Composition of lime-cement and air-entrained cement mortar as a function of distance to the brick-mortar interface: consequences for masonry

Abstract

A B S T R A C T R I~ S U M I 5The composition of a lime-cement mortar and an airentrained cement mortar was studied as a function of distance to the brick-mortar interface. Both mortars had the same cement-to-sand ratio and the same water-to-cement ratio; in the lime-cement mortar the binder-to-sand ratio was highest. The measurements indicate that the mortar composition (i.e. the contents of sand, cured binder and voids) and the contents of chemical substances of the cured binder (i.e. the contents of calcite, portlandite and ettfingite) change with distance to the brick-mortar interface. For the mortar composition the tendency of these changes is the same, but for the contents of the chemical substances of cured binder for the two mortar types the tendency of these changes is opposite and also the extent of the changes is significantly different. For the air-entrained cement mortar, the observations are explained by the enrichment of binder towards the brick-mortar interface, resulting from the compaction of flesh mortar. In the lime-cement mortar such an enrichment of binder hardly occurs and the observations are explained by the intense carbonation that takes place. As a result, the contents of the chemical substances in the mortars is very much different. In the air-entrained cement mortar, near the brick-mortar interface the enrichment of cement and the low water content (resulting from the low water retentivity of this mortar), lower the water-to-cement ratio and as a consequence the cement is not fully hydrated. In the lime-cement mortar, as the Ca(OH)2 content and the water content is higher, near the brick-mortar interface, a carbonated zone is formed which is hardly permeable for CO 2 (and probably water). This does not occur in the air-entrained cement mortar, it remains permeable. La composition d'un mortier de ciment et de chaux et d'un mortier de ciment h air entrafn~ a ~t~ examin& en fonction de la distance par rapport a l'interface brique-mortier. Les rapports dment-sable et eau-ciment (taient identiques pour les deux mortiers. Le rapport liant-sable ~tait le plus ~lev( clans le mortier de ciment et de chaux. Les mesures indiquent que la composition du mortier (teneurs en sable, liant durci et vides) et les teneurs en produits chimiques du liant durci (teneurs en calcite, portlandite et ettringite) changent en fonction de la distance par rapport h l'intetface brique-mortier. Pour Ia composition du mortier, la tendance de ces changements est identique, par contre, en ce qui conceme les teneurs en produits chimiques du liant durci, la tendance de ces changements est oppos& pour les deux types de mot

Gypsum efflorescence on clay brick masonry: Field survey and literature study

“…Masonry joints do carbonate much faster though, as the permeable bricks provide more access to thin mortar joints. The complete carbonation of 12 mm thick cement mortar joints within two years is reported by Brocken et al [7].…”

“…In the UK cement/lime mortars have been gradually replaced by cement/air entrainer mixes. The presence of lime delays ettringite carbonation [25,7], and such shift to cementonly-based mortars might therefore facilitate the release of sulphates due to mortar carbonation. In Belgium, cement-based mortar came into use in the 1950's; while cement/air entrainer mixes are preferred by masons nowadays [19].…”

Materials Science Challenges in Radiocarbon Dating: The Case of Archaeological Plasters

“…Tracking changes in the stable carbon isotope ratios ( 13 C/ 12 C) can be one of the most powerful ways to track plaster diagenesis. 40,41 Fresh plaster that has all of its carbon incorporated from atmospheric sources has slightly less 13 C than the geogenic limestone from which it is made. Since this geogenic stable carbon isotope ratio is constant throughout the world, it is common to report the lighter plaster mass as a fractional percent, in parts per thousand (d 13 C), relative to the standard geogenic value.…”

“…Lime plaster forms in a multistep calcination and recarbonation process. 12,13 When calcium carbonate (CaCO 3 ) is heated to temperatures above 750°C, it decomposes to calcium oxide (CaO, lime) by the release of CO 2 . Upon exposure to ambient humidity, a thin layer of Ca(OH) 2 (portlandite) encases the CaO.…”

“…1 and 2 can change depending on the composition of its components. 13 The earliest plaster is known to be in Eynan (Israel) dating back to the Natufian period, approximately 12,000-15,000 years ago. 15,16 From that time period forward, plaster has been observed in archaeological contexts throughout the world, including the Far East, the Levant, Africa, Europe, Scandinavia, and the Americas.…”