Facts About Concrete and Clay Brick
- Concrete bricks are made with a combination of sand, aggregate and cement. The primary aggregate is typically limestone.
- Clay bricks are made with surface clays, shales, and fire clays.
- In both cases, the raw materials for clay and concrete brick are mined, ground to specifications and mixed with water.
- Concrete bricks are typically formed in molds using hydraulic pressure while clay bricks are typically extruded through a die.
- Concrete bricks are cured through a chemical reaction between the water and cement. This process is accelerated through the use of kilns that have a high relative humidity and a temperature of around 150 degrees.
- Clay bricks are typically cured by a process called vitrification. Vitrification of the clay occurs in a kiln at temperatures reaching upwards of 2,000 degrees.
- Both concrete and clay bricks are manufactured to meet a series of ASTM specifications that set the minimum design characteristics of each product.
- Concrete bricks will initially shrink after manufacturing due to the loss of moisture.
With no voids in the brick, Bilco bricks use about 30% less mortar and sand. Which can be a significant savings.
Clay bricks will typically expand after manufacturing due to the addition of moisture. Most of this expansion occurs during the first few weeks, but will continue at a much slower rate for several years. This expansion of clay bricks is not reversible.
- Both concrete and clay bricks experience expansion and contraction due to heat gain and loss.
- Clay bricks typically have core holes while concrete bricks are usually frogged. Cores and frogs are designed to reduce weight and aid in the drying and firing process.
- A concrete brick typically weighs more than a clay brick due to its higher density.
- The higher density of concrete brick is correlated to fewer air pockets and consequently to a lower water absorption rate.
- Concrete bricks will typically have a higher compressive strength than clay bricks.
- Although concrete bricks have a higher density than clay bricks, there is virtually no difference in the R value of clay and concrete bricks.
- A typical exterior brick veneer wall is designed to have a void space between the back of the brick and exterior wall sheathing. This void acts as a barrier to keep moisture formed on the back of the brick wall unit from being transferred to the exterior wall sheathing. This void is also an active air space allowing for moisture to escape through weep holes placed at the bottom of the flashing. Because of this design the exterior brick veneer adds very little additional insulating value to the overall exterior wall system.
The effect of concrete brick on slab design:
- Due to its higher density and strength, a concrete brick will generally weigh more than a similar sized clay brick.
- A typical foundation is designed for a perimeter wall loading of from 700 to 1,200 pounds per lineal foot. Any additional weight added by concrete brick falls within the normal design parameters and will not have a negative effect on the performance of the foundation.
- One of the more desirable properties of concrete bricks is its strength. Unlike clay bricks, concrete bricks continue to gain strength over time.
- The high strength of concrete bricks is important when resisting the forces of nature.
- Although the ASTM (American Society for Testing and Materials) specifications for manufacturing clay brick (C216) and concrete brick (C1634) are similar in scope, the requirements for concrete bricks are more stringent in several important areas.
- Compared to clay bricks, concrete bricks are required to have a higher compressive strength and a lower water absorption rate and are also required to have tighter dimensional tolerances as well as smaller allowances for chippage.