The temperature of the old concrete must not exceed 100 F (38 C). The manufacturer can incorporate the old concrete into a new batch up to 8 hours after its original mixing time. The dose depends on the temperature, setting time, and mixture proportions of the concrete as well as how long it must remain fresh. If the concrete is 90 or more minutes old, use an extended set control admixture. If the specifications reference ASTM C94 for concrete that may contain returned fresh concrete, the purchaser should specify Option A, which places the responsibility for ensuring that the new concrete meets the purchaser’s requirements on the manufacturer of the concrete. Provisions of ASTM C1798 ASTM C1798 specifies how to reuse returned fresh concrete in a new batch. The requirements of ASTM C1798, “ Standard Specification for Returned Fresh Concrete for Use in a New Batch of Ready-Mixed Concrete,” are in addition to those of the purchaser and the project specifications. ASTM C1798 specifies how to do that without jeopardizing the quality of the new concrete.

Now, however, it’s possible to incorporate fresh concrete into a new batch. In times past, the driver would dump that concrete on the ground. Another source of construction waste is fresh concrete that must be returned to the plant. A previous blog discussed how to reuse water from concrete production. CALGreen requires the reuse, recycling, or salvage of at least 65% of the waste from construction and demolition.

Astm c94 90 minutes