In a blender container, combine half the tequila, half the limeade concentrate and half the pineapple. Fill the jar to the top with ice cubes, cover, and blend on high until slushy and thick. Transfer to a pitcher. Repeat with the remaining tequila, limeade concentrate, pineapple and ice. Stir to blend, pour into glasses that have been salted, if desired. Squeeze a lime quarter into each glass and serve immediately.