a concrete contribution to the environment ™
The EcoSmart project started in 1998 from discussions between operators of local cement plants in the region of Vancouver, BC and representatives of Industry Canada, Environment Canada, Natural Resources Canada and the Greater Vancouver Regional District – now Metro Vancouver.
Vancouver had (and still has) two cement plants owned by Lafarge and Tilbury cement (now Lehigh). They were the two largest industrial emitters in the city and the main issue was how to control their greenhouse gas (GHG) emissions.
Contrary to ordinary industrial emissions such as dust, nitrogen or sulfur dioxide (PM, NOx and SOx), no ‘CO2 filter’ existed to cut GHG emissions and therefore the problem was: how to avoid the GHG emissions in the first place – a concept known as “Pollution Prevention” or P2 or in other words how to decouple CO2 emission from the production of cement.
Portland cement is the glue that binds together aggregates and sand in concrete. It is produced by calcining limestone, a process that produces CO2 from 2 different sources: The reduction of limestone into lime ( CaCO3 -> CaO + CO2 ) and the combustion of fuel (typically coal: C+O2 ->CO2) that heats the raw material to the high temperature required by the calcination process. As a result cement production is extremely carbon-intensive. Depending on the efficiency of the process, producing one tonne of cement emits between 0.8 and 1.2 t of CO2.
Nobody produces cement for the sake of producing cement. Cement is manufactured in order to make concrete, a ubiquitous construction material. Likewise, nobody produces concrete for the sake of producing concrete. Concrete is used to create structures and infrastructures: houses, buildings, roads, bridges, etc,. Cement and concrete are only a means to a useful end.
If cement is so GHG-intensive and the end-product so important to society, it is logical to try to produce concrete structures with the same quality and strength using less cement.
Supplementary Cementing Materials (SCMs) are a class of materials that can be used in the manufacture concrete as partial replacement of Portland cement. The most frequently used SCMs are: fly ash – a by-product of coal-fired power plants; ground granulated blast furnace slag (GGBFS)- a residue of steel production; and silica fume – also known as micro-silica. Less-commonly-used SCMs include: natural pozzolans (or volcanic ash); metakoalin (which could be mined or produced from Alberta oil sands tailing ponds); metallurgical slag (known as GSCem); and rice husk ash.
Every SCM has unique properties that help improve various aspects of concrete, and all share at least one advantage : they help reduce the amount of Portland cement required per unit of concrete.
From a GHG-buster point of view, the less Portland cement, the better. But this goal needs to be placed in the context of the construction industry: from an engineering perspective, the performance and safety of the concrete structure is paramount; for the contractor, the ease of installation of concrete is a key economic factor; and for the supplier of concrete known performance and liability are critical concerns.
Hence the EcoSmart Concrete objectives:
Optimizing the amount of SCM in concrete while maintaining or improving performance, cost and constructability.
The CanMet laboratory of Natural Resources Canada in Ottawa had developed a concrete mix design in which half of the cement normally required is replaced by fly ash, with no adverse effect on concrete strength and performance. Known as High Volume Fly Ash (HVFA) concrete, the mix had thus a 50% lower GHG-signature than normal concrete for the same performance. EcoSmart with the help of federal funding started a series of demonstration projects or case studies using 50% fly ash concrete. Reports listed on this web site give the technical details of these projects. ( For example Liu Center, Nicola Valley Institute of Technology , or York University Computer Science Building) .
The 50% HVFA case studies brought precious lessons. The slowing of setting time was one of the most obvious. In Canada, concrete is poured in cold weather almost half of the time. Fly ash does not have the heat of hydration that normally keeps concrete warm during initial setting. Having less cement, HVFA concrete takes more time to set in cold weather. This will result in delaying removal of forms, reducing construction speed and potentially bringing additional cost to the contractor. The EcoSmart case studies demonstrated that a one-size-fits-all 50% HVFA concrete is not the best solution. An optimization approach where the amount of fly ash and SCM would be adapted to the construction context, weather and performance goals would have a better chance of being adopted by the construction industry. Consequently, EcoSmart started a new series of cases studies focusing on cement replacement optimization (see example such as Bayview High-Rise, Little Mountain Reservoir and High Design Study by RJC and Halcrow-Yolles).
These cases studies lead to the decision to develop a web-based expert system tool, called SOS – for SCM Optimization System – with the objective of helping construction professionals understand the effect of using SCM in a particular project. (See SOS)
Bigger bang for the buck
While the application of SCM concrete technologies in Canada and the US is an important step in reducing the GHG impact of the construction industry in North America, it is small compared to the benefits it could bring to fast growing countries such as China and India.
EcoSmart began efforts to export SCM technology by approaching the UAE (Dubai and Abu Dhabi) market. At the time, Dubai was the fastest construction market in the world, and it was said that half of the word construction canes were in the UAE. Some of the world’s best engineers and contractors were working in the UAE, making it an excellent place for implementing SCM technology outside Canada.
(see UAE for case studies and technical reports)
China produces 100 times more cement than Canada (about 1.3 billion tonnes per year). China is also the world’s largest producer of fly ash and slag. It is said that one new coal-fired power plant is built in China every week. The GHG-reduction potential for transferring SCM concrete technologies to China is enormous. EcoSmart has worked with key players of the Chinese cement/concrete/construction industry to develop a similar program in China. (See China)
EcoSmart will now continue supporting a greater use of SCM in concrete, particularly through the promotion of the SOS Software in North America and other countries such as China.
If you are interested in participating in future EcoSmart Concrete activities please contact us.