8 C O N T E X T 1 5 0 : J U L Y 2 0 1 7 Heritage with Tomorrow’s Technologies’, held in San Antonio, Texas, late last year. One of the themes of the conference related to concrete materials, including the various cements and aggregates used in its composition; the history of the material from the 17th through to the 20th centuries; the many forms of concrete, including monolithic structures and precast and concrete-masonry units; innovative construction techniques, including successes and failures; and concrete as a decorative material. These themes are reflected in the articles in the current issue. In the first paper, Thomas E Boothby and Sharyn Clough examine how the design of buildings in general, and building structures in particular, has changed over the past two centuries, proceeding from experiencebased (‘empirical’) design to predictive mathematics and physics-based (‘rational’) design. From a historical review of the design methods used for reinforced concrete, the authors conclude, first, that there are some weaknesses in the design approaches of exclusively rationalist models; second, that there is a ubiquitous role of empiricist elements in all design; and, third, that the ubiquity and inevitability of empiricist elements are necessary to correct idealised designs generated by rationalist design methods. Two good examples are given. The first is at the 19th-century work of WJM Rankine in England and MA Howe in the USA, related to the rationalist methods of building concrete arches. The authors cite the thin concrete shell structures built in the early 1900s, designed by Auguste Perret before the development of a rationalist theory for these was developed. The historical review makes explicit that commitments to empiricism were commonplace, and that structures designed according to those principles performed as well as those contemporary structures conceived according to rationalism. While the design of reinforcedconcrete structures moved from an explicitly empiricist approach in the mid-1800s to a more rationalist approach by the 1900s, implicit appeals to empiricist methods often remain, and for good reason. Because idealised rationalist models can make use of false assumptions, empiricism is needed to correct such assumptions on particular schemes. Rapid advances in digital technology are facilitating cost-effective repairs of features on building facades. Replacing damaged historic architectural features is an involved and expensive process, especially for elaborate ornamentation. While maintaining authenticity is of the utmost importance, heritage professionals are often challenged by owners to seek high-quality repairs that are also cost-effective. The paper by Diego Romero and Alfredo Bustamante focuses on the replacement of 14 high-level ornamental cast-stone spandrel panels from the historic Lancaster Hotel, a 12-storey structure built in 1926 in Houston, Texas. They explain how a cost-effective mapping technique, structure-from-motion photogrammetry, enabled replication of the original panels in order to overcome budgetary and scheduling constraints, and to meeting the difficulty of access at the top of a tall building. The severely deteriorated panels were removed from the facade and replaced by replicas. The new spandrel panels were cast using a rubber mould generated from the photogrammetry model. Although the replicated panels have very slight differences from the originals, the process met the parameters of the project.Where in other instances precise replicas are necessary, photogrammetry remains a viable option provided detailed evaluation is done using professional scanning equipment. Structure-from-motion photogrammetry provided a lowcost option for the non- destructive fabrication of the moulded architectural ornamentation on what a difficult-toaccess location. It shortened the design and fabrication timetable compared to the traditional method of removing a sample, or hand-fabrication of a mould. The technique allowed control of the quality of the finished product by digitally repairing any defects found in the original sample panels, and it removed the risk associated with extracting a sample in good undamaged condition while making a mould. A paper by Jeffrey M Chusid examines the concrete experiments of Joseph Alan Stein in the USA and India. Stein moved from the San Francisco Bay area to India in the 1950s to avoid McCarthyism, giving him the opportunity to experiment and innovate with concrete. The result was buildings that are still widely celebrated for his adept way of building sophisticated modernist structures using small, simple, precast elements. Stein also developed novel ideas around the surfacing of concrete panels with stone chips and hand-rubbed concrete finishes. One of the most interesting papers is by Camilla Mileto and Fernando Vegas, who look at Article 5 of the 1931 Athens Charter for the Restoration of Historic Monuments. This was the first international charter to approve the use of modern technological resources in the preservation of monuments, stating that ‘Modern techniques and materials may be used in restoration work’. The conclusions of the Athens conference also stated in the fifth section that ‘The experts heard various communications concerning the use of modern materials for the consolidation of ancient monuments. They approved the judicious use of all the resources at the disposal of modern techniques and more especially of reinforced concrete’. The fourth section stated that ‘architects and curators of monuments should collaborate with specialists in the physical, chemical and natural sciences with a view to determining the methods to be adopted in specific cases’. Unsurprisingly, this approach was not without its problems. There are differences of view on the philosophy of repair on each side of the Channel. The authors provide an audit trail of the technological preservation resources originating from 19th-century England and France towards the Athens declaration. They also show that the evolving techniques and technologies have been present throughout history. They illustrate this with examples from the buttressing of
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