FLEXURAL STIFFNESS PROPERTIES OF ASPHALT CONCRETE AT LOW TEMPERATURES WITH DISCUSSION

THE MODULUS OF RUPTURE AND MODULUS OF ELASTICITY OF A PAVING MIXTURE CHANGE CONSIDERABLY WITH DIFFERING GRADES AND TEMPERATURE SUSCEPTIBILITY OF THE ASPHALTS USED IN THE MIX. THE MODULUS OF RUPTURE IS A MEASURE OF THE TENSILE STRENGTH OF THE MIXTURE AND THE MODULUS OF ELASTICITY IN FLEXURE IS A MEASURE OF THE STIFFNESS. THE GREATER THE STIFFNESS MODULUS, THE GREATER THE THERMAL STRESS DEVELOPED IN THE PAVEMENT BY TEMPERATURE CHANGE. THE MIXTURE SHOULD BE DESIGNED AND AN ASPHALT GRADE SELECTED TO HAVE A HIGH MODULUS OF RUPTURE TO INSURE ADEQUATE TENSILE STRENGTH, BUT A LOW STIFFNESS MODULUS SO THAT THE MIXTURE WILL BE PLIABLE RATHER THAN STIFF AND BRITTLE. TO DETERMIINE THE EFFECT OF ASPHALT CEMENT VISCOSITY ON THE STIFFNESS OF MIXTURES AT LOW TEMPERATURES, BEAMS WERE FABRICATED FROM ASPHALT CEMENTS OF THREE DIFFERENT PENETRATION GRADES AND WERE DESIGNATED AS 40/50, 85/100, AND 200/300. THE RHEOLOGICAL PROPERTIES FOR EACH ASPHALT CEMENT WERE DETERMINED. THE ASPHALT PAVING MIXTURE BEAMS WERE ALSO TESTED IN FLEXURE AT MINUS 35 F, MINUS 5F, AND PLUS 25 F, TO DETERMINE HOW THE STIFFNESS MODULUS AND MODULUS OF RUPTURE VARIED WITH ASPHALT CONSISTENCY AND TEMPERATURE. RESULTS OF THE FLEXURE TESTS ARE RECORDED IN TABULAR FORM. REGRESSION ANALYSIS WAS APPLIED TO DEVELOP A MATHEMATICAL MODEL OF THE RELATIONSHIP BETWEEN STIFFNESS, TEMPERATURE, AND ASPHALT VISCOSITY. THE FOLLOWING CONCLUSION ARE REACHED: THE FLEXURAL STIFFNESS AND MODULUS OF RUPTURE AT LOW TEMPERATURE APPEAR TO BE SUITABLE CONTROL TESTS FOR USE IN DESIGNING ASPHALT PAVING MIXTURES AND SHOULD BE USED AS DESIGN CRITERIA. A DESIGN LIMIT OF 250,000 PSI FOR FLEXURAL STIFFNESS SHOULD BECOME PART OF THE MIX DESIGN PROCEDURE. THE MINIMUM TEMPERATURE FOR A PROPOSED MIX CAN BE DETERMINED AND COMPARED WITH EXPECTED FIELD TEMPERATURES. ALONG WITH THIS, A MINIMUM OF 800 PSI AT MINUS 5 F FOR THE MODULUS OF RUPTURE SHOULD BE PART OF MIX DESIGN PROCEDURE TO INSURE ADEQUATE TENSILE STRENGTH TO RESIST CRACKING. THE ASPHALT CEMENT WITH THE LOWEST VISCOSITY THAT CAN MEET HIGH TEMPERATURE STABILITY REQUIREMENTS SHOULD BE USED. IF HIGH TEMPERATURE STABILITY REQUIREMENTS CANNOT BE MET, A LESS DESIRABLE ASPHALT WILL HAVE TO BE CHOSEN AND SOME CRACKING EXPECTED. AS AN EXAMPLE, THE TYPICAL MIDCONTINENT 85/100 ASPHALT HAS A MINIMUM DESIGN TEMPERATURE OF MINUS 17 F. TO REACH MINUS 20 F WITHOUT CRACKING REQUIRES A 115 PENETRATION ASPHALT. A DISCUSSION IS INCLUDED WHICH DEALS WITH VARIOUS QUESTIONS CONCERNING THIS STUDY.

• Authors:
  • Busby, E O
  • Rader, L F
• Conference:
  • Association of Asphalt Paving Technologists Proc
• Publication Date: 1972

Media Info

• Features: Figures; References; Tables;
• Pagination: p. 163-87
• Serial:
  • Volume: 41

Subject/Index Terms

• TRT Terms: Asphalt cement; Asphalt concrete; Asphalt pavements; Bituminous mixtures; Flexural strength; Low temperature; Mathematical models; Mix design; Modulus of elasticity; Modulus of rupture; Pavement cracking; Pendulum tests; Regression analysis; Rheological properties; Stiffness; Temperature; Tensile strength; Thermal stresses; Viscosity
• Subject Areas: Data and Information Technology; Highways; Materials;

Filing Info

• Accession Number: 00211819
• Record Type: Publication
• Files: TRIS
• Created Date: Sep 17 2002 12:00AM