Things you need to know before using concrete blocks as a building material

Introduction

Throughout history, humans have constructed various types of shelter to meet their needs. As civilisations developed, construction methods evolved from natural caves to purposefully designed structures. Buildings comprise multiple essential components, including foundations, stairs, walls, floors and roofs, each contributing to structural safety and integrity.

Traditional construction relied on red bricks, stones, mortar and wood. However, concrete has become extensively used for durable building projects. Common masonry units include clay bricks, natural stones, concrete blocks and fly ash bricks.

Definition of concrete block

A concrete block is a building block made totally of concrete, which is then bonded together with mortar to form a long lasting structure. These buildings utilise either hollow or solid blocks in varying sizes based on project requirements.

Types of concrete blocks

Hollow concrete blocks. More commonly used than solid variants, hollow blocks offer several advantages.

• Lighter weight and easier to handle

• Can be grouted and reinforced for complex structural needs

• Contain 50 to 70% solid material by volume

• Feature a single cavity or multiple large cavities

Hollow blocks divide into Grade A and Grade B categories. Grade B blocks, sometimes called cinder blocks, contain cinder in their material composition. Modern hollow blocks come in various shapes, including corner blocks, jamb blocks, bullnose blocks, stretcher blocks, partition blocks, frogged brick blocks and lintel blocks.

Solid concrete blocks. These blocks contain over 75% concrete fill by mass. They are increasingly rare due to their added weight and are reserved for special requirements, such as enhanced fire resistance.

Advantages of concrete blocks

• Expand usable interior space through reduced wall thickness compared to brick masonry

• Provide noise pollution protection by absorbing sound

• Offer fire resistance and good thermal insulation

• Enable faster, stronger construction than traditional brick masonry

• Preserve agricultural land otherwise excavated for clay brick production

• Allow custom sizing and shapes, reducing mortar consumption while increasing structural integrity

• Require less plaster than standard brick alternatives, making them cost effective

Solid block benefits: relatively easier to design, and highly resistant to severe weather such as storms, high winds and floods.

Hollow block benefits: require no additional formwork for reinforcement, and are manageable by fresher or semi-skilled labour.

Disadvantages of concrete blocks

• Become costly when essential raw materials lack convenient availability

• Require experienced, skilled labour for rapid, stable production

Solid block drawback: difficult to conceal wiring and plumbing.

Hollow block drawback: risky during earthquakes without internal reinforcement structures.

Applications and uses

Building walls. Concrete blocks enable fast partition wall installation. Steel reinforcement adds extra strength. Solid blocks suit fireplaces and chimneys, plus non load bearing and garden walls. Hollow blocks work extensively for load bearing walls, boundary walls, panel walls and partitions.

Material bins. Blocks protect stored materials from varying climatic conditions, making them ideal for material bin formation. Manufacturing companies use them to reserve materials long term, such as rock and aggregate.

Landscape projects. Applications include flower beds, outdoor bars, outdoor seating, decorative screens, patios and outdoor furniture.

Properties of concrete blocks

Blocks are referenced by nominal dimensions, including mortar joint thickness. Actual dimensions run approximately 10 mm shorter than nominal measurements. Per Indian Standard Code 2185:

• Length: 400, 500 or 600 mm

• Width: 50, 75, 100, 150, 200, 250 or 300 mm

• Height: 100 or 200 mm

Density: solid blocks, minimum 1,800 kg/m3; hollow Grade A, minimum 1,500 kg/m3; hollow Grade B, 1,100 to 1,500 kg/m3.

Compressive strength (minimum average at 28 days): solid blocks, 4.0 to 5.0 N/mm2; hollow Grade A, 3.5 to 15.0 N/mm2; hollow Grade B, 3.5 to 5.0 N/mm2.

Water absorption should not exceed 10% by mass.

Drying shrinkage should remain below 0.06%.

Moisture movement is typically less than 0.09% due to repeated swelling and shrinkage cycles.

Raw materials

Cement: Portland cement, Portland slag cement or Portland pozzolana cement conforming to the respective standard codes.

Aggregate: various types including cinder, clinker, gravel and crushed stones. Quality depends on careful grading per Indian Standard Code 383.

Water: potable water is essential during production.

Additives and admixtures: water reducers, accelerators, air entraining agents and superplasticisers per Indian Standard Code 9103, plus waterproofing agents per Indian Standard Code 2645.

Manufacturing process

• Proportioning: materials are measured according to Indian Standard Code 2185 or strength requirements

• Mixing: exact batching and thorough mixing for a homogeneous consistency

• Compacting: vibro compaction to proper size without broken edges

• Curing: blocks are kept repeatedly moist in water tanks or curing yards for at least 14 days, with tank water changed every 4 days at minimum

• Drying: after curing, blocks dry for 2 to 3 weeks before use; skipping this step risks shrinkage cracks

Production methods

Fully automatic plants produce high strength blocks with superior quality but require significant capital investment. Manually operated machines offer alternatives and can be installed at project sites, reducing transportation costs.

Conclusion

Architects, owners and engineers selecting masonry units should consider dimensional stability, thermal properties, rain penetration resistance, fire rating, availability, strength requirements, durability, architectural style and cost economics.

Concrete blocks have gained widespread use throughout the country due to their fire resistance, insulation properties, durability, strength, structural stability and sound absorption capabilities. They prove particularly suitable where quality brick or stone masonry materials lack availability at reasonable costs. With proper aggregate variety selection, these blocks work effectively for load bearing or non load bearing walls, partitions and panel walls.