I have investigated situations where this has occurred and did not find evidence of poor quality issues, although I do not recommend exceeding the time constraints without studying the effects first. Many ready-mix producers have transported concrete more that 60 to 90 minutes on their own accord. Even though additional admixture will increase slump to maintain workability, hydration is occurring and changes are ongoing in the concrete mixture. These are relatively safe time frames considering the impact on the quality of the concrete. ASTM C94, “Standard Specification for Ready-Mixed Concrete,” allows for 90 minutes until discharge.
Most states limit concrete delivery to 60 minutes from the time water hits the cement to the time of discharge.
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