I . . . . . Synopsis The performance of structural lightweight concrete in a

I..~~ Irl ...1r;. ....rlSynopsisThe performance of structural lightweight concrete in a marine environment is reviewed beginningwith the construction of concrete ships in World War I. Major laboratory programs, utilizing differentmethods of evaluating the durability characteristics of structural lightweight concretes are described.Physical properties that influence the weathering characteristics of structural lightweightconcrete, that differ significantly from corresponding properties of normal weight concretes arereported. Long term field exposure of lightweight concrete structures, including a 60 year old shipand a 25 year old bridge deck are reported. Criteria for the construction of durable lightweightconcrete structures exposed to marine conditions are recommended.KeywordsBridge decks; compressive strength; concrete construction; cores; field tests; freeze-thaw durability;lightweight aggregate concretes; marine atmospheres; modulus of elasticity; performance;physical properties; ships; weathering.Authorized reprint from American Concrete Institute Publication SP-65 "Performance of Concrete in MarineEnvironments," International Sym posium, St. Andrews By- The-Sea, Canada, August 1980.

Figure # 1 -Generalview- -Dry cargo lightweight concrejship, World War IIFigure # 2-Lightweight concrete barge passingunder lightweight concrete bridge deck-World War II

Thomas A. Holm is an active member of ACI, and is a memberof Committees 530,531 and213 of which he is past chairman.He is the Director of Engineering of Solite Corporation .The use of lightweight concrete in a marine environment ishardly a novel concept. Indeed, the origin of the lightweightaggregate industry as we know it today is to a large degreedue to the collaboration in 1918 of American shipbuildingauthorities with Stephen J. Hayde's development of astrong, inert, durable, lightweight aggregate producedfrom a shale, clay or slate in a rotary kiln. Feasibility studiesby marine engineers at that time indicated that a concreteship would be practical if the concrete used could meet therequirements of strengths exceeding 35 MPa (5 ksi) at adensity less than 1760 Kg/M3 (110 pcf) (1). Extensiveinvestigations revealed that while naturally occurring lightweightaggregates could not meet these conditions, rotarykiln produced expanded shale could exceed the requirements.On a practical basis the first commercia) productionof aggregate was conducted in a brick plant near Birmingham,Alabama with enough aggregate produced to supplyconcrete for the 3000 ton Atlantus launched in December1918 (2). Again in 1941, with the advent of WorldWar II, immediate consideration was given to the use oflightweight aggregate instead of natural sand and gravelfor the concretes to be used in the shipbuilding program.The same type of lightweight aggregate successfully usedin the World War I program was recommended for theconstruction of the second concrete fleet. Samples fromseveral commercial rotary kiln lightweight aggregate productionplants were sent to the laboratory of the PublicRoads Administration for tests and, after comprehensiveinvestigations, the rotary kiln lightweight aggregates proposedfor use were deemed satisfactory (3,4). In all, 104ships were constructed at five separate shipyards, withseveral different designs, with follow-up reports indicatingthe hulls to be watertight and having good riding qualitieswith little vibration (Figures 1, 2, 3).After World War II there was a rapid development in theproduction capacity of the lightweight aggregate industryin North America, in order to meet the growing demands forthe use of lightweight concrete masonry units. There wasalso the emerging use of structural lightweight concrete i~all forms of standard construction, principally in urbanareas for high rise concrete structures. At about the sametime lightweight concrete was incorporated into precast/prestressed plants where the strength levels were considerab)yhigher than the requirements of cast-in-placestructures. This widespread construction use of rotary kilnproduced expanded shale concretes was accompanied bymany technical papers, reports and investigations that aresummarized and digested in the "Guide for StructuralLightweight Aggregate Concrete" of the American ConcreteInstitute Committee 213 (5). At the present time,structural lightweight concrete in North America is notthought of as a fundamental departure from normal weightconcrete, but merely a concrete with more efficient physicalproperties.It appears that a third major application of concrete inmarine environments is presently underway, particularly inthe development of ocean resources for our future energyrequirements. Mobile floating platforms that could be towedto forward sites to provide operational or strategic functions,as well as massive permanent floating structureshousing ocean thermal-energy conversion systems couldbe effectively produced from structural lightweight aggregateconcretes of high specific strength (i.e. ratio ofstrength to density) (6, 7). In several seaboard locationsthere presently exists the production capacity of existinglightweight aggregate plants necessary to supply the hugedemands of such programs. In addition, the ability toproduce high quality, high strength-to-weight concretes iscurrently available. Further improvement over the successfulpast experience of structural lightweight concrete isalso possible through the use of modern techniques involvingproportioning concrete mixes with high-range waterreducers, the significant advantages of prestressing andpost tensioning as well as sophisticated structural designtechniques.This report will deal only with the durability performanceof concretes produced with structural lightweight aggregatesas well as several significant physical propertydifferences from regular weight concretes that have adirect, phenomenological relationship to resistance toweathering. For physical properties and related aspectsthat are common to all concretes in a marine environment(admixtures, cement type and chemistry, compactiontechniques, steel reinforcement, embedded items, etc.) thereader is referred to the comprehensive presentationsprovided by Gerwick (8,9).Figure # 3-Construction of lightweight concrete ship-World War II

The first major industry-wide laboratory investigation intothe freeze-thaw resistance of structural lightweight concreteswas conducted by Klieger and Hanson (10) at thePortland Cement Association Laboratory. Concretes fncorporatingnine lightweight aggregates manufactured byseveral different processes were tested with the primaryvariable being strength level, 20 and 31 MPa (3 and 4.5 ksi)with and without air-entrainment. Results were comparedwith tests on a reference normal weight concrete with agood service record in field performance. After a moistcuring period of 14 days, at 23°C (73°F), 100% RH, followedby drying in lab air for 14 days at 23°C (73°F), 50% RH, andthen a 3 day immersion in water, concrete prisms weresubjected to rapid freeze-thaw in water (formerly ASTMC-290, presently ASTM C-666 Method A). Severe laboratoryconditions were imposed on some of the specimens:low cement contents, non-air-entrainment, short dryingperiod, freeze-thaw continuously under water at an earlyage, and repetitive extreme moisture gradients that areunrepresentative of the weathering of actual structures. Itwas not surprising to have the authors conclude, "thespread in durability among the concretes made with thedifferent lightweight aggregates appears no greater thanmight be encountered with normal weight aggregates".High durability (small weight loss, insignificant expansionsand almost no decrease in sonic modulus) was demonstratedafter 300 cycles of freezing and thawing by theproperly proportioned, air-entrained lightweight aggregateconcretes. Expanding on the extensive date provided in thefirst PCA series, Pfeifer (11) continued with durabilitystudies of structural lightweight concretes and included astudy of the influence of replacement of a part of all of thelightweight fine aggregate fraction with natural sand.In an attempt to correlate the good field durability experienceof structural lightweight concretes in a number ofNorth American projects, the Expanded Shale Clay andSlate Institute sponsored three comprehensive series offreeze-thaw tests at the University of Toledo (12). In the firstseries eight rotary kiln produced lightweight aggregatesand one reference normal weight aggregate were testedwith the main variables being sand replacement of fineaggregate and moisture content of the lightweight aggregateat time of mixing. Rapid freeze-thaw in water procedureswere repeated. However, concretes were proportionedin accordance with usual field practice (aircontents at 6% and 1 %, 100 mm (4") slump and cementcontents for all mixes at 360 Kg/M3 (611 pcy). This programdemonstrated that structural concretes with high qualitymortar fractions and containing rotary' kiln produced lightweightaggregates performed satisfactorily for at least 300cycles of freezing and thawing in water, both with or withoutsand replacement. Comparing drying times of 14, 28 and56 days, the results obtained on the 32 concrete mixestested showed little variation, indicating that a drying periodof 14 days prior to the first freeze-thaw cycle was sufficientfor concretes mixed with aggregates at usual field moisturecontents.The results of these major programs that include hundredsof laboratory tests may be simplistically summarizedby noting that air-entrained lightweight concretes proportionedwith a high quality binder provide satisfactorydurability results when tested under usual laboratoryfreeze-thaw programs.Additionally, freeze-thaw test programs were conductedfor analysis by the technical committees of various engineeringsocieties. One series of tests (13) included comparisonsof testing environments, (freezing in air or water)as well as attempts to correlate freeze-thaw laboratoryconcrete tests with more convenient and rapid aggregatesoundness tests using cycles of wetting and drying in saltsolutions. These tests indicated that, in general, low soundnesslosses on aggregates correlated with good freezethawlaboratory performance of properly proportionedconcrete made from the tested aggregates. Suggestedsoundness and freeze-thaw criteria from these tests wereincorporated into the material specifications of some governmentorganizations.Each particular lightweight aggregate has a limitingstrength "ceiling" beyond which there can be no appreciablestrength gain despite large increases in cementitiousmaterials. This strength "ceiling" is a function of thestrength of the vitreous material and the quantity, size,shape and distribution of the enveloped pores, but thedecisive factor is the strength of the largest individualparticle. In one high strength lightweight concrete investigation(14), 10 mm (%") coarse aggregate top size consistentlyproduced strengths equal to or greater than normalweight concretes with equal binder content. One series ofresults is shown in Figure 4. Long term strength gain of thestructural lightweight concrete is generally greater than thecompanion normal weight concretes, due to the continuoushydration of the binder with the moisture available from theslowly released reservoir of water absorbed within thepores of the lightweight aggregate. This process of "internalcuring" is possible when the moisture content of the lightweightaggregate at the time of mixing is at least equal tothat achieved by soaking for one day. The effect of "internalcuring" is further enhanced if a pozzolan (fly ash or suitablelightweight aggregate fine fraction) is introduced into themix. It is well known that the pozzolanic reaction of a finelydivided alumino-silicate material with calcium hydroxideliberated as cement hydrates is contingent upon theavailability of moisture. It should be pointed out that thepozzolanic activity of some lightweight fine aggregates is adependable. consistent property that is fully exploited as acement replacement in the high temperature curing ofconcrete masonry units. In this application however, thepozzolanic behavior should be considered as a desirable,additional virtue, and not for cement reduction.

eo1."..{;;;0:7'""",~P--10910 mm SOLITEI , I---j--- 106 10 mm SOLITE-1110lUQ.~:I:1-"ZW11:1-00W>Ci500w11:Q.~O()6030120,,1,,' I-' 9~-11020 mm SOLITE (FiYASh)I--.L--~---1. 11115mmSTONE(AyAsh) 1~.:'~-~~--t-- o 107 20 mm SOLITE ,---8-10815 mm STONEIIL- 57643!~~w~w>~wa:0.~our--'f--21050 100 150 200AGE AT TEST-DAYSFigure # 4-Compressive strength versus age of lightweight and normal weightconcrete (1975-1979 series)

It is curious that in the material recommendations of theFederation Internationale de la Precontrainte (15) for thedesign and construction of concrete sea structures, there isa suggestion for the addition of pozzolanic material forordinary Portland cements having a C3A content greaterthan 8% , while in the aggregate section there is a recommendationagainst the use of fine aggregates which mayreact with the cement. Somewhere, within the continuum ofgradation, fine lightweight aggregate with the properphysical and chemical characteristics may transcend thisarbitrary division of mineral constitl)ents and simultaneouslyprovide roles of aggregate as well as cementitiousbinder. The U.S.S. Selma, a 7500 ton reinforced expanded shaleconcrete tanker launched in 1919 is perhaps the most vividtestament to the durability in a marine environment ofstructural lightweight concrete. After several years of servicethis vessel was purposely sunk in 1922 in GalvestonBay, Texas where it has remained partially submerged eversince. The hull has been in sea water for over 60 years with aband width of approximately 1 meter exposed to wettingand drying in salt air caused by wind and tides. The deckOne explanation for the excellent durability service recordof high strength lightweight concrete may lie in the similarityof the strength and stiffness characteristics of the coarselightweight aggregate and the remaining "mortar" fraction.It has been reported (14) that the stress-strain curves ofhigh strength lightweight concrete are linear to levelsapproaching 90% of the failure strength, (Figure 5) indicatingthe relative compatibility of the elastic and strengthcharacteristics of the coarse lightweight aggregate and themortar component (cement paste and natural sand), thatsurrounds the large aggregate. "Elastic Matching" of thetwo components, producing relatively "homogeneous"concrete, will be possible if the coarse aggregate partic)eshave sufficient particle strength to match the strengthcharacteristics of the mortar fraction. This separation of thestrength and elastic properties of the two components of aheterogenous concrete system has been thoroughlystudied by others (16, 17), but generally, in relation to a"stiff" aggregate in a "soft" mortar (high strength normalweight concretes), where EM < Ec < EA, concretes fail dueto bond limitations or microcracking initiated by an extremelyrigid coarse aggregate; or a "soft" aggregate in a"stiff" mortar (low density insulating lightweight aggregateconcretes), EM > Ec > EA, where failure is due to crushing ofthe very light, lightweight aggre.gate particles. A thirdsituation may exist wherein the coarse aggregate particlestrength and elastic characteristics closely match and aresecurely bonded to a high quality mortar fraction (EM ~ Ec ~EA). Analysis of this mechanism is currently underway andwill be reported at a later date. "Russian studies, approaching concrete durability from aphenomenological aspect, have also noted the high innerstress conditions due to different deformation responses ofthe various cj)nstituents, ". ..as elasticity modulus decreases...thestresseS'ln the conglomerate falloff, it leads...to the increase in frost resistance. And really, concretewith keramzite (lightweight) gravel and' sand, the elasticitymodulus of which is much less than that of volcanic solidrocks possess often greater frost resistance than, forexample, concrete made with granitic crushed stone" (18).and upper section of the hull have been exposed to salt airand occasionally awash with sea water due to wave actionin storms (Figure 6).A study of the concrete was sponsored by The ExpandedShale Clay and Slate Institute in 1953 and reported in thepublication, "Story of the Selma-Expanded Shale ConcreteExplores the Ravages of Time" (1 ). This study reportedthat cubes and cores taken from the waterline areahad compressive strengths of approximately 55 to 75 MPa(8 to 11 ksi) when normalized to 150 x 300 mm (6" x 12")cylinders. Modulus of elasticity was reported at 20 x 103MPa (3 x 106 psi) and a bond strength on plain reinforcingbars of 3.56 MPa (516 psi). Surprisingly little corrosion wasnoted despite a coverage of only 16 mm (5/8"} (Figure 7).In 1980 the Selma's performance was reviewed againwith cores taken for an up-date on the extensive testsconducted in 1953. Examination of both the submergedand waterline area cores of the sixty year old lightweightconcrete revealed little if any deterioration (Figure 8). Formmarks on the core's exterior surface were visible and noevidence of microcracking was observed when viewedunder a magnifying glass. The concrete was extremely wellcompacted (the first known application of internal vibrationtechniques) with only a small number of macroscopjc airvoids, coarse aggregate (minus V2") was well bonded to themortar fraction, uniformly distributed and without any indicationof water gain under large aggregate particles indicatinga fluid easily pJaced, but not wet concrete. (Anengineer in charge of the Emergency Fleet Corporation in1919 developed an apparatus to control the workability ofthe concrete from batch to batch and provided the industrywith the initial slump cone test). Particle shape of theaggregate was semi-angular to rounded, typical of modernlightweight aggregates. Visible pore structure of the lightweightaggregate was fine to medium.Core samples cut through the undeformed steel reinforcingbars showed little evidence of rusting. There wasalmost no sign of corrosion at the reinforcing bar to concreteinterface that could be observed when cut sections ofsteel were inadvertently separated from broken cores.Compression strength measured on the concrete cores,normalized to 150 x 300 mm (6" x 12") cylinders was 70MPa (10.2 ksi); the modulus of elasticity in compressionwas 25 x 103 MPa (3.59 x 106 psi). These values arecomparable to the results of the cores and cubes test

esults from the 1953 investigation. In addition, the result ofthe Selma concrete stress-strain curve is superimposed inFigure 5 on the results of recent(y completed high strengthlightweight concrete test program (14). The similarity of thedata on the concrete specimens, cast almost 60 yearsapart, is evident.Explanations of this unusual resistance to weatheringand corrosion is difficult to quantify and may include someor all of the following physical and chemical mechanisms:1. Superior resistance to microcracking due to high bondof aggregate to mortar fraction combined with thereduction of inner stresses due to elastic matching of thecoarse aggregate and the mortar phase.2. High ultimate strain capacity provided by a concretewith a high strength to modulus ratio.3. A well dispersed void system provided by the finelightweight aggregate fraction that may serve an absorptionfunction in weathering resistance as well asreducing salt concentration levels in the mortar phase.4. Long term pozzolanic action provided by lightweightfine aggregate with the proper physical and chemicalcharacteristics that could combine with the calciumhydroxide liberated during cement hydration. This couldminimize the leaching of soluble compounds and inaddition may reduce the possibility of sulphate saltdisruptive behavior.5. Low mortar permeability provided by the combination ofhigh cement contents and the water available in thelightweight aggregate for internal curing.Attempts to evaluate the potentially beneficial contributionof these mechanisms will continue in the future.MODULUS OF ELASTICITY (SECANT MODULUS) OF "SELMA" CONCRETEFIRST TEST LOADED TO 3950 P.S.I. -E = 3, 100,000 P.S.I. -SOLIDSECOND TEST LOADED TO 5930 P.S.I. -E = 3,000,000 P.S.I. -DASHED--.2QQQj~...1QQQuju..-~',#0.'~"""7'"".,.,.;0-13000U)-U)I~~./J".w.£QQQ1000Q.0002 00040006 .0008 .0010 .0012 .0014 .0016DEFORMATION-STRAININ. PER INCH0018Od20Adrian PauwU. of Missouri9/23/53Figure # 8-Stress-strain curve of U.S.S. Selma lightweight concrete from 1953 tests

:igure # 9. -Chesapeake Bay Bridge- ~nnapolis, Maryland, constructed 1954Many lightweight concrete bridge decks have been constructedin marine environments throughout North America,including major projects such as the 7 km (4.5 miles)Chesapeake Bay Bridge, constructed in 1954 at Annapolis,Maryland with a design strength of 24 MPa (3.5 ksi) and anair dry density of 1680 Kg/Mg3 (105 pcf) (Figure 9). Aftercompletion in 1975 of a second parallel crossing to handlethe increased traffic load, the asphalt wearing surface ofthe original bridge was removed and an extensive investigationinto the serviceability of the concrete deck conductedby an independent testing laboratory (19). Freezing andthawing combined with rapid temperature cycling, roadsalt exposure, vibration and stress reversals typical of longspan bridges may constitute an environment that is moresevere than continuous immersion. Extensive physical tests(core drilling, petrographic and ultrasonic) revealedexcellent condition of the non-air-entrained lightweightconcrete of the main spans. Deterioration of the non-airentrainednormal weight concrete of the approach spansrequired a significant amount of concrete removal andrepair. After the investigation demonstrated that repair ofthe lightweight concrete spans was not necessary, a newwearing surface was applied and the bridge put back intoservice.It is especially interesting that Fagerlund's extraordinarilycomprehensive theoretical and laboratory investigationsinto the "Frost Resistance of Concretes with Porous Aggregates"(20) suggested extra frost resistance could beavailable in some lightweight concretes in that, "The reasonfor this feature could be that lightweight concretes did alsocontain a lightweight sand fraction. These porous grainscould very well have acted as air-entrained pores. ..sandparticles of a size smaller than .025 mm (.01 inch) have aspacing that is of the same order of size as air-entrainedpores". While the actual in-service experience of theChesapeake Bay Bridge precisely fulfijls Fagerlund's observations,it must be emphasized (as in fact Fagerlundalso noted) that appropriate air-entrainment and high qualitymortars are essential for maximizing durability as well asminimizing scaling, bleeding and permeability.Some transportation engineers are now specifyinghigher concrete strengths for bridge decks in order todevelop high quality mortar fractions (high strength withhigh air content) that will minimize maintenance costs. Onestate authority has several bridges presently under constructionwhich utilize a lightweight concrete with a targetstrength of 36 MPa (5.2 ksi) with 6-9% air content. Anotherhighway authority (21) has systematically replaced deterioratingexisting normal weight concrete bridge deckswith structural lightweight concrete because of demonstratedimprovements in durability. A bridge deck surveysponsored by the Expanded Shale Clay and Slate Institutefound the vast majority of lightweight concrete bridgesproviding good service performance (22).

Numerous other applications of structural lightweight concretesin marine environments include floating bridges,boat marinas. and large submerged concrete pipe structures(Figure 10). Where available, service records indicatelow maintenance costs and insignificant rates of deterioration.~Figure # 10-Lightweight concrete pipe used in PacificCoast Power Plant water systemLarge scale concrete structures in marine environmentsto assist worldwide energy source development hasbrought about a re-examination of the durability characteristicsof structural lightweight aggregate concrete(23,24).Extensive laboratory freeze-thaw testing programs havedemonstrated that structural lightweight aggregates, incombination with high quality pastes containing the properspacing and amounts of air, and permitted a drying periodof at least 14 days prior to first freezing, will produceadequate laboratory tested concrete durability.Investigations of a number of in-service lightweight concretestructures in marine environments for up to 60 yearsverify the laboratory indications of good weathering resistartceand suggest the following criteria for future applications:A. Use high quality structural lightweight aggregate (bothcoarse and fine) that has a proven record of durableperformance in severe weathering exposure.B. Use a minimum cement content of 360 Kg/ M3 (611 pcy)for structures with moderate exposure (build ingfacades, garages) and 440 Kg/M3 (748 pcy) for concreteswith severe exposure (bridge decks, marineenvironments).C. Use air contents suggested by ACI 201 (25) as aminimum starting point, 6% for 20 mm (3/4"), 7.5% for10 mm (3/8") aggregate.D. Place concretes at reasonable slumps 75 mm (3"),using best recommended practice for compaction,finishing and curing.The author is thankful for the assistance of Harry C. Robinson,Executive Director of the Expanded Shale Clay andSlate Institute, for locating documents describing the historicaldevelopment of the concrete ship program and toRobert robin of the Portland Cement Association for informationon the performance of Pacific Coast lightweightconcrete pipe structures. The author is especially gratefulfor the special efforts of Mike Jones of Texas Industries andL. K. Childress of Solite Corporation in obtaining coresamples from the U.S.S. Selma.

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Materials shall be proportioned in accordance with AC1211.2 so as to produce concretewith the properties listed below:A. 28-day compressive strength Wet Density Calculated Equilibrium:t 3 pcf (50 kg/m3) Density :t 3 pcf (50 kg/m3)3000 psi (21 MPa)(C-138)(C-567)4000 psi (28 MPa)5000 psi (34 MPa)B. Air content determined in accordance with ASTM C-173 shall be 6-8 percentby volume.C. Slump shall be as listed below: - -on slabs-on vertical surfacesD. Concrete cylinders shall be molded and cured in accordance with ASTM C-31with the following exception: after 7 days of moist curing in the laboratory, thecylinders shall be removed from the moist room and cured at 50% :t 2 relativehumidity and 73.4°F :t 2 (23 :t 1.7°C) until time of test.E. Design data, creep, shrinkage and design coefficients shall be made availableto the architect/engineer for prior approval.F: The lightweight aggregate producer specified for the project shall make availableto the architect/engineer tests conducted in accordance with ASTM C-496indicating tensile splitting strength on concrete composed of coarse lightweightaggregate and natural sand in excess of .85 of the values called for in ACI 318for the particular compressive strength called for in the specification (.75 for alllightweight concrete).The aggregate producer shall provide field service for initial placements andupon request shall provide such service to the architect/engineer and ready-mixproducer at no cost to the owner.