Sources: CP staff; National Ready Mixed Concrete Association, Silver Spring, Md.; Missouri University of Science & Technology, Rolla
More than 300 producers, design and engineering professionals, and academics from 30-plus countries who attended the International Concrete Sustainability Conference (ICSC) and 6th North American Conference on Design and Use of Self-Consolidating Concrete (SCC 2016) saw the green building revolution’s profound influence on the past two decades’ most consequential mix technology.
Plenary speakers and session presenters at the co-located ICSC and SCC 2016 discussed growing interest in recycled aggregate and supplementary cementitious materials for self-consolidating and conventional mixes. Along with green or recycled material adoption, SCC 2016 participants were presented a program heavy on advances in rheology control, geared for everyday quality assurance and to position SCC for 3D printing-modeled element or structure fabrication. Among notable conference presentations and trends:
• ASTM C1798-16 Standard Specification for Returned Fresh Concrete for Use in a New Batch of Ready-Mixed Concrete. NRMCA Senior Vice President, Engineering Colin Lobo outlined processes and protocols in a new Subcommittee C09.40 on Ready-Mixed Concrete standard tailor made for waste reduction and water savings. A five-year effort easing ready mixed producers’ deployment of hydration stabilizing admixtures on returned material, and subsequent use of delayed-set mixes in new orders, culminated with the standard’s December 2015 approval. The document stipulates material volume, time/age and temperature criteria, along with ready mixed customer approvals.
• High performance concrete’s dominant share in tall buildings. Christopher Drew, director of Sustainability at Adrian Smith + Gordon Gill Architecture, traced the prevalence of reinforced concrete in the current generation of super tall (> 300 meter) and mega tall (> 600 meter) buildings. The latter include Jeddah Tower in Saudi Arabia, the largest project under way at his Chicago firm. Engineering schemes calling for all reinforced concrete, or combinations of reinforced concrete with composite concrete and steel above, are the norm in high-rise buildings—a category once the domain of structural steel. Drew reflected on high-rise building practice in “The Role of the Concrete Industry in Reducing the Environmental Impact of the Built Environment.” Regardless of project height, he stressed the emergence of such green building practice metrics as materials’ embodied carbon dioxide emissions and how project teams are measuring them against buildings’ operating-phase carbon factors.
In a separate presentation, “Performance of Self-Consolidating Concrete Developed for Iconic and High-Rise Structures in North America,” BASF Construction Chemicals’ Van Bui reflected on SCC mixes’ pivotal role in the United States’ top two reinforced concrete buildings by height: New York City’s 1,396-ft. 432 Park Ave., supplied by Ferrara Bros. and topped out in 2014; and Chicago’s 1,134-ft. Trump International Hotel & Tower, supplied by Prairie Material and topped out in 2007. SCC success in conditions requiring 10,000 psi and higher compressive strengths has BASF testing what he calls ultra high performance SCC. As demonstrated in the 432 Park and Trump projects, SCC mixes’ modulus characteristics—specified up to 8,000 ksi—are as important to high-rise building assemblies as compressive strengths.
• Build with Strength roundtable. Within the ICSC program, NRMCA staged the first of a series of design/build community roundtable discussions to highlight the strength and durability of cast-in-place concrete in low- to mid-rise buildings. Joining the (above-noted) Christopher Drew as guests were Eric Coleman, development coordinator for Charleston, S.C.-based EYC Companies; Massachusetts Institute of Technology Principal Research Scientist Randy Kirchain, a contributor to the MIT-hosted Concrete Sustainability Hub; and, National Association of State Fire Marshals Director of External Relations Jon Narva. The roundtable was the first public event tied to the Build with Strength campaign NRMCA launched in mid-April.
• “New Trends in Rheology Driven by Sustainable SCC.” IFSTTAR (France) Senior Researcher Nicolas Roussel referenced strong concentration of ICSC and SCC 2016 presentations focusing on SCC robustness (six sessions) and crushed or recycled aggregates (14 sessions) as indicative of market and practice direction. Market forces will drive a continuing decrease in mixes’ portland cement clinker content and an increase in crushed or recycled aggregate use, he noted, and the latter will require new admixtures to curtail yield stress and control viscosity. As chair of RILEM Technical Committee on Digital Fabrication with Cement-Based Materials, he pointed to SCC improvements central to projects at the University of Southern California and ETH Zurich, respectively: Contour Crafting and Smart Dynamic Casting (note next item).
• “Digital Fabrication and Concrete: Opportunities and Challenges.” Former Sika AG principal scientist and (post-doctoral) Princeton University researcher Robert Flatts discussed an ambitious 3D printing project at ETH Zurich, where he serves as Physical Chemistry of Building Materials professor. Backed by Switzerland’s National Centre of Competence in Research, Smart Dynamic Casting will have he and colleagues testing the feasibility of large scale printing—or layering of tightly controlled mixes—to automate concrete element production. He underscored rheology’s critical role in the build up of mixer layers and avoidance of cold joints.
• “Smart Casting of Concrete Structures by Active Control of Rheology.” Ghent University (Belgium) Professor Geert de Schutter described a five-year, European Research Council-backed investigation (SmartCast). Scheduled to commence in October 2016, it will target what he described as Active Rheology Control and Active Stiffening Control, each realized through signals directed at mixer trucks, mix-conveying equipment or concrete formwork. Development of signal-based rheology and mix set time adjustments holds much promise for plant and construction site productivity, and attainment of commercial-grade concrete produced through 3D printing methods.
Plenary session and keynote speakers also included Northwestern University Department of Civil & Environmental Engineering Professor Emeritus Dr. Surendra Shah, a leading SCC and fiber-reinforced concrete authority and widely known as Center for Advanced Cement-Based Materials founding director. ACBM encompasses Northwestern, University of Illinois, University of Michigan, and Purdue University engineering departments, plus the National Institute of Standards & Technology. Peers who assisted Dr. Shah in organizing SCC 2016, along with a contingent of past students represented across academia, honored him with themed dinner and conference sessions.
This year’s ICSC was the 11th annual staging under NRMCA. Scheduled on a three-year cycle, SCC 2016 was organized by Missouri University of Science & Technology, American Concrete Institute and Paris-based RILEM (International Union of Laboratories and Experts in Construction Materials, Systems and Structures).