ASTM_D_4612_-_08.pdf

Designation:D461208Standard Practice forCalculating Thermal Diffusivity of Rocks1This standard is issued under the fixed designation D4612;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope*1.1 This practice involves calculation of the thermal diffu-sivity from measured values of the mass density,thermalconductivity,and specific heat at constant pressure.It isapplicable for any materials where these data can be deter-mined.The temperature range covered by this practice is 20 to300C.NOTE1The diffusivity,as determined by this practice,is intended tobe a volume average value,with the averaging volume being$2 105m3(20 cm3).This requirement necessitates the use of specimens withvolumes greater than the minimum averaging volume and precludes use offlash methods of measuring thermal diffusivity,such as the laser pulsetechnique.NOTE2This practice is closely linked to the overall test procedureused in obtaining the primary data on density,specific heat,and conduc-tivity.It cannot be used as a“stand alone”practice because the thermaldiffusivity values calculated by this practice are dependent on the natureof the primary data base.The practice furnishes general guidelines butcannot be considered to be all-inclusive.1.2 The values stated in SI units are to be regarded as thestandard.The values given in parentheses are mathematicalconversions to inch-pound units that are provided for informa-tion only and are not considered standard.1.3 The practice is intended to apply to isotropic samples;that is,samples in which the thermal transport properties do notdepend on the direction of heat flow.If the thermal conductiv-ity depends on the direction of heat flow,then the diffusivityderived by this practice must be associated with the samedirection as that utilized in the conductivity measurement.1.4 The thermal conductivity,specific heat,and mass den-sity measurements must be made with specimens that are asnear identical in composition and water content as possible.1.5 The generally inhomogeneous nature of geologic forma-tions precludes the unique specification of a thermal diffusivitycharacterizing an entire rock formation.Geologic media arehighly variable in character,and it is impossible to specify apractice for diffusivity determination that will be suitable forall possible cases.Some of the most important limitations arisefrom the following factors:1.5.1 Variable MineralogyIf the mineralogy of the forma-tion under study is highly variable over distances on the sameorder as the size of the sample from which the conductivity,specific heat,and density specimens are cut,then the calculateddiffusivity for a given set of specimens will be dependent onthe precise locations from which these specimens were ob-tained.1.5.2 Variable PorosityThe thermal properties of porousrock are highly dependent on the amount and nature of theporosity.A spatially varying porosity introduces problems of anature similar to those encountered with a spatially varyingcomposition.In addition,the character of the porosity maypreclude complete dehydration by oven drying.1.6 All observed and calculated values shall conform to theguidelines for significant digits and rounding established inPractice D6026.1.7 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 safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2C177 Test Method for Steady-State Heat Flux Measure-ments and Thermal Transmission Properties by Means ofthe Guarded-Hot-Plate ApparatusC518 Test Method for Steady-State Thermal TransmissionProperties by Means of the Heat Flow Meter ApparatusC642 Test Method for Density,Absorption,and Voids inHardened ConcreteD3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD4611 Test Method for Specific Heat of Rock and SoilD6026 Practice for Using Significant Digits in GeotechnicalData1This practice is under the jurisdiction of ASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.12 on Rock Mechanics.Current edition approved July 1,2008.Published July 2008.Originally approvedin 1986.Last previous edition approved in 2003 as D4612 03.DOI:10.1520/D4612-08.2For 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM International