**7.2 CBR**

The CBR ratio limitation for subballast, subbase, and base are 25, 30, and 80, respectively [40, 41]. Application of RRP235special increases CBR value in general. But *Developing a Novel Superstructure System for the Ballasted Railways Using RRP235special... DOI: http://dx.doi.org/10.5772/intechopen.111470*

### **Figure 13.**

*The effect of RRP235 special on CBR value.*

the strengthening is not proportion to the additive dosage. As shown in **Figure 13**, the CBR ratio increases from 0 to 0.15 lit/m<sup>3</sup> additive dosage and then is reduced and then by further use of the additive, is increased and strength again. In the optimum dosage of additive (0.15lit/m<sup>3</sup> ), the CBR increased more than 400% compared to the sample with no additive.

Clay colloids absorb a certain amount of additives, and the excess remains between the colloids. A large amount of excess material seems to reduce the soil's physical properties and make the situation glide colloids. Due to the concentration of the ions, the zeta potential decreases, and cations and anions are liberated from the diffuse double layer; thereupon, the swelling properties of soil reduce [42].

### **7.3 Compressive test results**

To place the sleepers on the stabilized layer, the minimum strength of soil is needed to be evaluated by compressive test. Similar to the CBR test results, the use of additives gives higher strength to the specimens. The strengthening process ascends from 0 to 0.15 lit/m<sup>3</sup> and then descends. This pattern is repeated at different ages. As indicated in **Figure 14**, the use of RRP235special had caused a 46 and 300 percent increase in compressive strength compared to the sample with no additive. Therefore, the optimal required amount of additive, according to **Figure 14** is 0.15lit/m<sup>3</sup> .

### **7.4 Indirect Brazilian tensile test results**

The tensile strength has improved using RRP235Special. Like the previous sections, increasing the additive usage up to 0.15 lit/m<sup>3</sup> increases the tensile strength and then descends. As shown in **Figure 15**, the sample with 0.15 lit/m<sup>3</sup> additives has the best result and is selected as the optimum dosage. Compared to the sample with no additive, the strength improves by more than 20%. Comparing **Figures 14** and **15** reveals that more compressive strength mirrors more tensile strength.

**Figure 14.** *RRP-stabilized soil compressive strength with different amounts over time.*

**Figure 15.** *Tensile strength of samples with different RRP235 special at 46 days of age.*

### **7.5 Direct shear test results**

As depicted in **Figure 16**, the maximum shear stress was obtained from Mohr– Coulomb diagrams.

To evaluate shear stress, different samples with RRP235special were made and tested. The additive has a positive role in the shear parameter. As illustrated in **Figure 17**, same as in previous tests, the strengthening pattern ascends up to 0.15 lit/m3 additive and then decreases, and further use causes increases again. The 0.15 lit/m<sup>3</sup> amount is determined as the optimum value among the used additive dosages.

*Developing a Novel Superstructure System for the Ballasted Railways Using RRP235special... DOI: http://dx.doi.org/10.5772/intechopen.111470*

**Figure 16.** *Shear stress–strain diagram (the sample with 0.15 lit/m3 additives).*

**Figure 17.** *Maximum shear stress diagram.*

Good compaction and high density of soil increase the shear strength. When the reaction has occurred, less water can accumulate in the soil than was originally possible. As a result, the swelling capacity is reduced, the internal moisture of the soil is also reduced, and complete compaction to zero content of air-tilled voids becomes possible because of the space that has become available from the expelled pore water. Subsequent additions of water cannot reverse this process once the latter has been accomplished (the swelling capacity is destroyed and the shearing strength increased) [43].
