Posted by: Prospector PJ12 SEP 2012
If you or your children were disappointed with your sandcastles this summer it could have been because your sand was too wet. Researchers writing in the journal Nature Scientific Reports have concluded that the ideal castle building mixture is sand containing just 1 per cent water.
Using this ratio of sand to water, a column of sand with a radius of 20cm could be as tall as 2.5m. The strength of the mixture is down to the formation of capillary bridges between sand grains, with the curvature of the liquid creating a capillary pressure that causes a force of attraction between the grains.
But the research was not simply a frivolous exploration of seaside amusement. The handling and flow of granular materials is responsible for around 10 per cent of the world’s energy consumption, and yet few quantitative studies have looked at the mechanical properties of wet sand.
For those with a need to build extreme sandcastles, the researchers suggest that even better constructions can be built underwater. All you need is some commercially available hydrophobic sand. The roles of the air and water reverse when using this type of sand so that the air “wets” the grains but with the same bridging force as water. Because this mixture weighs much less when immersed in water it can be used to build more spectacular sandcastles.
Ed Jarret, who holds the Guinness world record for the tallest sandcastle, may even be able to improve on his 11.53m construction if he takes notes from this research. It took 1,400 volunteers 3,000 hours and 800 tons of sand and water to get his sculpture into the record books.