Supplementary Cementing Materials (SCM) Optimization System
There is an increasing awareness amongst building professionals and officials that the use of higher levels of supplementary cementing materials (SCMs) in concrete can bring substantial benefits in terms of performance, cost, and constructability in addition to dramatic improvements to sustainability and the greenhouse gas (GHG) signature of concrete construction. However, there is also concern about potential pitfalls, such as lower setting time, longer curing requirements, or the potential for SCMs to introduce harmful chemicals into the concrete.
Canada-wide, SCMs currently replace an average of about 10% of Portland cement in concrete. However, research in federal laboratories and universities has demonstrated that greater levels of SCMs can be used provided that there is a judicious selection of materials, mix proportions and construction practices. EcoSmart Foundation, a not-for-profit foundation established with government support to promote greater use of SCMs in Canada, has facilitated a number of case studies demonstrating that a significant percentage of Portland cement can be replaced by SCMs without affecting cost, performance or constructability.
Most of these demonstration projects had the benefit of a high level of expert guidance from academics and industry professionals. This high level of expert involvement and knowledge has given the developers and builders involved in the demonstration projects the confidence to embark on a relatively novel approach to working with concrete. In addition, it has ensured that technological barriers have been overcome, and that risks and potential liabilities have been minimized. However, it is not practical for this level of expertise to be used on all projects, both because of cost and the relatively small number of experts available. To close this gap between the application of the technology to a few hand-picked projects and its wide acceptance by the market, EcoSmart’s industrial advisors have strongly recommended that we develop a computer-based advisory/expert system: a sophisticated tool that will be simple to use, can draw on a continuously updated data bank of expertise and knowledge, and will help to determine for a given project the optimal level of cement replacement as well as the best materials and construction practices to use.
The optimized type and level of SCMs for a given project is usually reached through a compromise between the various – and sometimes conflicting – interests and objectives of its participants. For example, use of SCMs may reduce material cost for the ready-mixed concrete supplier but result in a longer setting time, more stringent curing requirements and increased construction costs for the contractor. The owner may want to get additional LEED® (Leadership in Energy and Environmental Design) Green Buildings Rating System credits by requiring the highest feasible level of SCMs; a government infrastructure project may have a rigorous GHG mitigation agenda; the structural engineer may require a particular design strength or durability within a period of time; the architect may want more fly ash for colour or surface appearance. SCMs may affect water/cement ratio, reaction with aggregates, durability, permeability, or expected life of concrete. The advisory system will be complex, mirroring the complex decision-making process in concrete construction, but the scientific and technical experience exists within the group to fully develop such a system.
The computer system – the “SCM Optimization System” or “SOS”- will allow those involved in a concrete construction project – owners, designers, suppliers, and contractors – to simulate the effects of varying the type and level of SCMs on the whole project and to interactively settle on a best case optimum. This system will be web-based and will be maintained and continually updated with the results of new research and projects.
The SOS tool will provide substantial competitive advantages to its users, including:
- Cost: SCMs are often more economical than the Portland cement they replace. Users of the SOS tool will be able to optimize SCM content according to cost criteria.
- Design: The optimum use of SCMs improves the quality, durability and overall performance of concrete. Ready-mix operators and engineers will have an easy and fast way to determine the optimum level of SCMs for desired performance specifications.
- Construction: Effect on construction schedules (and concomitant costs) is often seen as the main barrier to increased use of SCMs. Contractors will be able to identify additional costs or issues related to particular levels of SCMs and also receive advice on how to overcome these difficulties and avoid pitfalls.
- Green building: Sustainability is increasingly becoming a key specification in new projects due to more stringent federal sustainability requirements as well as the growing adoption of LEED in Canada. Emphasis on sustainability and the environment will grow dramatically in the next 10-20 years; this tool will help accelerate that growth. Developers, building owners and architects will be able to establish embodied GHG signature targets and calculate LEED credits. By providing ways to meet these requirements, the SOS program will also give a competitive advantage to contractors bidding on such projects.
- Collaboration: The SOS tool will facilitate a collaborative decision-making process, bringing significant benefits and economy to the project.
- Repository: The SOS will provide a repository for the results of new research and case studies and therefore fast-track transfer of knowledge and expertise.
By allowing increased reduction of the GHG signature of concrete, the SOS will also support the Canada Climate Change initiative. The SOS tool is therefore a win-win solution for all participants: this tool makes the industry more competitive and profitable and supports Canada’s GHG reduction commitments. In addition, the advisory system is not limited to use in Canada and, through extensions to the information databases, will appeal to practitioners throughout all of North America, Europe, and Asia.