There's not much about concrete that's set in stone. "The concrete industry is changing almost on a weekly basis," says Ed Kalis, executive director of the Alberta Ready Mixed Concrete Association (ARMCA). New products, technologies, and applications are constantly being developed as ready-mix suppliers strive to improve quality and lower costs.
In 2006, approximately four million cubic metres of concrete were poured into roads, bridges, and other structures throughout Alberta. It's a popular building material; worldwide, it's second only to water. Concrete is often the material of choice because of its durability, strength, thermal properties, and relatively low cost.
Strength and beauty combined
Ultra-high performance Ductal® is one new product that's making its mark in Alberta. Lightweight yet incredibly strong, Ductal has a smooth surface finish and superior resistance to environmental and climatic conditions.
Lafarge North America recently made history in Calgary with the Glenmore/Legsby footbridge. This is the second footbridge made of Ductal in North America. Weighing 100 tonnes and completing a span of 53 metres, the Glenmore/Legsby project has the distinction of being the largest ultra-high performance pour completed in the world.
"The City of Calgary is very concerned about the aesthetics and impact of infrastructure that they construct," says Don Zakariasen, director of marketing, Lafarge North America. "With the high strength of Ductal, we were able to provide a more elegant, shallower structure than could be attained using regular concrete."
Due to the need for tight quality control, Ductal is a precast product. Zakariasen says that precasting was perfect for this application. "Glenmore is the second busiest artery in Calgary," he explains. "There was no opportunity to disrupt traffic." Lafarge produced the footbridge component in-house and was able to erect the superstructure between midnight and 7:00 a.m. on a Saturday.
Further down the GE5, Ductal is also being used strictly for art's sake. Colourful fish measuring 15 feet in length and five feet in height adorn a precast high-performance concrete wall. At that size, the approximately 1.5-inch thick fish would have been too heavy with regular concrete. Ductal provided the perfect solution. According to Zakariasen, Ductal is also ideal for building envelopes and in many applications where stainless steel would normally be used.
Revised specifications pave the way for innovation
A recent change to the CSA, the code that governs the concrete industry, is expected to allow for increased innovation in concrete.
Traditionally, building owners and their consultants were able to choose between three ways of specifying concrete. In the first, the owner or consultant tells the ready-mix supplier what to put into the concrete in order to achieve the desired objective. This is called a prescriptive specification and the owner or consultant is responsible for the quality of the end product.
The second way of specifying concrete is referred to as a performance specification. This method allows ready-mix suppliers to decide on the design of the concrete, using whatever they think is best to meet end targets specified by the owner. The supplier is then responsible should the concrete fail.
Both performance and prescriptive specifications work. The problem, at least from the standpoint of the concrete industry, has been the common method. "Producers were being told very much what to do and how to do it but then they were blamed if the concrete didn't work," explains Dave Robson, senior concrete engineer, EBA Engineering Consultants Ltd. "The CSA recognized the inequity of that and revised the specification methods."
The revision allows for only prescriptive or performance specifications. "Now, the code basically says you either tell the producer what to do or give him targets to meet," says Robson. "The line of responsibility is much clearer from within the industry," adds Kalis.
Performance specifications aren't new. Alberta Transportation began using them on asphalt projects over a decade ago. Rather than tell the supplier where to get gravel and specifying particular ratios, the government department simply stated what it wanted out of the asphalt and left it up to the supplier to ensure the product performed.
"There were a couple years of hiccups as people got used to the asphalt companies making and improving their own product," says Robson. "But after those hiccups in the mid-nineties, it's been a really popular move in terms of getting better quality materials out there."
The hiccups Robson refers to were mainly due to reluctance on the part of owners and consultants to give up control over the makeup of the product, something the concrete industry is presently experiencing. But ready-mix suppliers are adamant that there will be no decline in quality. In fact, the revisions are expected to result in better quality products.
"If an engineer is specifying on a prescriptive basis, he's going to use the tried and true. He's got no desire to make it cheaper, better, faster, whereas a producer is competing in the marketplace. He's going to want to do it cheaper, better, and faster than his competitor so he can have an economic advantage," explains Robson. "From an industry standpoint, who tests our concrete more than the individual ready-mix company?" asks Kalis. "We know better than consultants how our materials react with different types of aggregates in various regions across Canada."
Supplementary cementing material may change the face of concrete industry
The potential introduction of an inexpensive form of the pozzolan metakaolin to the North American market has many in the industry excited. Pozzolans are additives that can replace a portion of the cement in concrete. According to Roger Kennedy, marketing and sales representative, Lehigh Cement, these supplementary materials increase the capacity of cement producers.
"Because this market, particularly in Alberta, but in the Prairies in general, is expanding so rapidly, we're having to do everything we can," says Kennedy. In order to avoid a repeat of the 2005 cement shortage, Lehigh and its competitors are engaging in plant modifications and using supplementary cementing materials, like flyash and silica fume, in blended products. "We are determined to service this market," says Kennedy. Metakaolin, made of a fine, white clay called kaolin, has been used to make high-performance concrete since 1966, but widespread use hasn't been possible due to price and availability issues. Kaolin has been mined in South Carolina and Georgia for over 100 years, mainly for use in the paper industry.
"To make paper-grade kaolin, you need a very capital intensive process," says Kelly Babichuk, president, Whitemud Resources. All impurities must be removed during processing in order to achieve a paper-white product. The cost of the paper-grade kaolin hovers around the $600 per tonne mark, too much when compared to the cost of cement.
Whitemud Resources is focused on producing WhitemudMK, a cement-grade metakaolin. The company is currently constructing a mine and processing facility in southern Saskatchewan where there is a large, untapped kaolin deposit.
Cement-grade metakaolin can be produced with a dry process that brings the price of the product into line with the cost of cement. Although WhitemudMK is white, it's not the pure white required by the paper industry, and Whitemud Resources doesn't need to worry about getting rid of all the sand. "The industry we're serving uses sand in the finished product," says Babichuk.
Like fly ash, a byproduct of coal-fired generating stations, and silica fume, a byproduct of the production of silicon metal and ferrosilicon alloys, metakaolin improves the environmental sustainability of concrete. The production of cement, a major ingredient in concrete, produces approximately one tonne of CO2 for every tonne of cement. The production of WhitemudMK produces about 55 per cent that amount.
Ongoing third-party testing is revealing the potential uses of WhitemudMK , including the possibility of enabling the use of more fly ash. Presently, owners wishing to achieve LEED certification are rewarded for using higher percentages of fly ash. Due to problems with curing concrete made with fly ash, however, there is a limit to the amount that can be used.
Metakaolin gets harder faster than fly ash and shows better early age performance. It's hoped that using a combination of metakaolin, fly ash, and cement will allow producers to decrease the environmental footprint of concrete without sacrificing strength or durability.
Robson says that the consistency in the quality of the product will also be important. Alberta is home to four sources of the world's highest quality fly ash, but efforts to reduce the environmental impact of coal-fired generating stations may impact that quality.
"Some of the technologies that reduce emissions render [fly ash] useless for anything," Robson says. "Metakaolin has a big advantage in that it will be a stable product, as far as we know."
There's no doubt that Alberta's cement and concrete industries will embrace metakaolin, as long as it works. "We have relatively costly materials and unfavourable climatic conditions so we're very good at using the new innovations in admixtures and materials. We can't afford to do it the old way all the time," explains Robson.