Base course modification through stabilization using cement and bitumen

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

[FIGURE 6 OMITTED]

Modulus of elasticity versus bitumen emulsion is plotted in Fig. 7. Figure 7 shows that, for a certain bitumen emulsion, with increase in cement, E-Module increase up to 4% and decreases afterward, while, when cement increase to %5, the modulus of elasticity decreases considerably. This might be due to the chemical reaction of cement-bitumen emulsion in the mixture.

[FIGURE 7 OMITTED]

According to traffic statistics obtained from construction site in Afghanistan and E-Module of 1500 MPa used for design, Fig. 7 shows that, the minimum cement which, can be used to get E-Module of 1500 MPa is 3%. Thus, it seems the optimum value for both bitumen emulsion and cement for our design criteria is 3% respectively.

The results of this series of the tests indicate that, the roles of the cement and bitumen emulsion in mixtures are increasing the stiffness and elasticity of the stabilized layer respectively. Increase in cement percentage will decrease the elasticity and consequently causes shrinkage cracks in the layer, thus, it seems using 3% for both optimized cement and bitumen emulsion contribute the best results in stiffness and elasticity, this was observed visually and by measurements, one year after the construction was finished.

DESIGN METHODS

The main road was designed with two methods, conventional variant and stabilizing with cement and bitumen emulsion variant. The PADS Software (12), (14) used for determination of layer thickness. In this way, the fatigue functions for pavement layers are extracted from Shell Pavement Design Method. (13) The new fatigue functions are based on fatigue specifications for stabilized layers with cement. It also presents a new method for calculation of combined bitumen emulsion and cement. The design parameters and traffic load are extracted as follows:

For asphalt layers, the stiffness coefficient is extracted from SPDM (13) and functions used for calculation were (Table 7):

Table 7: Input data-layer specification

                                         Module of          Poisson
          Pavement layers              elasticity (MPa)       ratio

Surface course S1-50                 3000                      0.35

Binder course S2-50                  1500                      0.35

Black-base S2-50                     1500                      0.35

Binder course with high performance  2500                      0.35

Black-base with high performance     2500                      0.35

Stabilized layer with cement and     1500                      0.35
bitumen emulsion

Sub-base                             300 (CBR[greater than     0.35
                                     (or) equal to ]60)

Sub-grade                            240 (CBR[greater than     0.35
                                     (or) equal to ]25)

Underneath soil                      100 (CBR[greater than     0.35
                                     (or) equal to ]10)

* Function S1-50 for surface course

* Function S2-50 for binder course and black-base