A Material for a Finite Planet
by David Hertz, AIA

A paper presented to the PCA (Portland Cement Association) conference on sustainability in Las Vegas 1994, and the ADPSR (Architects, Designers and Planners for Social Responsibility) conference on ecology in 1995 held at SCI-Arc (Southern California Institute of Architecture)

In a world of dwindling resources, a new generation of advanced cement-based products emerges as heir apparent to traditional building materials.

Introduction

Our society is living beyond the means of the Earth to sustain it. Our patterns of resource exploitation will dispossess the Earth of its natural resources within the space of a few lifetimes. In the next few years the construction industry must move to an approach which views the Earth and its resources--including people-- as capital to be carefully tended.

Balancing society's expenditure of natural and human resources should be a first priority for everyone in the building industry. The key is 'sustainability', a word we hear more and more often. It means providing for the needs of the present without detracting from our ability to fulfill the needs of the future. Indigenous people acted on the concept of stewardship of the Earth's resources for thousands of years, leaving the Earth undamaged by their passage. We could learn from a culture which treats the resources on which it depends for survival as sacred.

The reality of sustainability and environmental impact are only beginning to be felt in the building industry. Construction consumes about 40% of the U.S. annual resource expenditure. And on the output side, construction and demolition waste account for over 20% of the municipal solid waste stream. Other than structural suitability, the criteria for selecting economical building materials today have been largely based on aesthetic or based on first cost. Unfortunately, durability or life-cycle considerations are only generally a factor in institutional or high-end commercial construction projects. But as we begin to look more closely at the overall effect of resource use, these criteria must extend to residential construction as well.

While we are unlikely to achieve zero impact on the natural environment, the new measure will be how much we can minimize the depletion of our natural resources. We must look at the embodied energy of materials through their life-cycles--a cradle-to-the-grave analysis. As discussed earlier, we must compare the net and cumulative effect of materials on our resources and energy consumption through acquisition, manufacturing, use and final disposal.

Today I want to discuss concrete and other cement-based products as alternatives to the nonrenewable, energy consuming petroleum-based products widely used in construction. I will also touch upon some of our work and the future of advanced cement-based composites and building systems, some of which are exhibited here today, and given the short time, try and offer tangible sources and guidelines for using concrete wisely.

It is important to define the difference between concrete and cement-terms which will be used interchangeably through this discussion.

To fully appreciate concrete's potential for sustainability, it's helpful to look at its history. Concrete has been used as an architectural material for almost 2,000 years. The earliest evidence of its use is found in the ruins of Roman construction from the 1st and 2nd centuries A.D. These early sites show the remarkable durability and strength of concrete materials. Made with a natural cement mixture of volcanic pozzolan and lime, the ruins of Emperor Hadrian's villa reveal the use of unreinforced concrete in the construction of domes and walls. In some instances, walls made of stone or brick were fill ed with concrete to more effectively mortar the stone. Today the concrete filling remains long after the stone or brick have disappeared.

Following the fall of Rome, knowledge of concrete construction was lost until the later half of the 18th century. Its modern counterpart surfaced in 1824, when Joseph Aspen, an English stone mason, patented a manufactured cement he called Portland cement. It was so named because it resembled a fine, highly valued building stone quarried on the Isle of Portland off the coast of England.

Concrete has three major components: aggregates, water and Portland cement. The aggregates are usually a mixture of coarse and fine materials, such as gravel or crushed stone and sand. In a process called hydration, Portland cement and water combine chemically to bind the materials together. The resulting concrete is a rock-like mass with remarkable strength and durability. Beyond concrete's three basic components, modifying agents called admixtures can either retard or advance setting time; provide resistance to freeze-thaw damage; enhance strength; improve placing characteristics; and add color.

Two characteristics of concrete account for its use as the most widely used building material: its remarkable compression strength and its ability to be shaped into a variety of different applications. Concrete used in construction typically has a compressive strength of between 3000 and 6000 psi. newer formulations can exceed compressive strengths of 20,000 psi, and new advanced cement composites reach 100,000 psi. Such strength means that relatively small concrete components can support tremendous loads. It can also be formed into structural shapes that accommodate both strength and aesthetic value with great economy. It can be precast and delivered to the construction site or cast directly in place, used as masonry components as a finishing material.

Cement is made up of Earth's most abundant and universally available raw minerals containing limestone, chalk and shale, which are blended and heated to about 2700 degrees in an industrial furnace called a kiln. The conversion of these raw materials into cement consumes a large amount of energy. To mitigate its environmental impact, the cement supplements fossil fuels with high energy wastes such as used scrap tires, which have an energy content rivaling that of coal. Each cement kiln can consume over 1 million tires each year, which obviously displaces them from the landfill and saves coal. Other common waste fuels include used motor oils, spent solvents, printing inks, paints and cleaning fluids. Indeed, for some chemicals, thermal destruction in a cement kiln is the safest method of disposal.

The kiln's intense heat-- nearly twice as hot as a municipal incinerator-- plus long residence time and turbulence within the kiln ensure complete destruction of the waste. The process is strictly controlled and closely monitored by the EPA and it is estimated that waste fuel will eventually supply up to 50% of the energy required to manufacture cement. The cement industry, in general, has, in fact, reduced fossil fuel consumption by 77% in the last 20 years.

Cement represents only about 9-13% of concrete and accounts for 92% of the embodied energy. The aggregates of sand represent under 2% and crushed stone under 6%. Obviously, minimizing the percentage of cement will lower the embodied energy of concrete.

Concrete itself is an ideal matrix in which to recycle and encapsulate a wide range of industrial and consumer wastes. Industrial by-products include readily available pozzolans, such as fly ash--produced by coal combustion at electric utilities, and silica fume-- a by-product of silicon manufacturing. These materials increase the strength of concrete while recycling industrial waste and minimizing cement consumption. Use of fly ash in concrete already saves us about 44 million BTUs of energy annually in the U.S. alone. Increasing the rate of fly ash from 9% to 25% would save an additional 75 trillion BTUs. Fly ash can be substituted for 15 to 35% of cement. According to recent E.P.A. studies, some applications such as autoclave cellular concrete can contain up to 70% of the 51 million tons of fly ash produced in 1991. Only 7.7 million tons were used, accounting for only 9%.

Many other consumer and industrial wastes can be recycled as aggregate. Reground polystyrene from packaging, ground porcelain from recycled plumbing fixtures, glass, plastic, wood and metallic, or even lightweight aggregate made from municipal sludge can be extracted form society's waste stream and used as raw materials for concrete. We need to close the loop by re-using materials that we have traditionally discarded into the landfill because recycling is not just collection.

Aside from resource efficiency, energy and recycling concerns, construction itself is a significant waste-generating industry. I mentioned earlier that construction wastes and rubble from demolition account for 20% of municipal solid wastes. Here again, we must re-evaluate our current building systems-- the fitting and assembly of sheet goods and lumber to produce scrap.

We must dramatically change the way we build. The cycle of wood construction is not sustainable. Until now, "long run" consequences haven't been enough to galvanize the construction industry into action. But today's skyrocketing lumber prices have finally forced the search for alternatives. According to NAHB, the recent jump in lumber prices translates into an increase of more than $4,500 in the cost of building a new home. Every time you build a house, you use 41 trees. Twenty three go to the construction of floors and walls, 13 to the roof, and 5 to the interior.

The new world's bounty of timber resources has made North America one of the last regions of the world to cling to wood construction. Basic U.S. construction practices have not changed in more than 50 years. Hopefully, the new administration's commitment to responsible environmental practices guarantees that a new force will continue to affect the traditional cycle. Unlike traditional U.S. building methods, concrete is used only on an as-needed basis-- there is no inventory or waste of materials, which minimizes scrap and disposal. Precast concrete has the environmental benefits of being able to handle all the dry materials and water effluents in a concentrated facility. And today's formwork can be re-used or, in the case of modern integrated forming systems, stay in place as insulation for the finished wall.

Cement and concrete supplies are highly local or regional; ultimate energy or fuel requirements for handling or transportation are very low. Cement is usually shipped within a 50-mile radius of its production. Ready mixed concrete and concrete products are supplied even more locally. In contrast, wood and steel products are routinely shipped across the country in their journey from forest and mill to the job site.

We can both reduce waste and debris from demolition and conserve resources by simply building longer lasting, more durable structures. Concrete's service life exceeds that of other comparable products used in construction today, such as wood, steel and brick. Concrete compares very well, in fact, to aluminum, steel, brick, glass, ceramics and plastics in the uses of energy consumed in its manufacture , transportation and ultimate use. At the end of its service life, concrete can be recycled and reused by crushing into aggregates for new concrete or as fill material for road beds or site works.

Concrete boasts excellent thermal properties. The fact that it can store and re-radiate heat means that buildings of concrete naturally require 70% less energy for heating and cooling than buildings constructed of other materials. Concrete construction can reduce or even eliminate the need for air- conditioning --reducing the need for ozone-depleting CFC emissions.

No Off-Gassing

Concrete promotes a healthier indoor atmosphere since it is one of the most chemically inert materials, and requires no volatile organic compound based coatings or preservatives. It's naturally waterproof and fire-resistant, and unlike wood or steel, it will not decay or deteriorate, so it doesn't need special coatings or sealers. Concrete does not require paint to achieve a given color; natural-mineral pigments and coloring agents provide a rainbow of options.

In addition to the benefits of conventional concrete outlined above, a new generation of cement based materials heralds a whole new philosophy of building. These new concrete materials rely on the use of by-products from other industrial processes or post-consumer waste and can substantially reduce overall waste streams by exploiting materials that have been considered waste. The new materials that you'll start to hear about will include autoclave cellular concrete, Rastra and Insteel, and of course, my own product, Syndecrete.

These new products also challenge people's traditional conception of concrete as a cold, unfriendly material. In fact, color and textures can render the material quite organic, which is an important psychological consideration in creating a natural environment.

In conclusion, let me just highlight a few quick tips in specifying and using cement and concrete wisely.

1) Consider slab on grade and pier foundations-- This replaces raised floor systems minimizing lumber framing and sheathing and flooring and opens opportunities to leave the slab exposed and take advantage of the thermal mass and radiant heating options.

2) Consider pre-cast systems-- This minimizes disposable forming material, wash water run-off, on-site environmental site damage and conc. overage.

3) Consider in place forming systems and integrated panelizing or masonry systems-- To minimize scrap and additional labor to install thermal and moisture and interior and exterior finishes.

4) Specify minimal admixture use-- to omit the possibility of off-gassing.

5) Omit curing compounds, sealers or paints--leave it natural.

6) Specify fly ash

7) Specify recycled aggregate.

8) Consider gray water use.

9) Use concrete rubble on site as fill or site attenuates.

10) Specify Syndecrete!!!

I would like to end with a quote from Albert Einstein.

"We cannot solve today's problems with the same level of thinking that created them."--Albert Einstein

Thank You.


*Architect, builder, designer, and eco-preneur David Hertz is founder and president of Syndesis, a multidisciplinary firm that has pioneered the use of lightweight precast concrete in environmental design. Hertz crafts his Syndecrete into tiles, fireplaces, sinks, vases, doors, countertops and more--casting his vision of concrete as an environmentally sound alternative to any building component. Hertz's work earned him Inc. magazine's 1993 Design Leadership award. His Syndecrete furniture and product designs are published and exhibited world-wide. Hertz is an active member of the environmental community and consults to the A.I.A. and P.C.A. on environmental issues. David Hertz would like to dedicate his life's work to his family, Stacy, Collin and Sophie, and Max Without them, none of this would be possible.