**3.3 Chemical stabilization of Amazonian soils with soil: Asphalt emulsions**

To observe the behavior of an application of soil–asphalt emulsion mixture, Sant'Ana [5] studied a 200-m unpaved experimental section located at gate 3 of the access to the State University of Maranhão (Point 3 of **Figure 1**), which had a highly irregular surface, composed of a base course in laterite that was very deteriorated (**Figure 8**) overlying a subgrade layer formed by fine sandy soil (no subbase layer was observed). After the collection of deformed samples to characterize the existing *Challenges in the Construction of Highways in the Brazilian Amazonia Environment: Part II… DOI: http://dx.doi.org/10.5772/intechopen.105017*

#### **Figure 7.**

*Use of SCACC in highway paving: a) scattering of the mixture of lateritic soil and SCACC for the execution of the base course; b) completed experimental runway, with asphalt course in double surface treatment. c) Conditions of the experimental runway approximately 2 years after completion [4].*

**Figure 8.** *View of the experimental section before stabilization with asphalt emulsion [5].*

layers, satisfactory results of the subgrade were observed (CBR of 12% under the normal compaction energy). On the other hand, the material of the base layer fit the subbase properties (CBR of 23% under intermediate compaction energy), so it needed to be reinforced and regularized with material imported from a deposit, resulting in a new base course.

Regarding the stabilization of the new base layer with RL-1C asphalt emulsion (cationic, slow rupture), the surface (base) was regularized and the existing road widened, keeping the transverse slopes at 3–5% to allow the accelerated flow of rainwater. Then, over the first 100 m, scarification was performed at a thickness of 5 cm (**Figure 9a**), followed by wetting until the layer reached the optimum moisture content; homogenization with a disc harrow (**Figure 9b**); application of RL-1C asphalt emulsion at the rate of 5 l/m<sup>2</sup> , corresponding to 5% by weight of the dry soil, but in three stages (**Figure 9c** and **d**); and homogenization with the disc harrow between asphalt emulsion steps. A grader was used to move the soil–asphalt emulsion mixture to the side of the road, sometimes on one bank, sometimes on another (**Figure 9e**). Next, the mixture was compacted with a smooth roller (**Figure 9f**). Finally, the preliminary sealing layer was applied, with the emulsifying

**Figure 9.** *Some records of the execution stages of the experimental section with soil–emulsion [5].*

agent spreading (**Figure 9g**) and the release of clean sand (**Figure 9h**), which was then compacted again by a smooth roller. **Figure 9i** shows the finishing appearance of the stabilized base 7 days after execution. The remaining 100 m were subjected to the same procedure as above.

To evaluate the stabilization efficiency, two non-destructive tests using Falling Weight Deflectometer (FWD) equipment were carried out on the finished surface, one 12 days and the other 20 months after execution. The current service value of the road surface was characterized using the method developed by the United States Department of Army in 1995, with the objective of calculating the Unsurfaced Road Condition Index (URCI). Surface distress surveys were carried out in December 2007 and September 2008, that is, 10 months and 20 months after the stabilization was completed, respectively.

Although the material was in good general condition, the defects that were most common in the analyzed sections were surface dust, the loss of aggregate due to abrasion, and the "pothole" or "potholes". The classification of all sections of the experimental stretch as "very good" or "excellent" by URCI method, after almost 2 years of operation (**Figure 10**), showed that the soil–asphalt emulsion technique is applicable in the region where it was studied for roads with low traffic volume.
