Mortar and Lime in Construction

 Email This Post

Mortar and lime are the two most important binding materials in building and road construction. Thus every civil engineer must learn as it is very important that every civil engineer knows about its properties. Here, all important information has been pointed out in bulleted form so that memorization becomes easy for students. It is highly recommended for competitive exams. Some important information is discussed as follows-

• Bulking of sand criteria –
  • For moisture of 5% to 8% leads to an increase in volume by 20% to 40%.
  • If the material is finer, then more will be more bulking of sand. This is called bulking.
• Mortars
  • Bulk density
  • Type of Binding material
  • Nature of application
  • Special mortars

Fig 1: Mortar used on construction site
Courtesy: Dreamstime

1. Bulk Density

It is classified into two types:

• Heavy Mortars – Such mortars have a bulk density of 15 kN/m³ or more. They are prepared from heavy quartz or other sand.
• Light Mortars – Such mortars have a bulk density of less than 15 kN/m³. They are prepared from light porous sand, pumice, and fine aggregates.

Type of Binding Material

According to this, mortars are classified as –

• Lime Mortars
• Surkhi Mortar
• Cement Mortar
• Gauged Mortar

Lime Mortars

• Lime is a binding material.
• Fat lime shrinks and requires 2-3 times the volume of sand.
• Lime should be slaked before use.
• It is unsuitable for use in a waterlogged or damped area.
• For hydraulic lime, the proportion of lime to sand by volume is 1:2.
• It has high plasticity and can be placed easily.
• It shrinks little, is durable, and hardens slowly.

Surkhi Mortar

• In such type of mortar, the sand is replaced by surkhi or is replaced by half of sand in the case of fat lime mortar.
• It is used for ordinary masonry works like foundations or superstructures.
• Because surkhi is prone to disintegration, it cannot be utilised for plastering or pointing.

Cement Mortar

• • Here cement is the binding material.
  • eThe proportion of cement and sand varies from 1:2 to 1:6.
  • It is used for high-strength structures, water resisting purposes in the case of underground structures.

Gauged Mortar

• • • • It is used for achieving early strength.
      • It is also referred to as gauging.
      • It makes lime mortar economical, strong, and dense.
      • The proportion of cement to lime is by volume 1:6 to 1:8.
      • It is also known as Lime-Cement mortar or Composite mortar and is formed by the combination of cement and clay.
      • It is used for thick brick walls and

Special Mortar

Fire-resistant Mortar

It is prepared by adding aluminous cement to finely crushed powder of fire bricks.

• • • • It is applied as per proportion- 1 part of aluminous cement to 2 parts of powder of fire bricks.
      • It is used for lining furnaces, fireplaces, ovens, etc.

LightWeight Mortar

• • • • It is prepared by adding saw-dust, and wood powder to lime or cement mortar
      • Materials are added (optional) – asbestos fibers, jute fibers, coir, etc.
      • It is used for soundproof and heatproof construction/

Packing Mortar-

• • • • It is used to pack oil wells, prepare special mortar possessing high homogeneity, water resistance, form solid waterproofing plugs in cracks, voids of rocks, etc.
      • Composing of this mortar is decided by taking into account hydrological conditions and packing methods of timbering.

Sound absorbing Mortar –

• • • • It has a bulk density of 6-12 kN/m³.
      • It may be consisting of binding materials like portland cement, lime, gypsum, etc.

Properties of Good Mortar –

• • • • It should stick well to bricks, stones, and other hard surfaces.
      • t should be able to generate designed stresses.
      • It should be cheap, durable, have good workability, sets quickly, should not affect the durability, should not have cracks in joints.

Uses of Mortar

• • • • It should be able to bind bricks, stones, etc.
      • It should be able to carry out pointing and plastering.
      • It should form an even and soft bedding layer for budding units.
      • It should form joint pipes, hide open joints of brickwork and stonework.
      • It should be able to improve general appearance.

Functions of Sand in Mortar

• • • • Bulking, setting, shrinkage was avoided due to sand.
      • Strength sets are impaired due to sand, but it doesn’t affect binding strength and shrinkage.

Tests for Mortars

• • • 1. Adhesiveness to building units-
         • Bricks are placed at right angles. Mortars are set to form horizontal joint and brick size id 19 cm x 9 cm x 9 cm, so horizontal joint of 9 x 9 = 81 cm²will be formed.
         • Ultimate adhesive strength = Maximum load / Area (81 cm²).
      2. Crushing strength –
         • Brick or stone masonry is tested in a compression machine. Load at crushing gives crushing strength.
      3. Tensile strength –
         • In a tension testing machine, briquettes are tested.
         • The cross-sectional area of the central portion is 38 mm x 38 mm or 1444 mm² or 14.44 cm².
         • Lime –
           • It is a cheap alternative to cement.

Some important definitions

• • • • Calcination – Healing of limestone to redness in contact with air.
      • Hydraulicity – Property of lime by which it sets or hardens in damp places, water, or thick masonry walls with no free air circulation.
      • Lime – During calcination, moisture and carbon dioxide are removed, leaving behind lime.

CaCO₃ ——> CaO + CO₂

• • • Quick Lime –
      • Calcination of pure limestone is called quick lime.
      • It is capable of slaking with water.
      • It has no affinity for carbonic acid.
      • It has a greater affinity for moisture.
      • It comes from kilns known as lump lines.
      • It releases immense heat upon slaking.
    • Slaked Lime –
      • CaO + H₂O —–> Ca(OH₂) + Heat.
      • The thin, pourable suspension of slaked lime is the milk of lime.
    • Slaking –
      • A reaction occurs when water is put to quick lime.
      • The quick lime cracks, swell, and fall into powdered form as Ca(OH₂)/ Hydrated lime.

Classification

• • • Fat lime or High Calcium Lime or Rich lime or White lime (Popularly known as Fat lime)-
  • • • It is 2-2.5 times the volume of quick lime.
      • The percentage of impurities is less than 5%.
      • It hardens slowly.
      • It has a high degree of plasticity.
      • It is soluble in water and changes frequently.
      • It is white in color.
      • It slakes vigorously.
      • It is used in whitewashing, plastering, forms mortar with sand, cement manufacturing, and the metallurgical industry.
  • • Hydraulic Lime or Water lime –
  • • • It contains some clay and ferrous oxide.
      • It is divided into – Feebly hydraulic lime, Moderately hydraulic lime, and Eminently hydraulic lime.
      • It is high in percentage of clay which makes slaking difficult.
      • It has higher hydraulic properties.
      • It sets underwater and forms thick walls where there is no free circulation of air.
  • • Poor lime or Lean lime or Impure lime –
  • • • It contains more than 30% of clay.
      • It slakes very slowly.
      • It forms a thin paste and sets slowly.
      • It has poor binding properties.
      • It is used in places where limestone is not available.

Impurities

• • • Magnesium Carbonate –
  • • • It is hard, heavy, and compact in texture.
      • It displays irregular properties of calcination, slaking, and hardening.
      • About 5% of it is best for properties.
  • • Clay –
  • • • It is responsible for the hydraulic properties of lime.
      • It is present around 10%-30%.
      • When it is present in the range of 3%-5%, there are no hydraulic properties and no setting.
      • When it is present in 20%-30%, then it exhibits excellent hydraulic properties and is suitable for an aqueous foundation.
  • • Silica-
  • • • In free form, it is detrimental to the properties of lime.
  • • Fe Compounds –
  • • • It occurs in small proportions as oxide, carbonates, and sulphides.
      • Pyrite of iron sulphides is highly undesirable.
      • 2%-5% is necessary for hydraulic lime.
  • • Sulphates –
  • • • It slows down slaking and increases setting time.
  • • Alkalies –
  • • • It is undesirable in pure lime.
      • Up to 5% of it has no ill effect.

Classification on strength basis for Mortar

Table 1: Mortar designation as per strength

• • • Richer than 1.3, Cement Mortars are not used in masonry work because of no gain of strength and are prone to high shrinkage.
    • Adding surkhi to pure lime leads to artificial hydraulic lime.
    • Kankar calcination gives hydraulic lime.
    • Modulus of rupture at 28 days of Mortar should not be less than 1.5 MPa.

Table 2: Sand classification as per buckling

Table 3: Sand classification as per fineness modulus

Conclusion
All this information is vital for an engineer to produce a good structure. It is recommended that an engineer understands the properties and specifications before commencing work in the field. Lack of such knowledge will lead to failure of structures and wastage of money.

If you have a query, you can ask a question here.