What is a Prescriptive Specification?
A prescriptive specification is one that includes clauses for means and methods of construction and composition of the concrete mix rather than defining performance requirements. Many times intended performance requirements are not clearly indicated in project specifications and the prescriptive requirements may conflict with the intended performance. The producer is always called on when the mix does not perform even though this is in conflict with the basic premise of a prescriptive specification as clearly indicated in ASTM C 94, Specification for Ready Mixed Concrete. For example, a low water-cementitious materials (w/cm) ratio at high paste content might increase the potential for shrinkage and cause more curling in a concrete floor while the intent was to reduce it. This might also cause a stiff mix that will adversely affect placing and finishing. Many project specifications include prescriptive limits on w/cm ratio as a surrogate for durability. The intent is to reduce permeabi
