TIME AND LOAD INDEPENDENT PROPERTIES OF BITUMINOUS MIXTURES

A NEW APPROACH IS PRESENTED TO CHARACTERIZE THE TIME-DEPENDENT BEHAVOUR OF ASPHALTIC CONCRETE BY A TRANSFER FUNCTION THAT IS DERIVED FROM THE FREQUENCY RESPONSE OF THE MATERIAL USING SINUSOIDAL LOADING TESTS. THE RATIO OF THE LAPLACE TRANSFORM OF THE OUTPUT TO THE LAPLACE TRANSFORM OF THE INPUT TO ANY SYSTEM IS DEFINED AS THE TRANSFER FUNCTION IS OF THE SYSTEM BETWEEN THE INPUT AND THE OUTPUT. THE TRANSFER FUNCTION IS A FUNCTION OF A COMPLEX VARIABLE CONSIDERING THE FREQUENCY OF THE INPUT AND THE IMAGINARY UNIT. IN THIS STUDY ASPHALTIC CONCRETE WAS TREATED AS A DAMPED, LINEAR SYSTEM IN WHICH THE APPLIED FORCE WAS THE INPUT AND THE RESULTING DISPLACEMENT WAS THE OUTPUT. BOTH THE INPUT AND OUTPUT WERE FUNCTIONS OF TIME. BY VARYING THE FREQUENCY OF THE INPUT, THE OUTPUT-INPUT MAGNITUDE RATIO WAS OBTAINED FOR EACH FREQUENCY, AND ITS PLOT AGAINST LOG FREQUENCY YIELDED THE FREQUENCY SPECTRUM. ALSO, THE TIME LAG BETWEEN THE OUTPUT AND THE INPUT WAS NOTED FROM WHICH THE PHASE AGNLE WAS CALCULATED. A SIMPLE GEOMETRIC TECHNIQUE TO OBTAIN THE TRANSFER FUNCTION DIRECTLY FROM THE FREQUENCY SPECTRUM WAS USED. THIS TECHNIQUE WAS APPLIED TO THE RESULTS OF THE TEST SPECIMENS OF ASPHALTIC CONCRETE CUT FROM LABORATORY COMPACTED BEAMS OF 2 DIFFERENT COMPOSITIONS TESTED AT 3 TEMPERATURES. IT IS SHOWN THAT THE TRANSFER FUNCTION FOR BITUMINOUS CONCRETE THUS DERIVED FROM A DYNAMIC TEST CAN BE USED TO PREDICT THE DISPLACEMENT OF THE TEST SPECIMEN SUBJECTED TO A STATIC LOAD BY TREATING THE LATTER AS A STEP FUNCTION OF TIME AND THROUGH THE USE OF LAPLACE INVERSE TRANSFORM. THE EXCELLENT AGREEMENT BETWEEN THE CALCULATED AND MEASURED VALUES OF THE DISPLACEMENTS INDICATES THAT THE TRANSFER FUNCTION REPRESENTS A MATERIAL PROPERTY THAT IS INDEPENDENT OF LOAD INPUT. THE CONCEPT OF TRANSFER FUNCTION MAKES IT POSSIBLE TO REPRESENT THE TIME-DEPENDENT BEHAVIOR OF ASPHALTIC CONCRETE BY A FOURTH ORDER LINEAR DIFFERENTIAL EQUATION WITH CONSTANT COEFFICIENTS WITHOUT ASSUMING ANY SPRING-DASHPOT MODEL. THE COEFFICIENTS CAN BE COMPUTED FROM THE ROOTS OF THE DENOMINATOR AND NUMERATOR OF THE TRANSFER FUNCTION. /ATHOR/

Media Info

  • Media Type: Print
  • Features: Figures; References; Tables;
  • Pagination: pp 63-78
  • Monograph Title: Bituminous materials, mixes and compaction
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00211564
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Oct 26 1970 12:00AM