By now, all engineers have heard about, and likely have opinions of, Boston's Big Dig troubles. And as recently as late last month, Quebec, Canada saw its own tragic overpass collapse, in which five people were crushed to death and six were injured.

A public inquiry into the latter collapse began earlier this month. Pierre Marc Johnson, former Quebec premier, and the two engineers who round out a commission visited the site of the tragedy to begin an inquiry into what went wrong. The Canadian Press has pointed out that Quebec, like so many other cities across North America, has been criminally under-funded to keep its bridge infrastructure up to snuff.

Because resources allocation remains an issue for many cities when it comes to bridge/overpass maintenance, it seems important to acknowledge light, affordable and innovative materials and designs.

The Concrete Centre is noting a new spin on an old building staple: concrete. Take, for example, an interesting mandate that underscores concrete's flexibility:

A new generation of innovative concrete products and construction techniques has been, and is being, developed. New construction philosophies aim to improve design and construction efficiency, generate innovation and enhanced performance as both client and members of the project team strive to achieve even greater quality and profitability. For these reasons, engineers are re-examining the use of concrete.

A fairly high-falutin' mandate, indeed, but The Concrete Center has provides plenty of concrete examples that cement the material's use as a solid foundation for all types of future building endeavors.

To wit: "high-performance concrete," which meets special performance and uniformity requirements that cannot always be achieved routinely by using only conventional materials and normal mixing, placing and curing practices.

Consider Berlin's Holocaust Memorial, which opened in May 2005. The memorial was created by 2,711 gunmetal grey, reinforced concrete stelae, each uniquely positioned on a uniform grid to form a wave-like progression across undulating topography, which drops to as much as 2.4m below surrounding street level in places.

Actually, the concrete sector is an important industry for the U.K. It is worth some £5 billion a year with up to 120 million tons of concrete being used in U.K. construction projects per annum.

According to the latest issue of Concrete Quarterly, on the edge of London a new complex of four principal towers — one of 19 stories, another of 12, one of six, and a stepped building of nine and 12 stories — and a small two-story pavilion are being built with concrete frames. The floor slabs will use two-way, post-tensioned (PT) techniques to make them strong, flat and thin.

According to Peter Runacres, an associate at designer Bennetts Associates working on the project, there was considerable discussion at the outset on whether to use concrete or steel. At 19 stories, the cost and speed of the two options were about equal. "What finally swung it was the concrete guys saying they could keep within the [program] times," says Runacres. The designer associate is pleased to be using concrete for a variety of reasons: fire protection is instant, concrete makes the installation of services relatively simple because no secondary steel work is required, and concrete gives a building a thermal mass that can be used for heating and cooling purposes.

Also, the price of steel is making concrete an even more attractive proposition. Designers are constantly striving to minimize the use of materials (even more so now that sustainability has become a significant part of building). So Bennetts has aimed at using as little concrete as possible — hence the post-tensioned floor slabs. "The main reason we've gone for two-way, post-tensioned slabs is really sustainability," says Runacres.

PT suspended concrete floors have become more popular in the U.K. over the last five years. PT slabs are generally thinner than ordinary reinforced concrete slabs, and The Concrete Centre estimates that structural floor zones can be up to 300mm thinner than in a steel frame, thus minimizing the building's height to the extent that this could mean an extra story on a 10-story building. Further, PT slabs require fewer columns and foundations than ordinary reinforced slabs, which means greater flexibility in space planning. A PT slab can also accommodate irregular grids and can mean rapid construction and less concrete, the latter of which, of course, equals fewer trucks. There is less reinforcement, which reduces fixing time, and early stressing of the concrete allows the formwork to be struck quickly.

Or take John Newhook, an associate professor in civil engineering at Dalhousie University in Halifax, Canada, who recently noted that the construction industry is slowly moving toward the use of new, non-corrosive materials in concrete construction.

The Canadian Press (via iCivilEngeer) has also noted how some are making concrete more durable for new bridge construction.

"We are a part of a team trying to advance the idea of what we call structural health monitoring," said Newhook, who is project leader of a university research network called Intelligent Sensing for Innovative Structures (ISIS). "The essence of the idea is can we put some sensors on these structures that can give us feedback on their condition in real time and on a continuous basis. Canada is taking a reasonably strong leadership role in that area."

One branch of research is looking into the use of small fibers mixed into the concrete to strengthen the product at the micro-level and prevent the initial small cracks that can lead to disaster. Newhook said researchers are also promoting the use of glass fiber and graphite reinforcing rods in cement construction, in place of the traditional steel rebar that easily corrodes.

City of Toronto senior project engineer Victor Zubacs recently explained to The Globe & Mail why these two developments are so significant:

The most common death scenario for a bridge goes like this: Water, bearing road salt, seeps into the bridge through cracks in the road. Eventually, it slips through cracks in the concrete to contact the steel structure inside. Salt combined with moisture conduct stray electrical currents, which speed up the salt's ability to corrode steel. Steel expands up to 40 percent as it corrodes, popping open more cracks and dramatically weakening the concrete around it.

Newhook shares concerns, like other engineers who, in the wake of the Quebec tragedy, have warned that Canada's aging infrastructure is "a ticking time bomb." Like many concrete structures throughout the world, many of Canada's concrete structures date from the 1950s and '60s and earlier, and thus are well past their planned design life. David Lau, a civil engineering professor at Carleton University in Ottawa, shares the same sentiment, as he warns that many bridges are deteriorating more rapidly as they age. And many of them are carrying much more traffic — and much heavier trucks — than their designers had in mind all those decades ago.

"So that leads to the question, when is it all going to catch up with us?" asks Newhook.

The two professors' thoughts bring up associated issues regarding ethics in engineering.

In August, Civil Engineering News published an essay that delves into engineering ethics; in it, the importance of ethics is tied together with the delivery of quality products:

The combination of ethical conduct and specialized knowledge defines the professional, and are among the important building blocks necessary to achieve an excellent reputation. This status must be created over time, though, and is built one block and one event at a time…While it takes time and hard work to cultivate and maintain, an excellent professional reputation is the number-one ingredient for long-term success.

This "combination of ethical conduct and specialized knowledge" seems to speak directly to concrete engineering. By adopting some of these holistic views, in addition to the aforementioned innovations in how concrete is made and used, engineers in this niche industry will find themselves ahead of the pack and in high demand. And concrete design and construction can continue to evolve in order to fulfill new visions and meet new performance requirements.

Resources

Inquiry commission begin work with visit to site of overpass collapse
by Peter Rakobowchuk
The Canadian Press, Oct. 6, 2006

Innovations in Civil Engineering
The Concrete Centre

Holocaust Memorial, Berlin - Case Study
The Concrete Centre

Thin floors create roomy, flexible offices
by David Littlefield
Concrete Quarterly, Autumn 2006 (Issue No. 217)

N.S. engineers develop new materials, methods to make concrete bridges safer
The Canadian Press (via iCivilEngineer), Oct. 3, 2006

Sounding the alarm on Canada's bridges
by Jeff Gray
The Globe and Mail, Oct. 9, 2006

Foundation for an excellent professional reputation
Civil Engineering News, August 2006