Why is Ancient Roman Concrete So Durable?

(Excerpted from an article in Science Magazine)

Modern concrete—used in everything from roads to buildings to bridges—can break down in as few as 50 years. But more than a thousand years after the western Roman Empire crumbled to dust, its concrete structures are still standing.

Now, scientists have finally figured out why: a special ingredient that makes the cement grow stronger—not weaker—over time.

Scientists began their search with an ancient recipe for mortar, laid down by Roman engineer Marcus Vitruvius in 30 B.C.E. It called for a concoction of volcanic ash, lime, and seawater, mixed together with volcanic rocks and spread into wooden molds that were then immersed in more sea water.

History contains many references to the durability of Roman concrete, including this cryptic note written in 79 B.C.E., describing concrete exposed to seawater as: “a single stone mass, impregnable to the waves and everyday stronger.” What did it mean? To find out, the researchers studied drilled cores of a Roman harbor from Pozzuoli Bay near Naples, Italy. When they analyzed it, they found that the seawater had dissolved components of the volcanic ash, allowing new binding minerals to grow. Within a decade, a very rare hydrothermal mineral called aluminum tobermorite (Al-tobermorite) had formed in the concrete. Al-tobermorite, long known to give Roman concrete its strength, can be made in the lab, but it’s very difficult to incorporate it in concrete. But the researchers found that when seawater percolates through a cement matrix, it reacts with volcanic ash and crystals to form Al-tobermorite and a porous mineral called phillipsite.

So will you be seeing stronger piers and breakwaters anytime soon? Because both minerals take centuries to strengthen concrete, modern scientists are still working on recreating a modern version of Roman cement.

The Importance of Rebar in Concrete Construction Projects

At C.R.I., we’ve noted that the importance of rebar in most concrete projects comes as a surprise to many DIYers. This revelation usually prompts the question of whether rebar is always necessary in concrete. Let’s take a closer look at what rebar is, what it does for concrete, and why it’s so important.

When it comes to absorbing stress in the form of compression, concrete can be very strong. However, concrete does not stand up well to tensile strength; it crumbles when confronted with pressures that threaten to tear it apart. In construction, concrete is subjected to both types of stress, and while it will hold up if weight is applied from the top, it will flex, deform, and crack when exposed to tensile stress.

Metal rods, aka rebar, are therefore used to reinforce concrete constructions. When rebar is used in a concrete project, the finished product has significantly higher strength than concrete alone. Buildings and roadways all benefit from this strength.

Every concrete project does not necessitate the use of rebar; but, as a general rule, if you’re pouring concrete that’s more than 5 inches thick, you should use rebar for strengthening.

For a non-commercial project requiring additional concrete reinforcement, fiber or wire mesh are becoming increasingly popular as a very good, and less expensive, alternative to rebar.

Concrete reinforced with rebar, fiber, or wire mesh is not only more durable, but it also reduces the number of cracks that develop over time. This can help save money on repairs and keep your concrete looking good for years to come.

There are various types of rebar from which to pick… Welded wire, expandable metal, stainless steel, sheet metal, and epoxy coated are the most common varieties. Each type of rebar is best suited for various types of tasks, so do your homework, or consult with a concrete expert, before picking the one that will be perfect for you.

Here are some guidelines…

• Stainless steel rebar is very corrosion resistant and an excellent choice for any concrete job in corrosive environments.
• Fiber-reinforced concrete contains fibrous material, such as steel, glass, synthetic and natural fibers, to increase its structural integrity. For flat work and driveways, it is much easier to use and does an excellent job.
• Sheet metal is a common choice for concrete floors, roofs, and stairwells.
• Wire mesh is a two-dimensional grid that runs the length and width of poured concrete but not the height.
• Epoxy-coated rebar is even more corrosion-resistant than stainless steel. It is the most durable, but also most costly, concrete reinforcement option.

As in any construction project, if you feel like you’re unable to make a sound, informed decision, consult a professional. If you have questions or would like a quote on a project, click here to contact us.

C.R.I. is a diversified contractor and grounds support company serving New Jersey.

Photo courtesy of Ricardo Gomez Angel on Unsplash

The Palazzo Italia, in Milan, is the first concrete building in the world to effectively improve the quality of the air around it. The facade of the building consists of 900 biodynamic panels made with photocatalytic concrete and titanium dioxide.

The technology was invented by accident, by Luigi Cassar, a chemist at cement manufacturer Italcementi. While trying to create a construction material that keeps a bright white color even in polluted conditions, he hit upon a method called “photocatalysis”, which uses the sun’s energy to zap away dirt.

To his surprise, when the air around the treated concrete was tested, it contained up to 80% less nitrous oxide, which meant the concrete was cleaning the air as well as itself.

The material is also suited for use in road construction and roofing tiles.

From the repair of cracked, damaged, and broken concrete, to full concrete slab replacement, CRI can tackle concrete repair and removal jobs of any size. Call us, at 908-797-2305, or submit our online form to request an estimate or for general questions.

In our last post, we showed a video depicting a very creative construction crew moving cement from the mixing site, up one floor, to the installation site. But what if you need to move the cement even higher and, more importantly, safely and consistently?

The video below, titled “Concrete Pumping–The Future of Concrete Construction”, posted by the American Concrete Pumping Association (ACPA), demonstrates the economic, environmental, safety, and productivity benefits of concrete pumps.

The projects shown in the video employ truck-mounted concrete pumps with placing booms and stationary pumps. The video details the many uses of concrete pumps. Environmental benefits are also illustrated with footage of concrete pumping near rivers and streams, where precision placement and enclosed pipelines protect the surrounding area.

We’re not sure what country is home to this construction project but know for a fact that it’s not the U.S.A. – OSHA would shut down this operation in a heartbeat.

OSHA notwithstanding, this construction crew shows amazing skill and creativity… No concrete pump truck? No problem for this construction team; using skill, strength, and coordination, they quickly and efficiently move cement from the mixing site to the application site.

What are the advantages of concrete vs. asphalt? How do the initial installation and ongoing maintenance costs differ? Is asphalt or concrete the best choice for my project? You have questions… We have answers!

First, before examining the differences, let’s look at the similarities. Concrete and asphalt both require compacted bases of gravel before they are applied. Both take time to ‘cure’ before they can be driven on but, whereas concrete can take up to 21 days to come to 95% strength, asphalt only takes a few hours.

Interestingly, although they look very different, both are made from the same general material; i.e. stone and sand. The difference in their appearance is due to the adhesive used for bonding; in asphalt it is tar and in concrete its cement. That difference is what not only gives asphalt and concrete their unique characteristics but also affects the difference in cost, durability and maintenance.

When making the decision to choose either asphalt or concrete for your project, there are a number of factors to consider:

1. Aesthetics
   • Concrete, allows for a variety of finishes, which can also be stained or tinted to a wide variety of colors and patterns. In addition, concrete can be stamped into different designs, etched, or engraved. Asphalt, on the other hand, due to how it is applied (i.e. rolled and compressed), has very little in the way of unique finishes. But, although black asphalt is pretty much the standard, there are tints that can be added either during mixing or to the sealant. In addition, there are also a few patterns that can be rolled to create a design in asphalt.
2. Climate
   • Cold, freezing winters can cause a number of issues with concrete, such as cracking and frost heaving. And the associated use of salts for ice control can damage the appearance of concrete.* At the other end of the spectrum, the tar in asphalt can become soft during hot summers, becoming tacky and possibly even deforming. Climate is a very important factor when deciding to use either asphalt or concrete and one that should be discussed with a reputable, knowledgeable contractor.
     *Learn how salts used for ice control can cause significant damage to porous concrete.
3. Maintenance
   • A properly installed asphalt project, depending on the sub base installation and type usage, is usually only good for 20 years or less and must be maintained over that lifespan; i.e. it must be sealed every 3-5 years.
   • It is not necessary to seal concrete but doing so can preserve the look and finish, and help guard against oil-based stains.
4. Cost
   • Asphalt pricing is subject to variations in the price of crude oil but will generally fall into a range between $2.50 & $4.00 per square foot. By comparison, a basic concrete installation is in the range of $4 to $6 per square foot. However, concrete, with a longer life expectancy and less required maintenance, is usually the more economical choice.
     The thickness of each material also impacts the price; e.g. an asphalt overlay can be as thin as 2″ or, as in the case of a truck driveway, as thick as 8″, and concrete can be as thin as 4″ or, for installations such as truck pads, as thick as 8″.

In addition to the above, other important factors, specific to each unique project, must be considered before making an informed decision; e.g. the specific use of the surface, the condition of the subbase, area restrictions, regulations, etc. And, once the asphalt-or-concrete decision is made, there’s another round of comparative details to consider, as there are many types of asphalt mixes that are appropriate depending on the situation, and there are a variety concrete types and strengths, from a slurry mix used as a fill mix, to a high early mix that is appropriate for situations such as a highway bridge repair and can be driven on in a couple of hours.

Need more information or assistance in making the best decision? Contact us to discuss, and receive a quote on, your project.