Concrete Block Blast Wall Specifications

Reinforcement

• Due to the brittle nature of concrete, a traditional, non-reinforced concrete block wall is highly susceptible to shattering following a nearby explosion. In addition to disrupting the structural stability of the building it is a part of, a shattering concrete block wall can discharge hazardous -- and potentially lethal – flying debris. To increase the blast-resistance of a concrete block wall, the National Concrete Masonry Association recommends fully grouting the wall, or applying mortar to all of the spaces between the wall’s successive concrete blocks. This process serves to strengthen the wall. Furthermore, the association recommends that builders use both vertical and horizontal steel reinforcing bars in a concrete block blast wall’s construction. While the vertical reinforcing bars fit in the voids of the blocks, the horizontal bars fit between each layer.

Block Types

• Like a traditional concrete block wall, a concrete block blast wall consists of concrete masonry units (CMUs). CMUs are prefabricated concrete blocks that come in a variety of different types. As the National Concrete Masonry Association notes, some of the best CMUs for accommodating the reinforcement bars needed for blast walls include open-ended CMUs and bond beam CMUs. Open-ended CMUs, like the H-shaped and A-shaped varieties, are beneficial for blast walls because they can be threaded around vertical reinforcement bars. This eliminates the need to lift CMUs over the bars during construction. Bond beam CMUs, in comparison, can easily accommodate horizontal reinforcement beams. This is because the CMUs are designed with reduced webs or knock-out webs, the latter of which builders can remove prior to a wall’s construction.

Block Sizes

• Apart from the types of concrete blocks that go into concrete block blast wall construction, the sizes of the blocks have an impact on blast-resistance. According to the National Institute of Building Sciences, builders of concrete block blast walls should use 8-inch-thick CMUs. However, for increased blast resistance, the institute recommends using 12-inch CMUs.

Exterior Wall Considerations

• Because bombings and terrorists attacks often occur outside of buildings, exterior concrete block walls are particularly susceptible to blast damage. According to the National Institute of Building Sciences, exterior concrete block blast walls should be designed so that if they do fail as a result of extreme forces, they should fail in “a ductile mode such as flexure” as opposed to “a brittle mode such as shear.” In addition, exterior concrete black blast walls must be able to support the loads of doors and windows.