Shulou(Shulou.com)11/24 Report--

CTOnews.com, January 7 (Xinhua) over the past few decades, researchers have been trying to unravel the secret of why man-made concrete in ancient Rome has been preserved for more than two thousand years. A team of researchers from the Massachusetts Institute of Technology, Harvard University and laboratories in Italy and Switzerland have made new progress in this field.

According to MIT News, the team has discovered an ancient concrete manufacturing process that contains a variety of key self-repairing functions.

For years, researchers have believed that the key to the durability of ancient concrete is based on an ingredient: pozzolanic material, such as volcanic ash from the Bozoli region of the Bay of Naples. This special ash was even transported to all parts of the vast Roman Empire for construction and was described by architects and historians of the time as a key component of concrete.

After careful examination, these ancient samples also contain small and unique millimeter bright white minerals that have long been thought to be ubiquitous ingredients in Roman concrete. These white lumps, often referred to as "lime clasts", are derived from lime, another important component of ancient concrete mixtures.

CTOnews.com learned that previous studies have only proved the existence of "lime debris", and in the latest study found that these tiny lime fragments give concrete unprecedented self-healing ability.

Historically, it has been believed that when lime is added to Roman concrete, it first combines with water to form a highly reactive paste, a process known as ripening. But the process itself does not explain the existence of lime debris.

By studying samples of this ancient concrete, he and his team determined that the white inclusion was indeed made up of various forms of calcium carbonate. Spectral tests provide clues that these substances are formed at extreme temperatures, as expected by the exothermic reaction of using quicklime instead of hydrated lime in the mixture or in conjunction with hydrated lime.

During thermal mixing, lime debris forms a unique brittle nano-particle structure, forming a calcium source that is easy to break and react, which can provide a key self-healing function, as the team suggested.

Once tiny cracks begin to form in the concrete, they will give priority to passing through the high surface area of lime debris. The material can then react with water to form a calcium saturated solution, which can be recrystallized into calcium carbonate and quickly fill cracks, or react with pozzolanic materials to further strengthen the composites.

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