Difference between hollow concrete blocks and fly ash bricks

Introduction

Masonry remains a cornerstone of construction. While traditional clay bricks have been used historically, they present environmental concerns, including agricultural land depletion and carbon dioxide emissions during production. Modern alternatives like fly ash bricks and hollow concrete blocks offer more sustainable options for contemporary building projects.

Hollow concrete blocks

According to Indian Standard IS 2185 (Part 1) 2005, hollow concrete blocks contain one or more large cavities, with solid material comprising 50-75% of total volume. Raw materials include cement, aggregates, sand, gravel, water and industrial waste products like fly ash or bottom ash.

Fly ash bricks

These environmentally friendly units are entirely solid with no cavities. Manufacturing uses fly ash or pulverised fuel ash combined with cement, sand, lime and gypsum.

Applications

Hollow blocks are used in exterior and interior load bearing walls, partition walls, fireproofing and retaining structures.

Fly ash bricks suit load bearing and non load bearing applications, including factories, warehouses, power plants, high rise structures and infrastructure projects.

Key advantages

Hollow concrete blocks:

• High durability with reduced weight and dead load

• Faster masonry installation

• Good sound insulation and earthquake resistance

• Steel reinforcement capability

• Lower water consumption

Fly ash bricks:

• Recycle thermal power plant waste

• Good fire insulation properties

• Uniform sizing requires less mortar

• Strong and durable, with minimal breakage during transport

Notable disadvantages

Hollow blocks: Poor thermal insulation, higher costs, limited lintel and sill sizes.

Fly ash bricks: Lower mechanical strength, heavy weight, limited size options, steel reinforcement not feasible.

Technical properties comparison

• Dry density: hollow blocks 1,100-1,500 kg/m3; fly ash bricks 1,700-2,000 kg/m3

• Compressive strength: hollow blocks 3.5-15 N/mm2; fly ash bricks 3.5-35 N/mm2

• Water absorption: hollow blocks up to 10%; fly ash bricks 15-20%

• Thermal conductivity: hollow blocks 0.12-0.17 W/mK; fly ash bricks 0.3-0.4 W/mK

Cost considerations

Hollow blocks cost more individually but consume less mortar, reducing overall masonry costs. Fly ash bricks carry lower unit prices but require significantly more mortar, increasing total expenses.

Environmental impact

Both materials utilise industrial waste, making them environmentally responsible choices with minimal carbon dioxide emissions compared to traditional clay brick manufacturing.