Verifi Concrete Quality Blog

Posts Tagged ‘ASTM’

ASTM C94/94M Removes Drum Revolution Limit.

by Verifi

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

ASTM C94 Allows Water Addition in Transit

by Verifi

ASTM C94 / C94M (Standard Specification for Ready-Mixed Concrete) was revised in 2013 to allow water additions during transit for trucks equipped with automated slump monitoring and water measurement systems. Verifi meets these standards.

Why is this change being made?

Previously, ASTM C94 / 94M limited water additions to the job site so that an inspector or other qualified person could oversee any additions of water to ensure the maximum water content was not exceeded, the amount of water added was recorded, and the concrete was properly mixed. Truck-mounted equipment is now available to automatically add water in transit, measure and record all slump modifications. The ASTM C94 / C94M revision enables concrete suppliers, contractors, and engineers to take advantage of this technology.

What are the benefits of this change?

The addition of water in transit allows concrete to arrive at the job site at the correct slump and water content, ready to complete mixing and start discharging. This results in consistent quality concrete and faster construction.

What does the standard require?

The standard allows water addition in transit under the following conditions:

  • Water addition in transit must be permitted by the purchaser.
  • The truck must have automated equipment to monitor and report slump or slump flow based on pre-established correlations.
  • The truck must have a water meter with accuracy of +/-3%. At the request of the purchaser, the ready mix producer must provide calibration data for the water meter no older than 6 months.
  • The water added cannot exceed the maximum water content for the mix.
  • The concrete must be mixed 30 revolutions at mixing speed after the last addition of water and before the start of discharge. It is not necessary to mix concrete at mixing speed before the truck arrives at the job site, even if multiple water additions are made in transit.
  • The water added to the truck mixing drum must be provided on the batch ticket.

Download the Standard:

astm.org/Standards/C94.htm

Read the full article here (requires subscription):

concreteinternational.com/pages/featured_article.asp?ID=51685804