Crushed vs Round aggregate in concrete
Crushed vs Round aggregate in concrete
(OP)
Background:
ACI 318-05 and -08 does not appear to reward the designer for specifying crushed aggregate over rounded (usually "river rock") in structural concrete.
Chapter 4 refers to ASTM C33, and leaves it at that.
Certainly crushed rock has better interlock, and must have better shear friction for roughened surfaces. I do not have the data, but I would bet crushed rock is better in most or all performance measures.
The large aggregate (used in ready-mix concrete) in my area - Northern California - is either crushed 1"x#4 - or river rock 3/4". Crushed 3/4" is available at a premium. For high rebar congestion areas, I don't like using 1"x#4.
Most of my work is heavy civil structures, water and wastewater. Not residential, not light commercial.
Question:
Is there industry-accepted, published technical data to justify the specification of crushed rock and not allow rounded river rock? In real terms, this is about $5 to $10/yard difference. Enough for some contractors, with the help of ready mix plants, to fight over (I don't pick the contractors or ready mix plants).
ACI 318-05 and -08 does not appear to reward the designer for specifying crushed aggregate over rounded (usually "river rock") in structural concrete.
Chapter 4 refers to ASTM C33, and leaves it at that.
Certainly crushed rock has better interlock, and must have better shear friction for roughened surfaces. I do not have the data, but I would bet crushed rock is better in most or all performance measures.
The large aggregate (used in ready-mix concrete) in my area - Northern California - is either crushed 1"x#4 - or river rock 3/4". Crushed 3/4" is available at a premium. For high rebar congestion areas, I don't like using 1"x#4.
Most of my work is heavy civil structures, water and wastewater. Not residential, not light commercial.
Question:
Is there industry-accepted, published technical data to justify the specification of crushed rock and not allow rounded river rock? In real terms, this is about $5 to $10/yard difference. Enough for some contractors, with the help of ready mix plants, to fight over (I don't pick the contractors or ready mix plants).






RE: Crushed vs Round aggregate in concrete
Durability, cracking and other general parameters are not significantly different.
RE: Crushed vs Round aggregate in concrete
Dik
RE: Crushed vs Round aggregate in concrete
There is always a consideration with the bond to smooth, old durable rock if you need unusually high compressive strengths.
It is a local factor, as occurs with most aggregates.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Crushed vs Round aggregate in concrete
ACI allows both crushed rock and rounded aggregate, but goes over some of there differences in the guide. A couple highlights...
1) Both generally have same compressive strength for same cement content.
2) crushed typically requires higher water requirement than rounded.
3) Rounded aggregate may increase the pumpability of the concrete...
Read the guide for more info...
In the end I think either should be allowed provided they are staying with in your mix design requirements and have previous testing on the mix that show it meets your performance specs.
RE: Crushed vs Round aggregate in concrete
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Crushed vs Round aggregate in concrete
In very high strength concrete mixtures where coarse aggregate bond is critical, angular cubicle shaped coarse aggregates generally give higher strengths than rounded smooth aggregates. Where extremely high strengths are not required, acceptable concrete can be made with different types of aggregates, with some variation in w/cm required to provide the needed strength.
RE: Crushed vs Round aggregate in concrete
There is always the question of durability instead of strength. With our local aggregates the rounded natural aggregates can provide superior results over the local crushed limestone aggregates. Strengths are not a question with either type of aggregates.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Crushed vs Round aggregate in concrete
Thanks.
RE: Crushed vs Round aggregate in concrete
RE: Crushed vs Round aggregate in concrete
"The bond between cement paste and a given aggregate generally increases as particles change from smooth and rounded to rough and angular. This increase in bond is a consideration in selecting aggregates for concrete where flexural strength is important or where high compressive strength is needed."