# Experimental Study on the Strength and Durability for Slag Cement Mortar with Bentonite
## 4 Results and Discussion  
### Compressive Strength Development before the Sulfate Resistance Test  
The development of the compressive strength for the slag cement mortar cured in lime water for 7 days or 28 days with various substitution ratios of bentonite in the binding  
Figure 1: Flow-values corresponding to the replacement ratio of bentonite [27].  
material are presented in Figure 2, where (a), (b), and (c) correspond to the 0.445, 0.485, and 0.550 water/binder ratios, respectively. The blue colored bars are for the specimens cured for 7 days while the grey bars are for the specimens cured for 28 days. The progress of strength development can be clearly observed from these figures. It can be noted from these test results that 70-74% of the compressive strength was developed for the specimens without bentonite cured for 7 days. For the specimens with partial replacement of bentonite for the slag cement in the group of 0.458 and 0.550 w/b ratios as shown Figure 2b,c, a range of 70-76% compressive strength was obtained for the specimens cured for 7 days. An interesting phenomenon was observed is that for the specimens with bentonite and higher w/b ratios (e.g., w/b = 0.550) the compressive strength developed earlier, where the strength developed in 7 days reached as high as 78% for the specimen with 0.75% replacement of bentonite.  
One special phenomenon observed was for the case of 0.25% replacement of bentonite, which had the highest compressive strength at both 7 days and 28 days of curing but also had the slowest strength development at 7 days of curing, as presented in Figure 2a, where only 65.8% compressive strength was developed for the specimen of 0.25% replacement of bentonite after 7 days curing. The strength development at 7 days of curing for the specimen of 0.25% replacement was also the lowest (71%), as shown in Figure 2b,c compared to that of specimens without bentonite or with higher replacementrations of bentonite (i.e., 0.50% and 0.75%).  
Figure 2d shows the variation rate of the compressive strength for the slag cement mortar cured for 28 days when various ratios of binders (ce  
Figure 2: Compressive strength for various replacement ratios of bentonite. The gray colored column is for the specimens cured for 7 days while the navy column is for the specimens cured for 28 days: (**a**) w/b = 0.445, (**b**) w/b = 0.485, and (**c**) w/b = 0.550. (**d**) Variation rate of compressive strength corresponding to the replacement ratio of bentonite.  
by bentonite. For the case of 0.25% replacement of bentonite in various water/binder ratios, the compressive strength of the mortar increased, where for the 0.445 w/b ratio, the increment in the compressive strength of the mortar was about 15% higher compared to that of the specimen without bentonite. For the strength performance of specimens with higher replacement ratios of bentonite (other than 0.25), the compressive strength seemed to decrease, corresponding to the increase of the replacement ratios of the bentonite. The decreasing trend of the strength corresponding to the increase of replacement ratios of bentonite seems to be mitigated when the w/b ratio is high, such as the case of w/b = 0.55.