Queendom Tools

Superpave Estimated Properties at 4% Va Calculator

Enter the seven gyratory lab values for one trial blend. Trial Blend No. 1 from the FHWA workbook is preloaded: Gmm 2.475, Gmb 2.351, heights 117.4 mm at Ndes and 129.6 mm at Nini, Pbt 5.0 %, VMA 14.0 % and %Gmm max 96.1 % resolve to Pb,est 5.40 %, VMA,est 13.8 %, VFA,est 71.0 % and estimated densities of 87.1 % and 97.1 % at 4.0 % air voids.

%Gmm des—% of Gmm at Ndes
Va—% air voids at Ndes
%Gmm ini—% of Gmm at Nini
Pb,est—% binder at 4.0 % Va
VMA,est—% at 4.0 % Va
VFA,est—% at 4.0 % Va
Est %Gmm ini—% at 4.0 % Va
Est %Gmm max—% at 4.0 % Va
C coefficient—0.1 below 4.0 % Va, 0.2 at or above

For preliminary estimation only, not a substitute for review by a qualified/licensed engineer. The adjustment is the workbook linear estimate for small distances from 4.0 % Va. No pass or fail against specification criteria is given.

Estimating Superpave properties at 4.0 percent air voids

You have just finished gyratory compaction on Trial Blend No. 1 and the specimen did not land on 4.0 percent air voids. It rarely does on the first trial. The FHWA Superpave workbook, Step 2, handles this with a linear adjustment: measure how far Va sits from 4.0 percent, then shift binder content, VMA, VFA and the density values by that distance. Doing it by hand means carrying %Gmm des and %Gmm ini to one decimal, switching the VMA coefficient depending on which side of 4.0 you are on, and keeping the signs straight.

This page does that arithmetic as you type, the way the workbook does it, rounding %Gmm des and %Gmm ini half up in tenths before they feed the later steps. One data set is enough: Gmm 2.475, Gmb 2.351, heights 117.4 mm at Ndes and 129.6 mm at Nini, Pbt 5.0 %, VMA 14.0 % and %Gmm max 96.1 % give Pb,est 5.40 %, VMA,est 13.8 %, VFA,est 71.0 % and estimated densities of 87.1 % and 97.1 % at 4.0 % air voids.

One detail worth knowing: the workbook text writes the VFA,est formula with Va at Ndes in the denominator, but its worked example uses 4.0 (VMA,est 13.8 gives VFA,est 71.0). This page uses 4.0, because the estimate is taken at 4.0 % air voids. Source: FHWA, Superpave Asphalt Mixture Design Workshop Workbook, Version 8.0 (January 2002), Step 2 Selection of a Design Aggregate Structure, pages 50-51 and 57-58.

How to use it

  1. Enter Gmm from the Rice test and Gmb at Ndes for the trial blend.
  2. Enter the specimen heights measured at Ndes (h_des) and at Nini (h_ini) in mm.
  3. Enter the trial binder content Pbt (%), the VMA at Ndes (%) and the %Gmm at Nmax (%).
  4. Read the nine results as they update; note the C coefficient shown (0.1 below 4.0 % Va, 0.2 at or above).

FAQ

How does the calculator estimate binder content at 4.0 percent air voids?

It computes d = 4.0 − Va and applies Pb,est = Pbt − 0.4 × d, so a mix compacted above 4.0 % Va gets a higher estimated binder content — Trial Blend No. 1 (Gmm 2.475, Gmb 2.351, Pbt 5.0) gives %Gmm des 95.0, Va 5.0, d = −1.0 and Pb,est 5.40.

When is the VMA adjustment coefficient C equal to 0.1 and when is it 0.2?

C = 0.1 when the calculated Va is below 4.0 and C = 0.2 when Va is 4.0 or greater; VMA,est = VMA + C × d with d = 4.0 − Va, so at exactly 4.0 % Va the estimate returns the measured VMA unchanged.

How is VFA,est calculated at 4.0 percent air voids?

VFA,est = 100 × (VMA,est − 4.0) ÷ VMA,est — the 4.0 is used because the estimate is taken at 4.0 % air voids, so VMA,est 13.8 gives VFA,est 71.0.

How are the estimated initial and maximum density values obtained?

%Gmm ini = round(%Gmm des × h_des ÷ h_ini, 1), then Est %Gmm ini = %Gmm ini − d and Est %Gmm max = %Gmm max − d; for the same Trial Blend No. 1 the heights 117.4 mm and 129.6 mm give %Gmm ini 86.1 and the estimates 87.1 and 97.1.