Assessment of material characteristics of ancient concretes,Grande Aula,Markets of Trajan,Rome

The Grande Aula, or Great Hall, of the Markets of Trajan (AD 96 to 115) is an intact example of the domed, concrete architecture of imperial Rome. Petrographic, x-ray diffraction, chemical, and SEM analyses demonstrate that wall mortars contain Pozzolane Rosse volcanic ash aggregate (harenae fossiciae) and strätlingite, a complex calcium aluminate cement hydrate (C₂ ASH₈) that gives modern cements good durability and compressive strength. Specific gravity tests and a new petrographic method for assessing bulk densities indicate unit weights of about 1750 kg/m³ for the wall mortars and 1430–1640 kg/m³ for the pumice bearing, vaulted ceiling mortars. Innovative point load source tests record the tensile strengths (f_t) of the aggregate and interfacial elements of the conglomeratic concrete fabric. These suggest f_t of about 2.7 MPa for brick, 1.2 MPa for Tufo Lionato tuff, and 0.9 MPa for Tufo Giallo della Via Tiberina tuff coarse aggregate (caementa), based on a tentative, approximate correlation with splitting (Brazilian) tests. The pozzolanic mortar and interfacial zones have lower f_t in the range of 0.8 MPa to 0.5 MPa. The relatively low mortar strength and its somewhat tenuous adhesion to the coarse aggregate suggests that the caementa may have arrested the propagation of tensile microcracks that formed in the mortar, thereby increasing the composite tensile strength of the concrete. Roman builders selected the complex aggregate mixes to optimize the performance of the wall and vault concretes.     

INCE NTIVE SYSTEMS IN ENVIRONMENTAL REGULATION*

The central problem of environmental and other regulation is identified as a control problem similar to that faced by principals in controlling their agents. An incentive systems framework, featuring the concept of incentive relation, is offered as a means of integrating and systematizing discussion of alternative means of regulation. The distinction of incentive and directive means of environmental regulation, together with the levels of their targets and the penalties for enforcement, are employed to develop a typology of regulatory means and to categorize environmental regulatory alternatives. Shifting from control of regulatees to control of regulators, some results of a study of the incentive systems facing state reclamation inspectors are reported. Dual external incentive relations (to the mining industry and to the federal Office of Surface Mining) are observed, and the design consequences for regulation in the federal system are discussed.     

A Happening at Danebury Hillfort – But When?

A group of six radiocarbon dates for human skeletons found at the Iron Age hillfort of Danebury are suggestive of a major killing event. We consider here how the dates, mitigated by a careful consideration of the archaeological evidence for context, can be used in constructing site history.