Appendix D 8 Effect of Variables on Resilient Modulus
The effects of temperature and load duration on resilient modulus were discussed earlier as these variables are stipulated in the Australian Standard. Other variables also affect the resilient modulus and these are briefly discussed below.
The viscosity of a binder used in a mix design will affect the resilient modulus of asphalt. Soft‑grade binders such as those modified with SBS polymer will have a very low resilient modulus of about 2000 MPa or less. Straight-grade bitumens such as Class 170 and Class 320 will have resilient moduli in the range 2500 to 5000 MPa for typical dense graded asphalt. If a binder is modified with a hard polymer such as the EVA type then the resilient modulus could be as high as 7000 MPa. (Note: these are indicative values only.)
In addition to the viscosity of the binder, the quantity of binder will also affect the resilient modulus. Within the normal range of binder contents (say 3 to 10% by mass) the greater the binder content the softer (lower resilient modulus) the mix will behave.
Aggregate quality will affect the resilient modulus. Aggregates that are roughly cubical and rough textured will produced a mix with greater resilient modulus than the same mix with rounded, smooth textured aggregates.
The gradation of the aggregate also affects the resilient modulus. Mixes with larger maximum particles will tend to have greater resilient moduli than mixes with small particles. Mixes with a large percentage of coarse aggregate will have greater resilient moduli than mixes with a large percentage of fine aggregates.
The effect of oxidation on most binders is to increase binder viscosity and hence result in an increase in resilient modulus. For some PMBs, excessive oxidation results in degradation of the binder with resulting reduction in viscosity and hence a reduction in modulus.
A summary of the above discussion on the factors affecting resilient modulus is given in Table D 2.
|Increased binder content||Reduce|
|Increased binder viscosity||Increase|
|Grading (coarse to fine)||Reduce|
|Increased load duration||Reduce|
|Increased compaction level||Increase|
(though some mixes can have a reduction in resilient modulus if the compaction level passes a critical level)