![]() In the concrete employed at Roman harbors, these minerals formed thin fibers and plaques that made them more resistant and less susceptible to breaking. But what they have also confirmed is that, after the limestone has been used up, a second, much slower, phase begins.ĭuring this second chemical reaction, two minerals – neither of which were properly understood in Roman times – play a key role: tobermorite and phillipsite. According to the results of her investigation, published in the journal American Mineralogist, the limestone, when exposed to seawater, rapidly reacted with the volcanic ash. ![]() “We could identify different minerals and the complex, enigmatic crystallization sequences at the microscopic level,” says Jackson. Under an electron microscope at Lawrence Berkeley National Laboratory, a sample from a Roman harbor built between the first and second centuries CE revealed its secrets. ![]() State of the art technology has enabled Jackson and her colleagues to learn more about these materials. A 2,000-year-old piece of concrete from a breakwater in the bay of Naples, seen under a microscope. In fact, as Pliny wrote, that cement was improved through exposure to seawater. Whether by chance, geographic proximity, or trial and error, it was eventually discovered that the volcanic materials used were reacting with water, as Portland cement does today. Before the Romans, construction in the most advanced civilizations, like ancient Greece, employed a chalky mortar that agglomerated when it dried. Back then, any kind of rubble was employed.īut the secret is in the mix. Today, we use gravels and sands as an aggregate. Conversely, the Romans relied on a particular type of quicklime: calcium oxide. Today, the most common base of concrete is called Portland cement, composed of limestone and clay, heated to more than 1,500☌. Both then and now, an agglomerate – or hardening agent – was used. “Contrary to the foundations of modern concrete, based on cement, the Romans created a concrete that improved with open chemical exchange from seawater,” explains Marie Jackson, a geologist at the University of Utah who has spent years searching for the formula of Roman concrete. Marie Jackson, geologist at the University of Utah The Romans created a concrete that improved with chemical exchange from seawater
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