Abstract
Protecting the built cultural heritage is one of the most important tasks in architectural practice. The process of repair is time-consuming, weather-dependent, and sensitive to materials applied. Introducing new materials in historic building repair in order to decrease the time needed for repair, brings some risk in the preservation process. The most common material for masonry repair is lime mortar. Adding cement to lime mortar can improve the mechanical properties of mortar and speed up the repair process. The high amount of cement may increase the strength, but decrease ductility and permeability of mortar, causing damages to protected buildings. An increase in strength with the smallest amounts of cement demands optimization of water content in the mixture. Tests were performed to investigate the influence of the water/binder (w/b = water/(lime + cement) ratio on mortar strength and water permeability. An air-entraining agent (AEG) was introduced to improve permeability. Results confirmed that adding small amounts of cement to lime (20% by weight) and decreasing of w/b ratio, improves the strength, with almost negligible influence on water permeability. The addition of very small amounts of AEG did not decrease the strength, nor the permeability.
Highlights
The testing of specimens from Series 1 (Figure 2), with a constant water/binder ratio, shows that the addition of 5% of White Portland Cement (WPC) reduces compressive strength by 27%, whilst the addition of 10% of WPC reduces it by 36%
Significant change occurs with the addition of WPC of 20%, where the increase is more than 120% for the initial, 7-day compressive strength, comparing to the reference specimen (E) without WPC
Different amounts of WPC were used in order to understand how and if this addition has an influence on the mechanical and physical characteristics of lime mortars
Summary
Historical buildings have cultural significance, witness to architectural history, and preserve information about structural systems, materials applied and building techniques used [1]. Until the end of the 18th century, the use of lime mortar was considered as an element of continuity of architectural heritage, whether it was applied for rendering or as a structural component. The process of lime mortars hardening, i.e. transformation of Ca(OH) , into CaCO3 as a carrier of strength, occurs in the presence of carbon dioxide. As conservation of historic structures is quite complex and its accomplishment lies in the adequate interaction between the inherited structure and a new one, the rapid diffusion of PC was stopped because of its incompatibility with the original structure. A high concentration of soluble salts found in PC could cause damage to the original materials as salt and Cesare Signorini
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