V13C-3150
Authigenic Mineral Cycling in Roman Seawater Concrete with Campi Flegrei Pumiceous Ash Pozzolan
Monday, 14 December 2015
Poster Hall (Moscone South)
Marie D Jackson, University of California Berkeley, Department of Civil and Environmental Engineering, Berkeley, CA, United States, Sean R Mulcahy, Western Washington University, Geology, Bellingham, WA, United States, Heng Chen, Southeast University, School of Materials Science and Engineering, Nanjing, China, Qinfei Li, Harbin Institute of Technology, School of Transportation Science and Engineering, Harbin, China, Piergiulio Cappelletti, University Federico II, Dipartimento di Scienze della Terra, dell'Ambiente e delle Risorse (DISTAR), Naples, Italy, Carlo Carraro, University of California, Berkeley, Department of Chemical Engineering, Berkeley, United States and Hans-Rudolf Wenk, University of California Berkeley, Department of Earth and Planetary Science, Berkeley, CA, United States
Abstract:
Alteration of Campi Flegrei pumiceous ash in Roman concrete harbor structures along the central Italian coast produced zeolite and Ca-silicate minerals that have reinforced cementitious fabrics for >2000 years. X-ray microdiffraction experiments and electron microprobe analyses show that diverse alteration paths produced authigenic phillipsite and Al-tobermorite in the pyroclasts, pores, and cementing matrix of mortars in Romacons drill cores from Portus Cosanus, Portus Neronis, and Baianus Sinus. These minerals have cation exchange capabilities for some radionuclides and heavy metal cations and are candidate sorbents for concrete waste encapsulations. Compositions of phillipsite in certain Portus Cosanus and Portus Neronis pumice clasts are similar to those in the Neapolitan Yellow Tuff. Dissolution of this phillipsite and alkali feldspar produced new, authigenic phillipsite with less Si, greater Al and Ca, Al-tobermorite, and poorly-crystalline binder in pumice vesicles. Conversely, alteration of trachytic glass to clay mineral (nontronite) in a Baianus Sinus tuff clast is associated with new, authigenic phillipsite and Al-tobermorite in the tuff and cementing matrix. The Al-tobermorite has lower Al/(Si+Al) and Ca/(Si+Al) compared to Al-tobermorite in relict lime clasts. These more siliceous crystals, similar to those in hydrothermally-altered basalt, have 11.3 Å d-spacing in [001]. Raman spectra show symmetrical bending of Si-O-Si and Si-O-Al linkages, Si-O and Si-Al symmetrical stretching, and possible Q3 Si and Al tetrahedral peaks that suggest cross-linking of silicate chains–an important factor in cation exchange. The authigenic crystals refine pore space, contribute to binding in interfacial zones, and obstruct microcrack propagation. The well-constrained history of temperature variations and seawater immersion could provide further information for understanding alteration in volcanoclastic deposits and predicting regenerative processes in high performance concrete with pyroclastic rock pozzolan.
