For a producer working with high-strength concrete, the first issue to address is what constitutes high-strength concrete. The ACI's committee on high-strength concrete defines it as a concrete that has a design strength in excess of 6000 psi, though in some parts of the country it is possible to buy a mix that achieves 20,000 psi. Perhaps the best definition of high-strength concrete is concrete that has a strength requirement 1000 psi higher than any concrete the producer has ever supplied. Selecting constituent materials for high-strength concrete includes reviewing past test-data for each material and using the candidate materials in trial batches. Look for cements with 7-day mortar cube strength of at least 6000 psi. Coarse aggregates should be hard, dense, have low absorption, and have a maximum size of « inch. Sands should be angular with a fineness modulus between 2.6 and 3.2. Different admixtures should also be reviewed. Production, transportation, and placement of high-strength concrete does not require any extraordinary deviations from normal practice. Quality control testing must be performed in strict accordance with the standards. Laboratories chosen should have previous experience with high-strength concrete.