Cement plans for sustainable product
Concrete Embodied Energy
by Tom Schwarzkopf
Durable, solid, and strong are adjectives that spring to mind when one thinks of concrete - all qualities important in the creation of sustainable buildings. However, these qualities have traditionally come at a price: environmental degradation caused by materials extraction, high energy use and high greenhouse gas (GHG) emissions during the production process.
The introduction of high fly-ash concrete is perhaps the most well publicized innovation that the cement industry has implemented in an effort to balance the environmental equation. Others in the pipeline, including the development of carbon-absorbing concrete, may ultimately transform our perception of the world’s most ubiquitous building material.
Green Component Production
Consider cement-that grey powder that holds concrete together. Cement is produced in 15 plants and 45 distribution centres across Canada.
The industry is working to produce more blended cements - those that have fly ash or slag mixed in, reducing the CO2 producing clinker content. Other alternative raw “waste” material used includes iron mill scales, lime sludge, bottom ash and fluid cracking catalyst replacing minerals such as clay, shale and limestone. In addition, cement manufacturing byproducts, cement kiln dust, for example, are increasingly recycled back into the manufacturing process.
Manufacturing energy efficiencies improved slowly but steadily by 12% between 1990 and 2002, and greenhouse gas (GHG) emissions per tonne of cementitious product were reduced by 7.1% over the same period.
“Waste” fuels now make up 5-8% of total fuel consumed in cement production. Sources include scrap tires-over, 18 million of them in the last decade, waste solvents and used oil, asphalt shingles, oily rags and filters, wood chips, sludge, treated wood, paper and cartons. It should be remembered that cement, the most energy-intensive component, makes up only about 10% of concrete.
Pilot projects are developing energy- and environmentally-efficient furnaces to generate energy for cement clinker production. Moreover, most cement plants have continuous emissions monitoring, and by the end of 2006 all those in Ontario will meet legislated provisions.
The end product - concrete - has inherent sustainable qualities in that aggregates are extracted within 160 km of the plant, and ready-mix plants are generally within 160 km of a job site. Reinforcing steel is also often manufactured within 800 km of a job site, and is increasingly made from recycled materials from the same region.
Durability
Concrete can help buildings meet the criteria of LEED, Green Globes and other building rating systems. Precast concrete components can contribute to achieving points in most LEED sectors such as Minimum Energy Performance, Construction Waste Management, Recycled Content, Local/Regional Materials and Innovation in Design. See the web references noted in this article for more complete details.
Concrete is resistant to high winds, floods, fire and even to earthquakes when properly designed and reinforced. In flood-damaged areas, concrete buildings are often the ones that are most salvageable. The durability of concrete frames also facilitates the reconfiguration and adaptation of otherwise obsolete buildings.
Building Considerations
Concrete waste at a job site is minimal. Ready-mix concrete is placed in as-needed quantities and partial truck loads are returned to the ready-mix plant for recycling. Precast concrete is delivered to the job site as factory-made components ready for erection. Existing concrete and masonry can be diverted from landfill disposal by crushing and recycled into aggregate for road bases and construction fill.
Components constructed of concrete generally are considered “mass,” or having enough heat-storage capacity to moderate daily indoor temperature swings. Thermal mass can make a significant contribution to energy savings: this is demonstrated when mass effects are incorporated into building energy simulation programs. When buildings are properly designed and optimized, incorporating thermal mass can lead to a reduction in size of heating, ventilating, and air-conditioning equipment. And that represents energy and construction cost savings.
Environmental Design Considerations
Cement can be used in brownfield redevelopment to solidify and stabilize contaminated soils and reduce leachate concentrations to below regulatory levels. In addition, the familiar concrete underground parking garage reduces surface parking to minimize the building footprint area and site disturbance.
New types of concrete pavers help manage storm water runoff, a potentially disruptive and pollution source of natural ground water. Concrete grid pavers have large voids through which vegetation can grow and storm water can infiltrate. Similar results can be achieved by using pervious concrete pavers that contain coarse aggregate and lower cement paste that provides 20 to 35% volume of voids for high water flow-through.
Landscape and exterior design incorporating concrete can reduce the heat island effect that can make urban areas up to 4°C warmer than rural areas. For example, concrete rather than asphalt paving in dense urban areas will reduce the heat island effect and the demand for air conditioning. Again, reducing paved areas through use of elevated or underground concrete parking can further reduce urban temperatures.
Thermal Flywheels
Exposed in the frames and slabs of buildings, the thermal mass of concrete can contribute significantly to modulating diurnal temperature variations and improving thermal comfort for occupants. In so-called ‘constant temperature’ buildings (see the Fred Kaiser Building), the introduction of water-filled pipes cast into the floor slabs converts the structure into a vast radiant heating or cooling system, the temperature of which need never be more than a few degrees above or below the desired internal air temperature.
Similarly, hollow core flooring slabs, can act as ducts to circulate and condition air in a building. In summer daytime, warm outside air is cooled as it passes through the hollow cores in the slabs. The concrete also absorbs internally-produced heat from lighting, machinery and people. At night, outside air cools the slabs down for their next day’s temperature moderation. In winter, the floor absorbs and distributes surplus heat. The reduction or elimination of metal ducts is a saving, and the concept means that virtually 100% of the air taken into the building is fresh.
TermoDeck Canada [www.termodeck.ca] specializes in this building method that was recently used by Diamond and Schmitt Architects in the Sheridan College High Technology building in Brampton, ON. Here, voids in the hollow core slabs were connected to ducts bringing in fresh air that the slabs warm in winter and cool in summer.
New products
A new type of concrete by Essroc actually absorbs carbon dioxide in a “safe” manner. Safe in this context means that the carbon dioxide cannot penetrate the concrete to react with the structural steel and weaken it.
Further, the cement-based compound has a special chemical composition that enables it to absorb pollutants and transform them into non-toxic gases, which it then releases. Nitrogen dioxide and sodium dioxide, for example, are turned into calcium nitrate and sodium nitrate-gases that are present in nature and, in small quantities, are completely harmless. It can also absorb other harmful components of car exhaust.
Lehigh Inland Cement [www.inlandcanada.com] has recently launched InterCem™, created by intergrinding cement and fly ash. It has lower permeability as well as chemical properties that mitigate sulphate attack and alkali-silica reactivity, thus extending service life.
Lehigh claims the product contributes to sustainability by increasing recycled material content to 37.5%, reducing GHG emissions per tonne of cement by 30%, and by conserving raw material resources at quarry sites.
New products on the horizon include ductile and even translucent concrete that will broaden considerably the material options for building skins and interior walls, adding a new dimension to the already significant role played by concrete in sustainable design.
Web references
Cement Association of Canada, www.cement.ca
Canadian Pre-stressed Concrete Institute, www.cpci.ca
Tom Schwarzkopf is an Ottawa-based writer who covers the construction industry.
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Cement plans for sustainable product
Insulated Forms
Insulating Concrete Forms (ICFs) are increasingly attractive for their energy efficiency, low maintenance and durability. ICFs offer insulation levels of R20 versus R10 for conventional concrete walls, and provide good air tightness and sound control, reduced water penetration and simpler construction with less opportunity for mistakes. Their use in multi-residential units is increasing, helping to lessen the perception that MURBs are often leaky and poorly insulated. ICFs produce less waste than with conventional forms that must be replaced periodically.
Not yet in widespread use in Canada, the ICF system is being tested by Windmill Developments in its Dockside Green project, currently under construction in Victoria.
Dockside Green
Concrete supports sustainable systems
by Terry Williams
The first phase of the much anticipated Dockside Green development on the harbourfront in Victoria, BC is now under construction where concrete supports much of the sustainable infrastructure.
For example, the use of flyash concrete (43%) is supporting the implementation of several innovative site and water conservation strategies, most notably the advanced ‘hollow fibre membrane’ sewage treatment plant. Within the large concrete tank, thousands of suspended hollow fibres will be used to draw off and filter the liquid from the sewage generated on the site, removing micro-organisms and other pathogens. The liquid will be used to flush toilets, irrigate green areas and feed an artificial stream that will meander through the site. The residual sludge will ultimately be used to fuel a bio-mass power plant for the community.
Among the technologies being tested during Phase 1, is the insulated concrete formwork floor and wall systems manufactured by Quad-Lock. The wall system will be used on a three-unit townhouse complex totaling around 3600sf, while the floor system will be tested on the first of two mid-rise apartment towers.
The wall system comprises an inner and outer layer of rigid insulation made up of interlocking blocks and held together across the cavity at 12in. centres by steel ties. Ready-mix concrete is poured into the wall cavity and vibrated to eliminate voids. The walls can be poured in lifts connected by reinforcing steel. Bent rebar is then used to make the connection between wall and floor slabs. High walls are stabilized by exterior bracing until the concrete has set up. The forms remain in place, and contribute to R-values in excess of R20. In its turn, the concrete ensures low levels of air infiltration, and high levels of acoustic isolation.
Floor slabs are poured using conventional platform staging, but through the use of rigid insulating inserts placed on a regular grid, are cast as a waffle slab. For roofs this system contributes to high levels of thermal insulation, and forms a suitable substrate for green roof installation.
Data collected from Phase 1 will be used to confirm the thermal and acoustic properties and applicability for future phases.
Terry Williams is a partner with Busby, Perkins + Will, Victoria.
Credits
- Architects: Busby Perkins+Will, Vancouver/Victoria
- Structural Engineers: Read Jones Christofferson, Vancouver
- Electrical/Mechanical Engineers: Stantec, Vancouver
- Developers: Windmill Developments, Victoria and VanCity Enterprises, Vancouver
- Photo: Sharon Daly, Cement Association of Canada