Mix Design Parameters of Restoration Mortars: The Effect of Aggregate Characteristics

Abstract

Aggregates are an important ingredient of mortars as they can be a decisive factor for their performance just as much as for their production cost. This study aims to discuss the use of sand from local deposits in the design of restoration mortars in terms of compatibility with original building materials, along with the optimization of mix proportions regarding the binder to aggregates ratio and the geometrical characteristics of aggregates. In restoration interventions it is important to consider both the performance of mortars as well as economic requirements. Performance requirements, e.g. compressive strength and porosity together with original mortar compatibility, are essential to the success of the conservation treatment and the longevity of the structure. Whereas the choice of raw materials, utilization of local deposits, considerations of the total energy consumption and environmental footprints have to be considered as they are important economic variables. In this study, focusing on a more efficient use of raw materials in mortar design, it is shown that the use of local sand deposits should be favorable during the restoration intervention. This is due to the fact that raw materials used in the original construction were usually local, as that was the most efficient option. Thus, local aggregates may provide the optimum compatibility in a restoration project. Furthermore, it was concluded that regarding the alternative for reducing the amount of binder, the main aggregate characteristics to be considered are gradation and packing density and secondarily their shape. More precisely, for a given ratio of raw materials, the use of aggregates with higher packing density, leads to mortars with increased mechanical strength, while the use of more angular aggregates results in higher water demand during mixing and therefore, lower mechanical strength.