Minecraft wiki entry for Time-saving_tips, associated text: Instead of crafting concrete powder, turning it to concrete and then building, vertical walls can be made of concrete powder and then flushed with water.
The fastest way to make concrete from powder is to hold a pickaxe in your main hand and concrete powder in your offhand, then place the powder next to a water source or flowing water block and hold both mouse buttons down. The process of placing the powder and breaking the concrete will be automatic until the powder stack runs out. Arrange it so the water flows towards you and you'll collect all the broken concrete items.