Unlocking the water retention behaviour of turf construction materials

Turf is not a material frequently associated with construction. However, as a cheap, easily available, and versatile material it was used in antiquity (and has been used in various contexts since) to form unit-based and mass walls, embankments, and ramparts. Some of the best-preserved evidence for historical turf use comes from the Roman period, when it was a mainstay of military construction, being widely used in forts (e.g. along the Rhine and in Britain) and large-scale linear earthworks, most notably thewalls of Hadrian (northern England) and Antoninus Pius (central Scotland). To our knowledge, turf has never been examined as a construction material; its interest has, until now, been restricted to the soil and agricultural sciences and sports engineering. This paper presents the first exploration of turf water retention properties, assessed to understand whether turf behaviour can be collated with that of more traditionalearthen materials, for example cob or rammed earth. Tensiometer and psychrometer methods were used to estimate the water retention curves of turf, representative of that used for construction, harvested from two sites near Crieff, Scotland. The obtained data were analysed in terms of unimodal type functions to understand qualities of the full range of the soil water retention curve for Scottish turf. This work supports a larger project examining how engineering materials principles can explain ancient construction practices. In so doing, we will be well positioned to reintroduce this low-carbon material to the modern construction market.