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Title: Design of Concrete Mixtures with Recycled Concrete Aggregates

Author(s): Adam M. Knaack and Yahya C. Kurama

Publication: Materials Journal

Volume: 110

Issue: 5

Appears on pages(s): 483-494

Keywords: compressive strength; mixture design; modulus of elasticity; mortar; recycled concrete aggregate; slump; workability

Date: 9/1/2013

Abstract:
This paper investigates the workability, compressive strength, and elastic modulus of normal-strength concrete with recycled concrete aggregate (RCA) as replacement for coarse natural aggregate (for example, crushed stone, gravel). To represent the variability in material quality and properties, 16 different RCA sources are used in the experimental program. Three RCA concrete mixture design methods using varying amounts of direct volume aggregate replacement, direct weight replacement, and equivalent mortar replacement are compared. It is found that these different mixture design methods result in similar compressive strength and elastic modulus of RCA concrete; however, the workability of RCA concrete may be considerably reduced when using the equivalent mortar replacement method. While the effect of increased amounts of RCA on the concrete compressive strength is generally small for all three mixture design methods, the concrete elastic modulus is more significantly affected by RCA. A multiple least-squares regression analysis of the test results is conducted to develop predictive design relationships for the strength and stiffness of RCA concrete. The results suggest that the RCA water absorption and deleterious material content can be used to prequalify the material for selected concrete strength and stiffness performance objectives.


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