Florida DOT Concrete Batchman/Operator Practice Exam

What should be avoided when blending coarse aggregates?

1. Blending diverse sizes

2. Blending if the size is smaller than #78 rock

3. Mixing aggregates from different sources

4. Storing aggregates over long periods

The correct answer is: Blending if the size is smaller than #78 rock

The option regarding avoiding blending if the size is smaller than #78 rock is based on the considerations of aggregate gradation and performance characteristics in concrete. Aggregates that are too small can negatively affect the workability and strength of the concrete mix. If the aggregate is smaller than #78, it may lead to high water/cement ratios, making it harder to achieve the desired consistency and strength in the final concrete product. Furthermore, smaller aggregates can lead to segregation and more challenging compaction, which can ultimately impact the durability and integrity of the concrete. Thus, it is important to manage the sizes blended to maintain the quality of the concrete mix. In contrast, blending diverse sizes and mixing aggregates from different sources can be beneficial for achieving optimal gradation, while storing aggregates over long periods can lead to environmental issues, such as contamination or moisture absorption, rather than an issue directly tied to size. Therefore, avoiding blending aggregates that are smaller than #78 contributes to the overall effectiveness and quality of the concrete mix.