This study characterized mortars from a masonry fortification in Charleston, South Carolina (USA), harbor where construction was during the period 1839–1860. This location for analysis was interesting because of the sea water impingement on the structure. The study was included as part of an overall structural assessment with restoration as an objective. The mortars were found to be cement, lime, and sand mixtures in proportions similar to ones expected from the historic literature, that is, one part binder to two parts of sand. The binder was found to be American natural cement, a substance analogous to the European Roman cement. The results suggest that the thermal history of the cement during manufacturing affected setting rate explaining why the cements were considered as variable during the mid-to-late 1800s. Fine pores were found in mortars exposed to sea water resulting from corrosion. Contemporary natural cement was shown to release calcium in aqueous solution. While this release of calcium is necessary for setting in natural and Portland cements, excessive calcium solution, as exacerbated by sea water contact and repointing with Portland cement mortars, was shown to result in brick scaling or decay through cryptoflorescence. 1. Introduction Assessments of historic masonry structures include precise documentation of dimensions and elevations, analysis of structural stability, and characterization of materials. The characterization is a prerequisite to restoration and repair to insure that compatible materials are used and to protect the historic character of the structure. Masonry mortars throughout history have been composed of a binder material, aggregates, and additions, the latter of which alter the properties of the mortar during application or enhance properties in the hardened condition. The binders developed through history include natural pozzolanic materials (as used by Greek and Roman societies), lime and hydraulic lime, Roman cements (called natural cement when manufactured in the USA), and Portland cement. The historical development of binders is presented in detail by Blezard [1], von Landsberg [2], Eckel [3], and Cummings [4]. Elsen [5] provides comprehensive references on binders. Weber et al. [6] describe Roman cements in Europe with characterization of mortars by chemical analysis and petrography. Callebaut et al. [7] used advanced analytical techniques in mortar characterizations. Aggregates for masonry mortars are generally described as “fine” to distinguish the larger aggregate particles and stones used in concrete. The fine
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