The American Association for the Advancement of Science (AAAS)’s “Science Online Magazine” recently reported on modern-day scientists working on recreating a modern version of Roman cement that lasted over 1000 years. Modern concrete—used in everything from roads to buildings to bridges—can break down in as few as 50 years. But more than a thousand years after the western Roman Empire crumbled to dust, its concrete structures are still standing. Now, scientists have finally figured out why: a special ingredient that makes the cement grow stronger—not weaker—over time.
Scientists began their search with an ancient recipe for mortar, laid down by Roman engineer Marcus Vitruvius in 30 B.C.E. It was composed of a concoction of volcanic ash, lime, and seawater, mixed together with volcanic rocks and spread into wooden molds that were then immersed in more sea water.
History contains many references to the durability of Roman concrete, including a cryptic note written in 79 B.C.E., describing concrete exposed to seawater as:
… a single stone mass, impregnable to the waves and everyday stronger.
What did it mean? To find out, the researchers studied drilled cores of a Roman harbor from Pozzuoli Bay near Naples, Italy. When they analyzed it, they found that the seawater had dissolved components of the volcanic ash, allowing new binding minerals to grow. Within a decade, a very rare hydrothermal mineral called aluminum tobermorite (Al-tobermorite) had formed in the concrete. Al-tobermorite, long-known to give Roman concrete its strength.
(Please read further: Paper/Abstract: “Mechanical resilience and cementitious processes in Imperial Roman architectural mortar”: http://www.pnas.org/content/111/52/18484.abstract) can be made in the lab, but it’s very difficult to incorporate it in concrete.
American Mineralogist reported: But the researchers found that when seawater percolates through a cement matrix, it reacts with volcanic ash and crystals to form Al-tobermorite, and a porous mineral called phillipsite. (Please read further, to see figures (i.e., Photos, graphs, samples, maps, etc), and for other links: the GeoScience American Mineralogist Paper titled “Phillipsite and Al-tobermorite mineral cements produced through low-temperature water-rock reactions in Roman marine concrete”: http://ammin.geoscienceworld.org/content/102/7/1435).
Because both minerals take centuries to strengthen concrete, modern scientists are still working on recreating a modern version of Roman cement.
To read the full article, please go to: http://www.sciencemag.org/news/2017/07/why-modern-mortar-crumbles-roman-concrete-lasts-millennia.
LEFT: Authigenic mineral textures in tuff deposits and Roman marine mortar. Scanning electron microscopy backscattered electron (SEM-BSE) images. (a) Portus Cosanus pier, Orbetello, Italy (credit, J.P. Olson); (b) Bacoli tuff (BT), pumice class; (c and d) Neapolitan Yellow Tuff (NYT), dissolving alkali feldspar, phillipsite, and chabazite textures; (e) Surtsey tuff, Iceland 1979 drill core, dissolving phillipsite and associated Al-tobermorite, 37.0 m, 100 °C (credit, J.G. Moore); (f) Portus Cosanus, pumice clast with dissolved glass; (g) Portus Neronis, Anzio, Italy, dissolving alkali feldspar; (h) Portus Cosanus, phillipsite textures; (i) Portus Cosanus, dissolving Campi Flegrei phillipsite [1], pozzolanic C-A-S-H binder [2] and Al-tobermorite [3]; (j) Portus Baianus, Pozzuoli, Italy, dissolving in situ phillipsite and associated Al-tobermorite. (Please read further, to see figures (i.e., Photos, graphs, samples, maps, etc), and for other links: the GeoScience American Mineralogist Paper titled “Phillipsite and Al-tobermorite mineral cements produced through low-temperature water-rock reactions in Roman marine concrete”: http://ammin.geoscienceworld.org/content/102/7/1435).
Home page photo: Portus Cosanus pier, Orbetello, Italy – see map above (credit, J.P. Oleson)