New research, published this month by the National Concrete Pavement Technology Center, Ames, Iowa, may lead to a profound change in the way concrete mixtures are proportioned in the future.
The study, An Innovative Approach to Proportioning Concrete Mixtures – Technical Report March 2015, analyzes the relationships between the selected mix characteristics and their corresponding effects on tested properties. It aims to move industry norms from prescriptive- to performance-based-mixes.
"... the bad news is that most of the requirements that are in current specifications are not useful. Having figured out what we want to deliver then, we start to fool around with the proportioning side of the game,which is looking at, 'ok I've got this material and this material, how much of each,'" said Peter C. Taylor, associate director, National Concrete Pavement Technology Center, in a 2014 American Concrete Institute presentation on the subject of proportioning.
According to the report:
As budgets grow tighter and increasing attention is being paid to making mixtures that are more efficient in their usage of materials without compromising performance, a performance-based mixture proportioning method is needed to provide the desired concrete for a given specification.
Findings could also help improve sustainability.
Current prescriptive-based specifications deliberately promote overdesigning mixes by using cement content as a safety factor. This has the effect of adversely affecting the environment because of the CO2 footprint associated with manufacturing portland cement (Hendriks et al. 2004, Battelle Memorial Institute 2002). Therefore, developing a mixture proportioning method that is based on performance criteria and does not limit the efficient use of materials will be beneficial in improving sustainability.
The report – sponsored through the Federal Highway Administration (DTFH61-06-H-00011 (Work Plan 25) and Pooled Fund Study TPF-5(205): Colorado, Iowa (lead state), Kansas, Michigan, Missouri, New York, Oklahoma, Texas, Wisconsin – provides step-by-step instructions and spreadsheets to guide the selection of required aggregate and paste systems based on the performance requirements for concrete pavements or other applications. Further, the proposed method is user-friendly, easy to apply in practice, and flexible in terms of allowing a wide range of material selection.
Founded in 2000, the mission of the National Concrete Pavement Technology Center is to unite key transportation stakeholders around the central goal of advancing concrete pavement technology through research, tech transfer, and technology implementation.