The latest version of ASTM C94/94M – 13a, published in August 2013, removes the requirement that concrete be discharged within 300 revolutions and leaves it to the purchaser and manufacturer to set a maximum number of revolutions. Therefore, both purchasers and manufacturers need to be ready to establish a limit, if any, in contract documents.
Section 6.3 of ASTM C94/94M states the following:
“Purchaser shall state any drum revolution limit as to when the concrete discharge must begin. If no drum revolution limit is stated by purchaser, the manufacturer shall determine and communicate the limit to the purchaser prior to delivery.”
The original motivation for including a revolution limit in ASTM C94 is unclear. Outside the US, specifications typically do not limit the number of revolutions. For instance, Canada (CSA), Europe (EN), and Australia (AS) have no such requirement. Many other ASTM requirements–such as for temperature, water addition, and jobsite testing–are in place to ensure concrete quality at the time of discharge and make a limit on revolutions redundant and in many cases unnecessary.
Concrete producers have a wide variety of options to ensure concrete quality well beyond 300 revolutions. For example, during hot weather, producers can add chemical admixtures (retarders or hydration control admixtures) and reduce concrete temperature (chilled water, liquid nitrogen, or ice). For long hauls, they can maintain slump by adding superplasticizers with long slump retention (2+ hours of slump retention is commonly available in the US) or add superplasticizer on the truck during transit or at the jobsite.
The number of drum revolutions can affect slump and entrained air content. Therefore, keeping a consistent number of revolutions on a specific mixture and project helps the ready mix producer consistently compensate for any such changes.
Additional mixing results in truck wear and increases fuel cost. Verifi has determined that each revolution costs approximately $0.02 at current fuel prices. More importantly, operating a drum at high speeds when driving is a serious safety risk.
Verifi tracks drum speed and number of revolutions. It also prompts the driver to operate the drum at mixing speed after loading and, if required, at the jobsite. At all other times, the driver is prompted to keep the drum at agitating speed. Ensuring consistent mixing is one of multiple ways Verifi helps concrete producers deliver consistent quality concrete. Learn more at VerifiConcrete.com