When should the special inspector immediately notify the contractor?

The need for immediate notification by the special inspector upon observing rebar not tied correctly is critical to maintaining the structural integrity and safety of a construction project. Properly tied rebar is essential for ensuring that the reinforcement will function as intended within the concrete. If the rebar is not tied correctly, it can lead to significant issues, such as misalignment during concrete placement or failure to meet load-bearing requirements, which compromises the entire structure.

In comparison, while a slump deviation like going from a specified 4 inches to 3 inches is certainly important, it may not necessitate immediate action. Such variations can often be addressed through adjustments in the mix or by retesting. Similarly, while exceeding the minimum lap splice could pose risks, it is typically an issue that can be documented and corrected through re-inspection or remedial work without immediate notification. Lastly, a concrete temperature of 80 degrees F, while relevant for curing and other considerations, does not usually require instant communication unless it's potentially outside specified limits, which would more commonly be addressed through documented guidelines rather than immediate concern.

Thus, the scenario involving improperly tied rebar stands out as an urgent matter, warranting immediate notification to the contractor to prevent potential structural failures.