Base course modification through stabilization using cement and bitumen

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

[FIGURE 1 OMITTED]

Table 1: Technical specification of the test materials

Unified                        Sand     D60   D30    D10    CC   CU
classification  Plasticity  equivalent  (mm)  (mm)   (mm)
                                (%)

SP              NP                 82      9     1   0.13  1.17  69

Table 2: Bitumen specification for producing bitumen emulsion

Penetration       Flash       Softening    Penetration       Unit
index at           point         point         at           weight
25[degrees]C  ([degrees]C)  ([degrees]C)  25[degrees]C  at 25[degrees]C
and
softening
point

-0.27              320           52           60          1.012

Table 3: Bitumen emulsion specification

Specification  Bitumen  Water  Emulsifier  Solvent   Acid (Hcl)
                60-70

Producing         140     30       30-40     Oct-40       30-40
temperature
([degrees]C)

Unit weight      0.95      1        1.07       0.8         1.15
during
production (g
[cm.sup.-3])

Percentage by     58   39.75           1       1.5         0.25
weight (%)

First Series Test Results Analysis: At first stage and to determine the optimum cement and bitumen emulsion, a total of 153 mixed designs, in four series of Marshal Tests were made and tested. The first three series included 27 samples with constant cement percentages of 1.5, 2 and 2.5% and variation of bitumen emulsion from 2.5, 3 and 3.5% respectively. The fourth series of tests were 72 samples with various cement percentage of 0.5, 1, 1.5, 2, 2.5, 3, 3.5 and 4% with variation of bitumen emulsion from 2.5, 3 and 3.5%.

The average test results for optimizing cement and bitumen emulsion are shown in Fig. 2 and 3.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

Figure 2 shows the variation of Marshal Stability versus cement for 2.5, 3 and 3.5% of bitumen emulsion after seven days curing. The results indicate that, with increase in cement percentage the stability for all three series of tests increases; however, the samples with 3% of bitumen emulsion shows the average difference of 30% more increase in stability in compare with 2.5 and 3.5% bitumen emulsions samples, thus, it seems choosing 3% for bitumen emulsion may contribute the predicted strength results in stabilizing the base course. Thus, it was decided to choose this value as an optimum bitumen emulsion for our mixture.

For optimizing the amount of cement, the variation of Marshal Stability versus cement was plotted for constant 3% of bitumen emulsion in Fig. 3. The results show that, the stability increase with increase in cement, but it is not possible to find optimum cement needed properly. Since using too much cement in the mixture, causes shrinkage cracks which, is a big problem for pavement structure and layers from water penetration viewpoint and also increase the unit cost, a new series of ITS and UCS tests carried out to optimize the percentage of cement and minimize the costs.

In second series of experimental tests, stabilization mix design method used. In recent years, the mechanical tests such as ITS, is standard criterion for determination of mix strength against fatigue cracks in all mix designs and usually UCS tests are performed along ITS (8-11).