Dr. R. Douglas Hooton is Professor Emeritus and NSERC/Cement Association of Canada, Senior Industrial Research Chair in Concrete Durability and Sustainability in the Department of Civil & Mineral Engineering at the University of Toronto where he taught for 35 years. He is a Professional Engineer in Ontario.
He is an Honorary member of American Concrete Institute, RILEM, ICT, and ASTM Committees C01 & C09, a Fellow of the Canadian Academy of Engineering, ASTM, EIC and CSCE. He chairs ACI committee C201 on Durability of Concrete, and ACI C130A on Sustainability of Materials. He also chairs CSA Committee A23.1/A23.2 on Concrete Materials and Methods of Construction and ASTM Committee C01 on Cements.
His research focusses on concrete sustainability and the fundamentals of cementitious materials as well as sustainability and durability performance of concrete including fluid transport properties, sulfate resistance, freezing and thawing resistance and avoiding alkali-aggregate reaction, as well as on developing related durability performance tests and specifications for cement and concrete. He has published over 300 journal and conference proceedings papers.
Progress towards sustainability through performance-based standards and specifications
Historically, specifications for cement and concrete materials, as well as for concrete mixtures, have been largely prescriptive-based and evolved from local or national experience. Specific performance criteria such as strength requirements are obviously used, but performance requirements reflecting other properties, such as durability, are not common. Prescriptive limits such as water to cement (w/c) or water to cementitious materials (w/cm, or water to binder, w/b) ratios and minimum cement contents are largely based on experience with concrete performance using portland cements and were adopted prior to the widespread use of supplementary cementitious materials (SCMs), blended cements, and chemical admixtures. As an example, the durability of concrete in aggressive exposures is largely related to its resistance to the penetration of aggressive fluids, and concretes made with blended cements or SCMs have much better resistance than portland cement concretes made at the same w/cm. It would therefore be better (and more sustainable) to use a performance test to evaluate equivalent fluid penetration resistance for different concrete mixtures rather than to set a required w/c. The result is that prescriptive specifications often provide barriers to use of more sustainable materials combinations and as we work to attain specific sustainability goals, prescriptive specifications often are counter-productive to achieving those goals.
To address these issues, standard tests and specifications are evolving and industry is moving towards performance specifications. For portland cement and blended cement concretes using conventional SCMs and admixtures, testing to support performance specifications has also evolved. Examples of these advancements will be discussed along with remaining challenges. Also, the use of alternative materials is increasing, leading to new and more complex concrete mixtures. With more complex mixtures, there is increased potential for unexpected interactions between new cement and SCM combinations when used together with a wide range of chemical admixtures, which can result in unexpected performance. For these new materials, specifications will be developed but it will not be sufficient to rely solely on those materials specifications without evaluating their performance in concrete mixtures. To address this, several ASTM tests have been developed to evaluate the performance of the entire cementitious plus admixture system in mortars or pastes. Some of these developments as well as future needs are discussed.