ACI provides guidelines as suggestions or recommendations on the water content to provide the desired compressive strength. Never add more water than what is necessary to provide the desired workability. More water equals lowered strength.
Admixtures enable concrete producers and placers to easily mix, place and/or finish the concrete in multiple environments and conditions. Admixtures also provide a way to produce higher-quality concrete without increasing the cementitious content of the concrete mixture, which keeps the cost of the concrete down.