- Academy to host first overseas ceremony to honor young filmmakers
- No doctor necessary: US okays nasal spray flu vaccine for self-use
- Former delivery man Baldwin leads star names at PGA Championship
- Trump shooting: Secret Service admits complacency
- Can an ambitious Milei make Argentina an AI giant?
- Haiti, its suffering growing, in 'race against time': UN expert
- Ibrahim Aqil, the Hezbollah elite unit commander wanted by the US
- Chinese forward Cui signs NBA contract with Brooklyn Nets
- US Fed dissenter calls for 'measured' pace of rate cuts
- Guardiola tells players to lead change over workload as Kompany demands cap on games
- Norway limits wild salmon fishing as stocks hit new lows
- Top Hezbollah commander killed in Israeli strike on Beirut
- Rotterdam fatal knife attacker suspected of 'terrorist motive'
- First early votes cast in knife-edge US presidential election
- Top-ranked Swiatek out of Beijing due to 'personal matters'
- Hard-right Reform UK looks to the future after vote success
- Embiid agrees to NBA contract extension with 76ers
- Joshua aims to complete road to redemption in Dubois bout
- World champion Bagnaia sets pace with lap record at Misano
- Biden says 'working' to get people back to homes on Israel-Lebanon border
- Pope criticises Argentina's crackdown on protesters
- Court limits screenings of videos in France mass rape case
- Gurbaz century takes Afghanistan to 311-4 in 2nd ODI
- Central banks face 'difficult balancing act': IMF chief
- Guardiola tells players to lead change over workload fears
- Paris Olympics sports equipment moves to new homes
- 'Happy' Kinghorn relishing life at Toulouse
- Norris sets Singapore pace as Verstappen only 15th
- Germany to bid to host women's Euro 2029
- Portugal brings deadly forest fires under control
- Postecoglou defends Solanke after slow start to Spurs career
- US nuclear plant Three Mile Island to reopen to power Microsoft
- Arteta urges Arsenal to take next step in Man City showdown
- Stock markets fall after Fed-fuelled rally
- Poland charges Russian over attack on Navalny ally: prosecutors
- Man City have rest 'advantage' in Arsenal showdown: Guardiola
- Maresca has 'no doubt' in Jackson as Chelsea's number nine
- EU chief announces 35 bn euro loan plan for Ukraine before winter
- From TikTok to Hollywood, the irresistible rise of Italy's Khaby Lame
- Verstappen punished for swearing in Singapore press conference
- Sri Lanka lead by 202 in first New Zealand Test
- Brook 'not too fussed' by England's batting in heavy Australia loss
- India's Ashwin 'happy' to embrace pressure
- A modern 'Trojan Horse': two days of mayhem in Lebanon
- Third of Burundi mpox cases in children under five: UN
- Man Utd appoint Foster + Partners to develop Old Trafford 'masterplan'
- French mayor sorry for 'no one died' remark over mass rape trial
- Mohamed Al-Fayed, outsider shunned by British high society
- Lawyers say 'monster' late Harrods owner abused dozens of women
- India in box seat after Bumrah takes four against Bangladesh
Researchers dig up secrets of 'self-healing' Roman concrete
How have Rome's ancient aqueducts and architectural marvels such as the Pantheon, which features the world's largest unreinforced concrete dome, endured the test of time?
Researchers at the Massachusetts Institute of Technology (MIT) and other institutions believe they have uncovered the mystery of the durability of the 2,000-year-old structures -- self-healing concrete.
The secret lies in an ingredient of the ancient concrete used by the Romans that the researchers, whose findings are published in the latest edition of the journal Science Advances, said has been overlooked in previous studies.
The durability of the concrete used by the Romans has most frequently been attributed to the use of volcanic ash from Pozzuoli on the Bay of Naples, which was shipped across the Roman empire for construction.
But the researchers focused their attention on another component of the ancient concrete mix, small white chunks called "lime clasts."
"Ever since I first began working with ancient Roman concrete, I've always been fascinated by these features," said MIT professor of civil and environmental engineering Admir Masic, an author of the study.
"These are not found in modern concrete formulations, so why are they present in these ancient materials?"
The researchers said the lime clasts had been thought to be the result of "sloppy mixing practices" or poor-quality raw materials.
But they are in fact what gives the ancient concrete a "previously unrecognized self-healing capability."
"The idea that the presence of these lime clasts was simply attributed to low quality control always bothered me," said Masic.
"If the Romans put so much effort into making an outstanding construction material... why would they put so little effort into ensuring the production of a well-mixed final product?"
For the study, the researchers examined 2,000-year-old Roman concrete samples from the masonry mortar of a city wall in Privernum, Italy.
They found that a process known as "hot mixing" is what gave the concrete its "super-durable nature" in which the Romans mixed quicklime with water and the volcanic ash at high temperatures.
"The benefits of hot mixing are twofold," Masic said.
"First, when the overall concrete is heated to high temperatures, it allows chemistries that are not possible if you only used slaked lime, producing high-temperature-associated compounds that would not otherwise form.
"Second, this increased temperature significantly reduces curing and setting times since all the reactions are accelerated, allowing for much faster construction," he said.
It is the lime clasts that give the ancient concrete its "self-healing functionality," according to the research team, which also included scientists from Switzerland and Italy.
Tiny cracks in the concrete would tend to travel through the high-surface-area lime clasts and, when exposed to water, would recrystallize as calcium carbonate, filling the crack almost like glue.
"These reactions take place spontaneously and therefore automatically heal the cracks before they spread," said the researchers, who conducted tests using modern concrete and the ancient formula.
T.Batista--PC