More Sustainable Concrete

While concrete is made primarily from natural materials, the process of creating it requires significant effort and energy, which impacts its determination of sustainability. The best method used to determine the degree of sustainability of any material is to conduct a life-cycle assessment that addresses extraction of raw materials, transporting them, processing them (particularly with energy), incorporating them into buildings, and finally recovering them at the end of the service life of the building for either recycling, reuse, or disposal. National and international standards have been developed for conducting such a life-cycle assessment that begin with product category rules (PCRs) for a particular type of material or product. ASTM International has produced just such a document for assessing cement known as UN CPC 3744, “Portland, Blended Hydraulic, Masonry, Mortar, and Plastic (Stucco) Cements.” This document can be used by cement manufacturers to produce environmental product declarations (EPDs) that identify the specific environmental impacts of their products. Those impacts are presented in terms of environmental, energy, and material/waste effects from using the product. By requesting EPDs from different cement manufacturers and comparing the results, architects and others can determine the differences in the short- and long-term environmental impacts of those products.

Source: ASTM International

ASTM International has produced UN CPC 3744, “Portland, Blended Hydraulic, Masonry, Mortar, and Plastic (Stucco) Cements.” This document can be used by cement manufacturers to produce environmental product declarations (EPDs) that identify the specific environmental impacts of their products.

Many who have looked at portland cement, concrete, and sustainability have determined that the long-term benefits of the material can be shown to outweigh initial impacts of producing it, thus producing a more favorable life-cycle assessment. In 2009, the Concrete Sustainability Hub (CSHub) was established as a research center at the Massachusetts Institute of Technology (MIT) in collaboration with the PCA to address the sustainability and environmental implications of the production and use of concrete. Its research aims to fine tune the composition of concrete, reduce the greenhouse gas emissions of its production, and quantify its environmental impact and cost during the entire life span of an infrastructure or building project.

Among the findings of CSHub and others, concrete can contribute to green and sustainable building designs in several ways.

• Permeable concrete allows rainwater to percolate into the soil more naturally, helping to promote better drainage for more sustainable sites.
• Thermal mass can be provided in buildings using concrete that, when designed appropriately, can improve overall energy performance.
• Recycled materials can be incorporated into concrete mixes as substitutes for stone aggregates in order to avoid new material extractions. The use of fly ash or slag in particular in concrete mixes has been seen as a positive way to harvest and neutralize some otherwise problematic products of coal combustion.
• Local manufacturing of concrete and cement helps to reduce the energy used in transporting heavy materials.
• Durability as a material means that concrete has a long-lasting service life compared to many other building materials. It’s inherent strength and resistance to weather allow very resilient structures to be constructed out of concrete.

Based on these attributes and a full life-cycle assessment, architects, engineers, cement manufacturers, concrete mix companies, and construction operations can all address green and sustainable attributes of buildings by selecting the most appropriate cement and concrete formulations for their projects.

Using Building Information Modeling for Concrete Design and Construction

The advances in the science and technology of concrete in buildings has been notable and impressive over the past 100 years or so. But even more rapid and significant changes have taken place in the design and construction processes as computerized design and documentation have become the norm around the world. Specifically, the availability of design software that works in three dimensions and allows design professionals to literally model a building out of stock or custom components and materials has helped to completely redefine the way buildings are being designed.

A computerized building information model (BIM) uses specific 3-D components to design, shape, and assemble a virtual building. Each of the components have definable attributes that match the size, shape, and specifications of the systems, materials, or products that they represent. In practice, the implication is that the task is no longer one of drafting but of creating, assessing, revising, and recreating in three dimensions as needed. This can allow a great deal of design experimentation to be done rapidly, as different aspects of the design can be explored in great detail and over multiple iterations. When it comes to using concrete, it means that forms, shapes, geometries, and other attributes can be modeled using the power of the computer to do the math and provide real data on the differences between designs.

Beyond experimenting with forms of concrete through BIM, computer analysis can be used to determine the structural performance of concrete designs. In this case, the geometric parameters can be linked with the identified structural loads imposed on the concrete to determine the needed physical properties of the concrete for compressive and flexural strength. Coordination of the BIM software with structural engineering software may be the most appropriate way for a design team to work on such projects and allow full collaboration on optimizing the design not only visually but structurally as well. In that way, the best thickness and quantity of concrete can be determined to perform as intended without over-designing, thus controlling costs.

BIM also allows for computerized visualization of the connectivity of concrete with other materials used in the building construction. These may be other structural elements, such as steel, masonry, or wood members, that attach or are embedded in the concrete, or it may be openings such as windows and doors. It can also be used to coordinate proper insulation and air-sealing techniques when architectural concrete is used as part of the building enclosure that effects energy performance. If the focus is on decorative concrete or aesthetic issues, then BIM is ideal at presenting three-dimensional visualizations in great detail in order for designers to assess and determine the best choices.

Overall, the use of computerized building information models makes the process of designing innovative concrete buildings quite effective. The nature of a shared BIM allows collaborative opportunities between all disciplines and even community members. The high-quality visualizations coupled with the technical and structural coordination to create precise and accurate models empower truly collaborative decision making because all participants can share an articulated understanding of the relevant design issues and together determine the most appropriate solutions.