- Author
-
Bentz, D. P.
|
Irassar, E. F.
|
Bucher, B. E.
|
Weiss, W. J.
- Title
- Limestone Fillers Conserve Cement. Part 1. An Analysis Based on Powers' Model.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
Universidad Nacional del Centro de la Provincia de Buenos Aires, Olavarria, Argentia
Purdue Univ., West Lafayette, IN
- Journal
-
Concrete International,
Vol. 31,
No. 11,
41-46,
November 2009
- Keywords
-
limestone
|
cements
|
fillers
|
curing agents
|
compressive strength
|
mortar
|
mixtures
|
equations
|
specifications
|
water
|
powders
|
hydration
|
volume fraction
- Identifiers
- Powers' Model; theoretical limits; compressive strength results for mortar cubes; compressive strength results for concretes
- Abstract
- "Green" concrete has become a rallying cry for the twenty-first century. In addition to its field performance, a concrete mixture is now judged by its recycled material content, embodied energy, and carbon footprint. Bonavetti et al. have proposed that limestone powder substitution for cement makes perfect sense in concrete mixtures with lower water-eement ratio (w/c) values, as space limitations or water deficiencies in these mixtures can make it impossible for all of the cement to hydrate. Because unhydrated cement is essentially expensive filler, limestone powder substitution can cut costs as it saves energy and reduces carbon dioxide emissions resulting from cement production. While limestone/cement blends have been employed for many years in Europe, it was only in 2004 that the ASTM International C150 standard specification for portland cement was modified to allow the incorporation of up to a 5% mass fraction of limestone in ordinary portland cements, and this was done only after an extensive survey of the available literature led to the conclusion that "in general, the use of up to 5%limestone does not affect the performance of portland cement." Higher addition rates of 10 to 15% are currently beiing discussed in the U.S., and in 2009, the Canadian Standards Association has in fact approved Portland Limestone Cements with up to 15%.In the U.S., some ready mixed concrete producers already add limestone powder above a 5% level directly to their concrete mixtures. In the Netherlands and elsewhere, limestone powder is commonly employed as a filler in self-consoIidating concretes, once again at values well above the 5% level. In Part 1 of this article, we use Powers' model to analyze total capillary porosity in limestone-filled cement pastes to suggest appropriate replacement levels. We'll address durability issues and the effects of limestone fineness on the performance of mixtures in Part 2.