Question

In a quality control test for pavement construction, the engineer cut out a core of the asphalt mix. Laboratory tests were conducted on the core to determine the volumetric properties of the mix. The dry mass of the core is 1200 g, the saturated surface dry mass is 1202.5 g and the submerged mass is 691.9 g. The engineer separated the bitumen from aggregate and found that the dry mass of the aggregate was 1132.8g. The specific gravity of bitumen is 1.05 and the percentage of bitumen absorption is 0.5%. The aggregate bulk specific gravity is 2.76, determine the following:

a) bulk specific gravity of the compacted mix

b) Effective specific Gravity aggregates

c) max theoretical specific gravity of asphalt mix

d) percentage by mass of effective binder content

e) percentage of air voids in the total mix

f) pencetage of voids in the mineral aggregates

Answer 1

Mass of dry core A = 1200 g

Saturated surface dry mass B = 1202.5 g

Submerged mass C = 691.9 g

Dry mass of the aggregate D = 1132.8 g

Specific gravity of bitumen G_B = 1.05

Percentage of bitumen absorption P_ba = 0.5%

Aggregate bulk specific gravity G_sb = 2.76

Aggregate content P_s = D/A * 100 = 1132.8 / 1200 * 100 = 94.4%

Bitumen content P_b = 100 - P_s = 100 - 94.4 = 5.6%

a) Bulk specific gravity of the mix

G_mb = A / (B-C)

= 1200 / (1202.5-691.9)

= 2.35

c) Max theoretical specific gravity of asphalt mix

G_mm = A / (A-C) = 1200 / (1200 - 691.9)

= 2.36

b)  Effective specific Gravity aggregates

G_se = P_s / [(100/G_mm) - (P_b/G_b)]

= 94.4 / [(100/2.36) - (5.6/1.05)]

= 2.55

d) Percentage by mass of effective binder content

P_be = P_b - (P_ba / 100 * P_s )

= 5.6 - (0.5/100*94.4)

= 5.13

e) Percentage of air voids in the total mix

V_a = 100 * [(G_mm - G_mb) / G_mm]

= 100 * [(2.36 - 2.35) / 2.36)]

= 0.42%

f) Percetage of voids in the mineral aggregates

V_ma = 100 - (G_mb * P_s / G_sb)

= 100 - ( 2.35 * 94.4 / 2.76)

= 19.62%