1、Designation: C 1579 06Standard Test Method forEvaluating Plastic Shrinkage Cracking of Restrained FiberReinforced Concrete (Using a Steel Form Insert)1This standard is issued under the fixed designation C 1579; the number immediately following the designation indicates the year oforiginal adoption o
2、r, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method compares the surface cracking of fiberreinforced concrete pa
3、nels with the surface cracking of controlconcrete panels subjected to prescribed conditions of restraintand moisture loss that are severe enough to produce crackingbefore final setting of the concrete.1.2 This test method can be used to compare the plasticshrinkage cracking behavior of different con
4、crete mixturescontaining fiber reinforcement.1.3 The values stated in SI units are to be regarded as thestandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate sa
5、fety and health practices and determine the applica-bility of regulatory limitations prior to use. (Warning freshhydraulic cementitious mixtures are caustic and may causechemical burns to skin and tissue upon prolonged exposure.)22. Referenced Documents2.1 ASTM Standards:3C 125 Terminology Relating
6、to Concrete and ConcreteAggregatesC 143/C 143M Test Method for Slump of Hydraulic-Cement ConcreteC 192/C 192M Practice for Making and Curing ConcreteTest Specimens in the LaboratoryC 403/C 403M Test Method for Time of Setting of ConcreteMixtures by Penetration ResistanceC 670 Practice for Preparing
7、Precision and Bias Statementsfor Test Methods for Construction MaterialsC 995 Test Method for Time of Flow of Fiber-ReinforcedConcrete Through Inverted Slump Cone3. Summary of Test Method3.1 Panels of control concrete and fiber reinforced concreteare prepared in a prescribed manner and are exposed t
8、ocontrolled drying conditions after finishing. The drying condi-tions (See Note 1) are intended to be severe enough to induceplastic shrinkage cracking in test panels made of controlconcrete. The evaporation rate from a free water surface ismonitored by pans placed next to the panels in the environ-
9、mental chamber.NOTE 1An important parameter in this method is the rate of evapo-rative water loss, which is controlled by the atmospheric conditionssurrounding the test specimens. Since the concrete specimens will notalways have the same rate of water evaporation as the pan of water (dueto evaporati
10、ve and bleeding effects), the rate of evaporation of 1.0 kg/m2hfrom the pan of water represents the minimum evaporation rate that mustbe attained for this test (1).4The moisture loss from the concrete testpanels can also be monitored and reported, however, the rate of evapora-tion from the free surf
11、ace of the water in the pan is the parameter thatshould be used to quantify the drying environment.3.2 The test is terminated at the time of final setting of theconcrete determined in accordance with Test Method C 403/C 403M. At 24 h from initial mixing, the average crack widthis determined.3.3 A cr
12、acking reduction ratio (CRR) is computed from theaverage crack width for the fiber-reinforced concrete panelsand the average crack width for the control concrete panels.4. Significance and Use4.1 The test method is intended to evaluate the effects ofevaporation, settlement, and early autogenous shri
13、nkage on theplastic shrinkage cracking performance of fiber reinforcedconcrete up to and for some hours beyond the time of finalsetting (See Terminology C 125).4.2 The measured values obtained from this test may beused to compare the performance of concretes with differentmixture proportions, concre
14、tes with and without fibers, con-cretes containing various amounts of different types of fibers,and concretes containing various amounts and types of admix-tures. For meaningful comparisons, the evaporative conditionsduring test shall be sufficient to produce an average crack width1This test method
15、is under the jurisdiction of ASTM Committee C09 onConcrete and Concrete Aggregates and is the direct responsibility of SubcommitteeC09.42 on Fiber-Reinforced Concrete.Current edition approved Feb. 15, 2006. Published March 2006.2Section on Safety Precautions, Manual of Aggregate and Concrete Testing
16、,Annual Book of ASTM Standards, Vol. 04.02.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4The boldface numb
17、ers in parentheses refer to the list of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.of at least 0.5 mm in the control specimens (2, 5) (See Note 2).In addition, the evaporation rate from a fr
18、ee surface of watershall be within 6 5 % for each test.NOTE 2To achieve evaporation rates that result in a crack of at least0.5 mm in the control specimens, it may be necessary to use anevaporation rate higher than that discussed in Note 1.4.3 This method attempts to control atmospheric variablesto
19、quantify the relative performance of a given fresh concretemixture. Since many other variables such as cement fineness,aggregate gradation, aggregate volume, mixing procedures,slump, air content, concrete temperature and surface finish canalso influence potential cracking, attention shall be paid to
20、 keepthese as consistent as possible from mixture to mixture.5. Apparatus5.1 Molds:5.1.1 For maximum coarse aggregate size equal to or lessthan 19 mm, use a mold with a depth of 100 6 5 mm andrectangular dimensions of 355 6 10 mm by 560 6 15 mm (SeeFig. 1). The mold can be fabricated from metal, pla
21、stic, orplywood.NOTE 3If plywood is used for molds, the plywood should have lowmoisture absorption. The mold should be constructed to be lightweightand stiff. The molds, when properly constructed, should last for approxi-mately 50 uses.5.1.2 This test method is designed for aggregate less than orequ
22、al to 19 mm. For coarse aggregate greater than 19 mm, thedepth of the mold shall be at least 65 mm plus at least 2 timesthe maximum coarse aggregate size.5.2 Stress Riser and Internal RestraintsThe internal re-straints and stress riser shall be bent from one piece of sheetmetal, as illustrated in Fi
23、g. 1, or made from a solid piece ofsteel. The sheet metal shall have a thickness of 1.2 6 0.05 mm(18 gauge) (See Fig. 1 and Ref 2). Two 32 6 1 mm highrestraints are placed 90 6 2 mm inward from each end of themold. The central stress riser is 64 6 2 mm high and serves asFIG. 1 Specimen and Stress Ri
24、ser Geometry (4, 5)C1579062an initiation point for cracking. This sheet metal stress riserwith internal restraints shall fit at the bottom of the mold.5.2.1 Use form release oil to coat the metal insert and moldsides to reduce bond with concrete. The insert and mold areconsidered to be properly oile
25、d when the entire surface iscoated and excess oil has been removed with a clean, dry rag.5.3 Variable Speed Fan(s)The fan(s) used shall be ca-pable of achieving a wind speed of more than 4.7 m/s over theentire test panel surface area.5.4 Environmental ChamberThe use of a fan box in anenvironmental c
26、hamber is a method for producing a uniformairflow over the panel surface (See Fig. 2). A clear cover overthe panels will aid in obtaining uniform airflow and allow forobservation of cracking.Another method of producing uniformairflow is to use a specifically designed environmental chamberas shown in
27、 Fig. 3. A commercially available heater, humidi-fier, and dehumidifier can be used to maintain the specifiedenvironmental condition. This test is conducted using eitherapparatus shown in Fig. 2 or Fig. 3 by exposing the panels toan evaporation rate of at least 1.0 kg/m2h (See Note 1). For thestanda
28、rd test, the temperature must be maintained at 36 6 3 C,the relative humidity must be 30 6 10 %, and the wind velocitymust be sufficient to maintain the minimum evaporation rateduring the test.NOTE 4Before casting the concrete panels, atmospheric variables inthe environmental facility should be chec
29、ked to determine that thenecessary evaporative conditions can be achieved. A wind velocity of 4.7m/s should be sufficient to achieve the minimum specified evaporationrate, but a higher wind velocity may be needed to obtain sufficient averagecrack width in some control panels.5.5 SensorsUse temperatu
30、re, humidity, and wind velocitysensors to measure ambient air and concrete surface tempera-ture to the nearest 0.5 C, relative humidity to the nearest 1 %,and air speed to the nearest 0.1 m/s.5.6 Vibrating PlatformAny device that can fully consoli-date the test panel that meets minimum frequency req
31、uirementsas stated in Practice C 192/C 192M for an external vibrator issuitable.5.7 Surface Finishing EquipmentAn angle iron screedshall be used for the concrete after vibration. A magnesium,steel, or wood trowel shall be used for finishing the surface ofthe specimen after screeding.5.8 Monitoring P
32、anA pan suitable for exposing water tothe air stream for each concrete test panel is required. The sidesof the pan shall be vertical. The pan shall be of sufficient sizeto expose at least 0.1 6 0.01 m2of water to the air stream. Theexposed lip of the pan shall not extend more than 5 mm abovethe wate
33、r level at the start of the test.NOTE 5The test panels and monitoring pans can be placed in anenvironmental chamber designed for this test method (See Fig. 3)orthepans can be placed downstream from panels in a fan box (See Fig. 2).5.9 ScaleIf the rate of moisture loss from test panels isrequired by
34、the specifier of tests, weigh test panels with a scalehaving a capacity of at least 100 kg and accurate to within0.1 % of the test load. Weigh the evaporation rate monitoringpans with a balance or scale having a capacity of at least 3 kgand accurate to within 5 g.5.10 Crack Measurement ToolOptical h
35、and-held micro-scope, crack comparator, or image analysis system can be used.The measurement tool should be capable of measuring crackwidth to at least the nearest 0.05 mm. If an automated imageanalysis system is used, it should be demonstrated to providean accurate measurement. To demonstrate the a
36、ccuracy of themeasurement, the system shall be used to measure a 0.5 mmnotch that is machined into a piece of steel and the reportednotch width shall be within 6 0.05 mm of the machined width.6. Sampling, Test Specimens, and Test Units6.1 Test PanelsCast test panels in accordance with theapplicable
37、provisions of Practice C 192/C 192M, using thesame source of materials, preparation, mixing and finishingprocedures.6.2 Test UnitA test unit is comprised of at least twocontrol specimens and at least two fiber reinforced concretespecimens with the same mixture proportions. A group of twocontrol spec
38、imens has to be tested each time in order todetermine the plastic shrinkage crack reduction of fiber rein-forced concrete.7. Procedure7.1 Determine the slump of each mixture in accordance withTest Method C 143/C 143M. If the slump is too low for aconcrete mixture containing fibers, use the time of f
39、lowthrough an inverted slump cone to measure workability inaccordance with Test Method C 995.7.2 Fabricate specimens for setting time determination inaccordance with Test Method C 403/C 403M. If fiber rein-forced concrete cannot be wet sieved readily, use the controlconcrete specimen to measure time
40、 of final setting of both thecontrol and the fiber-reinforced mixtures. Place the time ofsetting specimens in the air stream so that they are exposed tothe same environmental conditions as the plastic shrinkagepanels.7.3 Fill the panel molds using one layer. Consolidate theconcrete with external vib
41、ration until the concrete is approxi-mately level with the top of the mold. Screed each specimenperpendicular to the stress riser three times.7.4 After screeding, trowel specimens using a predeter-mined number of passes. If moisture loss from the panel is tobe determined, remove any waste concrete a
42、dhering to theoutside of the mold and weigh each panel while in the mold.7.5 Place a fiber reinforced concrete mixture panel andcontrol mixture panel in the environmental chamber down-stream from the fan(s) (See arrangements in Figs. 2 and 3).7.6 Turn on the fan(s), which have been preset to achieve
43、the air speed to obtain the required evaporative conditions (SeeNote 4). The evaluation of cracking commences at this time.7.7 At the start of the test and at 30-min intervals, record airtemperature, relative humidity, and air flow speed at a location100 6 5 mm above each panel surface. If required
44、by thespecifier of tests, record the time at which cracking is firstobserved for each panel surface. Perform penetration tests atregular time intervals according to Test Method C 403/C 403M. Continue recording the environmental variables untilthe time of final setting.C1579063FIG. 2 Example of Fan B
45、ox to Maintain Environmental Conditions (2) (Not to Scale)C15790647.8 The evaporation rate is determined by initially weighingthe full monitoring pans at the start of the test and at 30-minintervals thereafter (3). Record the mass loss to the nearest 5 gat each weighing. To determine the evaporation
46、 rate duringeach time interval, divide the mass loss between successiveweighings by the surface area of the water in the weighing panand the time interval between successive weighings (See Note6). The test is not valid if the average evaporation rate is lessthan 1.0 kg/m2h.NOTE 6Adjustments to wind
47、velocity should be made if necessary tomaintain the evaporation rate at the required level. It is suggested that themonitoring pans be placed on scales in the air stream for continuousmonitoring without periodic removal during testing. If this is not possible,the monitoring pan should be removed fro
48、m the air stream, weighed, andreturned to the air stream within 15 seconds.7.9 After final setting occurs (use the later of the measuredtime of setting in the two specimens), record the atmosphericvariables, stop the fans, record the time, and determine the totalwater loss from the monitoring pans.
49、If panel moisture loss isto be determined, weigh the test panels in their molds. Store theFIG. 3 Example of Chamber to Maintain Environmental Conditions (4)C1579065panels in the laboratory at 23 6 2 C and under plastic sheetsto minimize evaporation until time of crack width measure-ment.8. Quantification of Cracking8.1 Quantify the amount of cracking by measuring crackwidths at the surface of the panels 24 6 2 h after mixing.NOTE 7Studies have shown that, when panels are covered withplastic, there is no appreciable change in average crack width from a timeof
