1350.07.04.02 – Discharge…

1350.07.04.02 – Discharge Time
The specified discharge time limits raise the following concerns:

• The requirement to discharge concrete within 1.5 hours, and within 1 hour under elevated temperature conditions, is more restrictive than CSA A23.1, which permits longer discharge times provided the concrete maintains required properties.
• CSA A23.1 takes a performance-based approach, allowing extended discharge times where concrete quality (e.g., slump, air content, temperature, and strength) remains within specified limits.
• Fixed time limits do not account for the use of modern admixtures, such as set retarders and hydration stabilizers, which are specifically designed to maintain concrete workability and performance over longer periods.
• The restriction does not consider project-specific factors such as haul distance, traffic conditions, or placement logistics, all of which can be effectively managed while still meeting CSA performance requirements.
• Imposing rigid discharge times may lead to unnecessary rejection of compliant concrete, increasing material waste, cost, and environmental impact.
• The shortened time limit under hot weather conditions duplicates controls already addressed through CSA requirements for temperature, consistency, and performance testing.
• The clause shifts focus from measurable performance criteria to arbitrary time-based limits, which is inconsistent with the intent of CSA A23.1.
• It is recommended that discharge time be governed by compliance with CSA A23.1 performance requirements rather than fixed maximum time limits, allowing flexibility while ensuring concrete quality.