Secret of how Roman concrete survived tidal battering for 2000 years revealed

Postado Julho 04, 2017

He was not overstating. The phenomenon explains why 2,000-year-old Roman piers and breakwaters are not only still standing, but stronger today than they were 1,000 years ago.

Her team found seawater filtering leads to the growth of interlocking minerals that lend the concrete added cohesion. Any reaction with the cement paste could form gels that expand and crack the concrete. If reactions do occur in these aggregates, they can cause unwanted expansions in the concrete that crack it.

Geologist Marie Jackson has been studying factors that make Rome's concrete so durable.

The ancient Roman recipe is very different than the modern one for concrete, though. One such factor, she says, is that the mineral intergrowths between the aggregate and the mortar which prevent cracks from lengthening, while the surfaces of nonreactive aggregates in Portland cement only help cracks propagate farther.

Prof Jackson has a simple explanation for why Roman concrete isn't still used - despite its advantages.

She said this revealed another process that was also at play. Synthesizing it in the laboratory demands high temperatures and results in only small amounts.

The scientists used electron beams, X-rays from particle colliders and other tools to analyze samples of Roman concrete drilled from ancient harbors. The new study, published on Monday in American Mineralogist, is helping researchers to piece together how and where this mineral formed during the long history of the concrete structures. From earlier research, the team knew that the pozzolanic curing process of Roman concrete was momentary.

She added, "This is a concrete that apparently grows aluminum-tobermorite mineral cements over millennia".

Ms Jackson said: 'No one has produced tobermorite at 20 degrees Celsius. Oh - except the Romans!. "So how does change influence the durability of Roman structures?" said Jackson in a statement.

'Change is a constant for earth materials. So will you be seeing stronger piers and breakwaters anytime soon? Platy crystals of Al-tobermorite have grown amongst the C-A-S-H cementing matrix. The interlocking plates increase the concrete's resistance to brittle fracture.

'We're looking at a system that thrives in open chemical exchange with seawater'.

But while this ancient Roman technique of making concrete is better and friendlier to the environment, the recipes have been lost through time.

The ancient Romans used concrete everywhere, particularly in their mega-structures like the Pantheon and Trajan's Markets in Rome. "We don't have those rocks in a lot of the world, so there would have to be substitutions made", Jackson said.

She is now working with Geological Engineer Tom Adams to prepare a replacement recipe, however, using materials from the Western U.S. The seawater used in her experiments was collected by Jackson herself from the Berkeley, California, marina.

Additionally, Roman concrete takes time to develop strength from seawater and features less compressive strength than typical Portland cement. For those reasons, it is doubtful that Roman concrete could become widespread, but could be beneficial in specific contexts. For instance, the Roman cement could be very useful for a tidal lagoon project to be built in Swansea, United Kingdom, meant to harness tidal power. "I never gave concrete a thought beforehand, but my interest in Roman concrete really grew over time". A Roman concrete prototype, in contrast, could stay intact for centuries.

Jackson says that while researchers have answered many questions about the mortar of the concrete, the long-term chemical reactions in the aggregate materials remain unexplored. The research has also inspired a hunt for the original recipe so that modern concrete manufacturers can do as the Romans did. If we're going to build in the sea, we should be concerned with it too.