Base course modification through stabilization using cement and bitumen

American Journal of Applied Sciences, Jan, 2009 by Marandi S.M., Safapour P.

* The mean yearly ambient temperature for the layers, 25[degrees]C

In second variant, in spite of above items and assuming asphalt layers with higher module of elasticity, excess calculations were carried out. For stabilized layer, the selected design E-Module was less than the value obtained from the fatigue tests.

According to traffic statistics obtained from construction site area in Afghanistan, three types of loading were considered in calculations: 80 and 100 kN for tandem axles and 115 kN for single axle. Details of input data are shown in Table 8 and 9.

Table 8: Input data-loads and axles

 Axle type             Wheel load (kN)   Tire pressure (kPa)

80kN tandem axles            20                  577
100kN single axle            50                  700
115kN single axle            57.5                800

Table 9: Design calculation-stabilized layer with cement
and bitumen emulsion

Pavement layers             Module of          Thickness
                        elasticity (MPa)          (mm)

Asphalt layer           3000                   50

Stabilized layer        1500                   250
with cement
and bitumen emulsion

Sub-grade               240 (CBR[greater than  600
                        or equal to ]25)

Sub-soil                100 (CBR[greater than  [greater than or
                        or equal to ]10)       equal to]1000

Standard allowed
axle repitition

80 kN tandem
axle = 7.33x1[0.sup.6]

100 kN single
axle = 1.61x1[0.sup.6]

115 kN single
axle = 1.13x1[0.sup.6]

Design was made with different E-Module for asphalt layers. The results indicate that, the asphalt layer with normal stiffness module is not proper for high loading traffic condition such in Afghanistan. Thus, calculations repeated with higher E-Module to find out the effect of stiffness on ultimate structure bearing capacity. Design results are presented in Table 10-12. The results of the design methods revealed the following features:

Table 10: Design calculation-asphalt layer (conventional method)

Pavement layers             Module of          Thickness
                        elasticity (MPa)          (mm)

Surface course          3000                   40

Binder course           1500                   60

Black-base              1500                   60

Sub-base                300 (CBR[greater than  150
                        or equal to ]60)

Sub-grade               240 (CBR[greater than  600
                        or equal to ]25)

Sub-soil                100 (CBR[greater than  [greater than or
                        or equal to ]10)       equal to ]1000

Standard allowed
axle repitition

80 kN tandem
axle = 0.66x1[0.sup.6]

100 kN single
axle = 0.26x1[0.sup.6]

15 kN single
axle = 0.13x1[0.sup.6]

Table 11: Design calculation-asphalt layer with high
performance (conventional method)

Pavement layers               Module of         Thickness
                          elasticity (MPa)         (mm)

Surface course          3000                   40

Binder course           2500                   60

Black-base              2500                   60

Sub-base                300 (CBR[greater than  150
                        or equal to ]60)

Sub-grade               240 (CBR[greater than  600
                        or equal to ]25)

Sub-soil                100 (CBR[greater than  [greater than or
                        or equal to ]10)       equal to ]1000

Standard allowed
axle repitition

80 kN tandem
axle = 2.81x1[0.sup.9]

100 kN single
axle = 0.44x1[0.sup.6]

115 kN single
axle = 0.23x1[0.sup.6]

Table 12: Temperature of construction

Temperature [degrees]C  From km   Section (km)

10,0                      0,000    0,000-23,000
12,0                      7,600
15,0                     14,500
15,0                      0,000    0,000-23,000
12,0                      9,100
10,0                     18,600
16,0                     23,000   23,000-32,300
10,0                     24,900
12,0                     23,000   23,000-32,300
10,0                     27,200