4.4 ASTM C143 Scope, Equipment, and Setup
Key Takeaways
- ASTM C143 measures slump of plastic hydraulic-cement concrete and is not intended for nonplastic, noncohesive, or highly flowable concrete outside its scope.
- The slump mold is a 12 in. high cone with an 8 in. bottom opening and a 4 in. top opening in U.S. customary units.
- The tamping rod is a straight round rod, commonly 5/8 in. diameter, with a rounded end and permitted standard length.
- The mold and base are dampened and placed on a flat, rigid, nonabsorbent surface before filling.
Slump Test Scope and Equipment
ASTM C143 measures the slump of plastic hydraulic-cement concrete. Slump is a field indication of consistency and workability, not a direct measure of water content, strength, or quality by itself. The result is meaningful only when the concrete is within the method's scope and the test is performed with the correct equipment on a representative C172 sample.
The slump test is not considered suitable for every concrete. It is aimed at plastic, cohesive concrete. Very stiff nonplastic concrete may not slump in a useful way, and very flowable or self-consolidating concrete may need a different workability test such as slump flow. If aggregate is too large for the method, the sample may require wet sieving before testing. These scope points are common written-exam traps because candidates may assume every fresh concrete can be tested by C143.
The standard slump mold is a frustum of a cone. In U.S. customary dimensions, it is 12 in. high, 8 in. in inside diameter at the bottom, and 4 in. in inside diameter at the top. The tamping rod is a straight round steel rod, commonly 5/8 in. in diameter, with a rounded end and an accepted standard length. The base must be flat, rigid, moist, and nonabsorbent.
| Equipment item | What to remember | Why it matters |
|---|---|---|
| Slump mold | 12 in. high, 8 in. bottom, 4 in. top | Controls specimen shape |
| Tamping rod | Round rod with rounded end | Produces consistent consolidation |
| Base | Flat, rigid, moist, nonabsorbent | Prevents leakage and movement |
| Sample | Representative C172 concrete | Connects result to batch |
| Measuring device | Reads slump to required increment | Controls report accuracy |
Setup is part of the performance exam. Dampen the mold and base so concrete does not stick or lose water to dry surfaces. Place the mold with the larger opening down on the prepared base. Hold it firmly in place, usually by standing on the foot pieces, during filling and rodding. If the cone shifts, leaks, or lifts during filling, the specimen shape has been disturbed before measurement even begins.
The sample should be ready and uniform before the slump test starts. Do not begin filling the cone until the sample has been remixed after C172 collection. Once filling begins, the C143 test has its own uninterrupted timing requirement. Equipment setup should therefore happen before the first scoop goes into the mold.
Setup checklist:
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Confirm the concrete is within C143 scope.
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Use a clean, damp mold and a flat, damp, nonabsorbent base.
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Hold the mold firmly before adding concrete.
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Keep the rod, scoop, and measuring device within reach.
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Start only when you can complete the test without interruption.
What does ASTM C143 measure?
What are the U.S. customary inside dimensions of the slump mold?
Why are the mold and base dampened before a slump test?