ScienceDirect has published an article titled Extended discharge time of ready-mixed concrete: Myth or necessity? The piece is based on a previously published report, Impact of Extended Time to Discharge on Concrete Durability and Performance, a study conducted at the New Jersey Institute of Technology (NJIT) with support from the Concrete Advancement Foundation (formerly known as the RMC Research & Education Foundation).
The study explored the impact of extended discharge time on concrete properties. Previously, in accordance with ASTM C94, Specification for Ready Mixed Concrete, freshly mixed concrete could be rejected if it exceeded 90 minutes at the end of discharge. The NJIT study demonstrated that with applicable adjustments, extended discharge times are feasible with minimal impact to fresh and hardened concrete properties required for projects. ASTM C94 has since removed a specific time limit to discharge concrete with an alternative that any limit should be established between the producer and purchaser for specific project conditions. The concrete producer has to meet the specified properties and comply with other requirements of the specification.
For more information on the work of the Concrete Advancement Foundation, please visit www.concreteadvancement.org.
National Ready Mixed Concrete Association