To understand this relationship, let’s visualize a cube. The ratio of its surface area to volume is 6/b, where ‘b’ represents the cube’s side length. This demonstrates an inverse correlation: as volume increases, the surface area-to-volume ratio decreases.
Applying this principle to concrete, when the maximum aggregate size increases, the surface area requiring wetting per unit volume decreases. This means less water is needed for the mix, allowing for a lower water-to-cement ratio. Consequently, concrete strength increases due to the reduced water content.
However, there’s a trade-off. Larger aggregates can create discontinuities and reduce contact areas within the mix. Generally, for maximum aggregate sizes below 40mm, the benefits of reduced water demand outweigh the drawbacks of these discontinuities, as suggested by Longman Scientific and Technical (1987).
In essence, increasing aggregate size in concrete is a balancing act. It can lead to stronger concrete due to lower water demand but may also introduce structural challenges if the aggregate size becomes excessively large. Finding the optimal balance is key to achieving the desired concrete properties.