ACI 506.4R-1994 Guide for the Evaluation of Shotcrete《喷浆混凝土评估指南》.pdf

1、ACI 506.4R-94 became effective October 1, 1994.Copyright 1994, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or by anymeans, including the making of copies by any photo process, or by electronic ormechanical device, printed, written, or oral, or

2、 recording for sound or visual reproductionor for use in any knowledge or retrieval system or device, unless permission in writingis obtained from the copyright proprietors.ACI Committee Reports, Guides, and Commentaries areintended for guidance in planning, designing, executing, andinspecting const

3、ruction. This document is intended for the useof individuals who are competent to evaluate the significanceand limitations of its content and recommendations and whowill accept responsibility for the application of the material itcontains. The American Concrete Institute disclaims any andall respons

4、ibility for the stated principles. The Institute shallnot be liable for any loss or damage arising therefrom.Reference to this document shall not be made in contractdocuments. If items found in this document are desired by theArchitect/Engineer to be a part of the contract documents, theyshall be re

5、stated in mandatory language for incorporation bythe Architect/Engineer.506.4R-1Guide for the Evaluation of ShotcreteReported by ACI Committee 506ACI 506.4R-94(Reapproved 2004)Evaluation of in-place shotcrete requires experience, education, andengineering judgment. This document serves as a guide fo

6、r engineers,inspectors, contractors, and others involved in accepting, rejecting, orevaluating in-place dry- or wet-mix shotcrete.Keywords: brooming; construction practices; cracking (fracturing);defects; dry mix; finishing; in-situ testing; inspection; lenses; nozzleman;overspray; permeability; qua

7、lity; sags; sand pockets; screeding; shotcrete;trowel cutting; visual appearance voids; wet mix.CONTENTSChapter 1Introduction, p. 506.4R-2Chapter 2Strength, p. 506.4R-22.1General2.2Destructive testing2.3Nondestructive testingChapter 3Bond and voids, p. 506.4R-33.1General3.2Sounding3.3Direct tension

8、(tensile bond)3.4Sonic and radar methods3.5Infrared thermography3.6RadiographyChapter 4Density, p. 506.4R-84.1General4.2DensityChapter 5Permeability, p. 506.4R-95.1General5.2Permeability testsChapter 6Evaluation of freshly mixed shotcrete,p. 506.4R-106.1General6.2Tests applicable for wet process sho

9、tcrete6.3Tests applicable for dry-mix process shotcreteChapter 7Determination of shotcrete mixture proportions, p. 506.4R-107.1General7.2Sampling7.3Test procedureChapter 8References, p. 506.4R-118.1Specified references8.2Cited referencesSteven H. Gebler*ChairLars Balck, Jr.SecretaryRaymond J. Schutz

10、*Subcommittee ChairSeymour A. Bortz Kristian Loevlie Vern SchultheisPaul D. Carter Dudley R. Morgan Philip T. Seabrook*Gary L. Chynoweth Dale A. Pearcey W. L. Snow, Sr.I. Leon Glassgold John E. Perry, Jr. Curt E. StraubCharles H. Henager V. Ramakrishnan*Lawrence J. TottenRichard A. Kaden*Thomas J. R

11、eading Gary L. VondranBruce K. Langson Ernest K. Schrader R. Curtis White, Jr.Albert Litvin*Members of the subcommittee that prepared this report.506.4R-2 ACI COMMITTEE REPORTCHAPTER l-INTRODUCTIONl.l-The purpose of this report is to present proceduresthat can be used to evaluate the quality and pro

12、perties ofin-place shotcrete.1.2 -Considerable literature is available on testing freshconcrete, concrete specimens, and in-place concrete. Pro-cedures for the production and testing of concrete arecovered by ACI and ASTM Standards. The developmentof in-place (nondestructive) test procedures for eva

13、l-uating concrete structures has progressed to the pointwhere the use of such procedures has become common.1.3 -Procedures for in-place evaluation of shotcrete havenot been well developed or widely used This may be dueto the lack of understanding of the difference betweenshotcrete and concrete. The

14、most important factor inproducing quality shotcrete construction is the skill of thenozzleman. While ACI 506. 2 requires preconstructiontesting to verify a nozzlemans ability, such testing is notalways done. Additionally, inspectors who are knowledge-able in shotcreting are not ordinarily available

15、to monitorshotcrete quality. Thus, if properly skilled nozzleme n arenot used, defects such as improper encasement of rein-forcing steel, voids behind steel, excessive crackingcaused by shrinkage, sand pockets, and defects caused byinclusions of overspray and rebound can occur.CHAPTER 2-STRENGTH2.1-

16、GeneralStrength is widely used to evaluate shotcrete quality.Although both compressive and flexural strength can beobtained, the compressive strength is most commonlyused. Many of the sampling and testing methods for shot-crete are similar to those used for concrete and can bebroadly categorized as

17、destructive and nondestructivedeterminations. Because it is generally not possible tomold standard test specimens for shotcrete, the samplingand testing of shotcrete are usually performed on in-place hardened material or on test panels as described inACI 506.2 and ASTM C 1140, which cover preparing

18、andtesting specimens from shotcrete test panels.2.2-Destructive testingUnder this category, samples obtained from hardenedshotcrete by drilling cores, sawing cubes, or prisms aretested to failure. Core samples are most frequently used.In addition to providing specimens for strength tests,drilled cor

19、es offer an excellent opportunity to visuallyexamine the shotcrete, at depth, for consolidation, em-bedment of reinforcement, contact with substrate, sandstreaks, and other faults, as discussed below.2.1.1 Obtaining core samples -Obtaining core samplesfrom the actual structure is not always possible

20、 and insituations where core samples can be obtained, the integ-rity of the structure may be damaged to varying degreesdepending on the size, number, and location of the coresamples. ASTM C 42 describes the testing procedure andexplains how the results should be corrected for height-to-diameter rati

21、o. The nominal core diameter should notbe less than 2 in. (50 mm) with 3 in. (75 mm) being thepreferred diameter for shotcrete. ASTM C 823 stateswhen and how cores should be taken, and the requiredmoisture condition of the cores at the time of test. It isrecommended that interpretation of results be

22、 made byan engineer experienced in shotcrete technology. Thefollowing factors should be considered:2.2.1.1 Damage to samples-Minor chipping of theperimeter of core ends during drilling is not significant.Cracks may invalidate the test result. Sharp diamond drillbits on watercooled drills rigidly fix

23、ed to the structurenormally produce suitable samples.2.2.1.2 Density -Each 1 percent of void volume inshotcrete will reduce the strength approximately 5 per-cent (Neville 1986). If undercompaction is significant,considerable voids will be present and the extent towhich it is typical of the shotcrete

24、 in the structure inquestion should be determined2.2.1.3 P resence of reinforcing bars-It is highlydesirable that cores do not contain reinforcing bars.However, there is no established standard to account forthe effect of reinforcement on the strength of the speci-men. Examination of the core failur

25、e pattern will helpdetermine if the bar has significantly affected strength.Embedded reinforcement can be located using a mag-netic detector.2.2.1.4 Evidence of alkali-aggregate reaction, freeze-thaw damage, sulphate or other chemical attack- If there is doubt as to what factors have caused apparent

26、 damage,the advice of a petrographer should be sought.2.2.2 Testing drilled cores -Normally, cores are drilledfrom the structure after the shotcrete has hardened andare tested in order to evaluate the quality of in-placeshotcrete, particularly in terms of uniaxial compressivestrength. Although the s

27、trength test itself is fairly simple,the details of the procedure should be carefully estab-lished and followed. Numerous factors can affect thestrength which, in turn, can influence judgment of theoverall quality of shotcrete. Some of the factors are thediameter of the core, its height-to-diameter

28、ratio, direc-tion of coring in relation to the placing of shotcrete andthe location in the structure, curing and moisture condi-tions of cores prior to testing, and maximum size aggre-gate and presence of reinforcing steel in the core.2.2.3 Cubes and prisms -Such specimens may be sawedfrom test pane

29、ls but they are difficult to obtain fromshotcrete that is bonded to the substrate. It has beenreported that the variation between tests on sawed cubesis less than that for drilled cores from the same shotcrete(Rutenbeck, 1976).2.3-Nondestructive testing2.3.1 Rebound and indentation testsEVALUATION O

30、F SHOTCRETE 506.4R-32.3.1.1 The rebound method and the indentationmethod both measure relative hardness of surface layers,which is generally related to strength. Both methods arewell known and are used. However, the methods are em-pirical in nature and several precautions must be takento obtain sign

31、ificant results. The methods give only anestimate of the strength of shotcrete, and then only theshotcrete near the surface.2.3.1.2 Hardness methods i n combination wit h othernondestructive methods have been used to make strengthpredictions. It is desirable to take advantage of thepotential offered

32、 by the hardness methods because of therelatively low cost of these methods.2.3.1.3 The Schmidt Rebound Hammer is the mostcommonly used apparatus for measuring the hardness ofconcrete by the rebound principle (Malhotra, 1976).ASTM C 805 de scr ibe s the test procedure. Although thisrebound hammer pr

33、ovides a quick, inexpensive means ofchecking uniformity, it has many limitations which mustbe recognized. The results of the rebound hammer areaffected by the texture, degree of carbonation, andmoisture condition of the shotcrete surface, thickness andage of the shotcrete structure, and type of coar

34、se aggre-gate. Estimation of strength of shotcrete within anaccuracy of however, it may be used tolocate nonuniform areas within a shotcrete structure orto compare the relative strength of one shotcrete withanother. It is suggested that Schmidt Rebound Hammersfor use on shotcrete be calibrated again

35、st shotcretes fromthe same materials but with a range of strengths.2.3.2 Penetration test-This method is described inASTM C 803. A driver, usually powder-activated, deliversa known amount of energy to a steel pin. The penetra-tion resistance of the concrete is determined in place bymeasuring the exp

36、osed length of the probes, which havebeen driven into the concrete. This method measures thesurface hardness of concrete and relates to the strengthproperty at a depth greater than indicated by the re-bound hammer method2.3.3 Pull-out test-In the pull-out test, ASTM C 900,a dynamometer is used to me

37、asure the force required topull out a specially shaped steel insert with an enlargedend which has been cast into the shotcrete. A cone ofshotcrete is pulled out with the insert, and the shotcreteis simultaneously in tension and in shear. The pull-outforce can be correlated with shotcrete compressive

38、strength. The cost is relatively low and the testing can bequickly done in the field There may be some damage tothe shotcrete surface which wiI l require patching. How-ever, the test need not be done to failure of shotcrete; ifa pull-out force of a give nminimum value is applied andthe shotcrete has

39、 not failed, then the shotcrete can beassumed to have attained the compressive strength speci-fied. The equipment is simple to operate and the testsare reproducible. It should be recognized that pull-outtests do not measure strength in the interior of shotcrete.They have been used effectively for mo

40、nitoring strengthdevelopment at early ages. This method presents somedifficulties when used with shotcrete, since the techniquesused by the nozzleman to embed the insert will, ofnecessity, be different than those employed in applyingthe shotcrete to the surrounding areas. Therefore, thetest results

41、may not be representative of the bulk of theshotcrete.2.3.4 Other tests-Some relatively new in-place pull-outtests have been developed for testing the in-placestrength of concrete or shotcrete. In one test method, asuitably shaped hole is drilled into concrete using anunderreaming tool, and an expan

42、dable insert is installedin the hole. The insert is then pulled out in the samemanner as in the pull-out test and the data are analyzedsimilarly. This method has the advantage over pull-outtest C 900 in that sampling can be random and notdependent on the nozzlemans skill in shooting around anin sert

43、 .CHAPTER 3-VOIDS AND BOND3.1-GeneralThis section discusses the techniques, tools, and testscurrently available to detect lack of bond to underlyingsurfaces and voids in shotcrete.3.2-SoundingThe most frequently used technique for locating sub-surface voids is sounding. Sounding can be accomplishedb

44、y using a hammer or a “chain drag” method may beused for horizontal surfaces.3.2.1 Hammer- Sounding surveys may be conductedby striking the finished surface with a hammer. Theoperator listens to the ring or sound that the shotcreteimparts. A sharp ringing sound is indicative of soundshotcrete. A “dr

45、ummy” or hollow sound is indicative oflack of bond between layers of shotcrete or between theshotcrete and the substrate. Large voids can also bedetected with a hammer. The “drummy” sounding areasare marked and data transferred to field records. Beforeusing this method, several hammer weights should

46、 betried to determine the best one for the wall thickness andthe materials to reveal the “drummy ” sounds. Often 1- to5-lb (0.5 to 2.3 kg) hammers are used; heavier hammersbeing used for thicker shotcrete.3.2.2 Chain drag -Horizontal areas can be sounded bydragging a metal chain across the shotcrete

47、. Voids anddelaminations will be indicated by a change in the soundemanating from the shotcrete. This method is describedin ASTM D 4580; areas indicating voids and delamina-tions can be recorded as described in 3.11.506.4R-4 ACI COMMITTEE REPORTTENSILE BOND STRENGTH TEST.;3 h. . l / and, in the 1980

48、s, attention focusedon using it to locate delaminations in bridge decks. Thetechnique is known by various names such a s short-pukeradar, impulse radar, and ground penetrating radar.EVALUATION OF SHOTCRETETransmittedpulse506.4R-7(a)IQ4TimeScanAntem(b)w$yGElphiCrecorder_0 + -lJt2Threshold90G-9FI Void

49、8Ic1 iiIIBottom(c)Graphic recorderoutput duringscanIHlllllllllllllllllllllllllllllllllllllllllllllllllllr-11111111111111111l1111111111illll1llllllllllllllllllllllIIIlIHIIIII!Il1lllllllllll4Paper Movementa. . . . . . -A:.y:.:.:.:.y.:.:.p (b) idealized waveform from receiving antennaand threshold platting by graphic recorder; (c) schematic of output from graphic recorder during scan over slab with a voidFrom an electromagnetic viewpoint, materials can beclassified as conductors, such as metals, and insulators ordielectrics