Concrete Blocks – Key Vocabulary

Vocabulary flashcards covering definitions, classifications, advantages, disadvantages, manufacturing details, and tests related to concrete blocks.

Concrete Block

A masonry unit, often larger than a brick, made of a cement-aggregate mix and used for load-bearing or partition walls.

Solid Concrete Block

A block whose net cross-sectional area is 75 % or more of its gross cross-sectional area.

Hollow Concrete Block

A block whose net cross-sectional area in any plane parallel to the bearing surface is less than 75 % of the gross area; lighter and better insulating than solid blocks.

Cellular (Lightweight) Block

A concrete block manufactured with light aggregates, containing air cells to reduce weight and improve thermal resistance.

Concrete Masonry Unit (CMU) Density Classes

Lightweight (< 1680 kg/m³), Medium-weight (1680–2000 kg/m³), and Normal-weight (≥ 2000 kg/m³) blocks, classified by dry unit mass.

Lightweight Aggregate

Materials like pumice, scoria, cinders, expanded clay or shale used to produce lightweight concrete blocks with improved thermal and fire resistance.

Maximum Water Absorption – Lightweight CMU

288 kg/m³ (average of three units).

Maximum Water Absorption – Medium-weight CMU

240 kg/m³ (average of three units).

Maximum Water Absorption – Normal-weight CMU

208 kg/m³ (average of three units).

Size Advantage of Blocks

One 400 × 200 × 200 mm block replaces about eight standard bricks, reducing mortar use and speeding construction.

Dead-Load Reduction

Using hollow blocks lowers the weight on beams and foundations, benefitting structural design.

Cost Advantage of Blocks

Concrete blocks are generally cheaper than equivalent brickwork on an overall project basis.

Shrinkage in Blocks

Volume change caused by moisture movement; more pronounced than in brickwork and can lead to cracking.

Mortar Strength Guideline

Mortar for blockwork should be weaker or equal to block strength to produce many small cracks rather than a few large ones.

Curing Requirement for Blocks

Blocks must be cured at least 14 days and dried for about 2 weeks before use to minimize initial shrinkage.

Lateral-Load Weakness

Unreinforced block walls resist lateral forces (e.g., earthquakes, roof expansion, cyclones) poorly unless reinforcement is added.

Typical Block Mix Ratio

Concrete mix not richer than 1 : 6 (cement : combined aggregate by volume); lean mixes up to 1 : 8 commonly used.

Aggregate Grading for Blocks

Recommended 60 % fine aggregate and 40 % coarse aggregate, with coarse particles 6–12 mm in size.

Appearance Test (Blocks)

Blocks must be free of cracks and visible defects before acceptance.

Compressive Strength Test (Blocks)

Three randomly selected blocks are crushed to determine average load-bearing capacity.

Dimensional Tolerance (Blocks)

Length ±3 mm or ±5 mm, and height/width ±3 mm from specified size.

Water Absorption Test (Blocks)

Determines the mass of water a block absorbs; must not exceed class-specific limits.

Dry Shrinkage Test (Blocks)

Measures linear shrinkage after drying to assess potential cracking risk.

Soundness Test (Blocks)

Checks for interior flaws using a tapping or resonance method to ensure structural integrity.