1Heat rhubarb and sugar to boiling in 3-quart saucepan over medium heat, stirring occasionally. Cook 8 to 10 minutes, stirring occasionally, until rhubarb is very tender. Stir in strawberries.
2Spoon half of the strawberry mixture into blender. Cover and blend on high speed until smooth. Pour into large nonmetal container. Cover and blend remaining strawberry mixture; add to container. Stir in vodka and 12-ounce can of carbonated beverage. Freeze at least 8 hours until frozen and slushy.
3For each serving, stir together 1/2 cup frozen mixture and 1/2 cup chilled carbonated beverage in tall glass until slushy. Garnish with strawberry slices.