Florida DOT Concrete Batchman/Operator Practice Exam

When should an accelerator ideally be added to a concrete mix?

1. Before mixing at the plant

2. At the jobsite

3. Only after curing

4. During transportation

The correct answer is: At the jobsite

The ideal time to add an accelerator to a concrete mix is at the job site. Adding an accelerator at this stage allows for better control over the concrete setting time, which can be crucial depending on environmental conditions, such as temperature and humidity. This practice helps to ensure that the desired workability and performance characteristics of the concrete can be achieved immediately before placing it. When an accelerator is added at the job site, it can be mixed thoroughly immediately before pouring, ensuring that the entire batch benefits evenly from the acceleration process. This timing is essential, especially in cooler weather conditions where setting times can be prolonged. Adding an accelerator before mixing at the plant may lead to premature setting, which can complicate the mixing process and affect the final quality of the concrete. Likewise, waiting until after curing means it would not influence the initial setting time, which defeats the purpose of using the accelerator. Adding it during transportation could also lead to inconsistencies in the mix and potential premature hardening before the concrete reaches its final placement.