The ACI's Strategic Development Council (SDC), which is responsible for encouraging technology acceptance within the industry, has identified SCC as an “industry critical technology.” As such, SCC is a high priority for ACI, and the organization will focus on removing barriers to its adoption and ensuring its widespread acceptance as quickly as possible.
According to Phelan, the SDC's goal is “15 by 15.” This means SCC will account for 15% of all ready-mixed concrete produced in the U.S. by 2015. He has been designated the SDC champion of SCC and is responsible for reporting on the status of these efforts every six months.
Gibbons, who has also served on several ACI committees, agrees. “SCC is the single biggest game changer in the concrete industry today,” he says. “It allows us to design a mix according to what makes sense for the specific needs of a job.” He credits polycarboxylate water reducers with providing this flexibility.
Although superplasticizers have been the popular solution for extreme water reduction, they must be added in a single, pre-measured dose. “With superplasticizers, it's all or nothing,” says Gibbons. “Now polycarboxylates allow us to custom tailor the mix. You can use them for low slump to SCC, and anything in between.”
Gibbons also points to P2P, the prescriptive- to performance-based specification movement, as a major driving force that will encourage the adoption of advanced admixtures. SDC has also identified performance-based specifications as an industry-critical technology. Since 2004, ACI members have been developing a set of guidelines, the Report on Performance-Based Requirements for Concrete (ITG-8R-10). The is championed by ACI Committee 329, Performance Criteria for Ready Mixed Concrete.
According to CRSI's Gibbons, “Committee 329 recognizes the need to move beyond prescriptive mix specifications if the industry is going to meet the demands of today's rapid cycle construction schedules.”
Gibbons uses the example of post-tensioned concrete, which traditionally required a three-day set. But, now tensioning cables can be pulled after only a single day.
“This would not be possible without the creative use of chemical admixtures, and designing concrete mixes for performance, and not by prescription,” Gibbons says.
He notes that producing high-performance concrete based on project requirements, rather than generic specifications, also contributes to the industry's environmental stewardship. Tailoring materials and construction techniques to the exact needs of a job eliminates waste. By using supplementary cementitious materials on an as-needed basis, producers can add strength to concrete while recycling industrial byproducts.
To maximize their benefits, Gibbons says, “admixtures should be used for optimization, not in place of proper mix proportioning.”
From his remote vantage point, Ryan Costanti also sees a green future with cement replacement materials such as fly ash, silica, and slag becoming more popular. "We'll be focusing on creating the highest quality concrete and reducing environmental impact," he says.
For a copy of the 2010 Report on Chemical Admixtures for Concrete, visit the ACI bookstore. Contact Bill Phelan or Jack Gibbons.
New Developments in Chemical Admixtures
Members of ACI Committee 212 presented updates to its New Report on Chemical Admixtures at the ACI Spring 2011 Convention in Tampa, Fla., in early April. “The changes are enormous,” said Bill Phelan, senior vice president of marketing and technical services for Euclid Chemical. “We went from six to 16 chapters.” Topics include:
The rate of cement hydration can be controlled to produce high early strength concrete and extend set control. The update includes three chapters on this topic.
Self Consolidating Concrete (SCC)
With new polycarboxylate high-range water reducers and viscosity modifying admixtures, SCC can be produced and placed in a growing number of applications.
Shrinkage Reducing Admixtures (SRAs)
By controlling drying shrinkage, SRAs reduce curling and cracks that occur as concrete dries.
These extend the life of concrete that may be exposed to the corrosive effects of metal, such as reinforcing steel.
Alkali-silica Reaction Control
Pozzolans can reduce cracking caused by chemical reactions between cement and some aggregates.
Waterproofing admixtures may be gaining popularity in commercial applications, such as below-grade foundations.