# A Comparative Evaluation of Cement and By-Product Petrit T in Soil Stabilization
## 3 Results and Discussion
### Soil Strength  
The unconfined compressive strength (q\({}_{u}\)) was used as an indicator to investigate the enhancement in soil strength. These tests were conducted on the untreated and treated soil, both of which were prepared in a similar way, for the same curing period and conditions. For the untreated soil, Figure 10a shows almost no increases in the unconfined compressive strength (q\({}_{u}\)) over time. Figure 10b-d show the effects of adding the two binder types (cement and Petrit T) on the improvement in soil strength. Cement has four major clinker minerals, C\({}_{3}\)S (alite), C\({}_{2}\)S (belite), C\({}_{3}\)A (aluminate) and C\({}_{4}\)AF (Ferrit) [50]. The reactions of C\({}_{3}\)S and C\({}_{2}\)S have been the main contributors to the gain in strength, whilst the reactions of C\({}_{3}\)A and C\({}_{4}\)AF have made only a minor contribution. The reaction of C\({}_{3}\)S produced rapid hardening of cement during a short curing time. Whilst the reaction of C\({}_{2}\)S has a lower reactivity, therefore, the gain in the strength is observed after a long curing period. For the by-product Petrit T, the X-ray diffraction (XRD) (provided by the manufacturer) shows that Petrit T consists mainly of 57% dicalcium silicate (similar to the clinker mineral C\({}_{2}\)S in cement) 28.3% calcium silicon-aluminate, 11.5% silicon dioxide and 3% portlandite. The mineral part represents 74% of the whole mass, the rest consists of amorph carbon (21%) and iron (5%). The major component mainly of Petrit T is the dicalcium silicate and calcium-silicon-aluminate. Therefore, the improvement in soil strength over time can be explained by the slower reaction of C\({}_{2}\)S.  
An improvement in soil strength after treatment for both cement and Petrit T was observed by increasing in the amount of binder and curing time. This gives an indication of generating new components of CSH and CASH as a result of hydration and pozzolanic reactions. Figure 10: Unconfined compressive strength (UCS) versus curing time 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.  
At 1% and 2% binder content, the strength of soil increased to 50 kPa due to the addition of 2% of Petrit T, and 52 and 97 kPa due to the addition of 1 and 2% of cement content, respectively. For both binders, the main improvement in strength occurred during the first 28 days of curing. However, the long curing time at 60 and 90 days showed no further improvement in soil strength (see Figure 10b). The lack of soil strength improvement at the longer curing times can be explained by the pH value. The pH value are 9.2 and 9 for the 60 and 90 days of curing respectively for both cement and Petrit T (see Figure 9). As observed by several researchers [51; 52; 53], a soil-binder mixture with a pH value higher than 10 is enough to initiate the pozzolanic reaction by dissolving the silicates and aluminate and produce additional cementitious materials of CSH and CAH. The pH value at 60 and 90 days is lower than 10, therefore no additional effect for the long curing period on further improvement in soil strength. A gradual increase in strength of the soil is observed with curing time when the binder content was increased from 2 to 4% for cement and Petrit T (see Figure 10c). Similar trends were noticed when the amount of binder is increased from 4 to 7%, with notable strength development for cement during the first 28 days of curing compared to a gradual increase in soil strength over time for Petrit T as shown in Figure 10d. For the soil specimens treated with 4% cement content and cured for 60 and 90 days, the reduction in soil strength can be attributed to an increase in water content as discussed earlier (see Figure 4). A similar trend of reduced soil strength for low cement content under saturation conditions has been observed by [11; 39].