Reactive Synthetic Pozzolans in Mortars from Ancient Water Infrastructure Serving Rome and Pompeii

Abstract

Ancient Roman concrete constitutes many ancient structures that remain standing; however, little is known about how it has remained durable. Here, we investigate the mortars used in ancient water bearing infrastructure such as aqueducts, cisterns, and baths. In these structures, crushed ceramics are used as a pozzolanic additive on surfaces in continuous or frequent contact with water. The ceramic-lime mortars are probed using a multi-scale characterization approach including SEM-EDS and Raman microspectroscopy. The analysis shows the role of ceramics within these structures as a source of aluminosilicates, mapping the presence of both pozzolanic and post-pozzolanic phases. A hybrid binder consisting of cementitious hydrates and calcite is mapped at the interface of the ceramics and evidence of post-pozzolanic densification of pores and cracks is observed. Comparison across structures shows that material selection and chemistry benefit the infrastructure applications. Understanding these ancient materials provides inspiration for new, durable infrastructure materials.