Downhole tools that include an outer tubing disposed around an inner tubing for placement of a sealant mixture into a void in a subterranean formation and associated methods of use are provided. Furthermore, a method is provided for preparing a cement composition, which includes mixing a first cementitious component and an aqueous-based fluid in a first mixer to form an intermediate cement composition, and mixing the intermediate cement composition and a second cementitious component in a second mixer to form the cement composition.