The Romans’ self-healing concrete

One of the secrets to the success of Rome: self-healing concrete:

Photo by Life Of Pix on

Now, an international team has discovered ancient concrete-manufacturing techniques that incorporated several key “self-healing” properties. For years, researchers believed the key to the ancient concrete’s durability was one ingredient: pozzolanic material, such as volcanic ash from the area of Pozzuoli, on the Bay of Naples…

Historians say this specific kind of ash was shipped all across the Roman empire for use in construction projects, being described as a key ingredient for concrete at the time. After closer examination, these ancient samples also contain small, distinctive, millimeter-scale bright white mineral features. They were common component of Roman concretes. The white chunks — often called “lime clasts” — come from lime, another key ingredient in ancient concrete mix.

Masic adds that, during the hot mixing process, lime clasts develop a characteristically brittle nanoparticulate architecture. This creates an easily fractured and reactive calcium source, which could provide a “critical” self-healing ability for building materials. As soon as tiny cracks start to form within the concrete, they can preferentially travel through the high-surface-area lime clasts.

Prof. Masic explains that the material can then react with water, creating a calcium-saturated solution. It then recrystallizes as calcium carbonate and quickly fills the crack, or reacts with pozzolanic materials to further strengthen the material.

What I often wonder about inventions and techniques of the ancient world is how exactly they came about. How did Romans discover that a particular component – pozzolanic material – made concrete better in the long-term? I would guess there is evidence to suggest when this emerged and how it was dispersed but we may not know exactly how this formula developed.

If this could be incorporated into modern materials, could this make concrete even more important? I remember reading about the importance of concrete in How the World Really Works. Could this mean roads that do not need to be repaired as often, buildings that last longer, and numerous other applications?

This is also a reminder that infrastructure mattered for ancient empires and continues to matter today for modern everyday life. Even small improvements to basic materials or processes could have a tremendous effect given the scale and speed of today’s world.

Making a concrete McMansion with a 3D printer

A Chinese firm can put together a McMansion with a 3D printer:

WinSun Decoration Design Engineering Co., a Chinese architectural materials company with more than 70 patents to its name, has now come up with a way to construct a 12,000 square-foot home – a kind of McMansion – out of 3D printed blocks.

A special technique has resulted in a concrete building that, while requiring paint to be attractive, still manages to be perfectly functional.

The printer that created these buildings is 105 feet long, 33 feet wide, and 21 feet tall, larger than most rooms, but it works on basically the same principles as one of MakerBot’s printers. It uses a nozzle to pump a mix of concrete, sand and fiberglass (which are recycled; the company’s name seems to translate to ‘Surplus’) onto a flat substrate, slowly accumulating into a tough material that can be buffed to create a smoother edge and/or overlaid with various traditional-looking decorative elements. A zigzag design inside the pieces helps reinforce them, similar to corrugated cardboard.

It takes about a day to print all the components. The prefab blocks are then trucked to the construction site, where it takes just five days to put them all together. The final height of the building is 20 feet by 4,000 feet wide, and the total cost to build it was just $161,000. This method saves between 30 and 60 percent of construction waste, cuts down on time by 50-70 percent, and cuts labor costs from 50-80 percent.

While the cost seems attractive, I can only imagine what McMansion critics would say if some of these started showing up in American neighborhoods. Want mass produced? Want concrete as your primary material? Of course, this all may get refined over time but there is some work to do before this would meet single-family home standards in the United States.

Tremendous amount of concrete used in China between 2011 and 2013

Here is another metric regarding the amazing pace of construction and growth in China: Bill Gates references a graphic showing China using 6.6 gigatons of concrete between 2011 and 2013, more than 2 gigatons over what was used in the United States between 1901 and 2001. I’m not sure why you would want to but all this concrete in China would build a giant concrete cube that would dominate the Chicago skyline.

While this is clearly a lot of concrete, it would be interesting to know where it has all gone. Is China using a lot of concrete as opposed to other building materials that might be more expensive or take more time to gather?

Determining whether concrete buildings in LA are endangered by earthquakes

The Los Angeles Times looks at a number of concrete buildings in LA that could be at serious risk in an earthquake:

Despite their sturdy appearance, many older concrete buildings are vulnerable to the sideways movement of a major earthquake because they don’t have enough steel reinforcing bars to hold columns in place.

Los Angeles officials have known about the dangers for more than 40 years but have failed to force owners to make their properties safer. The city has even rejected calls to make a list of concrete buildings.

In the absence of city action, university scientists compiled the first comprehensive inventory of potentially dangerous concrete buildings in Los Angeles.

The scientists, however, have declined to make the information public. They said they are willing to share it with L.A. officials, but only if the city requests a copy. The city has not done so, the scientists said.

Pretty interesting look at how concrete buildings can be built to withstand earthquakes. The key issue here seems to be retrofitting: should it be required and if so, how much would property owners complain about the cost? As the article notes:

Earthquake safety has rarely been an issue that draws deep public passions and outrage. Most seismic regulations are approved in the wake of destructive earthquakes, but there hasn’t been one in California in nearly 20 years.

In other words, occasional disasters allows room for complacency. When the events are rare, people will question whether the money should be better spent elsewhere. This is part of the debate over other disasters as well like: how should buildings in Tornado Alley be constructed if tornadoes might occur? Should New York be protected from hurricanes and rising water levels by constructing gates and barriers? How much should be spent on levees in New Orleans to avoid situations like that after Hurricane Katrina?

A new way to fight pollution in Chicago: cement that absorbs smog

Chicago is the first American city to lay concrete that absorbs smog:

There are many sustainable technologies designers can utilize these days to make a project more Earth- and people-friendly, but smog-eating cement isn’t the most talked-about – until now. The City of Chicago is pioneering the use of a revolutionary type of cement that is capable of eradicating the air around it of pollution, potentially reducing the levels of certain common pollutants by 20 – 70% depending on local conditions and the amount of exposed surface area.

Photocatalytic cement isn’t exactly news – it was developed by the leading Italian cement maker Italcementi for the Vatican in honor of the 2,000th anniversary of the Christian faith. The Seat of the Catholic Church commissioned the construction of a new church to commemorate the event and wanted surface material that would retain its new appearance despite Rome‘s high levels of air pollution.

The cement that Italcementi developed uses titanium oxide that, when exposed to natural sunlight, triggers a chemical reaction that catalyses the decomposition of dirt or grime on the cement’s surface; thus, it is self-cleaning. What further research in Europe uncovered, however, was that this cement possessed pollution reduction properties that not even Italcementi could have foreseen, capable of cleaning up smog in adjacent air – up to 2.5 meters away – by breaking down the nitrogen oxides which are the result of burning fossil fuels.

Naturally, this makes the photocatalytic cement a perfect paving material as it successfully reduces the amount of toxins expelled by vehicles and inhaled by pedestrians. Italy and other areas of Europe have already paved many of their roads with the revolutionary material, but Chicago is reportedly the first city in America to adopt it, laying down a thin, permeable pavement for the bicycle and parking lanes on Blue Island Avenue and Cermak Road.

There might be a few issues associated with this:

1. What is the relative cost of laying down this kind of cement compared to other road surfacing material? In Illinois, I’ve read before that laying asphalt is cheaper in the short term compared to concrete but more expensive in the long term because it has to be replaced more frequently.

2. Some may not like this news because if the cement can help fight pollution, people may pay less attention to the effect of cars.

Here is more information on this concrete from an article last October:

According to Nguyen, the titanium dioxide on the cement surface absorbs UV light and uses this energy to react with water vapor in the surrounding air.

The result of this reaction is a highly reactive particle known as a hydroxyl radical.

It is these unstable hydroxyl radicals that in turn decompose a host of other compounds in the surrounding air, including nitrous oxide, a harmful greenhouse gas released in car exhaust…

David Leopold, project manager for the Chicago Department of Transportation, did say the photocatalytic cement is more expensive than regular pavement, but the city expects to see considerable improvement in street-level air quality as a result…

Based on pre-installation estimates, “on a windless day up to about eight feet from the pavement’s surface, you can see demonstrated improvements in air quality,” said Leopold. “Coincidentally, that’s about the height of a person on a bike.”

We’ll see what happens if this concrete is used more widely.

Rubble clearance in Haiti proceeds at a slow pace

Eight months after a 7.0 earthquake devastated Haiti, most of the rubble in Port-au-Prince has still not been removed:

By some estimates, the quake left about 33 million cubic yards of debris in Port-au-Prince — more than seven times the amount of concrete used to build the Hoover Dam. So far, only about 2 percent has been cleared, which means the city looks pretty much as it did a month after the Jan. 12 quake.

Government officials and outside aid groups say rubble removal is the priority before Haiti can rebuild. But the reasons why so little has been cleared are complex. And frustrating.

Heavy equipment has to be shipped in by sea. Dump trucks have difficulty navigating narrow and mountainous dirt roads. An abysmal records system makes it hard for the government to determine who owns a dilapidated property. And there are few sites on which to dump the rubble, which often contains human remains.

Also, no single person in the Haitian government has been declared in charge of the rubble, prompting foreign nongovernmental organizations to take on the task themselves. The groups are often forced to fight for a small pool of available money and contracts — which in turn means the work is done piecemeal, with little coordination.

This is a reminder that while large disasters such as this often prompt quick and widespread relief efforts, these efforts may be needed for long periods of time. After the initial needs are taken care of (water, food, medical care, etc.), there is often even more work to do in order to rebuild.

The opening of the NFL season last week provided another reminder of this in New Orleans. While that city has made some progress, there is still a long way to go and the necessity of these efforts often receive little attention from broader society.

h/t Infrastructurist