Definition
A concrete mix is the proportioned combination of cement, water, and aggregates (sand and gravel) that creates concrete when hardened. Mix ratios are expressed as parts by volume, such as 1:2:3 (cement:sand:gravel). The water-cement ratio, typically 0.4-0.6 by weight, critically affects strength. Common strengths include 2500 psi (foundations), 3000 psi (slabs), 4000 psi (driveways), and 5000+ psi (structural).
Formula
A standard 1:2:3 mix produces approximately 3000 psi concrete. For 4000 psi, use a 1:2:2 mix. Add about 5-6 gallons of water per 94lb bag of cement. Less water equals higher strength but reduced workability-use additives or plasticizers if needed.
Example
Mix Design Example
For a 10-cubic-yard pour requiring 4000 psi concrete: 16 bags of cement (94lb each), 32 cubic feet of sand, 32 cubic feet of gravel, and about 90 gallons of water. For slabs exposed to freezing, add air-entraining admixtures (5-8% air content) for freeze-thaw durability.