ACI Special Inspector cheat sheet

Formwork removal: minimum 500 psi (3.5 MPa) compressive strength before removing vertical forms; 70% of design strength before shore removal for structural members unless approved by engineer.

Slump test per ASTM C143: complete within 2.5 minutes after sampling begins; discard if slump exceeds 9 in. (230 mm) unless superplasticizer is used.

Specified slump tolerance: 1 in. for specified slump of 2 in. or less; 2 in. for specified slump of 3-4 in.; 3 in. for specified slump of 5 in. or more.

Concrete temperature limits (ACI 301): 90 F (32 C) max as placed in hot weather; 50 F (10 C) min for sections less than 12 in. thick, 45 F (7 C) for 12-36 in., 40 F (4 C) for over 36 in.

Cover requirements (cast-in-place, not exposed to weather): 1.5 in. for slabs/walls/joists up to No. 11 bar; 2 in. for beams/columns; 3 in. for footings.

Consolidation: internal vibrator spacing not to exceed 1.5 times radius of action; do not use vibrators to move concrete laterally more than a few feet.

Cold-weather protection: maintain concrete at 50 F (10 C) minimum for 7 days, or 40 F (4 C) for 3 days if Section 306 protection methods are used.

Construction joint surfaces: roughened to amplitude of 1/4 in.; shear transfer requires clean, laitance-free, pre-wetted surface before placing new concrete.

Post-tensioning: elongation measured and compared to calculated value; ±7% agreement is typical acceptance criterion.

ASTM C172: sample from middle of discharge; minimum sample volume 1 ft³ (0.028 m³); composite samples from multiple locations combined and remixed.

ASTM C143 slump: fill mold in 3 equal layers, rod each 25 strokes, lift mold vertically in 5 ± 2 seconds; results in 1/4 in. increments.

ASTM C231 air content (pressure method): fill in 3 layers, rod 25 strokes each; concrete must be free of aggregate larger than 1.5 in.; calibrate with known air content each day of use.

ASTM C173 volumetric air: requires isopropyl alcohol; applicable to lightweight and highly porous aggregate concrete where pressure method is unreliable.

ASTM C39 compressive strength: cylinders 6x12 in. or 4x8 in.; 4x8 in. results require correction factor; load rate 35 ± 7 psi/s for 6x12 in.

ASTM C31 curing: cylinders stored at 60-80 F (16-27 C) for first 24 hours; moist cure until test; test at 7 and 28 days.

ASTM C1064 temperature: probe inserted at least 3 in. into concrete; reading taken within 5 minutes of sampling; read to nearest 1 F (0.5 C).

Acceptance per ACI 318: average of any 3 consecutive strength tests must equal or exceed f'c; no single test below f'c minus 500 psi (or 0.85 f'c).

Cylinder strength vs. in-place: field-cured cylinders represent structure; standard-cured cylinders represent potential strength of the mix.