There are a variety of concrete blocks available commercially which range from dense blocks to lightweight with distinct properties such as sound and thermal insulation properties, load-bearing capacities, etc. Different types of concrete blocks are suitable for varied functions. For example,fair-faced blocks are selected where visual appearance is necessary.

Concrete blockwork weathers well when used externally compared to traditional brickwork, however, requires careful attention to the quality of the material and rainwater run-off details. Lightweight blocks have the advantage of speedy construction over traditional brickwork.

Types of concrete blocks

Concrete blocks can have either dense or lightweight aggregates. The main types of concrete blocks are

• Solid
• Cellular
• Hollow

Description of blocks includes standard number and date, type of unit, work size dimensions, tolerance limits, configuration, compressive strength, surface finish, Dry density, coordinating size, thermal properties, moisture movement, etc.

Fair faced blocks

Fair-faced blocks enhance visual qualities. They are available in a wide range of colors ranging from light to dark; whites, sandstone, yellow, pink, blue, green, etc. Textures range from polished, smooth, and weathered to striated and split faces.

Glazed Masonry units

They are produced by applying thermosetting material to one of the faces of concrete blocks, which are then heat-treated to cure the finish. Used both internally and externally.

Clay Blocks

• Fired-clay Blocks
  • Masonry clay honeycomb-insulating blocks are sometimes used as a single skin for external load-bearing construction as an alternative to standard cavity construction.These combine structural strength,insulation,and moisture protection for external surfaces.Internal surfaced are finshed with Gypsum plaster.
• Unfired-clay Blocks
  • Used for non-load bearing partition walls sometimes they are mixed with straw.They are recyclable biodegradable.Helps in stabilizing internal humidity and temperature by their natural absorption and release of moisture and heat.

Gypsum Blocks

The thickness of gypsum blocks ranges from 50-100mm. They are classified by density and water absorption. Gypsum blocks may be used as non-load-bearing partitions and internal insulation of walls.

• Density
  • Low density
  • Medium density
  • High density
• Water absorption
  • H3,H2,H1

Manufacture of concrete blocks

Dense concrete blocks are manufactured from natural dense aggregates including crushed granite, limestone, and gravel. Medium and lightweight concrete blocks are manufactured from expanded clay, expanded blast furnace slag, sintered ash, and pumice.

Concrete is cast into molds, vibrated, and cured.

Aerated blocks (autoclaved aerated concrete) are formed by mixing the aluminum powder with sand, lime,fly-ash, and portland cement.

Properties

Density and strength

The majority of concrete blocks fall in the range from 2.8 to 30 MPa, with associated densities of 420–2200 kg/m3 as per The British Standard BS 6073-2: 2008.

Durability

Dense concrete blocks and certain aerated lightweight blocks are resistant to freeze/thaw conditions below
damp-proof course (DPC) level.

Fixability

These blocks offer a good background for fixings. Nails are used for light loads and wall plugs and fixings are used for heavier loads.

Thermal Insulation

Buildings require U-values within the range of 0.27–0.30 W/m2 K as per The Building Regulation Approved Document Part L.Solid walls with high-performance lightweight blocks, Cavity walls with partially/fully filled insulation achieve these values.

Fire resistance

Concrete block construction offers good fire resistance. Fire protection can vary from 60min-360min fire protection depending on the type of concrete block.

Sound Insulation and sound absorption

The Building Regulations 2000 Approved Document E (2003) regulations require minimum airborne sound insulation of 45Rw dB for separating walls and 40Rw dB for internal bedroom or WC walls. The passage of sound depends on the density and porosity of a material.

Concrete blocks are highly reflective to sound. Acoustic absorbing concrete blocks are manufactured with a slot on the exposed face that admits sound into the central cavity.

Concrete Blockwork

Fair-faced concrete blockwork is mostly used for external purposes to enhance its visual appearance. Curved blockwork is constructed depending upon the design with the use of standard blockwork, radius varies with block size.

Thin joint blockwork may be constructed with mortar joints of 2-3mm. The special rapid-setting mortar sets typically within 60 minutes and the full bond strength is achieved after only 2 hours, allowing more courses to be laid each day.

• Advantages of thin-joint masonry
  • increased productivity
  • up to 10% improved thermal performance due to reduced thermal bridging by the mortar
  • improved airtightness of the construction
  • the accuracy of the wall, which allows internal thincoat sprayed plaster finishes to be used
  • higher quality of construction and less wastage of mortar.

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