Improving Concrete Pumpability with the Right Aggregate Type

When pouring concrete, what type of aggregate would allow concrete to pump easier?

Pea gravel.
Rounded such as river gravel.
Sand.
Crushed concrete.

Final answer:

Rounded aggregates like river gravel allow concrete to pump easier due to reduced friction. Lightweight concrete with appropriate fine aggregates also enhances pumpability. Adequate viscosity and water content are essential for easy pumping of concrete.

Explanation:

When pouring concrete, the type of aggregate that would allow concrete to pump easier is rounded aggregate, such as river gravel. Rounded aggregates, like pea gravel and river gravel, have smooth surfaces that reduce friction and facilitate easier movement through the pump and hoses. In contrast, angular aggregates such as crushed concrete tend to lock together, increasing resistance and making the mixture harder to pump. Moreover, using lightweight concrete with lightweight coarse aggregate mixed with fine aggregates like shale, clay, or slate can also reduce the load, increasing pumpability and resulting in a mix that is longer-lasting and has excellent thermal properties.

It is crucial to note that for concrete to maintain good pumpability, not only the aggregate shape but also other factors such as the mixture's viscosity and adequate water content play a significant role. The Roman invention of concrete has long utilized a mix that could be easily molded and handled, yet it retained flexibility to withstand moderate seismic activity. Today, we take advantage of improved concrete formulations that allow for efficient construction practices, including pumping.