Econocrete subbases have been used in many airports built to specifications developed by the American Concrete Pavement Association (ACPA) or by consultants. Now the Federal Aviation Administration (FAA) has added Item P-306, "Econocrete Subbase Course" as a standard for the construction of airport pavements. Econocrete is a Portland cement concrete made with locally available crusher run, natural or reclaimed aggregate that does not necessarily meet conventional standards for use in pavements. It is specifically designed to satisfy the requirements of each application and environment and provide an economical pavement structure through judicious use of materials. It is used for composite pavements, subbases, shoulders, street pavements and parking lots.
The April 1982 issue of the ACPA Newsletter reported on the important sections of this specification for econocrete subbases. Covered areas include aggregates, curing materials, admixtures, proportioning, air content and slump, field test specimens, joints, traffic on econocrete, and tolerance in thickness.
"Transverse joints shall be constructed every 50 feet by sawing or formed in the plastic concrete. All joints shall be offset at least 6 inches from joints in the surface course. In notes to the engineer this requirement is modified as follows: Joints are not considered necessary in econocrete subbases because of the normally lower strengths and moduli of elasticity of these subbases relative to these parameters in the overlying Portland cement concrete pavement. When a relatively high strength econocrete subbase is placed (compressive strength greater than 1200 psi), joints should be constructed, unless a good bond breaker, such as a waX-based curing compound, is used between the econocrete and the overlying pavement."