Structural Brick: Getting Technical

Structural Brick: Getting Technical

Words: MASONRY Magazine
Photos: Lex20

MASONRY Magazine had the chance to ask two industry professionals their thoughts on a wide range of topics related to structural brick. Chris Steppins from Phoenix Masonry, Inc. and Steven Judd, Technical Director at Interstate Brick. We would like to thank Chris and Steven for providing us with all of this great information! Be sure to sign up for our upcoming Structural Brick webinars on July 8 and August 5. For more information visit www.masoncontractors.org/live

How Structural Brick Is Made

First, Chris Steppins and Steven Judd provided us with an idea of how bricks are made.

1. Extracting the raw materials, principally clay and shale, from the ground in pits or quarries reasonably close to the manufacturing facility. 

2. The raw material is stockpiled either at the quarry or at the manufacturing facility until needed.  

3. The clay or shale is mixed with material from other quarries or pits to attain the desired product color and then the raw material is crushed and ground to a small particle size and conveyed to a holding facility – tanks or reclaimers. 

4. The mixed and ground clay is transported via conveyor belt, passing under dispersers that add mineral colorants and binders to the mix, on the way to the pug mill where the materials are mixed with water in preparation for the extrusion. 

5. Once fully mixed in the pug mill the material passes through a vacuum chamber to remove all the air (which eliminates bubbles in the extruded material), and then the moist clay is pressed through a die cap, or mold, to achieve the proper green clay size and profile. 

6. Once extruded, the continuous column of clay is cut to approximately 6-foot lengths and then passed through a lift or reel cutter to create the correct individual unit height.  

7. After cutting, the large format units are placed on trays and placed in a dryer to control the rate of evaporation of the moisture in the clay. 

8. Once sufficiently dried, the green bricks are stacked on steel-wheeled kiln cars and cycled through a linear kiln, that is more than 500 feet long, which heats the brick to temperatures to between 1950 OF and about 2100 OF. The firing process can take several days. 

9. Once fired the product leaves the kiln at around 250 OF and is then set aside to rest and cool to ambient temperatures before it is removed from the kiln cars and packaged for storage or shipping.

We found a great video from Interstate Brick Co. illustrating the brick making process  https://youtu.be/jWEGQR-8dEo All the bricks produced are made of local clay from mountains in Utah and Wyoming, giving a wide variety of color to select for projects. 

Advantages:

It is fire-resistant, weather-resistant, attractive, and adds to the value of a building. Structural brick provides a unique look and gives a building permanence and beauty. It is also more energy-efficient and more sound-resistant than buildings using other forms of construction. The use of structural brick also provides high resistance to wind and seismic activity. Brick buildings ultimately result in lower maintenance and insurance costs.

Brick is a very durable material that can withstand the ravages of man and nature and require very little if any, maintenance. Brick has low permeability and resists moisture intrusion better than other materials with the exception of some natural stones. Structural brick can be used to reduce wall thicknesses by eliminating the need for a back-up wall system designed to receive a brick veneer covering by providing a single wythe solution. 

Structural brick is highly fire-resistant – it doesn’t burn, it helps reduce energy use by nature of the mass wall effect, it can be designed to resist blast pressures, it can also be designed to resist extremely high wind pressures from hurricanes and tornadoes and impacts from wind-blown debris and even impacts from munitions.

Natural Disasters

Structural brick can withstand very high winds and extreme weather much better than its counterparts. There is evidence that structural brick withstands earthquakes very well. Reinforcing the brick with rebar and grout is key and sets structural brick apart from unreinforced masonry. 

A large earthquake may cause the structural brick to crack, but complete failure is much less likely than in wood-framed buildings. It can also withstand fire and heat very well. Masonry is often used when constructing storm shelters and other types of immediate occupancy emergency response facilities for these very reasons.

Structural brick is one of the most durable and resilient materials to consider for resisting the effects of earthquakes, hurricanes, tornadoes, tidal surges, and tsunamis. Reinforced structural brick has properties very much like reinforced concrete but provides the aesthetics of brick.  

There are many examples of structural brick facilities that have weathered hurricanes around the Gulf Coast and the Southeast US. The Seven Springs Elementary School in New Port Richey, FL, a structural brick school, has seen many hurricanes. The Bloomington Gym and Community Storm Shelter performed admirably during hurricane Harvey in Bloomington, TX.  The Galveston Maritime Museum survived hurricanes, Ike and Harvey.  East Beach Community Building, Galveston, TX, survived hurricane Harvey. Many Quiktrip convenience stores in the Southeast US, that have been built with structural brick, have survived several hurricanes. 

The Los Angeles Police Department’s Devonshire Station is a reinforced structural brick facility that survived the 6.7 magnitude 1994 Northridge California Earthquake intact and was reportedly used as an emergency service coordination center immediately after the earthquake. The facility is located 3 miles from the epicenter of that event.

Over the span of a few years, two different multi-family, multi-story apartment buildings caught fire in Winnipeg, Manitoba. In the first case, the building was a typical multi-level wood-framed facility. The fire started in one unit and spread to all the units, displacing around a dozen families. In the second case, the multi-story apartment facility was constructed of structural brick and the fire was contained in one unit, displacing only one tenant. Buildings have a distinct advantage in consideration of accidental fires and wildfires.

Structural brick assemblies typically have higher design strengths than regular structural concrete masonry assemblies, so the facilities built with structural brick tend to be more robust.  Consider providing more than the minimum required structural wall lengths which will add redundancy and excess capacity to facilities. Keep in mind the code provides minimum performance criteria for a reasonably probable event, not for every possible event, so overstrength and redundancy are key factors for a long-lasting, durable, and resilient facility.

Disadvantages:

As with most things, there are some disadvantages to structural brick. The biggest is usually the initial cost, but that can quickly be made up of energy efficiency and the very low maintenance cost throughout a building’s life cycle, Steppin stated. We cover this in more detail in the next section.

When construction is based solely on first cost, then structural masonry is often pushed farther down the material selection list. When facilities want a different look than brick then structural masonry is also pushed farther down the material selection list. When maintenance is not a critical factor (build it and sell it) then structural masonry gets pushed down the material selection list. If the project schedule does not allow time for special shapes or special colors that are not in stock, then choices tend to move away from brick. If a design theme is developed using materials other than brick, based on the preference of the owner or designer, then brick has no foothold in the design.

Lead time can also be a concern, but with advanced planning, one can eliminate another one of the main disadvantages for structural brick, which is production time, especially where special shapes are required. From start (grinding clay material) to finish (packaging after being fired), it can take several weeks to run a large batch of structural brick, compared to several days for concrete masonry units, Judd explained. 

Cost-effective?

Structural brick can be very cost-effective, especially if you are going for longevity. Low maintenance costs and high energy efficiency make structural brick very cost-effective in the long run. The materials might cost a little more initially to build with structural brick, but the percentage of increased cost at first is minimal compared to the money saved over time.

In as little as five to seven years, the lower maintenance cost of brick can more than make up the difference in initial cost, Judd pointed out. For example, some school districts in Utah that use a significant amount of structural brick due to the ROI in maintenance costs.

Resilience

Essential facilities, hospitals, schools, fire stations, police stations, libraries, emergency generator enclosures, tornado and hurricane shelters, residential buildings, houses, garages, and any other building you want to be secure and withstand time and natural elements are often built with structural brick.

But just about any type of facility can be built with structural brick, depending on the aesthetics one has in mind.  Structural brick has been used on multi-family residences, schools, hotels, medical facilities, courthouses, fire stations, convenience stores, sports facilities, storm shelters, office buildings, and many more. The reason for using it is the permanence and beauty of clay masonry combined with its high strength and lasting value.

Stronger

Both of our experts agreed that it was difficult to say how much stronger a structural brick building is compared to a CMU building, but one data point: the compressive strength of clay units is up to 12,000 psi while the compressive strength of a CMU unit is up to 4,000 psi.

Many different factors must be considered in comparing structural brick to other materials but if one were to take a typical well-designed and well-constructed building of typical concrete masonry units and swapped typical structural brick units for the concrete masonry units, and if the reinforcing, and mortar were the same and if the grout were proportioned to match the masonry unit strength (as required by code), and if the workmanship was equivalent, then the structural brick facility would have higher strength and would generally be able to resist higher applied loads than the concrete masonry building.  

So, in general, that probably means, given the parameters of this exercise, one would be safer in the structural brick building for any given event.  The design strength of the structural brick wall systems would be something like 25% to 67% higher than the concrete masonry assemblies depending on whether the axial load capacity, the bending moment capacity, or the shear load capacity were being evaluated. Some aspects of design and resistance, like overturning stability, or sliding, or foundation issues would not change from one material to another. 

Other uses:

Site walls, retaining walls, privacy walls, sound barrier walls, guard stations, courtyards, reinforced screen walls, property signage, and prefabricated structural brick panels.

Structural brick can be used in any application that requires reinforced masonry. It makes a great material for any building with the intent of a long building lifecycle. The resilient nature of structural brick starts in its manufacturing. The temperature that the bricks are fired at alone makes them a very strong and durable product. The minerals that are added mostly for color also result in a more resilient product. This, along with the bricks being reinforced and tied together with rebar and grout makes for a resilient wall system that can withstand extreme winds, heat, seismic activity, and even ballistic projectiles. Structural brick is a good choice if you are designing for resilience.

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