NFPA 24: Standard for the Installation of Private Fire Service Mains and Their Appurtenances Practice Exam

The correct response identifies the mixture as comprising one part cement, two and one-half parts sand, and five parts stone, which is a commonly used formulation for creating thrust blocks. Thrust blocks are essential in water distribution systems, particularly where changes in direction or elevation occur, as they help resist the thrust forces generated by the flowing water.

This specific mixture is designed to provide a strong, durable foundation that can effectively manage and absorb the significant forces exerted by the pipeline, ensuring stability and longevity. The combination of sand and stone enhances the structural integrity of the thrust block, enabling it to support the weight of the pipeline and accommodate dynamic pressures without failing.

The correct balance of materials is crucial; cement binds the aggregates together, while the sand and stone provide the necessary bulk and load-bearing capacity. In contrast, the other mixtures listed do not achieve the same structural properties needed for thrust blocks, which could lead to insufficient support and potential failure in a fire service main system.