Spirit leveling data from the Nepal Himalaya between 1977 and 1990 indicate localized uplift at 2–3 mm/yr in the Lesser Himalaya with spatial wavelengths of 25–35 km and at 4–6 mm/yr in the Greater Himalaya with a wavelength of ≈40 km. Leveling data with significantly sparser spatial sampling in southern Tibet between 1959 and 1981 suggest that the Himalayan divide may be rising at a rate of 7.5±5.6 mm/yr relative to central Tibet. We use two‐dimensional dislocation modeling methods to examine a number of structural models that yield vertical velocity fields similar to those observed. Although these models are structurally nonunique, dislocation models that satisfy the data require aseismic slip rates of 2–7 mm/yr on shallow dipping faults beneath the Lesser Himalaya and rates of 9–18 mm/yr on deep thrust faults dipping at ≈25°N near the Greater Himalaya. Unfortunately, the leveling data cannot constrain long‐wavelength uplift (>100 km) across the Himalaya, and unequivocal estimates of aseismic slip in central Nepal are therefore not possible. In turn, the poor spatial density of leveling data in southern Tibet may inadequately sample the processes responsible for the uplift of the Greater Himalaya. Despite these shortcomings in the leveling data, the pattern of uplift is consistent with a crustal scale ramp near the Greater Himalaya linking shallow northward dipping thrust planes (3–6°) beneath the Lesser Himalaya and southern Tibet. Aseismic slip on the potential rupture surface of future great earthquakes beneath the Nepal Himalaya south of this ramp appears not to exceed 30% of the total convergence rate between India and southern Tibet resulting in an accumulating slip deficit of 13±8 mm/yr.

The extraordinarily durable concretes of Imperial Age (27 B.C. through 3rd century A.D.) monument construction in Rome contain scoriaceous, highly potassic, altered volcanic ash from the Pozzolane Rosse ignimbrite, erupted at 456±3ka from the Alban Hills volcano as pozzolanic mortar aggregate. Stratigraphic, micromorphological, and chemical investigations demonstrate that during the relatively warm, humid period preceding marine isotope stage 11, intensive hydrolytic pedogenesis produced dense illuvial clay coatings in the upper horizon of the ignimbrite. Moderately altered ash of the Pozzolane Rosse transitional Bt to Bw soil horizon has opal coatings overlain by limpid, illuvial halloysite coatings. Less weathered ash from a lower C horizon apparently was altered in ground water. Where the ignimbrite filled certain paleovalleys, zeolitic alteration produced phillipsite and chabazite textures. Builders selected ash from these intermediate and least altered horizons for the highest‐quality mortars of the Imperial Age, as for the Forum and Markets of Trajan (A.D. 107 to 113). The alumina‐ and alkali‐rich compositions of cementitious complexes give some preliminary insights as to why the reaction of hydrated lime with the altered, alkali‐rich Pozzolane Rosse ash produced pozzolanic cements that have remained resistant to decay for nearly 2000 years. The results of the geological analyses fully confirm empirical observations made by Esther B. Van Deman in 1912 regarding the durability of the ancient mortars and the technical choices of Roman builders. © 2009 Wiley Periodicals, Inc.

Pozzolanic reaction of volcanic ash with hydrated lime is thought to dominate the cementing fabric\ud and durability of 2000-year-old Roman harbor concrete. Pliny the Elder, however, in first century CE\ud emphasized rock-like cementitious processes involving volcanic ash (pulvis) “that as soon as it comes\ud into contact with the waves of the sea and is submerged becomes a single stone mass (fierem unum\ud lapidem), impregnable to the waves and every day stronger” (Naturalis Historia 35.166). Pozzolanic\ud crystallization of Al-tobermorite, a rare, hydrothermal, calcium-silicate-hydrate mineral with cation\ud exchange capabilities, has been previously recognized in relict lime clasts of the concrete. Synchrotron-based\ud X-ray microdiffraction maps of cementitious microstructures in Baianus Sinus and Portus\ud Neronis submarine breakwaters and a Portus Cosanus subaerial pier now reveal that Al-tobermorite\ud also occurs in the leached perimeters of feldspar fragments, zeolitized pumice vesicles, and in situ\ud phillipsite fabrics in relict pores. Production of alkaline pore fluids through dissolution-precipitation,\ud cation-exchange and/or carbonation reactions with Campi Flegrei ash components, similar to processes\ud in altered trachytic and basaltic tuffs, created multiple pathways to post-pozzolanic phillipsite and\ud Al-tobermorite crystallization at ambient seawater and surface temperatures. Long-term chemical\ud resilience of the concrete evidently relied on water-rock interactions, as Pliny the Elder inferred. Raman\ud spectroscopic analyses of Baianus Sinus Al-tobermorite in diverse microstructural environments\ud indicate a cross-linked structure with Al3+ substitution for Si4+ in Q3\ud tetrahedral sites, and suggest\ud coupled [Al3++Na+\ud ] substitution and potential for cation exchange. The mineral fabrics provide a geoarchaeological\ud prototype for developing cementitious processes through low-temperature rock-fluid\ud interactions, subsequent to an initial phase of reaction with lime that defines the activity of natural\ud pozzolans. These processes have relevance to carbonation reactions in storage reservoirs for CO2 in\ud pyroclastic rocks, production of alkali-activated mineral cements in maritime concretes, and regenerative\ud cementitious resilience in waste encapsulations using natural volcanic pozzolans

No abstract

No abstract

Ancient Roman syntheses of Al-tobermorite in a 2000-year-old concrete block submerged in the Bay of Pozzuoli (Baianus Sinus), near Naples, have unique aluminum-rich and silica-poor compositions relative to hydrothermal geological occurrences. In relict lime clasts, the crystals have calcium contents that are similar to ideal tobermorite, 33 to 35 wt%, but the low-silica contents, 39 to 40 wt%, reflect Al 3+ substitution for Si 4+ in Q 2 (1Al), Q 3 (1Al), and Q 3 (2 Al) tetrahedral chain and branching sites. The Al-tobermorite has a double silicate chain structure with long chain lengths in the b [020] crystallographic direction, and wide interlayer spacing, 11.49 Å. Na + and K + partially balance Al 3+ substitution for Si 4+ . Poorly crystalline calcium-aluminum-silicate-hydrate (C-A-S-H) cementitious binder in the dissolved perimeter of relict lime clasts has Ca/(Si+Al) = 0.79, nearly identical to the Al-tobermorite, but nanoscale heterogeneities with aluminum in both tetrahedral and octahedral coordination. The concrete is about 45 vol% glassy zeolitic tuff and 55 vol% hydrated lime-volcanic ash mortar; lime formed <10 wt% of the mix. Trace element studies confirm that the pyroclastic rock comes from Flegrean Fields volcanic district, as described in ancient Roman texts. An adiabatic thermal model of the 10 m 2 by 5.7 m thick Baianus Sinus breakwater from heat evolved through hydration of lime and formation of C-A-S-H suggests maximum temperatures of 85 to 97 °C. Cooling to seawater temperatures occurred in two years. These elevated temperatures and the mineralizing effects of seawater and alkali-and alumina-rich volcanic ash appear to be critical to Al-tobermorite crystallization. The long-term stability of the Al-tobermorite provides a valuable context to improve future syntheses in innovative concretes with advanced properties using volcanic pozzolans.

No abstract

The pyroclastic aggregate concrete of Trajan's Markets (110 CE), now Museo Fori Imperiali in Rome, has absorbed energy from seismic ground shaking and long-term foundation settlement for nearly two millenia while remaining largely intact at the structural scale. The scientific basis of this exceptional service record is explored through computed tomography of fracture surfaces and synchroton X-ray microdiffraction analyses of a reproduction of the standardized hydrated lime-volcanic ash mortar that binds decimeter-sized tuff and brick aggregate in the conglomeratic concrete. The mortar reproduction gains fracture toughness over 180 d through progressive coalescence of calcium-aluminum-silicate-hydrate (C-A-S-H) cementing binder with Ca/(Si+Al) ≈ 0.8-0.9 and crystallization of strätlingite and siliceous hydrogarnet (katoite) at ≥90 d, after pozzolanic consumption of hydrated lime was complete. Platey strät-lingite crystals toughen interfacial zones along scoria perimeters and impede macroscale propagation of crack segments. In the 1,900-y-old mortar, C-A-S-H has low Ca/(Si+Al) ≈ 0.45-0.75. Dense clusters of 2-to 30-μm strätlingite plates further reinforce interfacial zones, the weakest link of modern cement-based concrete, and the cementitious matrix. These crystals formed during long-term autogeneous reaction of dissolved calcite from lime and the alkali-rich scoriae groundmass, clay mineral (halloysite), and zeolite (phillipsite and chabazite) surface textures from the Pozzolane Rosse pyroclastic flow, erupted from the nearby Alban Hills volcano. The clastsupported conglomeratic fabric of the concrete presents further resistance to fracture propagation at the structural scale.Roman concrete | volcanic ash mortar | fracture toughness | interfacial zone | strätlingite