Qilin Li

© 2014, National Academy of Sciences. All rights reserved.The pyroclastic aggregate concrete of Trajan's Markets, 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 cementing binder with Ca/ ≈ 0.8-0.9 and crystallization of strätlingite and siliceous hydrogarnet at ≥90 d, after pozzolanic consumption of hydrated lime was complete. Platey strätlingite 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/ ≈ 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, and zeolite surface textures from the Pozzolane Rosse pyroclastic flow, erupted from the nearby Alban Hills volcano. The clast-supported conglomeratic fabric of the concrete presents further resistance to fracture propagation at the structural scale.

In this paper, it is argued that there are (at least) two different kinds of ‘epistemic normativity’ in epistemology, which can be scrutinized and revealed by some comparison with some naturalistic studies of ethics. The first kind of epistemic normativity can be naturalized, but the other not. The doctrines of Quine’s naturalized epistemology is firstly introduced; then Kim’s critique of Quine’s proposal is examined. It is argued that Quine’s naturalized epistemology is able to save some room for the concept of epistemic normativity and therefore his doctrine can be protected against Kim’s critique. But, it is the first kind of epistemic normativity that can be naturalized in epistemology. With the assistance of Goldman’s fake barn case, it is shown that the concept of epistemic normativity that is involved in the concept of knowing, which cannot be fully naturalized. The Gettier problem indicates that Quine only gets partially right idea concerning whether epistemology can (and should) be natualized.

Adrian Heathcote has proposed a truth-making account of knowledge that combines traditional conditions of justified true belief with the truth-making condition, which would jointly provide us with the sufficient condition of knowledge, and this truth-maker account of knowledge in turn explains why a gettiered justified true belief fails to be regarded as a genuine instance of knowledge. In this paper, by the comparison of two different casual models that are illustrated by the thermometer and the clock respectively, however, it will be argued that Heathcote’s truth-making account of knowledge fails to cope with the Gettier case of the stopped clock and therefore is called for some further remedy.