Concrete and clay brick are two widely used construction materials with a long history. Bricks have been made and used in the Middle East since at least 4000 BCE (Simmons 149). Concrete, a comparatively newer material, was first developed by the Romans in the 1st Century BCE (Simmons 67). Both saw incredible technical improvements in the 19th and 20th centuries such as the introduction of steel reinforcement and the formulation of high strength cements and mortar. Brick and concrete continue to be used throughout the world. Because they are suitable for many of the same applications, engineers and architects need to be knowledgeable about their respective strengths.
One of the most important attributes of a material is its overall environmental impact. Concrete and brick each consume large amounts of energy and potable water during their manufacture. More energy and water is needed at construction time, as is wood. The amounts of these resources differ in scale, however.
The energy required to convert limestone into cement is many times higher than that required to fire clay into brick. In most cases the electricity is generated by processes which release carbon dioxide (the most significant green house gas) into the air. By many estimates, the concrete industry currently produces around five percent of the worlds carbon dioxide emissions (“Cement Makers Heed Environmental Concerns”).
Concrete also consumes much more water. Water is used to process the raw limestone. It is mixed with cement and aggregate to form concrete. It is also used to wash out trucks and to keep concrete slabs moist while they are are curing. In most cases, only fresh, drinkable water is suitable. There is an old adage in the building trade: “Don’t put water in your concrete unless it’s safe to drink.” Of course brick also requires water, but the amounts are far smaller than those for concrete. Its main use during production is to moisten the clay so it can be molded more easily. Some water is also used to make the mortar to hold the brick together. The volume of mortar in a brick wall is much smaller than that of concrete in a concrete wall. Mortars are also mixed with a smaller percentage of water than concretes because they are meant to be scooped with a trowel rather than poured or pumped into forms.
Another resource, consumed at construction time, is wood. Both materials use wood to build “centering”, which is a secondary structure that holds up arches, lintels, and floors until they have cured enough to support their own weight. After removal, this wood is often retrieved and used on other jobs. For concrete, however, wood is also used to build forms. Every column, wall, and slab is formed from plywood with timber bracing. Wooden forms degrade rapidly and can only be used a few times. After the cement soaks in they are useless. They will not even burn as firewood. Generally, they go straight to the landfill. Reusable metal forms are becoming more popular, but they are really only useful for standardized shapes. Special and “one-off” structures are still formed with wood.
Brick and concrete structures can both last for hundreds of years with proper maintenance. At some point, however, they will all become functionally obsolete and need to be demolished. Recycling programs are common practice throughout the construction industry. In the case of bricks (or any masonry), recycling is easy and requires little technology. Bricks are simply pulled off the building, hosed off, and sold for use in a new project. “Quarrying” old masonry structures for their bricks or blocks is a practice that goes back thousands of years. Many medieval and renaissance structures contain bricks and stones which were originally removed from Roman buildings. Damaged bricks can be crushed and recycled. They can even be safely buried since their principle materials, clay and shale, are completely inert and are already among the most common components of the Earth’s soils (“Building Green” 34).
Concrete is much harder to recycle. Removing the reinforcing steel and coarse aggregate (i.e. large rocks) from old concrete requires specialized heavy equipment and is an expensive and aggravating process at best. Once the concrete is isolated it is of dubious value. The best use for it that the concrete industry has yet discovered is to crush it into gravel-sized particles called “base”. This base can be spread under roads and concrete slabs to aid drainage. Unfortunately, the specifications for many government and private jobs explicitly forbid the use of crushed concrete base. Thus, the demand is currently quite small in relation to the supply.
Concrete consumes the greatest quantity of nonrenewable materials of any construction material (Simmons 66). Its terrible environmental impact is offset only by its longevity. Brick, also a long lasting material, is one of the most sustainable of building materials. Obviously, brick is a superior choice in many instances. In some cases, however, brick simply can not do the things that concrete can.
Reinforced concrete can be cantilevered. It can be used to make flat floor and roof slabs without the supporting vaults or arches which brick requires. Even the ubiquitous concrete parking structure would simply not work if designed with brick. Concrete bridges have reached spans which are surpassed only by structural steel. In contrast, brick buildings are generally limited by code to three or four stories. No large brick bridges have been built for centuries because the span between columns is severely limited.
Brick structural elements could never be made thin enough for the the sweeping roof lines and graceful thin-shell structures of post modern architecture. Nor does any masonry have the tensile strength that such designs require. Even utilitarian buildings like warehouses and factories often have tall, thin walls that would require buttresses or other supports if they were made from brick masonry. On the other hand, previous generations found brick to be quite adequate for everything from cathedrals to warehouses. Concrete became popular among architects mainly because of its low cost. Today the industry realizes that the “in place” cost of a material can be a small portion of its total “cradle-to-cradle” cost, which includes such items as damage to the environment, expenditure of resources, and cost to dispose of the material. When subjected to more modern cost analysis, concrete does not seem cheap at all.
Brick is a traditional, versatile, green material. Sustainable brick should always be chosen over unsustainable concrete when possible. Concrete is only preferable in highly engineered designs which require its greater strength. In such instances the design itself might well be questioned. In some cases, a simpler brick structure might serve as well, without the heavy resource cost.
“Building Green.” Ceramic Industry. 158.8 (2008): 34-35. Master File Premier. EBSCOHost. Orange County Library., La Habra, CA. 10 February 2009. .
“Cement Makers Heed Environmental Concerns.” Builders’ Merchants’ Journal. Oct. 2006: 38. Master File Premier. EBSCOHost. Orange County Library., La Habra, CA. 10 February 2009. .
Simmons, Leslie. Olin’s Construction Principles, Materials, and Methods. 8th ed. Hoboken: John Wiley & Sons. 2007.