Regional Materials

CMU plants are very common across the US and typically one can readily be found that is located with 50 to 100 miles of any developed area where project job sites are found. That means that it is typically very easy to demonstrate the use of regional materials when specifying CMUs since the LEED standard is within 500 miles of a project site.

Building Re-Use

Since CMUs are exceptionally durable with a service life that is measurably longer than many other building envelope products, it is very common to see buildings made from CMUs adaptively re-used and designed around pre-existing CMU walls, paver areas, etc. That means a substantial renovation of an existing building can be worked very successfully and economically when the building is found to contain substantial amounts of CMUs.

Glazed and polished CMUs in particular can be specified with significant amounts of recycled content that contribute to successful green building designs. Photos courtesy of Oldcastle® Architectural

 

Materials Re-Use

When CMUs are crushed they break down into smaller pieces of irregularly shaped material. Since it is a composite of natural materials to begin with, it is readily re-usable as an aggregate in other applications.

Construction Waste Management

In cases where CMUs need to be demolished or removed from buildings, then crushing and recycling it is an immediate means of diverting it from the waste stream. This crushed material can readily be used as aggregate or fill in road beds, pipe bedding, in other manufactured concrete products, or simply as general construction site fill. Hence a substantial amount of weight that might have otherwise gone to a landfill is diverted and put to productive use elsewhere in the community.

Note that all CMUs must meet the stringent standards of ASTM C90 therefore any recycled content or re-used materials must not compromise the quality of the finished product or its ability to meet that standard. It is also worth noting that products with recycled content vary regionally, so specifiers would do well to confirm with local suppliers what is readily available or not.

Indoor Environmental Quality with CMU

The quality of the indoor environment has received growing attention in recent years particularly related to the health and performance of occupants. While this is true of all building types, schools especially have been the focus of attention since so many children and adults spend so much time together inside these buildings. It is logical then that the definition of green building includes attention to this critical component of building use. In this case, CMU construction a significant player not so much for what it does do, but for what it does not do and the things that are not present from CMU materials including the following:

Mold Avoidance

The presence of mold growth in buildings has been front and center in recent years as a serious concern. It is commonly understood that three things are needed for such mold growth—water, organic material as a food source, and air. A mold avoiding strategy recognizes that if mold spores are ever present in the air, and water intrusion is a possibility, the building materials should not be made out of organic materials that provide a food source for mold. Hence, choosing non-organic building components that will not support mold growth is called for. CMUs are just such a material since it is completely inorganic and simply does not promote mold growth—period. Hence, one of the best defenses against mold growth in buildings is to specify concrete masonry.

Elimination of VOCs

LEED and other design standards promote greatly limiting or reducing the amount of volatile organic compounds (VOCs) that are present inside a building. These are commonly found in applied finishes such as paints and stains or in adhesives to secure other materials in place. These VOCs have been shown to directly cause adverse health effects on many occupants and are often accompanied by odors all too familiar in many newly finished spaces. A very realistic approach to eliminating VOCs in many cases is to choose materials for walls and partitions that simply do not require application of paints or finishes and hence do not contain any VOCs at all. CMUs are just such a product that can be prefinished without the use of any VOCs. Further, they are available in a variety of textures, colors, and other finishes providing a versatile range of options without the need for adding other finishes later in the life of the building.

CMUs are available in a wide range of prefinished colors and textures that eliminate the use of VOC-containing site finishes while also eliminating the possibility of mold growth in buildings. Photo courtesy of Oldcastle® Architectural

Acoustics

This is an indoor environmental issue that is gaining increasing attention, particularly in schools. Independent studies have shown that the performance of children in schools is, not surprisingly, directly affected by their ability to hear and discern the verbal instructions being given in classrooms. As such, LEED for Schools has added both pre-requisites and optional credits for improving and enhancing the acoustical performance of walls. The requirements address Sound Transmission Class (STC) ratings of walls which is a measure of how much sound passes through an assembly. A higher STC rating means that more sound is blocked by the wall (i.e., quieter), while a lower rating means that more sound passes through (i.e., noisier). In schools, it is common to seek an STC rating in the range of 45 to 60 to create effective indoor acoustical spaces. As has commonly been demonstrated, CMU walls are quite effective at achieving these increased STC levels and creating superior acoustics in interior spaces.

The second criterion for enhancing acoustical performance is the absorption of sound to reduce or eliminate echoes and keep speech fully intelligible. This characteristic is directly a result of the materials or treatments used in the space. CMU structural products have been developed specifically to meet this need of acoustical absorption acting much the way a car muffler works. The shapes of these block units are closed on the ends but include vertical slots in the face of the block to allow sound to penetrate, resonate inside, and dissipate harmlessly within the CMU. Sound absorbing insulation may be added if needed inside a portion of the open cores of the CMUs particularly in cases of difficult to control low frequency noise. The surface appearance of such CMUs are available in glazed, ground face or common gray block units of choice. For more detailed specific information on using CMUs for acoustic control, NCMA TEK bulletins 13-1 B and 13-2 provide guidance.

Specifying and designing with concrete masonry, particularly in interior spaces, then, directly contributes to positive indoor environmental quality through the elimination of mold, the elimination of VOCs and the control unwanted noise or sound reverberation.

CMUs specifically manufactured to create enhanced acoustical performance in interior spaces includes slots to receive and dissipate sound plus acoustical insulation inserts where needed. Photo/image courtesy of Oldcastle® Architectural