## 3 Results and Discussion
### Mechanical Properties
#### 3.1.2 Split Tensile Strength  
Results of split tensile testing are shown in Figure 5. At day 7, the tensile strengths of all MAB modified mixes were lower than that of the CON. Similarly to the compressive strength results, MAB incorporation of up to 10% produced maximal compressive strength after 28 and 180 days compared to CON. It is also worth mentioning here, that split tensile strength is more negatively influenced than compressive strength with increasing the incorporation of bentonite. This might be due to different natures of failure for the specimens under compression and split tensile tests. At higher levels of MAB, the filling effect of unreacted bentonite particles can play a good role in resisting compressive stresses, whereas, under splitting tension unreacted particles of bentonite may offer low resistance to failure (two failure surfaces can easily separate due to low cohesion in the binder); therefore, high levels of bentonite are more detrimental to tensile strength than compressive strength.  
TMAB showed significant improvement over MAB, due to increased reactivity of clay minerals in pozzolanic reaction. Split tensile strength was reduced by 12% at a 35% level of TMAB after 28 days, whereas after 180 days, all TMAB incorporated mixes exhibited comparable or higher tensile strengths than the CON mix. MAB showed 3% and TMAB 5% higher split tensile strength than CON mix at day 180. But at higher levels, TMAB mixes performed 10% better than MAB. TMAB may have more reactive alumina and silica to react with CH, so have large pozzolanic reactivity [57; 58]. Therefore, higher levels of TMAB show more strength development than those of the MAB.  
Relative analysis of the split tensile strength results is presented in Figure 6. 28 days' strength of the control mix (B0 (CON)) was taken as the benchmark. At day 28, there is no notable surpassing form the loop of reference mix/benchmark. For mixes modified with MAB (10%-15%), the replacement overlapped the reference loop. For mixes modified with TMAB (at 10%-25% level), they coincided with the benchmark. At day 180, mixes with MAB (10%-15%) outperformed the reference mix, while all the mixes with TMAB, except B35/G/T, beat the reference mix and crossed the loop. Overall no significant difference was evident for the split tensile strength of TMAB incorporated concrete.  
Figure 4: Compressive strength of each mix relative to the day 28 strength of reference mix (CON).  
As, already mentioned, variation in compressive strength and split tensile strength with increasing incorporation level of bentonite follows a similar trend. Therefore, a strong relationship exists between compressive strength and split tensile strength. In Figure 7, the compressive strength of each mix at a given age and replacement level of bentonite is plotted against the corresponding value of split tensile strength. Equation (1) can be used to predict the cylindrical split tensile strength of concrete mix with a coefficient of determination (R\({}^{2}\)) higher than 0.9.  
\[\mathrm{f_{ts}}=0.40\times\sqrt{\mathrm{f_{c}}}\,\Big{(}\mathrm{for}\;7,\;28, \;\mathrm{and}\;180\;\mathrm{days},\;\mathrm{R^{2}}\;=\;0.92\Big{)}, \tag{1}\]  
where \(\mathrm{f_{ts}}\) (MPa) is split tensile strength and \(\mathrm{f_{c}}\) (MPa) is compressive strength of cylindrical specimen.  
Figure 5: Split tensile strength of each mix after 7, 28, and 180 days.  
Figure 6: Split tensile strength of each mix relative to day 28’s strength of reference mix (CON).