ASTM C191 — Cement test methods

Time of setting of hydraulic cement by Vicat needle

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1. Purpose and scope

This standard covers test methods for determining setting times of hydraulic cements using a Vicat needle. Two procedures are provided:

1. Procedure A (reference test method): Manual operation of a standard Vicat apparatus.
2. Procedure B (automatic procedure): Use of an automatic Vicat machine that meets qualification requirements of this test method.

Important: Fresh hydraulic cement mixtures are caustic and may cause chemical burns to skin and tissue with prolonged exposure. Determination of appropriate safety and health practices is the responsibility of the user.

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2. Environment and laboratory conditions

For standardized setting-time measurements, control the environment as follows:

• Mixing room: Temperature, humidity, and mixing-water temperature shall conform to ASTM C511.
• Curing environment: Moist cabinet or moist room shall conform to ASTM C511.
• Materials: Before testing, all dry materials shall be within the same temperature range as the mixing room.
• Water: Potable water is acceptable for routine testing; reagent water shall be used for referee and cooperative testing.

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3. Vicat apparatus and equipment (manual Procedure A)

The Vicat apparatus (as described in Fig. A1.1) shall meet the following requirements.

3.1 Frame and movable rod

• Movable rod (B): Mass shall be 300 ± 0.5 g. The rod may be reversible and is locked in position with a set screw (E).
• Indicator (F): Adjustable indicator moving along a millimetre scale.

3.4 Other equipment

• Trowel: 100–150 mm long steel blade with sharpened straight edge; edge straightness deviation not more than 1 mm.
• Mixer and bowl: Mechanical mixer conforming to ASTM C305.

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4. Preparation and moulding of paste

Paste shall be brought to normal consistency before the setting-time test.

4.1 Mixing

1. Prepare a new batch using 650 g of cement and the percentage of water required for normal consistency (Test Method C187).
2. Mix mechanically in accordance with ASTM C305. (Optionally, paste remaining from the normal-consistency test (C187) or autoclave expansion (C151) may be used.)

4.2 Moulding (Procedure A)

1. Quickly form the mixed paste into a ball with gloved hands.
2. Toss the ball six times from hand to hand with hands about 150 mm (6 in) apart.
3. Press the ball into the large end of the conical ring (G) until the ring is completely filled.
4. Remove excess at the large end with one motion of the palm.
5. Place the ring on the base plate (H) with the large end down.
6. Strike off excess at the small upper end with a single oblique stroke of the trowel.
7. If needed, lightly touch up the top surface (without compacting the paste).
8. Place the specimen immediately in the moist cabinet and keep it there except during measurements.

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5. Determination of setting times (Procedure A)

5.1 Reading procedure and timing

1. Initial rest: After moulding, keep the specimen undisturbed in the moist cabinet for 30 minutes.
2. Frequency: At 30 minutes, take the first penetration with the 1 mm needle. Repeat every 15 minutes (every 10 minutes for Type III cement) until penetration is 25 mm or less.
3. Penetration:
   • Lower the rod until the needle tip just contacts the paste surface.
   • Tighten set screw (E); zero the indicator or record the first reading.
   • Release the set screw quickly; allow 30 seconds of penetration.
   • Read penetration depth from the indicator after 30 seconds.
4. Spacing: Each penetration shall be at least 5 mm from any previous imprint and at least 10 mm from the mould wall.

(Tip: For very soft early readings, the fall may be slowed by hand to avoid bending the 1 mm needle; for readings that determine setting times, release the rod fully by opening the set screw only.)

5.2 Initial setting time

• Elapsed time from first contact of cement and water until the needle penetrates exactly 25 mm.
• If 25 mm is not observed directly, calculate by interpolation.

5.3 Final setting time

• Final set is the first reading at which the needle does not produce a complete circular impression on the surface.
• When detected, perform two additional penetrations on different areas for verification within 90 seconds after the first final-set reading.

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6. Calculations and reporting

6.1 Initial setting time (interpolation)

Report initial setting time in minutes, rounded to the nearest 1 minute:

T = E + ((25 − C) × (H − E)) / (D − C)

Where:

• E = minute of the last penetration reading greater than 25 mm
• H = minute of the first penetration reading less than 25 mm
• C = penetration depth (mm) at time E
• D = penetration depth (mm) at time H

(C and D bracket the 25 mm threshold; if the denominator is near zero, take additional readings.)

6.2 Reporting

• Initial setting: round formula result to the nearest 1 minute.
• Final setting: total time from water–cement contact until the final-set criterion is met; round to the nearest 5 minutes.
• Report whether Procedure A or Procedure B was used.

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7. Automatic procedure (Procedure B) — key differences

1. Measurement interval: The device shall be capable of automatic measurement and recording at intervals not exceeding 10 minutes.
2. Moulding: Similar to manual procedure; finishing of the top surface may be more systematic (trowel ~30°, sawing motion, rotate 90° and repeat). Automatic devices often reference the top edge of the mould—surface flatness is critical.
3. Qualification: For acceptance/rejection testing, the automatic apparatus must demonstrate equivalence to Procedure A per Annex A2 using three cements meeting C150/C150M, C595/C595M, or C1157/C1157M. Mathematical standardization may be applied to correct bias.

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8. Precision — Procedure A

• Single-operator (within-laboratory): Standard deviation 12 min (initial), 20 min (final). Two tests should not differ by more than 34 min (initial) or 56 min (final).
• Multi-laboratory: Standard deviation 16 min (initial), 43 min (final). Results should not differ by more than 45 min (initial) or 122 min (final).