**3.1 Stabilization of Amazonian soils with chemical additives**

An unpaved rural road located at 53 km of the state highway AM-010, north of the city of Manaus (Point 1 of **Figure 1**), is used to access a military base. This road has a natural subgrade consisting of a layer of yellow-red sandy silt containing a 55% silt fraction, 35% sand, and 9% clay and is classified as a latosol, with a 30% LL, a PI of 10%, a CBR of 31% and an optimal moisture content of 12.6%, both in the intermediate compaction energy. The soil pH is acidic, with a value of 5.39, kaolinite being the predominant clay mineral. The soil is classified as CL (USCS), A-4 (TRB), and LG′ (MCT).

The efficiency of chemically stabilizing the subgrade soil with cement supplemented with ZS was evaluated, resulting as a single layer of the stabilized base; for this purpose, was constructed an experimental section of 70 m in length and 7.5 m in width. In order to control the performance of executive technical procedures, SCS and TSDC tests were made before, during, and after construction, in addition to evaluating the overall quality of the road paving and its superficial drainage elements. *Challenges in the Construction of Highways in the Brazilian Amazonia Environment: Part II… DOI: http://dx.doi.org/10.5772/intechopen.105017*

**Figure 1.** *Locations of the case studies analyzed.*

The ZS-based additive (RoadCem®) used is a fine, odorless, grayish powder with a specific mass of approximately 1,100 kg/m3 and pH of 10–12 (in water, at 20°C). Its chemical composition is mainly composed of alkali metals and alkaline earth metals (60–80%), including sodium, potassium, calcium, and magnesium chlorides; ZS and oxides (5–10%); and activators (5–10%).

Based on the characteristics of the experimental section subgrade soil, a soilcement–the additive mix was made with 1.7 kg/m3 of ZS (0.09% per dry mass) and 160 kg/m3 of cement (8.20% per dry mass).

The SCS test results of the specimens molded in the laboratory before the fieldwork found values of approximately 8 MPa at 28 days. In general, the construction stages begin with the addition and mixing of the ZS additive and cement, followed by leveling, compaction, and surface finishing. In this process, the ZS additive may be added one day before the application of the cement (**Figures 2** and **3**).

The mechanical strength of the stabilized base was verified by molding PCs in three stages. In the laboratory, before starting the stabilization process, specimens were prepared with the pre-established dosage, and the SCS and TSDC test results were evaluated at the rupture ages of 3, 7, 14, and 28 days in wet curing.

During the execution of the stabilization step, a new molding of specimens was performed by collecting the homogenized mixture of soil-cement–ZS immediately before starting the field compaction procedure. In the third stage, after 28 days of stabilization, six samples were extracted directly from the runway. The laboratory

#### **Figure 2.**

*a) Distribution of cement and ZS additive in the experimental runway by manual spreading; b) homogenization of the soil, cement, and ZS additive in situ by means of a recycler [1].*

*Steps of a) compaction; b) bulging; c) surface finishing; and d) curing of the stabilized base [1].*

results of the samples molded in the laboratory, those molded with a field mixture, and those extracted from the runway are shown in **Figure 4**.

Of the specimens molded with the field mixture during the construction, the SCS results were observed to be close to the values of those specimens molded in the laboratory. The quality of the mixture made by the recycler and the time between homogenization and compaction are the main factors underlying the difference between the SCS of the samples molded in the laboratory and molded with the filed mixture, around 16%.

*Challenges in the Construction of Highways in the Brazilian Amazonia Environment: Part II… DOI: http://dx.doi.org/10.5772/intechopen.105017*

#### **Figure 4.**

*a) Comparison of SCS for samples molded in the laboratory, during stabilization, and extracted directly from the experimental runway; b) TSDC for laboratory-molded samples [1].*

Conversely, the samples extracted directly from the runway reached only 42% of the SCS resistance value of the samples molded in the laboratory at 7 days of curing (**Figure 4a**), but these values were still higher than the minimum Brazilian road standard, which is 2.1 MPa. The difference is mainly caused by the construction techniques, the quality of the mixture, and compaction by the equipment in the field, under conditions not always optimal, while in the laboratory, technological control is easier to achieve. In addition, the extraction process of field samples can damage the cemented structure of the specimens, reducing their real strength.

Regarding the tensile stresses that the lower regions of the pavement receive due to the transient loads imposed by the traffic, the TSDC of the stabilized base material reached values above 1 MPa at a curing age of 7 days (**Figure 4b**).

In the visual inspection of the work during the first 48 hours of curing, some transverse, superficial, and isolated cracks with average depths of 1 mm emerged. In this period, there was the volumetric expansion that generated internal tensile stresses in the material that was still in the fresh state. The microstructure in the formation is subjected to secondary growth of the impure phase of ettringite; because of the continued hydration of C3S, hydrated calcium silicate began to form inside the hydrated carapace [2]. This effect was more intense in plastic clays with high levels of cement exposed to the high humidity of the night-time forest and the intense heat of the day. However, the continuous strength gain of the material interrupted the propagation of cracks in later days, which naturally incorporated dust, showing an aspect of natural base regeneration. Four years after construction, the pavement showed no cracks, abatements, or pathologies that would compromise the durability and assimilation capacity of traffic surcharges (**Figure 5**).

#### **3.2 Granulometric stabilization of Amazonian soils using SCACC**

Cabral et al. [3] and Cabral [4] conducted laboratory and field studies on the use of SCACC in asphalt mixtures, with raw material from the state of Pará. The authors obtained excellent results when comparing SCACC to the natural coarse aggregate (crushed stone), indicating that the synthetic aggregate supports severe mechanical compaction, according to the results obtained in the degradation tests (analysis of the comparison between the granulometric composition of the SCACC in the conditions of no compaction on the experimental runway, and after two years of service

#### **Figure 5.**

*Final aspect of the experimental section. a) One day of stabilization, in Oct. 2016; b) after 490 days, in Feb. 2018; c) after 4 years, Oct. 2020 [1].*

#### **Figure 6.**

*Use of SCACC in highway paving: a) burnt of ceramic bricks following a controlled firing temperature; b) crushing of the ceramic blricks. c) Stacking of the mixture of lateritic soil and SCACC in the field [4].*

completion). The study site was an experimental section of the pavement restoration work on federal highway BR-163, between 101 km and 102 km (Point 2 of **Figure 1**), whose differential treatment was the incorporation of SCACC in the base layer of the pavement.

The base course of this segment was built in mid-November 2007, totalling 1,000 m in length, 12 m in width (two lanes of 3.5 m each and two shoulder lanes of 2.5 m each), and 20 cm thick. Not only in this section, but throughout the extent of the pavement restoration work, the project established the need to incorporate approximately 30% of coarse aggregate into the lateritic soil (*piçarra*) obtained from the deposits prospected by the geological-geotechnical studies.

**Figures 6** and **7** show the stages of the use of SCACC, from the preparation of the ceramic bricks (which were later crushed into coarse aggregate sizes) to the execution of the base course in the field.
