m (61-ft)two-span deck girder unit at each approach (Wasserman 2012).In 1977,the bridge was modified from the original 7.3-m (24-ft)roadway and 457.2-mm (18-in.)safety curbs to a 13.4-m (44-ft)–wide deck to provide improved sight distance near the entrance to the newly constructed Edgar Evins Appalachian Craft Center.Widening was accomplished with the addition of cantilevers to the truss floor beams to support two new lines of stringers and two new lines of beams to the approach spans.Analysis of the modified system determined that the bridge could accommodate AASHTO HS-20(AASHTO 1973)loading at operating levels and HS-15(AASHTO 1973)loading at the inventory level,which was consid-ered satisfactory considering the low density of commercial traffic1Graduate Research Assistant,Dept.of Civil Engineering,Univ.of Tennessee,92Dune Lakes Circle,Santa Rosa Beach,FL 32459.2Fred N.Peebles Professor of Civil Engineering,Univ.of Tennessee,913Tampa Rd.,Knoxville,TN 37923(corresponding author).E-mail:eburdett@Note.This manuscript was submitted on March 5,2013;approved on July 29,2013;published online on July 31,2013.Discussion period open until October 20,2014;separate discussions must be submitted for indivi-dual papers.This paper is part of the Journal of Performance of Con-structed Facilities ,©ASCE,ISSN 0887-3828/04014011(7)/$25.00.D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y S h a n g h a i J i a o t o n g U n i v e r s i t y o n 08/04/14. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .on the route (Wasserman 2012).The concrete deck consisted of a TDOT Class A mix that requires a 20.7-MPa (3,000-psi)minimum 28-day compressive strength,334.6kg =m 3(564lbs =yd 3)of ce-mentitious material,0.45maximum water-to-cement ratio,6(Æ2)%air content,and 76.2Æ25.4mm (3Æ1in :)slump (TDOT 2006).In 2010,in light of the federal mandate to rerate all truss bridges with gusset plate connections due to the Minneapolis bridge col-lapse,TDOT launched a major bridge rehabilitation project on the Hurricane Bridge through TDOT ’s Better Bridges Program.Originally designed for the HS-15load,the bridge is being retro-fitted to accommodate HL-93(AASHTO 1973)loading.Retrofit work items include concrete repairs,sand blasting,repainting,and strengthening the substructure,selected compression diago-nals,floor beams,and stringers,as well as seismically strengthen-ing the bearings (Wasserman 2012).To decrease dead loads and increase durability,the new bridge deck will use a TDOT Class L ternary concrete mix,which has the same proportioning and quality assurance requirements as the Class D mix mentioned pre-viously.The Class L ternary mix is technically considered a sand-lightweight ternary mix according to the American Concrete Institute (ACI),meaning normal weight natural sand was used as the fine aggregate instead of lightweight fine aggregate.How-ever,because all bridge decks and tests being mentioned used sand-lightweight,for the remainder of the paper sand-lightweight will be referred to as simply lightweight (ACI Committee 318-2011).The cementitious material for the mix consists of 60%portland cement,20%Class C fly ash,and 20%Grade 100slag cement.Research SignificanceWhile there has been a fair amount of research done on improving concrete bridge deck durability,there have been no studies of whichthe authors of this paper are aware that were solely focused on the permeability of lightweight aggregate ternary concrete mixtures in bridge decks.The intent of using slag cement and Class C fly ash as partial replacement of portland cement for the lightweight aggre-gate concrete bridge deck was to reduce long-term repair costs by increasing the concrete durability.The study described herein not only supports the implementation of ternary lightweight concrete mixtures,but also addresses the correlation between the SR [AASHTO TP 95(2011)]and RCP [ASTM C1202(2010b )]test methods.Literature Review:Relevant TestingThis literature review focuses on research related to the durability of structural lightweight concrete.ACI defines structural light-weight concrete as structural concrete made with low-density ag-gregate that has an air-dry density of not more than 1;842.1kg =m 3(115lb =ft 3)and a 28-day compressive strength of more than 17.2MPa (2,500psi)(ACI 2000).Numerous bridges have incor-porated LW concrete in one aspect or another to reduce the struc-ture ’s dead loads and reduce transportation and structural costs.The use of LW concrete bridge decks can significantly reduce dead loads,which translates to longer spans,greater girder spacing,or the use of fewer girders.LW concrete can also lead to less main-tenance and longer life (Ozyildirim 2011).However,with LW con-crete there would appear to be a greater concern for durability from an increased rate of ingress of aggressive ions due to the porous nature of the LW aggregates.To a large extent durability is con-trolled by permeability.In order to increase the durability the per-meability must decrease,which depends on the type and amount of supplementary cementitious material (SCM),curing method,andFig.1.State Route 56Hurricane Bridge after completion (image courtesy of U.S.Army Corps of Engineers,Nashville,TN District)D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y S h a n g h a i J i a o t o n g U n i v e r s i t y o n 08/04/14. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .water to cementitious material ratio (w/cm)of the concrete mix (Ozyildirim 2009).Despite the porosity of LW aggregates,studies have shown that LW concrete has equal or less permeability compared to NW con-crete (Wall and Freeman 2003).This seeming anomaly is attributed to a combination of an improved interfacial transition zone,a more unified structure,and a reduction of internal stresses due to volume changes in the initial unloaded state.Throughout the United States,bridge decks are often subject to acidic chemicals through ocean saltwater or deicing salts (sodium chloride or simply NaCl)used to prevent and reduce ice forming on the deck surface during inclement weather.Shrinkage cracks and pores in the concrete provide access for harmful chemicals to pass through the concrete to the embedded reinforcement.Despite the normally high pH of the concrete,the passive layer around the reinforcing steel formed from the interaction of steel and concrete cannot resist the corrosive attack (ACI Committee 201-2008).Thus,SCMs are often introduced into the mix to enhance the ability of the slab to reduce the penetration of chloride ions through the concrete to the reinforcement.Mineral admixtures such as silica fume,fly ash,and slag cement are some common SCMs that have been proven to lower the permeability of LW concrete by rein-forcing the LW aggregate and the paste-aggregate interface (Wang 2005).In 2009,the Virginia Center for Transportation Innovation and Research (VCTIR),formerly the Virginia Transportation Research Council (VTRC),performed laboratory tests on high-performance lightweight (HPLW)concrete bridge beams and decks over the Manttaponi and Pamunkey rivers on Route 33in Virginia to evalu-ate various concrete properties with different curing conditions.For both bridge decks,a maximum penetration of 2,500coulombs and a 28-day compressive strength of 34.5MPa (5,000psi)were specified.The mixture proportions were the same for both bridge decks and consisted of 348.99kg =m 3[588pounds per cubic yard (pcy)]Type II cement,87.2kg =m 3(147pcy)Class F fly ash,563.6kg =m 3(950pcy)lightweight coarse aggregates,662.1kg =m 3(1,116pcy)normal weight natural sand,174.4kg =m 3(294pcy)water,and air-entraining,water-reducing,and water-retarding admixtures.The samples taken during each bridge casting were continuously moist cured until testing.The first and second batches from the Mattaponi Bridge deck had 28-day compressive strengths of 42.1MPa (6,110psi)and 43.5MPa (6,310psi),respectively,and 28-day permeabilities of 939and 976coulombs,respectively.The first and second batches from the Pamunkey Bridge had 28-day compressive strengths of 48.7MPa (7,060psi)and 41.6MPa (6,040psi),respectively,and 28-day permeabilities of 1,411and 1,940coulombs,respec-tively.Permeability values were all satisfactory and considered to be either low or very low (Ozyildirim 2009).In 2011,VCTIR did a similar study on HPLW concrete with LW aggregates from varying locations and subjected to different curing conditions while trying to determine if the SR test is a good indicator of permeability and could be used in lieu of the time-consuming RCP test.Both batches for the permeability study used LW aggregates from North Carolina,a w/cm ratio of 0.40,and 356kg =m 3(600pcy)of cementitious material.One batch used 30%fly ash and 70%portland cement for the cementitious material,and the other used 50%slag cement and 50%portland cement.Permeability was determined by the RCP test in accor-dance with Virginia Test Method 112(VTM 112)[Virginia Depart-ment of Transportation (VDOT)Materials Division 2007],which is based on the ASTM C1202standard (ASTM 2010b ).The VTM 112varies slightly from the 2010revision of the ASTM C1202in that it includes accelerated wet curing,which involves 1week at room temperature and 3weeks in a 37.8°C (100°F)water bath (Ozyildirim 2011).As shown in Table 1,the permeability improved with accelerated curing,and low permeability was obtained with the addition of fly ash or slag cement.Also in 2011,UT researchers tested two batches of TDOT field-cast Class L (lightweight binary)cylinders.The Class L mix used similar proportioning and quality assurance requirements as the Class D mix mentioned previously,but required a maximum water-to-cement ratio of 0.39instead of 0.40and used 25%Class C fly ash and 75%portland cement as cementitious materials.The compressive strength of the Class L cylinders exceeded TDOT ’s minimum 28-day strength of 27.6MPa (4,000psi)as expected,but the SR and RCP results were subpar.Both batches had 28-day RCP and SR values over 7,300coulombs and less than 9kOhm-cm,respectively,and 56-day RCP and SR values over 4,100coulombs and less than 12kOhm-cm,respectively,which are considered high chloride ion penetration values by Kessler et al.(2005)and extremely high values by UT researchers.In 2012,in addition to continued testing of TDOT 101.6×203.2mm (4×8in :)field-cast Class D cylinders,UT researchers performed SR [AASHTO TP-95(2011)]and RCP [ASTM C1202(2010b )]tests on UT laboratory-cast NW ternary cylinders and laboratory-cast LW binary and ternary cylinders.The LW binary (LWB)mix ’s cementitious material incorporated 25%Class F fly ash and 75%portland cement.The NW ternary (NWT)and LW ternary (LWT)mix ’s cementitious material was composed of 20%Class F fly ash,30%slag cement,and 50%portland ce-ment.All of the cylinders from the three mixes were cured in the same lime water bath.As shown in Table 2,the LWT mix out-performed the LWB and NWT mixes.According to the chloride ion penetration classification in Table 3,the binary mix had low pen-etrability and the two ternary mixes had very low penetrability.Surprisingly,the NWT and LWB mixes had relatively close 56-day SR values,but as expected the NWT mix had a lower 56-day RCP than the LWB mix,primarily because of the addition of slag cement.Other than the supplementary cementitious materials,the differences in aggregates used might account for any discrepancies in the results.Table 1.Virginia Penetrability Results (Data from Ozyildirim 2011)Curing conditionAge (days)Concrete with fly ashConcrete with Slag Cement RCP (coulombs)SR (kOhm-cm)RCP (coulombs)SR (kOhm-cm)Moist cure (MC)282,91215.141,35330.31MC 1wk 73°F +3wk 100°F 2829870.0161441.59MC 2wk 73°F +2wk 100°F 2854850.6268839.42MC 3wk 73°F +1wk 100°F 281,19025.7496030.29MC362,18718.80——D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y S h a n g h a i J i a o t o n g U n i v e r s i t y o n 08/04/14. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Hurricane Bridge Deck EvaluationThe study reported in this paper focused primarily on the LW con-crete used on the Hurricane Bridge on State Route 56in Dekalb County,Tennessee,and the performance of that concrete in terms of resistance to chloride ion penetration.The LW aggregates used for the Hurricane Bridge and UT laboratory mixes mentioned pre-viously were 18-mm (3=4-in :)Stalite rotary kiln expanded slate from North Carolina (Stalite 2008,2011).Engineering index properties of Stalite ’s 18-mm (3=4-in :)LW stone can be found in Table 4.The weight saving by using this mix was approximately 20%at an additional cost of roughly 25to 40%above that for a typical Tennessee Class D mix.For the Hurricane Bridge renovation there was no required mini-mum SR value or maximum permeability value (RCP)for the con-crete bridge deck,but a general desire for moderate or better chloride ion penetration was expressed by TDOT.As noted previ-ously,tests of the Class D binary mix used throughout Tennessee for almost all bridge decks indicated mediocre (at best)resistance to chloride ion penetration.While the number of decks that utilized lightweight aggregate were few,those few tests also yielded medio-cre penetration resistance.Thus,the conclusion followed that a change was needed if the desired chloride ion penetration resistance was to be achieved.This conclusion led to the decision to use a ternary blend mixture of portland cement,fly ash,and slag cement for the deck of the Hurricane Bridge.The role of the researchers at UT was (1)to suggest a mix design and (2)to evaluate the resulting resistance to the penetration of chloride ions.Unfortunately,theternary blend recommended by the researchers was,for unknown reasons,modified slightly to include 20%slag cement rather than 30%,and 60%portland cement rather than 50%of the cementitious material as recommended.Nonetheless,the mix used was expectedTable 2.University of Tennessee Laboratory Mix Designs and Penetrability Result Mix designNWT LWB LWT W/CM ratio0.370.400.40Total cementitious material (kg =m 3)368368368Cement (kg =m 3)184276184Fly ash class-F (kg =m 3)749274Slag cement grade 100(kg =m 3)1100110Water (kg =m 3)147147147Aggregates (kg =m 3)#57Lightweight1,10000#57Limestone 0552552Natural sand714770770Test results (102mm ×203mm cylinder)NWT LWB LWT 28Day compressive strength (MPa)52.351.354.528Day SR (kOhm-cm)46.125.877.628Day RCP (Coulombs)766207755056Day SR (kOhm-cm)60.660.3125.156Day RCP (Coulombs)5201471361Note:NWT =normal weight ternary;LWB =lightweight binary;LWT =lightweight ternary;SR =surface resistivity;RCP =rapid chloride penetration.Table 3.Chloride Ion Penetration Classification (Kessler et al.2005)Chloride ion penetration RCP test charge passed(coulombs)28day surface resistivity test102×203mm Cylinder (kOhm-cm)(a ¼1.5)152×305mm Cylinder (kOhm-cm)(a ¼1.5)Semi-InfiniteSlab High >4,000<12<9.5<6.7Moderate 2,000–4,00012–219.5–16.5 6.7–11.7Low 1,000–2,00021–3716.5–2911.7–20.6Very low 100–1,00037–25429–19920.6–141.1Negligible<100>254>199>141.1Table 4.Stalite 18-mm (3=4-in :)Expanded Slate Engineering Index Properties (Data from Stalite 2008,2011)Stalite physical characteristics and engineering properties 18-mm (3=4-in :)lightweight aggregatesTypical density (unit weight)Dry loose (ASTM C29)(ASTM 2009b )48lbs =ft 3768kg =m 3Dry rodded (ASTM C29)(ASTM 2009b )55lbs =ft 3880kg =m 3Saturated surface dry loose (ASTM C29)(ASTM 2009b )50lbs =ft 3800kg =m 3Maximum dry density (ASTM D4253)(ASTM 2000)60lbs =ft 3960kg =m 3Damp loose (ASTM C29)(ASTM 2009b )48–52lbs =ft 3768–832kg =m 3Typical relative density (specific gravity)Dry (ASTM C127)(ASTM 2012) 1.46Saturated surface dry (ASTM C127)(ASTM 2012)1.52Range in saturated surface dry (ASTM C127)(ASTM 2012) 1.47–1.54Sieve size %passing100(25mm)100%3=400(19mm)90–100%1=200(12.5mm)—3=800(9.5mm)10–50%#4(4.75mm)0–15%#8(2.36mm)—#16(1.18mm)—#30(600um)—#50(300um)—#100(150um)—AbsorptionSaturated surface dry (ASTM C127)(ASTM 2012)6.0%Soundness (%loss)Magnesium sulfate (ASTM C88)(ASTM 2013a )0–0.01%Sodium sulfate (ASTM C88)(ASTM 2013a )0–0.23%25cycles freezing and thawing (AASHTO T 103)(ASTM )0.22–0.80%ToughnessLos Angeles abrasion (AASHTO T 96)(AASHTO 2002)25–28%StabilityAngle of internal friction (loose)40–42°Angle of internal friction (compacted)43–46°Electrical resistanceLab (AASHTO T 288)(AASHTO 1991)30,000–40,000ohm-cm Field (ASTM G157-98)(ASTM 2013b )Over 500,000ohm-cmD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y S h a n g h a i J i a o t o n g U n i v e r s i t y o n 08/04/14. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .to represent significant improvement over the typical binary Class D mix.To evaluate the chloride ion penetration,two different test methods were used:the SR test and the RCP test.Both of these test methods had been employed by the UT research team during the three years leading up to the Hurricane Bridge project.Surface ResistivityThe surface resistivity test is a nondestructive test method that de-termines the electrical resistivity of concrete as an indication of its resistance to chloride ion penetration.The test is user friendly and applicable to concretes with various combinations of cementitious materials,but can produce misleading results when embedded electrically conductive materials like steel are present in the con-crete.For example,cores are the type of specimen that would be impermissible for the SR test because of potential contamination of conductive chloride ions.The SR apparatus is a meter with a Wenner linear four-probe array that measures the electrical re-sistivity of water-saturated concrete and provides an indication of the concrete ’s permeability.The test result is a function of the electrical resistance of the specimen (AASHTO 2011).The test method used by UT researchers follows the procedure outlined in AASHTO TP-95(2011).During the Hurricane Bridge deck placements,batches of 13101.6×203.2mm (4×8in :)cylinders were cast and (after final set)were delivered to UT where upon arrival they were unmolded,labeled,and immersed in a lime water bath in accordance with ASTM C31and ASTM C511(2010a ,2009a )for moist curing and extended moist curing (28and 56days of curing)according to ASTM C1202(ASTM 2010b ).Twenty-eight days after the cyl-inders were cast,3of the 13cylinders were removed from the bath for testing.SR tests consistent with AASHTO TP-95(2011)were then ter on,three more cylinders were removed from the lime water bath and subjected to the SR test for the 56-day tests,and then later on again for the 112day tests.Table 5presents the 28-day,56-day,and 112-day values for each SR test performed.All SR average values incorporate a 10%increase to account for lime water curing [AASHTO TP 95-11(2011)].Rapid Chloride PenetrationAfter completing the SR tests,the same three cylinders were then subjected to the RCP test,which follows the ASTM C1202(2010b )procedure.The RCP test is a measure of the electrical conductance of the concrete as an indication of its ability to resist chloride ion penetration (ASTM 2010).The RCP method is cumbersome and requires at least a day for sample preparation and a day for testing.At the end of the test the amount of coulombs passed through thespecimen was determined.Table 5provides the 28-day,56-day,and 112-day RCP test results of the Hurricane Bridge samples.All RCP average values incorporate a 12.1%reduction to account for the use of 101.6-mm (4-in.)cylinders instead of 95-mm (3.75-in.)cylinders [ASTM C1202(2010b )].Discussion of ResultsCylinders from eight bridge deck placements were collected and sent to UT for testing.Chloride ion penetration resistance was evaluated by the two methods just described,and three cylinders from each batch were tested at 28days for compressive strength.The results of the tests are presented in Table 5.As expected,all the cylinders exceeded TDOT ’s requiredminimum 28-day f 0cof 27.6MPa (4,000psi).They even could be considered high strength (ACI Committee 201-2008)because all of their values were more than 41.4MPa (6,000psi)as shown in Table 5.When compared to the limiting values in Table 3,the 28-day Hurricane Bridge SR and RCP values in Table 5reflect a moderate chloride ion penetration,which is good but not great.The RCP values lessen with time and the SR values increase with time,which can also been seen in the table.Ozyildirim (2003)stated that “a maximum value of 2,000or 2,500coulombs at 56days with stan-dard curing represents a good starting point for bridge deck con-crete.”As shown in Table 5,all of the batches have between 1,000and 2,000coulombs at 56days,which is considered low chloride ion penetration in Table 3.Another factor that impacts chloride ion penetration and sur-face resistivity is the cementitious blend percentages.While the Hurricane Bridge deck mix ’s cementitious blend of 60%portland cement,20%slag cement,and 20%Class C fly ash did achieve moderate chloride ion penetration,UT ’s similar LWT mix (Table 2),also with 367.8kg =m 3(620pcy)of cementitious material but with a cementitious blend of 50%portland cement,30%slag cement,and 20%Class F fly ash,achieved very low chloride ion penetra-tion in Table 3.Lower chloride ion penetrations should be attain-able regardless of which class of fly ash is used.While Class F is more readily available in Tennessee,concretes with Class C fly ash do typically offer higher early age strength from Class C fly ash ’s higher calcium content (Kosmatka et al.2002).Electrical conductivity and electrical resistivity are inversely related to one another;where conductivity can be defined as an object ’s ability to conduct electrical current and resistivity is the ability to resist electrical current (Ryan 2011).To justify the inverse relationship between SR (resistivity)and RCP (conductivity),the values from the Hurricane Bridge were plotted with 28-,56-,andTable 5.Hurricane Bridge “Class L-Ternary ”Mix Field-Cast 101.6mm ×203.2mm (400×800)Cylinder Test ResultsPlacement date 28day tests56day tests112day tests28day SR (kOhm-cm)28day RCP (Coulombs)28day f ’c (MPa)56day SR (kOhm-cm)56day RCP (Coulombs)112day SR (kOhm-cm)112day RCP (Coulombs)9/24/201213.2278944.426.9151449.27539/25/201213.9280442.129.1152756.384010/3/201212.4279041.824.3161350.974510/5/201215.1249850.029.8125450.771611/28/201211.6390646.325.81578NA NA 12/6/201215.4307553.427.11333NA NA 12/14/2012NA NA NA 24.1153260.36192/11/201315.1329548.433.91155NA NA Average13.6297746.327.2147051.7763D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y S h a n g h a i J i a o t o n g U n i v e r s i t y o n 08/04/14. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .。