What should be added to concrete to make it pump easier?

To enhance the workability and pumpability of concrete, using hydrated lime can be beneficial. Hydrated lime acts as a plasticizer, which improves the flow of concrete mixtures and can reduce the water content needed for achieving an ideal consistency. This is particularly valuable in pumping applications, where a smoother flow of concrete is essential to prevent blockages and ensure cohesion as the concrete is transported through pumps and hoses.

In contrast, fly ash, though it can improve certain properties of concrete such as strength and durability, primarily serves as a partial replacement for cement. It may not always directly contribute to the ease of pumping unless formulated specifically for that purpose. Granite dust, while it might add bulk, doesn't help with flowability. Polyethylene is generally used in construction for vapor barriers and does not contribute to the properties of concrete itself.

Focusing on the improvements that hydrated lime provides in terms of making concrete easier to pump clarifies its relevance in pumping applications, making it the most suitable choice in this scenario.