3.2 Slump Testing (ASTM C143) & Air Content Tests (ASTM C231 & ASTM C173)

3.2 Slump & Air Content Tests

A slump result describes the consistency of the sampled fresh concrete. Air testing measures total fresh concrete air under the selected method. Compare both results with the specified limits and sample location. A slump value by itself cannot establish the water-cementitious materials ratio.

ASTM C143/C143M-15a slump procedure

The method applies to plastic, cohesive concrete. The method cautions that very low results below about 1/2 inch or very high results above about 9 inches may be of limited significance. When aggregate larger than 1-1/2 inches is present, apply the prescribed wet-sieving procedure. Use ASTM C1611 slump flow for self-consolidating concrete where specified.

Use a clean, damp mold with nominal 8-inch bottom diameter, 4-inch top diameter and 12-inch height. Hold it firmly on a level, rigid, damp, nonabsorbent surface. The rod has a 5/8-inch diameter and a hemispherical tamping end.

If a distinct portion falls away or shears off, discard the reading and repeat with another portion of the sample. Two consecutive shear results indicate that the sample probably lacks the plasticity or cohesiveness needed for the test. Report the invalid tests and the observed condition for the specified disposition. A collapsed, noncohesive mass also calls for checking method applicability.

ASTM C231/C231M-17a pressure air, Type B meter

Use the method for relatively dense aggregate. The response of highly porous or lightweight aggregate to applied pressure is outside the method's scope. Determine the aggregate correction factor under Section 6 on a combined sample of fine and coarse aggregate that represents the concrete sample in amounts, proportions and moisture condition. The procedure applies pressure to the inundated aggregate. A dry material weight or an absorption percentage cannot substitute for the measured factor.

1. For rodded consolidation, fill the measuring bowl in three approximately equal layers, rod each 25 times and tap the bowl 10 to 15 times per layer. If using vibration, follow the applicable two-layer procedure.
2. Strike off the surface, clean the flange, clamp the cover and close the main air valve. Open both petcocks. Introduce water through one until it flows from the other and use the specified procedure to expel air above the sample.
3. Close the bleeder, pump the chamber, allow pressure to stabilize and adjust the gauge to its initial pressure mark. Close the petcocks, apply pressure to the bowl and tap as specified. Read the stabilized gauge.
4. Close the main air valve, then release pressure through the petcocks before removing the cover. Subtract the aggregate correction factor. For example, 6.4% apparent air minus a 0.3-point correction gives 6.1% for the sample tested. Report to the nearest 0.1 percentage point unless the meter reading exceeds 8%, when the corrected reading is reported to the nearest half scale division. Where wet-sieving was needed, apply the full-mixture calculation.

ASTM C173/C173M-16 volumetric air

The volumetric method is suitable for concrete containing normalweight, lightweight or other porous aggregate. It releases air by agitating the sample in liquid and measures the resulting volume change.

1. Fill in two approximately equal layers. Rod each 25 times and tap the bowl 10 to 15 times after each layer. Strike off flush, clean the flange and attach the top section.
2. Add at least one pint of water and the selected quantity of isopropyl alcohol to control foam, recording the amount. Add water to bring the bottom of the meniscus to zero and secure the cap.
3. Invert and agitate for at least 45 seconds without keeping the unit inverted more than 5 seconds at a time. Roll for approximately 1 minute at about 45 degrees. If it leaks, the result is invalid.
4. Set the meter upright and take the initial reading when the level changes no more than 0.25 percentage point in 2 minutes. If stabilization takes more than 6 minutes or foam exceeds two full percentage divisions, discard the trial and follow the method's restart procedure.
5. Repeat the one-minute rolling for confirmation. Agreement within 0.25 percentage point establishes the final reading. If the first confirmation differs more, follow the method's procedure for one more rolling and comparison. Disassemble and inspect for undisturbed concrete, which invalidates the test.
6. Report to the nearest 0.25 percentage point. Apply the Section 8 alcohol correction and calibrated-water-cup adjustment when applicable.

Apply the correct retest procedure

A C143 shear retest uses another portion of the same sample. A check following an out-of-range C94 result follows the applicable C94 provisions and project requirements. For example, C94/C94M-20 Section 17.6.1 requires an immediate check on a new test sample for a preliminary result above the upper limit. For a low preliminary result, Section 17.6.2 allows the applicable permitted adjustment and new sampling before using its check-test procedure. If permitted, water or air-entraining admixture adjustments require remixing and acceptance sampling after adjustment. Document the reported result and any corrective action.