Bricks are the building blocks of most modern buildings. But with the increasing price tag of building material and the high environmental implications caused by these materials, constructors have slowly moved towards more innovative solutions. Compressed Earth Bricks or CEBs are a better solution for the basic unit of a building, the brick.
Most of us have some idea of conventional bricks in use. Regular or large-sized mud bricks are also called Clay Bricks ( Gadol ) molded from clay and burnt while cement blocks are made using a cement aggregate. Mud bricks have existed almost as long as human civilization with the use of dried mud bricks seen as early as 6000-7000 B.C. in ancient Mesopotamian and Indus-valley civilizations. The technology in producing these blocks have barely evolved since these early days of building.
The process of producing both the mud brick and cement block has many environmental implications. These include the damage done to the environment in extracting the required base materials and the high energy cost caused by the firing process in mud bricks. In addition to these issues, these conventional bricks are relatively lower in strength and have lower insulation against heat. These bricks, especially the cement block is not aesthetically pleasing and therefore requires higher additional costs in plastering and finishing tasks.
The CEB is one such solution to these issues. A CEB is simply a brick produced by compressing earth or damp soil into a mold at high pressures. In addition to soil, cement is added (earlier times lime was also used) as stabilizers to improve the properties of the brick. CEBs can be seen in use in many countries worldwide since its inception in the 1950s. CEBs are common in Latin American and African countries and countries like India and Australia as well. Let’s try to understand the production process in the next section.
How are CEBs produced?
Characteristics of CEBs should comply with the standard SLS 1382:2009 when producing a brick.. The production of CEBs can be summarized into three main steps; preparation, compression and curing
- Preparation: The soil mixture used to produce the bricks is prepared. A typical mixture is made with a bulk of clay-retaining soil (Clay and Silt Content should be limited to 35%) which is widely available everywhere. This is typically underneath the fertile soil layer of the earth. Depending on the condition of the soil a required amount of stabilizer is added. This stabilizer is usually either cement or lime. Bricks with stabilizers are also called Compressed Stabilized Earth Bricks (CSEB). The stabilizers are usually kept under 10% of the total amount of soil. The mixture should be consistent and also should have considerable moisture content.
- Compression: The mixture is then transferred into a mold of the required shape and compressed under high pressures using hydraulic presses. A compaction ratio of 1.5 or above is required for high strength bricks.
- Curing: The bricks are allowed to cure for about 4 weeks in a humid room to complete the reaction of the stabilizers and strengthen the brick. Humidity should be above 70%. Producers may apply a wet gunny or a polythene tarp on the bricks to prevent rapid drying of the bricks during curing.
As seen, CEBs do not require firing as seen in conventional mud bricks. This reduces the energy used either as fossil fuels or biomass. This reduces the cost and the environmental effect caused by the production.
The material used can be easily obtained locally. Earth can be obtained from excavation sites such as from other construction projects reducing the requirement of clayey soil used in mud bricks or excessive gravel and cement used in cement block.
The mold used to produce the bricks can be designed to be interlocking to help in the laying of the brick when used in constructions.
The bricks can be produced using mechanized or manual presses. Hence the production is viable in both high and low developed countries as can be seen in specific examples of production in India. Hence CEBs are a viable option in Sri Lanka as well.
How does CEBs stack up against other blocks?
As seen in the above sections there are several comparisons that can be deduced between the different brick types. CEBs tend to be more environmentally friendly and energy efficient than typical bricks. A CEB releases about 12 times less Carbon dioxide during production when compared to mud bricks. In addition, CEBs can be sourced from material available locally.
Due to the ability to produce as interlocking bricks these bricks require a lower amount of sand and cement for mortar. Specially designed bricks can be used to easily allow for electrical and water lines within the walls.
CEBs also have a higher strength than conventional mud bricks and cement blocks and therefore will resist to failure. Due to the use of biodegradable material once the building is demolished at the end of its lifetime the bricks will easily be incorporated back into the environment rather than cement blocks.
Due to the use of earth as the base material, buildings built with CEBs will have a higher cooling effect (Drop of inside building peak temperature about 2-3 Celcius), leading to a favourable atmosphere within the building. In the long run, it reduces the operational cost of the building by reducing the need for Air Conditioning and Fans. The CEBs also do not require plaster due to its inherent appearance.
But due it being a considerably novel technology there are several drawbacks that may overcome with time.
- Knowledge of earth bricks is less in Sri Lankan construction community. Hence most Masons are not willing to adapt to this brick. Yet due to interlocking surface and smooth finish, these bricks can be easily used without much skill.
- Service line of the wall should be planned properly, since cutting groves after the construction of the wall may reduce the strength. The core inside the brick can be used for the service line of the building.
- Larger blocks tend to have a lower strength. If the soil is not properly prepared or tested for the composition the bricks tend to be of a lower quality.
|Type of Brick||Strength of a Brick per Area Nm/mm||Moisture Absorption||Heat Absorption||Construction Speed for 10ft*10ft||ECO Friendly||Living Comfort|
|Regular Mud Brick||1.2||High||High||4 Days||X||Average|
|large Size Mud Brick||1.4||High||High||4 Days||X||Average|
|Cement Brick||2||High||Very High||3 Days||X||Very Bad|
|CEBs||5+||Minimum||Minimum||2 Days||√||Very Good|
How cost-effective is a CEB?
At the end of the day for a laymen or constructor the important factor in deciding the material to use is the cost. Currently in the local market CEBs tend to have a higher price per unit due to being larger in size than common bricks and due to the lack of producers but is bound to reduce once the monopoly diminishes.
But the construction cost reduces considerably when factoring in the reduce of labor, time and other material used in construction.
Therefore, when comparing these values an estimate can be drawn up for the construction of a 1 sq. ft. of wall as follows.
|Type of Brick||Cost per 1 sq.ft. of wall (LKR)|
|Regular Mud Brick||442|
|Large Size Mud Brick||456|
Therefore, this comparison shows that despite a high unit cost CEBs have a lower cost overall when building. This cost is bound to reduce further with more competitors entering the market to produce CEBs
So, is CEBs for me?
If you are looking for a cost effective, eco-friendly building material to build your home or building CEBs are a promising choice. The requirement of minimum post processing and improved internal atmosphere are advantages that come with this choice. Just make sure the producer of the brick has high quality standards.
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