Question

3. (15 points) A bending beam rheometer (BBR) test was conducted on an asphalt binder specimen which has width of 12.5mm and height of 6.25mm. The distance between beam supports is 02mm. The following results were reported: ( (s points) At 60 seconds, the force was 0.9658N and the deflection was 0.1877mm Determine the creep stiffness, S(60). (2) (s points) A regression of the relationship between log(S) and log() log[S(t)]-2.86-0.21 [log(t)]1-0.03 [log(t)] 2 found to be was Determine the m-value at 60 seconds. (3) (5 points) If the BBR is run using PAV aged asphalt binder, does it meet the Superpave specification? Do we need to run DTT test in this case?

Answer 1

Answers:

Ans 3 -

Yes it meets the specification because the test is to be conducted on PAV aged asphalt binders.

According to Superpave, BBR is always run with combination of DTT in order to determine the asphalt binder's low temperature PG grade.

Ans 2 = log[ S(t)] = 2.86 - 0.21 *log(t) - 0.03*[log(t) ]^2

t = 60

log[ S(t)] = 2.86 - 0.21 *log(60) - 0.03*[log(60) ]^2

S = 4.46951

m- value is the slope of the curve represented from this equation.

m = S / t

= 4.46951 / 60

= 0.074

Ans 1 =

S(t) = P*L^3 / (4*b*h^3*d)

d =deflection

S(60) = 0.9658* 102^3 / ( 4*12.5*6.25^3 *0.1877)

S(60) = 447.315 MPa