## 4 Results and Discussion
### Evaluation of UCS Tests  
#### 4.2.1 Effect of Sawdust on Sulphate Resistance for 3 Days Curing  
The effect of adding SD on the UCS peak (\(q_{u}\)) values after 3 days curing time for \(MgSO_{4}\) exposed and benchmark samples was shown in Figure 6. \(q_{u}\) values for 3% PC treated benchmark samples increased from 180 to 401 kPa when SD content increased from 3% to 15%. Samples treated with 5% PC and 7% PC showed a similar increasing trend in a range of \(296\leq q_{u}\leq 473\) kPa and \(352\leq q_{u}\leq 574\) kPa, respectively [see Figure 6a-c]. For samples exposed to the \(MgSO_{4}\), the same increasing trend was observed but in a lower range. For example, specimens that treated with 3% PC and mixed with different SD content 3% to 15% showed increases in the \(q_{u}\) values from 20 kPa to 157 kPa. The values of \(q_{u}\) for SD treated benchmark samples increased with increasing PC content. \(q_{u}\) values increased from 73 to 223.5 kPa and from 102 kPa to 340 kPa when PC increased to 5% and 7%, respectively [see Figure 6b,c]. The observed results can be attributed to production of the hydration and pozzolanic products that increases the bonds strength amongst soil and PC particles. Hence, this causes a higher unconfined compressive strength for the samples with higher PC content.  
Figure 5: Trend of variation of compaction results for 0%, 3%, 5%, 10% and 15% sawdust.  
Figure 6: Effect of sawdust addition on Unconfined Compressive Strength (UCS) peak values (3 days curing) (**a**) 3% PC; (**b**) 5% PC; (**c**) 7% PC.  
Tables 4 and 5 present the effect of SD content on the improvement of USC values for PC treated specimens at 3 days curing time for benchmark and exposed specimens, respectively. Table 4 indicates that the \(q_{u}\) values of 3% PC treated samples increased from 241 kPa for 3% SD to 401 kPa for 15% SD inclusion. The same trend was observed with 5% cement and 7%, which showed increases from 322 to 473 and from 391 to 574 kPa, respectively. Table 5 presents the _IMP_ index and actual UCS values after sample exposed to sulphate. As can be seen, the samples all showed improvement in resistance from vanished condition for non-treated samples to a positive UCS strength. It should be noted that _IMP_ in Table 5 is not calculated as non-treated samples all dissolved quickly after exposed to sulphate. The calcium silicate hydrate (CSH) is one of the main hydration products that affected when the specimens exposed to the sulphate. In fact, the existing sulphate exhausts the formed calcium in CSH. This process is known as decalcification, which is the main reason for the strength reduction.  
The results present improvement in the values of UCS by adding in SD content linearly. It is worthy of mentioning, as can be seen in the results for 3 days of curing, the sample without any sawdust was easily dissipated once exposed to sulphate [18]. This may be attributed to weak bonding formation compared to actual sulphate attack to the sample [18]. Once the sawdust takes effect, higher levels of sawdust incorporated show better resistance to attack. Comparing the amount of cement addition from 3% to 7% also confirmed that having more cement in the sample makes the exposure of sulphate become less effective. That means better resistance was observed with higher percentage of cement.