New things to worry about –concrete and sand
March 4, 2023
It seems I have read more articles about two subjects I never thought I would have to worry about: Roman concrete and the fact we are running out of sand globally. I was aware it's been estimated we will run out of fossil fuel by 2060 but I was surprised to learn that we will run out of sand, the essential ingredient in concrete, in 2060, as well.
First, the good news is that scientists have finally figured out why Roman cement has lasted so many centuries. When I was in Rome, we went to see the Colosseum, still upright and stable after 2,000 years. Roads constructed in ancient Rome were still being used in many countries. Some had ruts worn away over the millennia by horse or oxen drawn carts, but are still usable.
Modern concrete structures have concrete that is susceptible to cracks and fissures that eventually allow water to penetrate and degrade resulting in the collapse of structures after 50 years. Roman-made concrete has stood the test of time and now the reason has been teased out. I remember going to a lecture where they discussed the concrete of Rome and they had criticized the chemical makeup of that era's concrete. They spoke about the small white chunks of lime that we moderns thought was a defect in the mixing process. Lime clasts were thought of as a defect but now the truth has been discovered.
Scientists searched for the Roman recipe. An ancient recipe developed by a Roman engineer, Marcus Vitruvius, in 30 BC had the following ingredients listed: volcanic ash, lime, seawater and volcanic rocks. The mixture was poured into wooden molds and then were placed in seawater. According to the article in "Science," the scientists realized that the seawater had dissolved the volcanic ash which allowed new binding minerals to grow. According to the article, "Within a decade, a very rare hydrothermal mineral called aluminum torbernite had formed." This mineral had given the concrete its strength. The cracks in the concrete had allowed the seawater to react with the lime clasts and "heal" the concrete. This discovery was amazing, but a news report came out at the same time stating we are running out of sand appropriate to making concrete on a global level.
We use sand for all kinds of items from computer chips, glass, paint, cosmetics and most important, for structures and roads. We think we are surrounded by sand, but most areas do not have the kind needed for these uses. For instance, Abu Dhabi imported sand from Australia to build the city. The sand Abu Dhabi sits upon would not have given the strength required for the huge building projects. Desert sand is not used because the grains of sand have been worn smooth. Sand from beaches or rivers are needed because it has angles that can lock together to strengthen the concrete. This type of sand is found in coastlines, quarries and rivers. The extraction of sand will result in environment challenges. Coastlines need the sand to prevent further erosion by wave action. Rivers will become polluted and most likely change course from mining. Quarries around the world are being depleted. It has become such an issue that the U.N. in 2019 issued a warning about a "thriving 'sand mafia,' with groups comprising of builders, dealers and businessmen known to be operating in countries..." People investigating this mafia have been threatened and even killed.
Here I was thinking that my worries were reducing in scope after retiring. I guess having the world news at our fingertips can be upsetting but hopefully awareness will promote solutions to new problems.