STUDY OF THE FIRST BOULOGNE-SUR-MER CEMENTS USED FOR A HISTORIC AQUEDUCT FROM THE 19TH CENTURY

Natural and Roman cements are generally considered as the first binders of the 19th century concrete but their widespread usage was short-lived as they were quickly replaced by artificial cements (Portland), still the most important and predominant today. The Boulogne-Sur-Mer area in the North of France is one of the cradles of the French cement industry where the first French natural cement was produced in 1802 and the first French Portland cement at around 1850. These cements, natural and artificial, quickly gained a national and international fame. This paper presents a case study of a 19th century aqueduct, still in operation, with a focus on identifying the binders of concretes and mortars. Several combined techniques – optical microscopy (OM), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD) – were carried out to characterize and determine the compositions of the binders present in the aqueduct. Phenolphthalein tests were carried out in order to evaluate the depth of carbonation in the concrete. Several concrete and mortar samples, from pinkish to greyish ones, were taken from the outer and inner parts of the aqueduct. Results show several clinker morphologies and compositions, and different types of hydrates. They also reveal important differences in the microstructure between natural and Portland cement, dated from an early period of the cement industry in France. The concomitance of the use of natural and Portland cement, and good durability of these materials highlight the know-how of the engineers in the 1860s on cement performances and characteristics.