Which devices are prohibited in spreading and finishing the mixture?

The correct choice indicates that both mechanically and manually operated strike-off devices are prohibited in the spreading and finishing of the mixture. This is based on guidelines that emphasize the importance of maintaining quality and consistency in the application of materials on roadways.

Mechanically operated strike-off devices can lead to uneven distribution if not calibrated correctly, which may affect the final surface quality. Similarly, manual devices can introduce variability based on the operator's technique and consistency, possibly leading to subpar results. Therefore, prohibiting both types of devices helps to ensure uniform application methods that enhance the integrity and durability of the mixture on the roadway.

Understanding the rationale behind eliminating both types of strike-off devices helps to maintain standards for construction processes, ensuring that the surfaces meet the required specifications for performance and longevity.