Concrete Mix Design
CSI Division 03, Concrete
The specific recipe, cement, water, sand, aggregate, and any admixtures, and their exact proportions, that an engineer specifies for a particular pour to hit a required strength and performance, rather than concrete being a single one-size-fits-all material.
Why it matters
Different parts of a building need concrete with very different properties: a foundation might need high strength, while a decorative slab might prioritize a specific finish or reduced cracking. The mix design is what translates those requirements into an actual, batchable recipe a concrete plant can produce.
On a real project
A structural engineer specifies a mix design calling for a higher cement content and a specific admixture to achieve a required compressive strength for a foundation, while a separate mix design with different proportions is specified for an interior slab that doesn't carry the same structural load.
Who this matters most to
A Structural Engineer specifies the mix design a pour must meet, while a Concrete Worker places and finishes concrete batched to that design.
Where this goes wrong
A concrete supplier substitutes a different mix design than the one specified, assuming the difference is minor. The substituted mix doesn't reach the required strength, and the error isn't caught until cylinder break testing weeks after the pour, by which point the concrete is already in place.