How does the Poisson's ratio generally change with concrete mixing?

• A. Increases
• B. Decreases
• C. Remains the same
• D. Fluctuates

Answer: (A)

Poisson's ratio describes how much a material expands laterally when it is compressed axially. In concrete, this ratio tends to rise when the mix becomes more porous or weaker—such as with higher water-cement ratios or poorer compaction—because the paste-void structure offers less resistance to lateral expansion under load. As the concrete becomes less stiff and more ductile in the transverse direction, the lateral strain increases for a given axial strain, increasing Poisson's ratio. Conversely, a very dense, well-compacted mix tends to be stiffer and more constraining, which would keep the ratio lower. So, in general, changes to the concrete mix that introduce more voids or reduce stiffness lead to an increase in Poisson's ratio.