A typical concrete mixture is 1:2:3, which means one component cement, two parts sand, and three parts rock or gravel. This approach is still widely used in many regions of the world. Cement is the key ingredient in concrete, so this means that more cement should be used if additional strength is needed. Concrete needs water to set up solid enough to support itself, but too much water makes it mushy instead. The amount of water required depends on the type of material used to create the mix. Coarse aggregate such as sand or gravel requires more water than fine aggregate like powderized cinder blocks. Concrete that will not dry out before its expected life requires a higher percentage of cement than fresher concrete. For example, 20% cement by weight is used when making mortar, while 30% is required for concrete. The ratio of air-void volume to total volume (AVV/ttv) indicates how well the concrete will resist compression damage over time. A concrete with an AVV/ttv of 0.15 or less is considered acceptable for most applications. Cement is the main ingredient in concrete, accounting for about 35% of the material by mass. Sand is next at about 20%, followed by gravel/rock at around 40%.