ACI CTCI cheat sheet

Formwork removal: vertical form faces may be removed once concrete is hard enough to resist damage; soffit/supporting formwork requires concrete strength sufficient to carry loads plus construction loads, per project specs or ACI 301 minimums.

Subgrade and forms must be inspected before placement: verify line, grade, stability, cleanliness, tightness of forms, release agent, and that reinforcement is clean and correctly positioned.

Reinforcement inspection: confirm bar size, spacing, cover, lap splice length, and support/chairs; tolerances per ACI 117 (e.g., cover tolerance typically minus 6 mm / plus 13 mm for members over 300 mm).

Placement: free fall of concrete should be limited (commonly 1.5 m / 5 ft unless using chutes or drop pipes) to prevent segregation; place in horizontal layers and consolidate before cold joints form.

Consolidation: internal vibrators should penetrate the previous layer a few inches and be withdrawn slowly; vibrator should not be used to move concrete laterally in forms.

Construction joints: locate at planned locations, roughen/clean and moisten the surface, and ensure reinforcement continuity; joints not shown on drawings need engineer approval.

Curing: maintain moisture and temperature; ACI 301/308 curing duration depends on cement type and temperature - typically 7 days for Type I, 3 days for Type III at mild temperatures, longer in cold weather.

Hot-weather placement: limit concrete temperature at placement (commonly ≤ 35 °C / 95 °F unless specified), control evaporation with windbreaks, fog spray, or evaporation retarders to avoid plastic shrinkage cracking.

Cold-weather: protect concrete from freezing until it reaches adequate strength; ACI 306 requires concrete temperature maintained and protection periods based on ambient conditions and cement type.

Slump test (ASTM C143): measure slump to nearest 6 mm (1/4 in.); discard samples that have been remixed or taken beyond 15 minutes after sampling; slump is not a measure of strength.

Air content: pressure method (ASTM C231) for normal-weight concrete; volumetric method (ASTM C173) for lightweight or when pressure method is unsuitable.

Compressive strength cylinders (ASTM C31): standard 150×300 mm (6×12 in.) cylinders; moist-cure until test; test at 7 and 28 days per spec; report average of two cylinders for a test result.

Acceptance of strength (ACI 301/318): strength level is acceptable if no single test falls more than 3.5 MPa (500 psi) below f'c and no average of three consecutive tests falls below f'c.

Temperature (ASTM C1064): measure in fresh concrete with a calibrated thermometer at least 75 mm into the concrete; record to nearest 0.5 °C (1 °F).

Sampling (ASTM C172): obtain composite sample from middle portion of the discharge; do not sample first or last portions; remix sample before testing.

Cylinder curing: initial cure in field within temperature range (commonly 16–27 °C / 60–80 °F) for 24 ± 8 hours before transport to lab; standard moist curing thereafter.

Flexural strength (ASTM C78): third-point loading on beam specimens; modulus of rupture reported; typically used for pavement acceptance.

Density/unit weight and yield (ASTM C138): verify batch yield and air content; unit weight differences help detect batching or air-content errors.