Mortar is a mixture used in construction for bonding building materials, such as bricks or stones. Its role is to fill the gaps between building materials.
Most consist of sand, water, and a binder (e.g., cement, lime).
Types of Mortars
Mortars are divided into:
- Hydraulic mortars are those that harden with the action of water (e.g., cement)
- Air-hardening mortars are those that harden with the action of air (e.g., construction mud)
Cement
Definition
The term cement refers to the binding powder, usually before mixing with water, without other inert additives such as sand and gravel. Whereas concrete refers to the mixture of cement with a quantity of other inert materials.
The chemical reaction of cement with water (cement hydration) produces products that have setting and hardening characteristics. The primary use of cement is in its reaction with water.
It has been experimentally proven that the more cement (up to a certain limit, of course) contained in a unit volume of concrete, provided that other factors (quality and granulometric composition of aggregates, water quantity, placement and compaction method, etc.) remain constant, the greater the strength the concrete exhibits. Naturally, this increase in strength is not unlimited but stops at the strength of the least resistant material in the concrete.
Categories from a chemical perspective
Depending on their composition, grinding degree, and additives, cements are classified into various types and strength categories.
According to the Greek cement regulation (EN 196-1), cements are divided into the following types:
By composition into:
- Type I (Portland Cement) Characterized by cements derived from the grinding of clinker with the addition of 2-3% gypsum and 3% filler <by weight.
- Type II (Portland Cement with pozzolans) Characterized by cements containing pozzolans. The insoluble residue amounts to 20% by weight.
- Type III (Pozzolanic Portland Cements) Contain pozzolan in a higher percentage than those of Type II. The insoluble residue amounts to 20-40%. They exhibit lower heat of hydration and are suitable for massive projects (e.g., PPC spillways, dams, etc.)
- Type IV (SR) (Sulfate-Resistant Portland Cement) Do not contain pozzolans, but tricalcium aluminate (Ca3A) must be less than 3.5% and the sulfur trioxide (SO3) content must not exceed 2.5%. It is used in the preparation of concrete for structures located in highly corrosive environments (e.g., biological treatment units, sewage pipes).
Categories by strength
By strength into the following categories:
- Category 35 (with 28-day compressive strength from 25-45 MPa)
- Category 45 (with 28-day compressive strength from 35-55 MPa)
- Category 55 (with 28-day compressive strength above 45 MPa)
Theoretically, there would be 27 types of cement. However, fewer types are produced in Greece because not all combinations are practically feasible or necessary in practice. For example, a pozzolanic cement (Type III) would require excessive fineness to achieve a strength of 55 or even 45 MPa.
Properties of Cement Paste
A primary property of cement paste in plastic form, the reduction of fluidity, is related to the phenomenon of reduced slump.
It is noted that the plasticity of cement paste is due to free water, the gradual loss of which, due to initial hydration reactions, its adsorption on the surfaces of minimally crystalline hydration products (such as ettringite and C-H-S), and evaporation, causes a reduction in fluidity, and ultimately setting and hardening. A second property is setting, which means the solidification of the plastic cement paste.