Concrete & Seawater

Welcome to my brief blog to educate people about the differences in concrete, and especially concrete either submerged in seawater or constantly being exposed to what’s called the splash zone, with constant wetting and drying.

On the Sunshine Coast we build houses all the time on the waterfront of the coast extremely close to the ocean, which is subject to the tidal splash zone especially in the winter months. These buildings require different spec concrete to handle the constant barrage of salt water. Salt water concrete requires a different kind of mix to last the years.

There is no more clear evidence of this than the Romans, who’s concrete is still standing today more than 2,000 years old. What was their secret recipe? Volcanic ash from Pozzuoli, which is possibly the place where Romans, by looking at nature, were inspired to make an iconic material. They developed a recipe for concrete that lasts for thousands of years using volcanic ash, lime, tiny volcanic rocks and water, while modern concrete often crumbles within 50 years.

Moving ahead to 2020 what are our Roman Pozzolan equivalents… It’s called Flyash.

Flyash is a by-product of a modern day Coal Fired generating station, and is the ash which is collected at the bottom of the kiln, just like the ash in the morning in your fireplace.

What does Flyash do? It Increases abrasion resistance. Natural pozzolan increases the compressive strength of concrete and makes the concrete matrix stronger and more dense. It also prevents the formation of pulpy, crispy, or water-soluble materials created by chemical attack. Therefore, it helps the concrete to durably resist abrasion.

Flyash particles under a microscope are spherical in nature, where cement particles are flat in nature under a microscope. Between the Portland cement and Flyash particles, they create a very dense concrete with barely any space between them.

This kind of mix is ideal for salt water exposure concrete, as long as the mix is no higher than a .40 W/C ratio which creates very dense concrete able to withstand the permeability of salt water infusion. The denser the concrete the better it is in keeping out salt water and sulfate attacks.

Just a little information to keep you up to speed on concrete technology in our ever changing world.

Don’t hesitate to call either myself, Mike Carter at Central Coast Concrete Inc (604) 885-2486, or Tullia Upton M.Sc. (604) 741-1986 at Sunshine Coast Materials Testing with any of your questions about concrete.