**Abstract**

Mortars are diachronic composite materials used in masonry construction to serve multiple roles. Their durability and esthetic harmonization in constructions of the different eras were the reasons why numerous research works have been realized over recent decades. Each time, the role of the mortars' components revealed significant pieces of information on the technology used. Despite the indisputable role of the binders on the mortar's quality, aggregates of different characteristics had a significant role in the behavior of mortars. The addition of aggregates to a binding system in mortars technology has proved to confer technical advantages as they contribute to volume stability, durability, and structural performance. Apart from the different types of aggregates, as their mineralogy and origin are concerned, the volume content in the mixture, the maximum size, and their gradation influences the structure of a binder—aggregate mixture and the performance of mortars overall. In the present article, the diachronic presence of mortars is presented. The role of aggregates is emphasized to understand their impact on the longevity and durability of the mortars.

**Keywords:** sand, mortars, composites, mechanical-physical properties

### **1. Introduction**

Mortars are among the first building materials used in constructions, even from prehistoric times. Their study reveals a great source of information regarding the evolution of their technological characteristics and application techniques, the availability and exploitation of raw materials, as well as the wider socioeconomic aspects of each era. In any case, it seems that ancient masons were fully aware of the significant role of mortars in constructions and could exploit the raw materials that were available along with the application techniques [1]. In particular, the role of the quality of aggregates on the properties of old mortars has been known since, at least, Roman times. Natural sands of different origins and nature (river, quarry, sea) and crushed bricks combined with binders which were usually lime-based, were used for many centuries (**Figure 1**). These mortars were of different types and served as bedding, renders or plasters, floors, and mosaics' substates forming masterpieces of the world cultural heritage [2].

It is evident from the classic authors that the Romans preferred sharp sands to rounded sands, as they knew that these would produce stronger mortars; for example,

#### **Figure 1.**

*Coarse aggregates of natural origin in bedding mortars of the fourth century AD (left) and crushed brick as aggregates in a bedding mortar of the sixth century AD (right).*

Palladius, Pliny, and Vitruvius refer to recipes and guidelines for criteria that can be used for sand selection in the mixtures [3–5]. Among the requirements they mention, the origin, the shape, and the cleanness of the sand are the ones that prevail. They noticed the direct relation of the sand quality to the setting and strength of the mortars, and they gave precise directions to avoid, for example, sea sand due to salt contamination that can accelerate the weathering of the mortar. Manufacturing mortar was the first milestone in building history which has been continuously evolved up to the modern concrete. The materials used for mortar manufacture since antiquity were binders (clay, lime, pozzolan, brick/tile dust), aggregates (sand, gravel, crushed brick, pumice), and materials that were less frequently found and used (such as chopped straw, egg whites, reeds, blood, palm fibers, milk, and goat hair.). In Akrotiri of Thera, Greece (1700–1400 BC), structural mortars were made of local origin clay, mixed with gravel, charcoal, and straw [6]. In Hellenistic monuments, such as Dilos residences (second century BC), lime-pozzolan mortars were mainly found, with aggregates of natural origin and of granulometry mainly 0–8 mm [7]. During the Roman period (second century BC–third century AD), the use of lime and pozzolan dominated in constructions, while brick dust and crushed brick also started to be used [8]. The systematic and in high proportion use of brick dust and crushed brick in lime or lime-pozzolan mortars were expanded during the Byzantine era fourth–fifteenth century AD [9]. Aggregates (natural origin and crushed brick) were of gradation 0–8 mm to 0–16 mm, with a B/A ratio 1/2–1/3 [10]. The effectiveness of the adhesion between the binder and the crushed brick aggregates achieved in those cases was impressive. During the Ottoman period (fifteenth–nineteenth century AD), structural mortars were manufactured by using the available raw materials [11]. They were mainly lime-based (pure lime or lime with clay), while in specific constructions demanded in resistance to humidity (baths, cisterns), pozzolan and brick dust were also added. Aggregates were of natural origin (in some cases crushed brick was also added), of 0–8 mm granulometry, and of B/A ratio 1/2 [12]. In Medieval times (fifteenth–nineteenth century AD), structural mortars mainly consisted of lime (in some cases pozzolan was added), natural or crushed aggregates, and crushed brick in gradations 0–4 mm to 0–8 mm and B/A ratio 1/1–1/2 [13]. During the nineteenth and beginning of the twentieth century, structural mortars varied depending on the building type and the local constructional tradition. Aggregates were usually of the

### *The Role of Sand in Mortar's Properties DOI: http://dx.doi.org/10.5772/intechopen.102489*

natural origin of 0–8 mm gradation [14]. Later, scholars such as Lanas [15] referred to the importance of the binder/aggregate interface as a zone that requires special attention. From the historic research of the components of mortars, it is obvious that the presence of sand was catalytic and continuous. In relation to the origin of the sand used, it was mainly local, from streams or rivers, and in special cases, crushed bricks or tiles in different gradation were added [16, 17]. Aggregates are the most ubiquitous materials in construction. Nowadays, the building industry uses aggregates as materials for construction, mainly in their bound state with cement to form concrete, bitumen to form asphalt, or as components for composite materials. Nevertheless, the utilization of aggregates has a long history in construction technology and especially in mortars. Over the last decades, due to the increasing cost of raw materials and the continuous reduction of natural resources, the recycling of industrial waste has become an interesting option for the building industry. Nowadays, many large industries use manufactured sand alone for producing mortar by partially replacing river sand. In these complex systems, the aim seems to be first, the utilization of lowcost materials from local resources and second ensuring the quality and performance of materials for specific applications. Therefore, there is still a continuous usage of sand in construction works. Alternative approaches to completely replacing sand in mortars have intensified over the last decades [18]. At the moment, the increasing awareness of society about safeguarding heritage buildings and at the same time protecting the environment promotes strategies of combining principles of restoration with environmental friendly materials and techniques.
