Since it has been snowing in Princeton this week, there is really no better time to write about how to construct structures out of ice. The motivation of building with ice – as opposed to another construction materials such as concrete- is that it makes experimenting much more economic and zero-carbon. Structural ice experiments also allow for the ability to discover a new medium that could fill the demand for a building material that will not see a dramatic decrease in its strength after being subject to several extreme freeze-thaw cycles . In many extreme cold environments, it would be desirable to have an inexpensive and safe way to reconstruct infrastructure or buildings out of ice to address annual need for shelters and roads rather than rebuilding or repairing these possibly concrete structures that will ultimately be damaged by the weather each year. In the following sections we provide a historic glimpse of key ice structures and how they were built.
Throughout history, ice has been used as an inexpensive and naturally available building material. The oldest known ice structures are igloos that were made from snow blocks . The igloos date from prehistory and have developed a form in which the structure takes exclusively compressive stresses and experiences zero bending moment everywhere in the shell. This form, called a catenoid evolves from the revolution of a parabolic cross-section into a dome. The igloos are constructed into this form using compacted ice blocks. The gaps between the blocks are filled with snow. Heating in the igloo then melts the inner surface of the igloo which then refreezes as a layer of ice that contributes to the overall strength of the igloo .
Iglulik Snowhouse (photo by Albert Low, 1903, image credit Library and Archives Canada/C-24522).
In 1739, Russian empress Anna Ivanovna order the first ice palace to be built . These impressive structures were made of blocks from rivers and lakes that were trimmed and stacked to form a masonry wall . This marked the beginning of functional ice structures that did not take the traditional catenoid shape.The form was imitated in the 1980’s using cast snow in which wooden molds were used to create compact snow walls to be sculpted.
Ice palace (left) for Russian empress Anna Ivanovna (right Louis Caravaque, 1730) (image credit wikimedia)
More practically, recent construction of ice hotels has seen the use of special wet snow being sprayed onto steel molds with heights up to 5m and spans up to 6m. In this process the snow is allowed a two day freezing period before the molds are removed. These structures get stronger as the snow melts and refreezes over time. This occurs on a diurnal cycle as the top layer of snow melts slightly each day and then freezes to solid ice during the night .
Ice Hotel Sweden constructed of wet snow sprayed onto steel molds (image credit holidayguru.ie)
Heinz Isler, who was known for his natural forms in shell construction, was intrigued by the structures minimal thickness . In his experiments with ice, Isler created structures by spraying water onto fabrics or inflatables . As a matter of feasibility this made using the inflatable membrane technique most practical for achieving one of Isler’s ideal shell forms.
Sculptural ice installations formed with pneumatic formwork (background left) and Heinz Isler (right)
The molds currently being implemented in research on structural ice involve inflatable forms that which are sprayed with a fiber-reinforced ice composite known as “pykrete” . In the winter of 2015, the students of the Eindhoven University Technology were the first spray the relatively unknown pykrete material, rather than snow and water onto pneumatic form of a 30m span dome. Currently, the “pykrete dome” holds the record as the largest ice dome ever built.
Pneumatic formwork (left) being sprayed with pykrete (right) (Image credit: structuralice. org)
Since its creation similar construction and design techniques have been used to create replicas of the Sagrada Familia, Candela’s hypar shell pavilion and a Da Vinci inspired bridge in order to demonstrate abilities of ice composite to reach great heights and develop strength in very low thickness-to-span ratio of the shell .
Tall pneumatic formwork sprayed with pykrete (left) and replica of Sagrada Familia (right) (Image credit: Bart Van Overbeeke)
Over the past years, the ice structure design and construction field has experienced an incredible boost which culminated in the establishment of the Structural Ice Association. In the next couple of years, we expect great developments in terms of material composition as well as construction techniques such as 3D printed structural ice. Expect to be dazzled and stay tuned for an update on our ice structure project!
 P.J.S. Cruz and J. Belis, “Compressive strength of ice and cellulose-ice composite” in Structures and Architecture. London, U.K.: Taylor & Francis Group, 2016, pp. 348-355.
 A. Pronk et al., “Historical development of structural ice,” in Structures and Architecture. London, U.K.: Taylor & Francis Group, 2016, pp. 339-347.
 J. Chilton, “Shells, the man, his philosophy and influences,” in The Engineer’s Contribution to Contemporary Architecture: Heinz Isler. Thomas Telford Limited 2000, July 2015.
 A. Pronk, “The calculation and construction of the highest ice dome—the Sagrada Familia in Ice,” in Proceedings of the International Society of Flexible Formwork Symposium (ISOFF ’15), Amsterdam,The Netherlands, August 2015.
Author: Michael Cox, edits by Sigrid Adriaenssens