To reduce CO2 emissions, bentonite clay is being studied for its potential use as an additive to Portland cement. However, different types of bentonites will also affect the properties of cement mortar and concrete differently. When Binh Thuan bentonite had replaced 1–6% wt. of Portland cement, the results in this study indicated that the mark of cement was guaranteed, meanwhile, the waterproofing ability of concrete increased. The waterproofing ability of concrete has also increased with bentonite content. The waterproofing effect was clearly shown with lower-mark concrete. The reaction of bentonite with alkali from cement hydration to form zeolite faujasite has increased the waterproofing ability of concrete.