Why preparation matters
- Aggregate distribution, air voids, and density affect mechanical measurements. A poor specimen can produce misleading results even when the equipment is precise.
- Plan specimen dimensions and quantities before mixing so enough material is available and sample-to-sample variation is reduced.
Mixing and compaction
- Condition aggregates and binder at the working temperatures defined by the method, then mix until the material is uniform.
- Compact using the selected procedure—gyratory, impact, or slab—and record temperature, energy or gyrations, mass, and density.
- Prepare a slab when the test requires a larger specimen; check uniformity before coring or cutting pieces.
Cutting and coring
- Core or cut beams and special geometries using guides that maintain parallel faces, dimensions, and orientation.
- Check every face, specimen integrity, and final height; reject or document defects that could affect the test.
Good practice
- Maintain identification and traceability from the original sample to each specimen; do not mix batches or lose fines.
- Cutting can create particles, splashes, and entanglement hazards. Use guards, cooling, and laboratory safety procedures.
Mix design and compaction calculations
- Combined grading: Pmix(d) = Σ[xj · Pj(d)], where xj is the mass fraction of aggregate j and Pj(d) its percentage passing sieve d. Check that Σxj = 1.
- Binder content: Pb = 100 · mb / Mmix, where mb is binder mass and Mmix is total mixture mass. State whether the percentage is based on total mix mass or aggregate mass.
- Density and voids: ρb = Mdry/Vbulk and Gmb = ρb/ρw; Va = 100 · (1 − Gmb/Gmm). ρw is water density at the reference temperature.
- Mass, volume, and density must refer to the moisture and temperature condition defined by the method. Do not treat gyration count as a substitute for a target density.
Educational reference guide. Check the current standard, calculation assumptions, and project specification before applying a procedure or acceptance criterion.