11 January 2023

Cement cracks. Rocks erode. Why does ancient Roman concrete last for thousands of years while ours falls apart in only 50?

The 2,000 year old concrete at the Roman ruins of Tróia, above, is in good shape while a 1960’s concrete wall below is so degraded that its rebar supports were already rusting by 2012.

The difference is how we mix our cement that binds the concrete together. This is a story of recipes and chemistry. (Concrete = cement + sand, gravel, rocks.)

• Modern day Portland cement is made by baking limestone and clay minerals at 600^oF, then grinding the result and adding gypsum.
• The Romans made cement from slaked lime (quicklime+water), volcanic ash and water.

Scientists discovered in 2017 that volcanic ash + seawater were the secret ingredients that made Roman concrete strong. Those two components were conveniently available in ancient Italy but not economically feasible today. Recently a team of scientists, headed by Admir Masic of MIT, discovered an inexpensive Roman ingredient that helps concrete heal itself.

Cement, when exposed to water, can heal very small cracks in concrete by minutely dissolving and recrystallizing. However the cracks must be very tiny in Portland cement-based concrete in order for this to happen — smaller than 0.2 to 0.3 millimeters across (0.0078 to 0.0118 inches).

During the study, the team made Roman-inspired concrete using slaked lime and found that it can heal cracks up to 0.6 millimeters across (0.0236 inches), twice the tolerance of Portland cement.

If our cement used this Roman innovation it would save a lot of damage control.

Find out more in Science Magazine at: Scientists may have found magic ingredient behind ancient Rome’s self-healing concrete

p.s. Slaked lime = quicklime + water. Quicklime is made by baking lime or seashells in a kiln to split the calcium carbonate (CaCO₃) into plain calcium oxide (CaO) + CO₂. Quicklime is unstable and will spontaneously react with CO₂ unless it is slaked with water to set as lime plaster or mortar. — parapharased from Wikipedia

2 January 2023

Think about the birds you saw last weekend. What species was your Last Bird of 2022?  What was your First Bird of 2023? Did you have a Best Bird?

Perhaps your Last and First birds were at your feeders. Mourning doves are often last of the day because they wait until near darkness to race to their roost.

First Bird may have been a northern cardinal that’s not afraid to come out in the half light of dawn.

My own sightings were larger species.

Last Bird of 2022: American crows seen while counting 20,000 of them flying to the roost.

First Bird of 2023: A red-tailed hawk flying above Fifth Avenue while I drove out to go birding in Lawrence County. I saw six more red-tails on my journey north.

Best Bird was a surprise. As our birding group paused on Plain Grove Road in Lawrence County a flock of 55 tundra swans flew over in a perfect V. (Steve Gosser photographed these in 2012.)

Last Bird? First Bird? Best Bird? Tell me what you saw.

(photos from Wikimedia Commons, Chuck Tague, Cris Hamilton, Kate St. John and Steve Gosser)