Change to ASTM C94-21 Time Limit

In April 2021, ASTM C94/C94M-21, Specification for Ready-Mixed Concrete, was updated with two significant changes that do away with the 90-minute default time limit for ready mixed concrete. Since its inception in 1933, the standard has required a time limit of 1.5 hours from the start of mixing to the completion of discharge.

While the American Concrete Institute has not made such revisions, ACI 301, Specifications for Structural Concrete, refers to C94 for discharge time limits.

Time Limits to Be Set by Customer, Producer

The revisions were proposed because delivery time can vary on projects depending on distance or placement methods. Technological advances made in the production of concrete can extend the quality of freshly mixed concrete beyond 90 minutes.

According to the 2021 revisions, the time limit can be stated by the purchaser at the time concrete is ordered. If the limit is not stated by the purchaser, the producer should establish a time limit. Either way, the established time limit must be stated on the delivery ticket.

Establishing that time limit is important. There may be some mixtures in some conditions where 90-minute-old concrete is not workable or suitable without using special means or excessive addition of water. Whatever the time limit, the concrete quality must be acceptable to clients and meet their requirements.

Revised Language

Below is the revised language in ASTM C94/C94M-21:

Section 12.9: Discharge of the concrete shall be completed within time limit as established in 6.1.10. This limitation may be waived by the purchaser if the concrete is of such slump or slump flow after the specified time limit has been reached that it can be placed, without the addition of water to the batch.

Section 6.1.10: Purchaser shall state a time limit from the start of mixing defined in 12.3 or 12.5 to when the concrete discharge must be completed. If no time limit is stated by Purchaser, the Manufacturer shall establish and communicate the limit to the Purchaser prior to delivery. The time limit to complete discharge shall be stated on the delivery ticket.

The Benefits to the Concrete Industry

A change in the ASTM C94-21 which removes time limit to discharge concrete would greatly benefit all involved with placing concrete. For the concrete pumping companies, it would allow them greater latitude to remedy problems they may arise: before the pour (traffic, flat tire), during prime out, equipment failure, etc. Oftentimes, the stress and hurriedness to save old concrete leads to shortcuts and unintended consequences which can result in accidents. It would also benefit the ready mixed companies from having to remove and dispose of returned concrete, which can be extremely costly and non-productive.

Time limit leniency would allow contractors to have greater control over their projects, eliminate waste and confrontations on job sites, and refrain from wasting money on concrete sent back that is perfectly within specifications if it were not for some antiquated standard created 90 years ago. For more information, visit