1、Standard Method of Test for Evaluating Stress Development and Cracking Potential due to Restrained Volume Change Using a Dual Ring Test AASHTO Designation: T 363-171Technical Section: 3c, Hardened Concrete Release: Group 1 (April 2017) American Association of State Highway and Transportation Officia
2、ls 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-3c T 363-1 AASHTO Standard Method of Test for Evaluating Stress Development and Cracking Potential due to Restrained Volume Change Using a Dual Ring Test AASHTO Designation: T 363-171Technical Section: 3c, Hardened Concrete Releas
3、e: Group 1 (April 2017) 1. SCOPE 1.1. This test method covers the evaluation of stress development and cracking potential in concrete when volume changes caused by shrinkage and temperature changes are restrained. The procedure is comparative for the degree of restraint of the ring and is not intend
4、ed to determine the time of initial cracking of a concrete cast in any specific type of structure. 1.2. The values stated in SI units are to be regarded as the standard. 1.3. This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibili
5、ty of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standard: R 39, Making and Curing Concrete Test Specimens in the Laboratory 2.2. ASTM Standards: C305, Stan
6、dard Practice for Mechanical Mixing of Hydraulic Cement Pastes and Mortars of Plastic Consistency C403/C403M, Standard Test Method for Time of Setting of Concrete Mixtures by Penetration Resistance C1581/C1581M, Standard Test Method for Determining Age at Cracking and Induced Tensile Stress Characte
7、ristics of Mortar and Concrete under Restrained Shrinkage C1698, Standard Test Method for Autogenous Strain of Cement Paste and Mortar F1684, Standard Specification for Iron-Nickel and Iron-Nickel-Cobalt Alloys for Low Thermal Expansion Applications 2.3. Other Document: Schlitter, J. L., A. H. Sente
8、r, D. P. Bentz, T. Nantung, and W. J. Weiss. A Dual Concentric Ring Test for Evaluating Residual Stress Development due to Restrained Volume Change. In Journal of ASTM International, Vol. 7, No. 9, ASTM, West Conshohocken, PA, 2010. 2017 by the American Association of State Highway and Transportatio
9、n Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 363-2 AASHTO 3. SUMMARY OF TEST METHOD 3.1. This test method measures the strains developed in two concentric metal rings providing restraint to a concrete specimen undergoing volume change. The measured strains in
10、 the restraining rings are used to calculate the stress development in the concrete specimen. This enables the stress that develops due to restraint to be quantified along with an assessment of the cracking potential of the concrete mixture. 3.2. This test method utilizes restraining rings made of a
11、 low thermal expansion iron-nickel alloy (Invar), allowing for the temperature of the test to be varied, while the rings remain nominally volumetrically stable. The test equipment is enclosed in an insulated chamber, with the temperature being controlled throughout the entirety of the test. The meth
12、odology set forth in this standard is to utilize the thermal capabilities of the dual ring test to assess the potential for cracking at 2, 4, and 7 days of age. The temperature of the test specimen is held at a constant 23 2C until the appropriate age, at which time the temperature is reduced at a r
13、ate of 2C/h until cracking is induced. This temperature drop approach yields the remaining stress capacity of the concrete specimens at early ages, quantifying the potential for cracking in the specimen at the given ages. 4. SIGNIFICANCE AND USE 4.1. This test method is suitable for evaluating the e
14、ffects of material variations on the cracking potential of restrained mortar elements. These variations may include aggregate source, aggregate gradation, aggregate absorption, aggregate-paste bond, cement type, cement content, water content, supplementary cementitious materials, fiber reinforcement
15、, or chemical admixtures. 4.2. Actual cracking during service or construction is dependent upon many variables including degree of restraint, hydration effects of the cement, curing methods, and environmental factors. This method is useful for comparing the relative likelihood of early age cracking
16、and for aiding in the selection of appropriate mixture designs. This method may also be utilized to evaluate the effect of temperature change on the thermal stress development and cracking tendency. 4.3. The details of the test method apply to nominal dimensions of specimens as set forth in this sta
17、ndard. Other specimen geometries may be used, with appropriate changes being made to ensure an equivalent degree of restraint in the specimens. The pertinent calculations can be found in the reference listed in Section 2.3. 4.4. The numerical results from this test method must be interpreted with ca
18、ution, especially in applications such as quality control and acceptance testing. 4.5. While the cracking test can evaluate a materials propensity to crack, it should be noted that other concrete tests that may be related to cracking tendency are the compressive strength, tensile strength, elastic m
19、odulus, Poissons ratio, drying shrinkage, unrestrained linear autogenous strain according to ASTM C1698, the single restrained ring test according to ASTM C1581/C1581M, and creep/relaxation testing. 5. APPARATUS 5.1. Restraining RingsThe standard restraining rings shall be made of a low thermal expa
20、nsion iron-nickel alloy (Invar) as specified in ASTM F1684 or equivalent. The inner and outer rings shall have wall thicknesses of 19 mm 3 mm (0.75 in. 0.12 in.), as provided by the specified dimensions in Table 1. The height of the rings shall be 76.2 mm 3 mm (3 in. 0.12 in.). The inner and outer f
21、aces shall be round, true, seamless, and polished smooth. 2017 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 363-3 AASHTO (a) (b) Figure 1Geometry of Dual Ring Test (a) and Dual Ring Test Setup in I
22、nsulating Chamber (b) (see reference listed in Section 2.3) Table 1Dimensions of Dual Ring Test Ring Face Radius (mm) RII146 3 RIC165 3 ROC203 3 ROO222 3 Note 1Bond low coefficient of thermal expansion type strain gauges at four equidistant, mid-height locations on both the interior of the inner rin
23、g and the exterior of the outer ring. 5.2. Data AcquisitionThe data acquisition unit shall be compatible with the strain instrumentation and automatically record each strain gauge independently at 5-min intervals. It is recommended that the system be capable of correction for thermal changes. 5.3. B
24、ase FormThe base form shall be nonabsorbent. Fabricate the base form of resin-coated or polyethylene-coated plywood to minimize frictional restraint of the concrete. 5.4. Insulating ChamberThe dual ring test setup shall be enclosed in an insulating chamber throughout the entirety of testing. The ins
25、ulating chamber shall be constructed such that it achieves an overall heat transfer coefficient of 0.04 W/m2/K or lower. Details of this calculation are can be found in the reference listed in Section 2.3. 5.5. Temperature Control SystemA temperature control system shall be used to regulate the temp
26、erature of the testing apparatus. The temperature control system shall have a minimum operating range of 30C to 10C with an operating rate of at least 2.0C/h. RIIROCRICROO 2017 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation o
27、f applicable law.TS-3c T 363-4 AASHTO Figure 2Temperature Control System for Dual Ring Test (see reference listed in Section 2.3) Note 2An electrical heating and cooling panel is recommended in order to minimize additional moisture from being introduced into the testing chamber. 5.6. Temperature Mon
28、itoringThermocouples or equivalent shall be utilized to automatically record the ambient temperature and the temperature of the restraining rings and specimen. Attach the thermocouples to the nontesting face of the restraining rings near the strain gauge sites using an appropriate conductive tape or
29、 equivalent method. Thermocouples should be accurate to 0.5C. 6. SPECIMEN FABRICATION 6.1. Coat the base form with a suitable form release agent. The test faces of the rings (outer face of inner ring and inner face of outer ring) shall be covered with a suitable adhesion resistant material such as a
30、cetate sheets or a form release agent. 6.2. Center the Invar rings on the base form within the insulating chamber. Note 3It is recommended to use a set of fabricated spacers to ensure the rings are concentric. 6.3. Mix and cure the test ring specimen in accordance with the applicable requirements of
31、 R 39 or ASTM C305. 6.4. Place the concrete between the two restraining rings in two equal lifts. The concrete shall be vibrated in situ after each lift using a suitable hand vibrator. Vibrate the concrete equidistantly 30 times per layer, ensuring that the vibrator head slightly penetrates into the
32、 previous layer with each insertion. 6.5. After consolidation, strike off the concrete surface. Clean any excess concrete from the top and sides of the form. Finish the specimen with the minimum manipulation necessary to achieve a finished, flat, and even surface. 7. TESTING PROCEDURE 7.1. Place the
33、 temperature control system on the finished specimen and testing apparatus. Program the appropriate temperature profile for the given experiment. 2017 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 3
34、63-5 AASHTO Note 4The temperature profile for the approach implemented in this standard is to set isothermal testing conditions at 23 1C until 2, 4, or 7 days on different specimens, whereafter the temperature is reduced at a rate of 2C/h to induce thermal cracking or until the lower temperature lim
35、it of the equipment is achieved. Note 5At very early ages, a thermal increase (beyond the 23C 1C limit) may be seen due to the heat of hydration. This is an artifact of the testing limitations and should be considered normal, as the material is highly compliant at early ages and thus little effect o
36、n the results of the testing procedure outlined in Note 4 are seen. Generally, the temperature of the specimen should return to 23 1C within 24 hours of casting. 7.2. Temperature compensation for the Invar ring strain gauge measurements shall be performed by monitoring the temperature change on the
37、ring surface at gauge sites. Note 6Prior to testing, a temperature compensation curve for each strain gauge shall be created by cycling the Invar rings (without any specimen) through any applicable temperature ranges. For the procedure described in Note 4, the temperature cycle should be from 30C to
38、 15C and back, at a rate of 2C/h. Plot the strain readings as a function of temperature to create the temperature compensation curve. It is recommended that a data acquisition system with built-in temperature compensation capabilities be utilized, otherwise the temperature compensation shall be perf
39、ormed manually during the calculations. 7.3. Record the individual strain gauge readings on the inner and outer Invar rings at 5-min intervals from the finish of casting until the end of testing. Note 7An instantaneous strain decrease of 20 microstrain in one or more gauges usually indicates crackin
40、g. When using fiber-reinforced concrete mixtures, a distinct decrease in strain may not be apparent. 7.4. Place any additional insulating panels on top of the testing apparatus then seal the insulating chamber for the remainder of the testing period. 8. CALCULATION AND INTERPRETATION OF RESULTS 8.1.
41、 The circumferential residual stress in the specimen at the inner face of the specimen, (RIC), is provided by Equation 1a: ( )( ) ( )22 2 2 2 2 2IC II OC IC OO OC OCIC IN I OUT I22 22IC OCOC IC OC IC2RR R R R R RRE ERR RR + = (1a) where: IN= average of the four strain gauges on the inner ring less t
42、heir temperature compensation (m/m) OUT= average of the four strain gauges on the outer ring less their temperature compensation (m/m) EI= Youngs elastic modulus of restraining rings, taken to be 141,000 MPa (20,450 ksi) for Invar RII= Radius to the inner face of the inner ring (mm) RIC= Radius to t
43、he inner face of the concrete specimen (mm) ROC= Radius to the outer face of the concrete specimen (mm) ROO= Radius to the outer face of the outer ring (mm) Using the standard dimensions as specified in Section 5.1, Equation 1a can be simplified to the following: 2017 by the American Association of
44、State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 363-6 AASHTO ( )IC IN I OUT I0.53 0.58R EE = (1b) 8.2. To calculate the remaining stress capacity, Remaining(RIC), of the specimen when using the testing approach described in Note 4,
45、 subtract the residual stress in the specimen prior to inducing thermal stress by varying the temperature, RESIDUAL, from the peak stress in the specimen after thermal cracking occurs, CRACK. In the event that cracking cannot be induced, CRACKis taken as the maximum stress withstood by the specimen.
46、 The remaining stress capacity represents the additional stress necessary to cause cracking in the specimen at that given age. This value yields insight as to how close the specimen is to cracking under the applied conditions. Report the temperature differential that the specimen endured during the
47、testing for remaining stress capacity. ( )Remaining IC CRACK RESIDUALR = (2) Note 8The stress values should be zeroed manually at the time of set. The time of set of the material should be determined in accordance with ASTM C403/C403M. Note 9This procedure shall be repeated at 2, 4, and 7 days of ag
48、e, so as to generate a remaining stress capacity curve for the given mixture. 9. REPORT 9.1. Report the following, if known: 9.1.1. Properties of the Concrete Mixturebatch materials and proportions, air content, consistency, unit weight, and temperature of fresh concrete; 9.1.2. Variations in formin
49、g, casting, or curing; 9.1.3. Restraining ring thicknesses and specimen dimensions; 9.1.4. Temperature of testing chamber, restraining rings, and concrete mixture at time of casting; 9.1.5. Plot of residual tensile stress versus time with specimen temperature profile versus time superimposed on the secondary y-axis; 9.1.6. Remaining stress capacity in the specimen at specified ages with the corresponding temperature d
