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Effects of Particle Shape and Surface Texture
of Aggregate on Concrete
- Rough textured and angular aggregates give better _______ between the aggregate and the cement paste and thus higher strength for the same water cement ratio.
- However, rough and angular aggregates requires _________ to produce the same workability in a fresh concrete.
- The two effects offset one another. With satisfactory gradation, both crushed and noncrushed aggregates (of the same rock type) generally give about the same ________ for the same cement content.
- It is undesirable to have _________________ particles.
FDOT Specifications for Coarse Aggregate for Concrete
Coal & lignite 1.0% max Clay lumps & friable particles 3.0% max Clay lumps 2.0% max Friable particles 2.0% max Materials passing No. 200 sieve At source 1.75% max At point of use 3.75% max Chert (spec. grav. less than 2.4) 3.0% max Free shell 1.0% max Cinders & clinkers 0.5% max Organic matter 0.03% max
FDOT Specifications for Coarse Aggregate for Concrete
L.A. Abraison Loss 45% max Soundness Loss (Sodium sulfate, 5 cycles ) 12% max Flat or elongated pieces 10% max (A flat or elongated particle is one having a ratio between the maximum and minimum dimensions exceeding 5 to 1) Gradation Must meet gradation requirements for the specified stone size
FDOT Specifications for Fine Aggregate for Concrete
Shale 1.0% max Coal and lignite 1.0% max Clay lumps 1.0% max Cinders and clinkers 0.5% max Organic impurity test Pass (If Fail, run Test for the Effect of Organic Impurities on Strength of mortar. Strength ratio at 7 and 28 days shall not be less than 95%) Materials passing No. 200 sieve 4% max Gradation requirement - Slightly different from ASTM C33. Slightly finer materials are allowed.
Recycled Concrete as Aggregate
- Old concrete crushed to proper gradation can be used as aggregate.
- The strength and durability of the concrete produced are limited by those of the old concrete.
- Generally has a higher absorption, a lower specific gravity, and a lower strength than a normal natural aggregate.
- FDOT spec. allows a maximum L.A. Abrasion Loss of 50% for recycled concrete aggregates.
Crushing Concrete Slabs – Making Recycled Aggregate
Recycled Aggregate -- Crushed PC Concrete
