Concrete Products

JUN 2019

Concrete Products covers the issues that attract producers of ready mixed and manufactured concrete focusing on equipment and material technology, market development and management topics.

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24 • June 2019 www.concreteproducts.com NEWS SCOPE PRACTICE A new Portland Cement Association report presents historical data, evidence from external sources, and structural material comparisons supporting the premise: Cast-in-place or precast concrete, or concrete masonry construction methods lead to longer lasting buildings owing to their ability to stand up to normal wear and tear plus resistance to extreme weather events. "The Real Value of Resilient Construction" addresses design, engi- neering and life cycle criteria for owners and lawmakers or officials behind policy affecting public or private building design. "U.S. tax- payers cannot afford to continue building and rebuilding the way we did in the past. Strong, robust structures ensure community con- tinuity and provide long lasting value for scarce taxpayer dollars," says PCA CEO Michael Ireland, emphasizing an industry position as Congress and government agencies take stock of escalating post-di- saster costs rooted in sub-par construction. Between 1996 and 2014, the National Weather Service finds, dam- ages in the United States due to hazards (hurricanes, tornadoes, floods, earthquakes, wildfires, etc.) surpassed $375 billion. Costs tied to natural disasters in 2017 alone reached $307 billion, according to the National Oceanic and Atmospheric Administration. "The Real Value of Resilient Construction" notes that reinforced concrete struc- tures reduce recovery costs after disasters hit, while the upfront costs of incorporating resilient concrete features are likely to save money in the long run. "Concrete systems can be competitive at every level of resilience. There is usually a concrete solution that fits the needs and budget of any project," the report affirms. "Real Value" also looks at how concrete is the basis of new "green" buildings, since structures that last longer equate to a lower life cycle environmental footprint. "Concrete structures are the back- bone of modern society, including residential, commercial, public, and industrial applications," authors argue. "High-use areas, in particular, benefit from its strength and durability. And concrete provides another benefit: It can serve as the structural system and architectural finish." Report qualifies life cycle aspect of robust construction methods Report is posted at www.cement.org/resilience. In their current Research Brief, "Simulating the Formation of ASR Gels," staff at the Massachusetts Institute of Technology-hosted Concrete Sus- tainability Hub (CSHub) shed new light on conditions, mechanics and protracted timelines surrounding alkali-silica reactivity in concrete. "Although it has received much research attention, an essential ques- tion remains—how does a soft gel, as is formed by this reaction, induce the critical level of stress to exceed the strength of, and crack the con- crete matrix?" researchers explain. "One possibility is that the ASR gel increases in viscosity as it imbibes calcium with age and a concomitant expansion causes the concrete failure. Another is that the gel's rate of flow into the porous microstructure is slower than the rate at which it forms, which builds up stresses that cannot be relieved." Simulating gel formation at the atomic level, CSHub researchers note, "This new method enables us to evaluate the impact of the water to silicon ratio. Modeled gels respond to chemical changes, such as water content, and relative composition of alkali and calcium. More impor- tantly, [the method] demonstrates that drying the gel strongly affects its structure. This drying effect has not been considered in past research and provides an opportunity to reconsider [previously] proposed mech- anisms … Additionally, we observed a reduction in the volume of gel as it calcifies, which offers further insight into reasons for concrete failure." MIT Research Scientists Romain Dupuis and Rolland Pellenq con- clude: Better control of ASR requires knowledge of a gel's molecular structure; a simulation approach at the atomic level is an efficient way of examining gel structure; and, progress in simulation techniques could help characterize gels, advancing the industry's approach to ASR. Their work continues with oversight of CSHub sponsors, the Ready Mixed Con- crete Research & Education Foundation and Portland Cement Association. MIT CSHUB RESEARCHERS MODEL ASR GEL'S DELETERIOUS TRAJECTORIES CSHub researchers picture pure silicate in a wet environment, calling the chains' structure "a complex 3D skeleton" with branching and silicate rings. Their "Simulating the Formation of ASR Gels" Research Brief is posted at www.cshub.mit.edu. ILLUSTRATION: Concrete Sustainability Hub

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