RELATIONSHIPS OF CONCRETE STRENGTH TO MAXIMUM SIZE AGGREGATE
Accession Number: 00217627
Record Type: Component
Abstract: THE CONCEPT THAT CONCRETE STRENGTH IS BENEFITED BY USING THE LARGEST MAXIMUM SIZE OF AGGREGATE PRACTICABLE IS DISPROVED. IT WAS FOUND THAT MAXIMUM STRENGTHS IN BOTH FLEXURE AND COMPRESSION WERE SECURED WITH COARSE-AGGREGATE OF ABOUT 3/4 IN. MAXIMUM SIZE. USE OF COARSER AGGREGATES, IN SPITE OF REDUCTION IN MIXING WATER, CAUSES A REDUCTION IN STRENGTHS. THE CAUSE OF THIS REDUCTION OF STRENGTH WAS SOUGHT IN CONCEPTS THAT GREATER SURFACE AREA FOR BOND AND CROSS-SECTIONAL AREA TO RESIST SHEAR ARE AVAILABLE WITH THE USE OF SMALLER SIZE AGGREGATES.
Supplemental Notes: Vol 38, pp 367-385
TRIS Files: HRIS
Authors: WALKER, S ; Bloem, D L; Gaynor, R D; Gray, J E

Anyone have info on aggregate size.vs strength?I assumed the larger aggregates provided more strength,but It appears this is not so.Larger aggregate can cause cracks which are longer than with smaller aggregate.Smooth or rounded aggregate are isotropic reiforcments.The question was brought up seeing some of the guys are trying sand only.
Would a mix of fines only, have better specs than one with 1/4 and1/2" aggregate?
Here is something from one of my plastics books:
"Spheres clearly have no aspect ratio to provide reinforcement properties,but their geometry affords important advantages.
Unlike fiber with its directional strength,the spheres effects are isotropic.Photoelastic stress is concentrated at the ends of a fiber,the edges of a flake or irregular particle,but stress around a sphereare even and predictable.spheres distribute stress evenly throught the matrix"
Smooth rocks seem to be in order.
Larry