Quite a few friends of mine have been contemplating buying houses of late and one actually making one on a piece of land on the outskirts of the city. This is, as many of you might have experienced, an important decision. Or rather a large set of decisions that will fundamentally affect one’s life for years to come. After food, clothing and shelter are the three primary requirements of human life.
The dilemmas associated with such a decision, such as I have seen my friends go through, are in fact some of the most recurring themes of human civilization. One particularly important issue is how durable should our housing be. Durability is one of the most important concerns of humankind reflected in our desire for immortality. Our houses however are not designed to last a very long time. In fact modern concrete has a life expectancy of about eighty years or so give or take a few.
Enough for a lifetime but perhaps not very good if you wanted to leave a legacy.
Modern materials, you say. If only we had been building with stone like the ancients. That really fine and dandy. Except ancient materials neither exist in enough quantity for a modern societies housing needs nor are they moldable enough as concrete. Concrete you can simply mix, pour and set into any shape you want. This kind of flexible material: strong yet moldable is something that you might think is a quintessential modern technology. Except it is not.
It turns out that the ancients knew concrete. And some of them, particularly the Romans – builders of an Empire full of great architectural and structural wonders, knew aspects of concrete construction better that any modern engineer. The evidence for that is ample if only we bother to look. Consider this. Our concrete lasts less than a century. Roman concrete has lasted almost two thousand years. Let me repeat that. Roman concrete as used in its buildings, from the aqueducts to the Pantheon, has lasted millenia. That is no mean feat. But that is not all. The romans also built walls to break up sea waves hitting their harbors and shores. Some of these have been found to be fine after two thousand years not just underwater but under seawater – which is far more corrosive than your regular fare.
Scientists have long been interested in understanding how the Romans did it. The empire, thankfully, left many records of their building practices. Vitruvius and Pliny the Elder, two master builders of the Roman Empire, left detailed prescriptions for how to make concrete including variations to optimize its properties for intended purpose. The Roman recipe for concrete was to use Lime, Volcanic Rocks, Volcanic Sand and Volcanic Ash. The key ingredient seems to have been volcanic ash. In modern concrete made using what is called Portland Cement – the slow setting forms a network of crystals comprising of Calcium, Silicon and Water – supposedly forming layered structures resembling those of naturally occurring minerals called tobemorite and jennite. While this is the theoretical ideal, close examination reveals the lack of such crystalline lattice structures in regular concrete made using the modern recipe.
Researchers from the University of California in Berkeley were taken aback to find that the Roman concrete samples from drilled cores taken out of volcanic ash and lime mortar concrete from the ancient Roman port of Baiae, near modern day Naples, showed a near ideal tobemorite like crystal structure when viewed under an electron microscope. Much work is happening on the composition of Roman seawater concrete. The current thinking is that the volcanic materials used have minerals, Aluminium in particular, that form crystal lattices combining with the lime, the silicates and the salt water simulating the strong structure of naturally occurring minerals. All of this comes with an extra benefit. Such concrete, on the balance, takes less energy consumption to produce with the potential to cut energy usage by over one third. That alone can make an enormous in the ecological footprint of modern structures. Couple that with the longevity of Roman concrete and you may well be saving significant amounts of energy, important for a leaner greener world.
What is remarkable is that the Romans seem to have had a firmer grasp of both theory and practice at the highest levels of the art that modern technologist might realize. The ethos that would have led to such mastery maybe hard to comprehend in today’s culture of learning. And yet it is captured in what Vitruvius – one of the immortals of Roman architecture wrote in his treatise on Architecture.
“Wherefore the mere practical architect is not able to assign sufficient reasons for the forms he adopts; and the theoretic architect also fails, grasping the shadow instead of the substance.”
So then there you have it. If your concrete buildings are in trouble you might do as Romans did. Over two thousand years ago.
Author: Santanu Chakraborty
Credits Bangalore Mirror