The Six Bag Mix refers to the standard general use mix for most exterior residential flatwork, including driveways, sidewalks and patios. A six-bag mix means that there are 564 pounds of Portland cement per cubic yard of concrete. Using a 3-inch slump and proper curing techniques, this concrete mix will develop a psi of 4,000 pounds. Many local municipal construction codes require a six-bag mix for residential flatwork.