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A very civil engineer…Hydraulic concrete turns green

A very civil engineer…Hydraulic concrete turns green


The phrase “Civil Engineer” was first coined by a jolly-looking fellow called John Smeaton, and he coined it to stop people confusing him with the horny-handed military engineers graduating from Woolwich back when America was still a colony because John was a very civil engineer, and he was pretty good at it too. So good, in fact, that he published a lift equation for powered flight in 1759 (144 years before the Wright Brothers took to the skies); Smeaton was also the first expert witness to appear before an English Court (giving evidence on inshore silting as if you needed to ask), and, most important of all, it was Smeaton who followed his hunch in 1756 and added hydraulic lime to his concrete: hey presto!...the concrete set faster, it was far stronger, and could be used in more extreme conditions (even underwater). If concrete ever had a Eureka moment…that was it.


Smeaton went on to build the Eddystone Lighthouse using hydraulic concrete, and it was still standing 120 years later until the rocks underneath started to crack and crumble away, so the whole structure was dismantled, carted off, and re-assembled at Plymouth Hoe, where we know it today as Smeaton’s Tower. Don’t say you don’t learn anything from these Newswires…in fact, here’s something else you might not know…


Hydraulic concrete will set once exposed to water (making it perfect for the Eddystone Light), and that’s because it’s been mixed with hydraulic cement: powder dry and produced by finely grinding limestone and clay together into a raw meal, which is then heated up to 1450°C in a cement kiln. To put it in context, that’s higher than the melting point of glass and plate steel. Small wonder, then, that hydraulic cement production is currently responsible (by itself) for 5% of worldwide carbon emissions ( In turn, aggregate CO2 emissions from the production and pouring of concrete directly refer to the amount of cement in the mix. According to the Portland Cement Association 88% of concrete emissions are directly referable to cement production (http//


Then, of course, there’s all that water (it’s what the “hydraulic” in “hydraulic concrete” means): you’ll need 150 litres of water to make 1m3 of concrete, so for a  20 x 10 meter, 4-inch thick ground slab, you’re looking at 3810 litres of water…and that’s for just the ground slab: never mind the footings, walls, and floors. So, a small hotel can cost the earth in water, not only for the developer’s bank balance but for the future of our precious planet, too.


This is where Green Concrete comes in…


Building Back Greener

Green Concrete works by minimising cement’s historic reliance on lime, clay, and water. Because limestone isn’t fiercely burned down with clay in a kiln, carbon emissions can be reduced by up to 80%. High carbon fly ash (a key constituent of Green Concrete, more of which in a moment) has a much lower water demand ratio, and when it comes to mixing and pouring the concrete, wash water can be reused to reduce overall consumption levels.  


So what goes into the cement in the first place, instead of all that crushed limestone? Well, everything from the aforementioned fly ash (previously combusted coal, otherwise destined for landfill), silica fume (a natural byproduct in the production of silicon from quartz), and even wood ash can be used. By replacing lime with fly ash, for example, final carbon emissions can be cut by more than 30% on a 20:80 ash to clay/water mix and by 80% on a richer mix (see “Wastes in Concrete: Converting Liabilities into Assets”: A. Samarin, 07.09.99).


And just like fly ash, blast furnace slag (“BFG”) can also be recycled and reused to make up to 70% of the cement content, without anything like the level of harmful emissions created by burning lime, added to which the BFG would simply be dumped if it wasn’t being used in Green Concrete production. BFG also improves the concrete’s long-term durability and creates less heat as part of its final combination (meaning, again, less water is needed as part of the production process).


All of this highlights just how effective Green Concrete can be when it comes to reducing global greenhouse gas emissions. Indeed, the Boston Consulting Group ( found in 2022 that, dollar for dollar, Green Concrete represented a better, more sustainable investment than any divestment from meat production (think harmful methane emissions) into crop-based products. And that, of course, is a perfectly rational view, given that 70% of the world’s population live and work in buildings made of concrete.


John Smeaton would have been pleased.


Red Ribbon Phoenix Green Hotel Fund (

Red Ribbon’s Phoenix Green Hotel Fund was established to create and renovate sustainable buildings capable of responding constructively to the challenges of high carbon emissions, as well as water and energy scarcity, including the projected use of Blast Furnace Slag as part of the construction process.


Invest in Red Ribbon Asset ManagementRRAM-3

Red Ribbon Asset Management ( aims to harness the full potential of fast evolving and emerging technologies to meet the needs of global communities as part of a circular economy, fully recognising the compelling demands of planet people and profit.

Suchit Punnose

Suchit Punnose / About Author

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