Shotcrete Incorporated Into ACI 318-19 Building Code

Shotcrete Incorporated intoACI 318-19 Building CodeA supplement to the commentary to ACI 318-19by Charles Hanskat, Terence C. Holland, and Bruce A. SuprenantSince the shotcrete processoriginated well over 100 yearsago, improvements in materials,equipment, and placement techniqueshave enabled it to become a well-provenmethod for structural concrete placement.The efficiency and flexibility ofshotcrete have been used to greatadvantage in sizable structural projects,as the high-velocity impact inherent inthe process provides the compactionneeded to turn low-slump concrete intofreestanding vertical and overheadplacements with minimal formwork.Shotcrete has been incorporated intothe International Building Code (IBC)for many years, but there was noassigned responsibility for reviewingand updating the provisions. Further,shotcrete was not expressly covered inthe ACI 318 Code. To address theseshortcomings, during the 2019 codecycle, Jack Moehle, Chair of ACICommittee 318, Structural ConcreteBuilding Code, requested that ACI 318subcommittees work to incorporateshotcrete provisions into the ACI 318Code. Thus, ACI Subcommittees 318-A,General, Concrete, and Construction, and318-B, Anchorage and Reinforcement,started a 5-year journey, ending in thesuccessful inclusion of shotcrete intoACI 318-19.1 Here is that story.IBC Shotcrete ProvisionsConversations between ACI andInternational Code Council (ICC) staffindicated that it would be possible todelete the shotcrete provisions fromthe IBC upon satisfactoryincorporation of shotcrete into theACI 318 Code. Thus, the first task forthe subcommittee members was tostudy the shotcrete provisions in theIBC. The topics covered in 2015 IBCSection 1908 Shotcrete are shown inTable 1.2 A table prepared for thesubcommittees to summarize theshotcrete provisions in the 2000,2003, 2006, 2009, 2012, and 2015editions of the IBC showed that verylittle change had occurred since 2000.Further, it was evident that the 2000IBC provisions3 were primarily basedon an extremely dated document,“Guide to Shotcrete (ACI 506R-90).”4ACI Shotcrete InformationThe next task for subcommitteemembers was to review relevant,current information in the followingACI documents:“Guide to Shotcrete (ACI 506R-16)”5;“Guide to Fiber-Reinforced Shotcrete(ACI 506.1R-08)”6;“Specifications for Shotcrete (ACI506.2-13 (Reapproved 2018))”7;“Guide for the Evaluation ofShotcrete (ACI 506.4R-94(Reapproved 2004))”8;“Guide for Specifying UndergroundShotcrete (ACI 506.5R-09(Reapproved 2016))”9; and“Visual Shotcrete Core QualityEvaluation TechNote(ACI 506.6T-17).”10 It should be noted that the latestedition of “Guide for the Evaluation ofShotcrete (ACI 506.4R-19)”11 wasapproved too late to be considered indeveloping the shotcrete provisions forACI 318-19.Table 1:Provisions in 2015 IBC Section1908 ions and lly tied columns1908.5Preconstruction ring1908.9.1Initial curing1908.9.2Final curing1908.9.3Natural curing1908.10Strength tests1908.10.1Sampling1908.10.2Panel criteria1908.10.3Acceptance criteriawww.concreteinternational.com Ci DECEMBER 201931

IBC versus ACI Code—Applying ASTM StandardsThe 2015 IBC provisions in Section1908 Shotcrete were created well beforeASTM developed testing standards forshotcrete, so no ASTM standards onshotcrete were referenced. Therefore,the IBC provisions considered forinclusion in ACI 318 had to be modifiedto reflect ACI Code usage of ASTMstandards. The following ASTMstandards for shotcrete were used andcited in ACI 318-19:C1385/C1385M-10(2017), “StandardPractice for Sampling Materials forShotcrete”; C1140/C1140M-11, “StandardPractice for Preparing and TestingSpecimens from Shotcrete Test Panels”;C1141/C1141M-15, “StandardSpecification for Admixtures forShotcrete”;C1436-13, “Standard Specificationfor Materials for Shotcrete”;C1480/C1480M-07(2012), “StandardSpecification for Packaged, PreBlended, Dry, Combined Materialsfor Use in Wet or Dry ShotcreteApplication”; andC1604/C1604M-05(2012), “StandardTest Method for Obtaining andTesting Drilled Cores of Shotcrete.”Incorporating Shotcrete inACI 318-19(a)(b)Shotcrete has been widely used for over a century: (a) a crew poses with their equipment inthe 1920s; and (b) a crew places a foundation wall in the 1940s (a)(b)(c)Shotcrete is ideal for placing complex structures: (a) the curved enclosure wall of StanfordUniversity’s Bing Concert Hall comprises shotcrete with a sand float finish; (b) a certifiednozzle operator and a blowpipe operator construct mockup panels for the enclosure wall; and(c) crews placed the 12 in. (300 mm) thick enclosure wall in multiple lifts, using a removablescreed rail to control the thickness (photos courtesy of Joseph J. Albanese, Inc.)32ACI 318-1412 did not include theword “shotcrete,” and it was silent as towhether the provisions applied toshotcrete. If shotcrete had beenincorporated into the ACI Code prior tothe 2014 edition, it would have beenappropriate to develop a new chapter onshotcrete that included all relevantprovisions on materials, placement, andacceptance. However, that was not afeasible option within the member-basedcode organization implemented in the2014 edition of the Code.Thus, the incorporation of shotcreteinto the Code required the application oftwo principles in the context of thecomplete 318 Code:Shotcrete is cast-in-place concrete;andShotcrete is a construction placementmethod.In effect, the subcommittees’ primaryobjective was to implement shotcrete asa cast-in-place method, and this requiredthem to consider and implement thefollowing rules:Respect the intent of the IBCshotcrete provisions;Update the IBC shotcrete provisionsto reflect current ACI information;Use ASTM standards in thedevelopment of the Code language;andIntegrate shotcrete provisions to becompatible with existing Codelanguage.DECEMBER 2019 Ci www.concreteinternational.com

This required shotcrete provisions tobe incorporated into ACI 318 where itwas appropriate to modify theprovisions in the 2014 edition. Thus,shotcrete provisions are distributedthroughout the relevant sections of theACI Code. As a result, ACI 318-19contains 135 instances of the word“shotcrete.”ACI 318-19: The ResultDrafts of the shotcrete provisionswere vetted by Marc Jolin, Chair ofACI Committee 506, Shotcrete, andCharles Hanskat, Executive Director ofthe American Shotcrete Association(ASA), along with members of ACISubcommittee 318-A. After numerous318 subcommittee and 318 maincommittee ballots, and review by theACI Technical Activities Committee(TAC) and the public, the shotcreteprovisions were incorporated intoACI 318-19. Table 2 shows the coveredshotcrete topics and their locationswithin ACI 318-19.the required air content for durability inthese exposures.14In wet-mix shotcrete, air entrainingis introduced into the concrete mixturebefore pumping and placing theconcrete. The air content can be testedat the point of delivery using normalASTM testing standards. In dry-mixshotcrete, the dry concrete materials arewetted at the nozzle so there is noopportunity to test for air content untilthe mixture is placed. Thus, ACI 318does not include a specific testingmethod for evaluating the air content ofdry-mix shotcrete and requires thelicensed design professional to specify amethod to be used.Field measurements of air content ofdry-mix shotcrete have been obtainedby shooting the material directly into abowl of an air meter.14 Samples for aircontent testing can also be taken fromCertificationACI 318-14 incorporated certificationrequirements for concrete field andstrength testing technicians andadhesive anchor installers. Similarly,certification requirements are includedin ACI 318-19 for shotcrete nozzleoperators: “A certified shotcrete nozzleoperator shall place all shotcrete”(Provision 26.5.2.1 (o)). TheCommentary Provision R26.5.2.1(o)provides the following information:“Nozzle operators become certifiedthrough testing and training programsTable 2:Shotcrete provisions and relevant ACI 318-19 sections1Topic coveredSectionTerminology2.3*Freezing and thawing19.3.3.3 through 19.3.3.6Reinforcement25.2.7 through 25.2.10, 25.5.1.6, and25.5.1.7When shotcrete is required or permitted26.3.1, 26.3.2Materials26.4.1.2, 26.4.1.4, and 26.4.1.6Proportioning mixtures26.4.3Documentation of mixtures26.4.4.1Placement and ation and acceptance26.12Extended CommentaryThe following sections provideextended commentary on ACI 318-19provisions addressing air content inshotcrete and certification requirementsfor nozzle operators. In addition, anerratum on acceptance testingrequirements for shotcrete is discussed.Air content of shotcreteBoth wet-mix and dry-mix shotcretecan be air entrained for enhancedresistance to cyclic freezing andthawing. Provisions for air entrainmentare provided in Table 3 for shotcreteexposed to cycles of freezing andthawing. The higher air content ofwet-mix shotcrete sampled at the pointof delivery accounts for expected airlosses during shooting.Dry-mix shotcrete without airentrainment has performed well infreezing-and-thawing environmentswith no exposure to saltwater or deicingsalts.5,13 For exposure to saltwater ordeicing salts, air-entraining admixtures,in either a wet or dry form, can beadded to dry-mix shotcrete to providematerial shot into test panels, into awheelbarrow, or onto the ground. Thesesamples can then be used for testing inaccordance with ASTM C231/C231M,“Standard Test Method for Air Contentof Freshly Mixed Concrete by thePressure Method.”15The terms shotcrete mockup panel, shotcrete test panel, shotcrete, and wet- and dry-mix shotcretewere added to Section 2.3—Terminology*Table 3:Total air content for shotcrete (based on Table 19.3.3 in ACI 318-191)Target air content,%Mixture typeSampling locationF1F2F3Wet-mix shotcreteBefore placement5.06.06.0Dry-mix shotcreteIn-placeN/A*N/A*4.5Entrained air is not required in dry-mix shotcrete for these exposures*www.concreteinternational.com Ci DECEMBER 201933