Geologic Column: Is it aged or mature?

ChessboardThe Game of Life painting by Pashang Salehi. Credit: Pashang Salehi.

The term “aging” is used and interpreted in a variety of ways depending on the realm in which it’s applied. For wine, Scotch and certain cheeses, aging is generally considered a good thing, whereas, for humans, it is not. In the geosciences and engineering, it can refer to changes in material strength or properties over time. But even in these fields, its use is inconsistent: “Aging” in sand is completely different from “aging” in concrete or asphalt, for example.

In sand deposits, aging describes an improvement in modulus and strength — after, for example, earthquake-induced vibrations pass through it. This improvement is related to an increase in shear-wave velocity and shear modulus, and, ultimately, densification of sand deposits after an earthquake event. The specifics of the aging process are dependent on the type of sand, the stress levels it experiences, and microbiological effects. Over geologic time, if the pressure and heat on sand intensify, sandstone will form, which is the final step in its aging process — unless you also count weathering and erosion, which breaks the sandstone down into sand again, in a never-ending cycle.

With concrete, the material’s strength improves during the initial stage of construction, usually a 28-day period after pouring, and may continue to improve for more than two years. After that, however, it begins progressing through a natural process of aging due to the very slow loss of moisture over a few years. The timing of this process is an important consideration in planning for safety when concrete structures are designed. Aging, contraction and chemical changes in the concrete, along with possible ground vibrations, can cause deterioration of concrete that reduces the strength of a concrete structure.

Using the single term “aging” to describe such widely varying processes in sand and concrete creates ambiguity for readers (especially those who are not familiar with geological and geotechnical terms) and confusion about whether someone is talking about strength and development, or weakness and destruction. Perhaps we can add another term to the mix to clarify things, like “maturing.”

Readers may be familiar with more vernacular uses of the two terms. In humans, aging is defined as the process of growing old: a slow, deliberate process that starts at birth and ends with death. Not fun! On the other hand, maturing and its many synonyms — such as developing, growing, evolving and thriving — have positive connotations and focus on strength.

In the geosciences, it has been shown that sand grains can rearrange and become stronger as a unit as a result of earthquake shaking. This strength gain could henceforth be called “maturation” for sand (and sandstone), whereas the long-term weathering and erosion of the sand could be called “aging.” Similarly, in engineering, the initial strengthening of concrete constitutes maturation, while its subsequent deterioration is more aptly described as aging.

Maturation and aging are different parts of the overall life cycle — be it of sand, concrete, wine, cheese or us. Maturation fosters stability, strength, firmness, growth and evolution, while aging leads to weakness, flaws, pain and, ultimately, death. We should seek to distinguish them more clearly.

Who can tell me the meaning of the word ‘old’?
To some pain and suffer, but to others gold.
We were born as a child destined to get aged.
Nothing can do because, life is being staged.
Growing up, getting old and falling asleep;
Knowing that not knowing secrets, burning deep.
What will happen to mountains, when they get old?
They turn into desert, so hot and so cold.
Getting old is getting weak and insecure.
Losing all your strength, your looks and contour.
How can I get strength, when lost it by age?
The only thing can do, is turn the next page.
You who want to mature, journey have no will;
You might gain your power, get old and get well.
But if you want the wine, wine is mature grapes.
Maturation to wine, grapes come in all shapes.
During earthquake, Earth will mature fast; 
The concrete will crack, sand will ever last.
I am mature enough under so much weight;
The way my molecules expand their
estate.
You can lose your strength, but you can get firm.
‘Maturing’ instead of ‘aged’ is a better term.

Behzad Amir-Faryar and Pashang Salehi

Credit: Behzad Amir-Faryar (left) and Pashang Salehi (right).

Amir-Faryar is a chief engineer with the Fairfax County Government, Department of Land Development Services, in Northern Virginia, and an adjunct professor at the University of Maryland, College Park. He can be reached at behzad@members.asce.org. Salehi is a retired science educator, painter and poet residing in Southern California.

Wednesday, May 24, 2017 - 06:00

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