Concrete is one of the most widely used building materials in the industry, but is commonly known to be highly energy intensive, emitting green house gases during production, processing, and transportation. So why then would we use concrete in a super-green Living Building ChallengeTM building? The short answer is that there is still no other material currently on the market that matches the durability of concrete for the life of a building as well. Invented by the ancient Romans, concrete has been used for thousands of years in various formulations, and is one of the longest lasting building products over its expected lifetime.
For the longer answer, let’s get to know a bit about concrete. Concrete is a composite consisting of an aggregate of materials like gravel and sand, cement, and water. Use of concrete – and each of its composite materials – in our project has gone through the rigorous submittal and vetting process required by the Living Building Challenge. This process requires that materials meet multiple criterion including: regional sourcing of materials within 500 km of the site, and elimination of specific Red List chemicals and toxic materials found in traditional building products.
The footings, foundation walls, and floors of our building are all concrete, serving to transfer the weight of the building to the ground. They are built to withstand New England’s freezing and thawing temperature changes, as well as providing a durable surface on which to conduct our daily programs and events. This durable material will serve our building for hundreds of years to come.
Components in our concrete products include (Product – Company – Location and distance):
Portland Cement – LaFarge Type I/II – St. Constant Quebec (215 miles)
Portland cement is a natural limestone component in our cement. It reacts and hardens in the presence of water and also helps form a water resistant barrier.
Slag Cement – Newcem – Baltimore, Maryland (298 miles)
Slag cement increases the durability of concrete reducing life-cycle costs. It is often used to replace a portion of Portland cement to increase flexural strengths, hardening properties, finish, and to lighten color. Slag cement is a by product of the iron manufacturing process.
Concrete Sand – Delta Sand & Gravel – Sunderland, MA (7 miles)
Concrete sand contributes to the overall strength of the final product. It fills voids in the coarser aggregate materials for strength and helps to reduce shrinkage during curing.
Mixtures – BASF Concrete Admixtures – Allentown, PA (196 miles)
Admixtures are typically added to concrete mixes to reduce cost and modify specific properties and ensure quality of the final concrete. Admixes in our concrete include: Air-Entraining, Full-Range Water-Reducing, and Accelerating Mixtures. Air-Entraining is required for all concrete mixtures exposed to the elements. It inserts tiny air bubbles into the mixture to aid in reducing internal pressure and increasing resilience as water expands and contracts within the finished product over time. Full-Range Water Reducing mixture typically aids in the reduction of water by a range of 5-10%. Accelerating mixture helps to lessen the curing time.
¾” gravel stone – Delta Sand and Gravel – Sunderland, MA (7 miles)
¾” trap rock – J.S. Lane & Son – Amherst, MA (2 miles)
Gravel aggregates are components in the concrete that provide strength and reduce overall cost.
Potable water – Public Water Supply – Northampton, MA & Springfield, MA (8 and 19 miles respectively)
Water is added to the concrete to catalyze the reaction that binds the materials together. Depending on the application, specific ratios of water to cement, sand, and concrete determine workability (improves with more water) and strength (improves with less water).
Concrete does have a high energy input, but regrettably right now there is no other alternative, unless we compromise the quality of the building (as in use of wood, metal, etc.). There is a so called “green cement” alternative that substitutes all or a portion of the Portland cement in a concrete mixture with fly ash, a waste byproduct from coal fired power plants. While it is laudable to utilize the fly ash waste for a positive purpose, there are some who express concerns about the safety of using fly ash based on the knowledge that it contains toxins. Further, flyash is derived from a traditional coal mining processes that are well documented as destructive to the environment and human health. The concrete used in the Hitchcock Center’s building contains no flyash.
Our building is only constructed with concrete where it is in contact with the ground because concrete is actually strengthened by long-term contact with water. We are proud to be a part of the next generation of buildings that questions this status quo and demands a future of better alternatives
Curious about the use of concrete in another Living Building? Learn how the Bullitt Center, a certified Living Building Challenge office building in Seattle, used Concrete in Green Building.
Jessica Schultz is Communication and Capital Project Coordinator for the Hitchcock Center. She guides on-going media relations, website and social media, publications, marketing planning and photography. She also supports the Executive Director and building committee in planning for a new environmental learning center.Click here to return to full list of blog entries. Or chose a specific Blog category below.