# A Comparative Evaluation of Cement and By-Product Petrit T in Soil Stabilization
## 3 Results and Discussion
### Soil Stiffness  
The effects of the two binder types (cement and Petrit T) on the stiffness of treated soil with various binder content and curing times is presented in Figure 16. The stiffness in terms of E\({}_{50}\) was determined as a secant modulus of elasticity from the stress-strain curves at 50% of the maximum unconfined compressive strength (q\({}_{\text{u}}\)). It can be seen that the stiffness of the treated soil increased as the binder content and curing time increased (see Figure 16).  
Figure 16: Modulus of elasticity versus curing time and binder content for (**a**) untreated soil; (**b**) treated soil with 1 and 2% cement and 2% Petrit T; (**c**) treated soil with 4% of cement and Petrit T and (**d**) treated soil with 7% of cement and Petrit T.  
Figure 15: Axail failure strain versus UCS strength for all tests.  
The development characteristic curve of the modulus of elasticity (E\({}_{50}\)) over time has very similar trends to the development of unconfined compressive strength as presented in Figure 10. This can be attributed to generating new cementing components of CSH and CAH as a result of hydration and pozzolanic reactions. A higher binder content produce more cementitious materials of CSH and CAH and vice versa. As mentioned earlier, the production and deposition of cementitious material is further increased with an increase in curing time and binder content and filling of the pores between voids. Thus producing a dense structure with a corresponding increase in the stiffness of the soil. The trend of increase the soil stiffness is consisted with [14; 15; 23; 39].  
Figure 17 shows the relationship between modulus of elasticity, E\({}_{50}\), and the unconfined compressive strength. For cement and Petrit T treatments (Figure 17), it is noticed that an increase in soil stiffness is accompanied by an increase in soil strength. The modulus of elasticity can be taken as being between 14 to 24 qu\({}_{\text{u}}\) for Petrit T, and between 16 to 85 qu\({}_{\text{u}}\) for the cement treatment.  
For a comparison between the effectiveness of cement and Petrit T as binders, an improvement in soil stiffness or strength after treatment can be clarified by the ratio between the stiffness or strength of the treated specimens to the stiffness or strength of the soil specimens without treatment. Table 1 presents the improvement in soil stiffness and strength, values of failure strain, and the relation between E\({}_{50}\)-qu\({}_{\text{u}}\) after treatment with cement or Petrit T. Table 2 shows that a comparable increase in soil stiffness and strength using cement as a binder can be achieved by adding double the amount of Petrit T and using long curing periods. A similar observation is also valid for the reduction in failure strain and the relationship between soil stiffness and UCS.  
Figure 17: Modulus of elasticity versus UCS strength (qu\({}_{\text{u}}\)) and binder content for (**a**) treated soil with 1 and 2% cement and 2% Petri T; (**b**) treated soil with 4% of cement and Petrit T and (**c**) treated soil with 7% of cement and Petrit T.  
In terms of the relationship between E\({}_{50}\) and q\({}_{u}\), many authors [14; 15; 18; 29; 55; 56; 57; 58; 59] have reached varying conclusions about this relationship. Table 3 presents a comparison between the previous studies and the present study. Moreover, many researchers used different techniques such as using the electrokinetics method and nanomaterials to improve the stability of collapsible soil [60], and developed new procedures and specifications to estimate the mechanical properties of compacted geomaterials for design verification [61]. The results obtained are consistent in general with previous studies.