22 Slump Test (ASTM C143) Practice Questions & Answers

Every Slump Test (ASTM C143) practice question from the ACI Concrete Field Testing Technician Grade I Practice Test, with the correct answer and a short explanation.

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1. Per ASTM C143/C143M, what does the slump test of fresh concrete primarily indicate?
- A.The consistency of the plastic concrete, used to check uniformity from batch to batch✓ Answer
- B.The strength the concrete will reach, since slump predicts compressive strength directly
- C.The air content of the concrete, since entrained air raises slump in a fixed proportion
- D.The workability of any mix, since equal slump means equal ease of placing in every mix
Slump is a measure of the consistency of plastic, cohesive concrete and is used mainly to confirm that successive batches of the same mix are uniform. It is not a direct measure of strength, of air content, or of workability across different mixes, because mixes with the same slump can place and finish very differently.
Ref QB-3SNWNNSource: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — significance and useReport a problem with this question
2. A self-consolidating concrete spreads into a wide, flat patty as soon as the slump cone is raised. How does ASTM C143/C143M apply to this concrete?
- A.Report the spread diameter as the slump, because spread replaces height for fluid mixes
- B.Repeat the test with fewer rod strokes, so the concrete keeps more of its original shape
- C.Report the slump as the full height of the cone, because the mass collapsed completely
- D.Use the separate slump-flow test, because C143 is meant for plastic, cohesive concrete✓ Answer
The slump test is meaningful only for concrete that is plastic and cohesive enough to keep a measurable shape. Self-consolidating concrete is far too fluid for that, so its consistency is checked with its own slump-flow test rather than by reporting a height or reducing the rodding.
Ref QB-J9GR3NSource: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — scope and significance (plastic, cohesive concrete)Report a problem with this question
3. Assume the method notes that concrete with slump below 1/2 in. (15 mm) may not be plastic enough for the test to be meaningful. A very stiff mix subsides only 1/4 in. (5 mm). What is the best interpretation?
- A.The result proves the mix will be very strong, since low slump always means a low w/c ratio
- B.The result proves the mix has too much water, since stiff mixes push water out to the surface
- C.The result may not be a meaningful measure of consistency, since the mix may lack plasticity✓ Answer
- D.The result proves the mix is ideal for pumping, since low slump means it holds together well
The slump test applies over a range of plastic consistencies; below the stated lower bound the concrete may not deform plastically, so the reading may not reflect consistency in a meaningful way. Slump alone does not establish pumpability, excess water or strength.
Ref QB-2SAKGMSource: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — significance and use (range of plastic consistency)Report a problem with this question
4. During a slump test, a decided portion of the concrete shears off and falls away from one side of the mass. What should the technician do?
- A.Push the fallen concrete back against the mass, then measure and report the slump
- B.Disregard that test and make a new test on another portion of the same sample✓ Answer
- C.Measure on the side that fell away and report the slump with a note about the shear
- D.Measure to the highest point left on the mass and report that value as the slump
A shear-off or falling away means the specimen did not subside in the uniform way the test assumes, so no valid slump can be read from it. The method requires discarding that result and running a new test on another portion of the sample; reshaping the mass or annotating a bad reading does not make it valid.
Ref QB-H95EWKSource: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — shearing off or falling away of the specimenReport a problem with this question
5. Why must the slump cone be set on a base that is flat, moist, nonabsorbent and rigid?
- A.So the base does not draw water from the concrete or flex while it is being tested✓ Answer
- B.So the cone can slide easily across the base when it is lifted off at an angle
- C.So the base can be tapped gently to help settle the concrete after strike-off
- D.So the concrete bonds to the base and the specimen cannot slump down too far
An absorbent base would pull water from the bottom of the specimen, and a flexible or vibrating base would disturb the concrete, either of which changes the slump. The cone is lifted straight up, not slid, and the base is never tapped to settle the concrete.
Ref QB-ZRX8BKSource: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — apparatus and base surface requirementsReport a problem with this question
6. A technician finds that the only tamping rod on site has both ends cut square and flat. What should be done before the slump test?
- A.Use the flat rod but rod more gently, since a soft stroke makes up for the flat end
- B.Use the flat rod anyway, since only the rod's diameter matters for the slump test
- C.Grind one end to a sharp point, since a pointed tip penetrates the layers more easily
- D.Obtain a rod with the required hemispherical tip, since a flat end does not comply✓ Answer
The method specifies a smooth, round, straight steel tamping rod with a hemispherical tip of the same diameter. A flat or pointed end consolidates the concrete differently, so the rod does not comply and must be replaced; rodding more gently does not cure the defect.
Ref QB-G9S3RJSource: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — apparatus: tamping rodReport a problem with this question
7. A crew asks to use a plastic slump cone instead of a metal one. Under what condition does ASTM C143/C143M permit it?
- A.When it is used for lab tests, since field slump tests always need a metal cone
- B.When it holds the required dimensions in use and gives results like a metal cone✓ Answer
- C.When the concrete is soft, since a fluid mix puts very little load on the cone
- D.When it is new, since any new cone is accurate enough for field slump testing
A nonmetal mold is acceptable only if it meets the same shape and dimensional requirements, is rigid enough to hold them during use, and has been shown to give results comparable to a compliant metal mold. Being new, being used in the lab, or the softness of the mix does not establish compliance.
Ref QB-YRKW5JSource: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — apparatus: mold (nonmetal molds)Report a problem with this question
8. A slump test is to be run on concrete delivered to a job. Which standard governs how the sample for that slump test is obtained?
- A.ASTM C31/C31M, because the slump sample is taken from the cylinder molds
- B.ASTM C1064/C1064M, because slump and temperature use one sample container
- C.ASTM C172/C172M, the practice for sampling freshly mixed concrete✓ Answer
- D.ASTM C138/C138M, because the slump sample is the concrete left in the bowl
ASTM C143/C143M requires the slump sample to be obtained in accordance with Practice C172/C172M, which covers composite sampling and protection of freshly mixed concrete. The other methods cover specimens, density and temperature, not how the slump sample is taken.
Ref QB-Q99EXTSource: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — sample obtained per ASTM C172/C172M, Standard Practice for Sampling Freshly Mixed ConcreteReport a problem with this question
9. Assume the governing practice requires the slump test to start within 5 minutes after the final portion of the composite sample is obtained. The final portion was taken at 10:02, and the technician is ready to start at 10:09. What should be done?
- A.Obtain a new composite sample, since the start window for this one has passed✓ Answer
- B.Remix the old sample well, since remixing restores its original consistency
- C.Add some water to the old sample, since that offsets the slump lost while waiting
- D.Test the old sample anyway, since a note giving the delay makes the result valid
Seven minutes have elapsed, which is outside the given start window, so the sample no longer represents the concrete as delivered. The remedy is a new sample; remixing cannot reverse slump loss, adding water falsifies the result, and a note does not cure a nonconforming test.
Ref QB-7S39CTSource: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — time to start testing after sampling per ASTM C172/C172M, Standard Practice for Sampling Freshly Mixed ConcreteReport a problem with this question
10. Assume the method requires coarse aggregate larger than 1-1/2 in. (37.5 mm) to be removed before slump testing. The mix has a 2 in. (50 mm) nominal maximum size aggregate. What should the technician do?
- A.Test the full sample unchanged, since the cone is wide enough for any aggregate
- B.Use a larger cone sized at three times the aggregate, as done for cylinder molds
- C.Wet-sieve the sample over that sieve per C172/C172M, then test the passing portion✓ Answer
- D.Pick out the large stones by hand while filling, and leave the rest of the sample
When the coarse aggregate exceeds the permitted size, the sample is wet-sieved over the stated sieve following Practice C172/C172M and the slump test is run on the passing material. Picking out stones by hand is not a defined procedure, and the size-ratio rule for molds belongs to the cylinder-specimen method, not to the slump cone.
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11. Slump is run on a sample that was wet-sieved to remove oversize coarse aggregate. What does the resulting slump value represent?
- A.The slump of the full mix, since removed stones have no effect on consistency
- B.The slump of the full mix, once a correction for the removed stones is added
- C.The consistency of the sieved portion, not of the full mix as it was delivered✓ Answer
- D.The water content of the full mix, computed from the mass of stones removed
Wet-sieving changes the material being tested, so the slump describes the consistency of the fraction that passed the sieve. The method gives no correction factor to convert it back to the full mix, and slump is not a water-content calculation.
Ref QB-K9SZD9Source: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — scope: concrete containing oversize coarse aggregateReport a problem with this question
12. Why does the method require the slump test, from the start of filling through lifting the mold, to be done without interruption and within a short elapsed time?
- A.Because the remixed sample would segregate and spoil the air test on that sample
- B.Because the concrete's consistency changes with time, so delays skew the slump✓ Answer
- C.Because cement paste would bond the concrete to the cone and make it hard to lift
- D.Because the moist base would dry out and start drawing water from the specimen
Fresh concrete stiffens as time passes through hydration and evaporation, so a slow or interrupted test measures a different consistency than the concrete had when sampled. Requiring one continuous, short operation keeps the reading representative.
Ref QB-2S8HN7Source: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — elapsed time for the testReport a problem with this question
13. Assume the method requires the whole test, from start of filling to lifting the mold, to be completed without interruption within 2-1/2 minutes. While rodding the second layer, the technician is called away for 3 minutes. What should be done?
- A.Discard this test and start over with concrete that still meets the time limits✓ Answer
- B.Re-rod the second layer with extra strokes, since that makes up for the lost time
- C.Finish the second layer and carry on, since the time limit restarts with each layer
- D.Complete the test and report the slump, with a note that the test was paused
The time limit applies to the test as one continuous operation, so a 3-minute pause already exceeds it and the result would not be valid. Extra rodding changes consolidation rather than restoring lost time, and annotating the report does not make a nonconforming test acceptable.
Ref QB-J9EP88Source: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — elapsed time and continuity of the testReport a problem with this question
14. Assume the method allows 5 ± 2 seconds to raise the mold its full height. A technician jerks the mold up in about 1 second. Why is this a problem?
- A.A fast lift only matters for stiff mixes, since fluid mixes slump the same either way
- B.A fast lift is acceptable if the cone is then held above the specimen for 5 seconds
- C.A fast lift is preferred, since less time means less slump loss before the reading
- D.A fast jerk can drag the concrete up or sideways, so the slump is distorted✓ Answer
A lift that is too quick, or that includes lateral or twisting motion, can pull concrete along with the mold or knock it sideways, so the specimen does not subside freely and the reading misrepresents consistency. The lift must be a steady vertical motion within the given time for every mix, and holding the cone afterward does not correct the disturbance.
Ref QB-5SAH6BSource: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — lifting the mold (steady vertical lift, no lateral or torsional motion)Report a problem with this question
15. When the cone is filled in layers of roughly equal volume, why does the first layer reach only part of the way up, well short of one third of the cone's height?
- A.The bottom layer is kept thin to save concrete, as it bears no load in the test
- B.The cone is filled in equal heights, so the first layer just looks shallow inside
- C.The bottom layer is kept thin so the rod can strike the base plate on each stroke
- D.The cone is widest at its base, so a layer of equal volume there is the shallowest✓ Answer
The cone tapers from a wide base to a narrow top, so the same volume occupies less height near the bottom and more near the top. Filling by equal volume, not equal height, is why the first layer is shallow; the rod should not forcibly strike the base plate.
Ref QB-N9GPRBSource: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — filling the mold in layers of approximately equal volumeReport a problem with this question
16. When rodding the second layer and the top layer, how deep should each stroke penetrate?
- A.Through all layers down to the base plate, so the whole cone is rodded together
- B.Through the layer being rodded, stopping exactly at the top of the layer below
- C.Into the upper half of the layer only, so the layer below is left undisturbed
- D.Through the layer being rodded and just slightly into the layer beneath it✓ Answer
Each upper layer is rodded throughout its depth with strokes that just enter the layer below, which knits the layers together without a weak plane between them. Stopping at the interface leaves a seam, and driving to the base re-rods the lower layers.
Ref QB-4SX6Z9Source: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — rodding the second and top layersReport a problem with this question
17. How should the rodding strokes be distributed in the bottom layer of the slump cone?
- A.Tilt the rod slightly for about half the strokes near the edge, then spiral in vertically✓ Answer
- B.Hold the rod vertical and place all strokes at the center, where the layer is deepest
- C.Tilt the rod for all strokes around the edge only, to seat the concrete against the cone
- D.Hold the rod vertical and strike the base plate hard, so the bottom is fully compacted
Strokes are spread uniformly over the cross section: because the bottom layer is wide and the cone wall slopes, about half the strokes are made near the perimeter with the rod slightly inclined, then the rest progress vertically in a spiral toward the center. Concentrating strokes in one zone leaves other zones under-consolidated, and the base must not be struck forcibly.
Ref QB-M95CKASource: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — rodding the bottom layerReport a problem with this question
18. While the top layer is being rodded, the concrete settles below the rim of the cone. What should the technician do?
- A.Add concrete so an excess stays above the rim at all times, and continue rodding✓ Answer
- B.Strike off level with the low surface, then measure the slump down from that level
- C.Finish rodding, then fill the low spot with mortar scraped from around the base
- D.Stop rodding at once, since settling shows the top layer is already fully compacted
The top layer is heaped above the mold before rodding, and if it subsides below the top edge more concrete is added so an excess is kept above the mold throughout rodding. That ensures the cone is completely full of consolidated concrete when it is struck off; mortar from the base or a low strike-off would leave the specimen short or unrepresentative.
Ref QB-7SZ6HDSource: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — rodding the top layer and keeping an excess above the moldReport a problem with this question
19. Why does the technician stand on the foot pieces of the cone during filling and rodding, without moving the feet until the cone is lifted?
- A.To squeeze excess water out through the base, so the slump is read on drier concrete
- B.To keep the cone from shifting or rising, so mortar does not leak out beneath it✓ Answer
- C.To press the cone into the base, so body weight helps compact the bottom layer
- D.To keep the base plate level, since standing on the cone removes tilt in the ground
Rodding pushes the concrete outward and upward against the cone, so it must be held firmly in place; if it lifts or shifts, mortar escapes under the rim and the specimen is disturbed. Standing on the foot pieces does not compact the concrete, level the base or remove water.
Ref QB-Q97C4ESource: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — holding the mold firmly in placeReport a problem with this question
20. Which sequence is correct immediately after the top surface has been struck off?
- A.Clear concrete from around the base, step off the foot pieces, then lift the cone
- B.Keep holding the cone down, clear concrete around the base, then lift it straight up✓ Answer
- C.Tap the cone sides to free it, clear around the base, then lift it with a slight twist
- D.Lift the cone straight up, then clear away the concrete spilled around its base
The cone is still held down while spilled concrete is removed from around its base, so the mold cannot move and loose material does not interfere with the specimen; then the mold is lifted immediately and vertically. Stepping off first lets the cone shift, and tapping or twisting disturbs the concrete.
Ref QB-ENJN2BSource: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — removing concrete from around the base and lifting the moldReport a problem with this question
21. After the mold is removed, the slump is the vertical distance from the top of the mold to which point on the specimen?
- A.The average of several points across the slumped top surface
- B.The highest point left anywhere on the slumped specimen
- C.The displaced original center of the specimen's top surface✓ Answer
- D.The lowest point along the outer edge of the slumped specimen
Slump is defined at the displaced original center of the top surface, measured by inverting the mold beside the specimen and laying the rod across it. Using the highest point, the edge or an average would give a different and non-standard number for the same concrete.
Ref QB-W5DGFASource: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — measuring slumpReport a problem with this question
22. A slump test shows a decided shear-off on one side. The retest on another portion of the sample also shears off. What does this most likely indicate?
- A.The cone was lifted unevenly both times, so the two readings should be averaged
- B.The concrete likely lacks the plasticity and cohesion for the slump test to apply✓ Answer
- C.The base was too wet both times, so it should be dried and the test run a third time
- D.The concrete has excess slump, so the higher of the two readings should be reported
When two consecutive tests on the sample both shear off or fall away, the concrete probably lacks the plasticity and cohesiveness needed for the slump test to be applicable. Readings from sheared specimens are not valid, so they are neither averaged nor reported, and a moist base is required, not a fault to be dried.
Ref QB-DN7BV9Source: ASTM C143/C143M, Standard Test Method for Slump of Hydraulic-Cement Concrete — shearing off on consecutive testsReport a problem with this question

1. Per ASTM C143/C143M, what does the slump test of fresh concrete primarily indicate?

2. A self-consolidating concrete spreads into a wide, flat patty as soon as the slump cone is raised. How does ASTM C143/C143M apply to this concrete?

3. Assume the method notes that concrete with slump below 1/2 in. (15 mm) may not be plastic enough for the test to be meaningful. A very stiff mix subsides only 1/4 in. (5 mm). What is the best interpretation?

4. During a slump test, a decided portion of the concrete shears off and falls away from one side of the mass. What should the technician do?

5. Why must the slump cone be set on a base that is flat, moist, nonabsorbent and rigid?

6. A technician finds that the only tamping rod on site has both ends cut square and flat. What should be done before the slump test?

7. A crew asks to use a plastic slump cone instead of a metal one. Under what condition does ASTM C143/C143M permit it?

8. A slump test is to be run on concrete delivered to a job. Which standard governs how the sample for that slump test is obtained?

9. Assume the governing practice requires the slump test to start within 5 minutes after the final portion of the composite sample is obtained. The final portion was taken at 10:02, and the technician is ready to start at 10:09. What should be done?

10. Assume the method requires coarse aggregate larger than 1-1/2 in. (37.5 mm) to be removed before slump testing. The mix has a 2 in. (50 mm) nominal maximum size aggregate. What should the technician do?

11. Slump is run on a sample that was wet-sieved to remove oversize coarse aggregate. What does the resulting slump value represent?

12. Why does the method require the slump test, from the start of filling through lifting the mold, to be done without interruption and within a short elapsed time?

13. Assume the method requires the whole test, from start of filling to lifting the mold, to be completed without interruption within 2-1/2 minutes. While rodding the second layer, the technician is called away for 3 minutes. What should be done?

14. Assume the method allows 5 ± 2 seconds to raise the mold its full height. A technician jerks the mold up in about 1 second. Why is this a problem?

15. When the cone is filled in layers of roughly equal volume, why does the first layer reach only part of the way up, well short of one third of the cone's height?

16. When rodding the second layer and the top layer, how deep should each stroke penetrate?

17. How should the rodding strokes be distributed in the bottom layer of the slump cone?

18. While the top layer is being rodded, the concrete settles below the rim of the cone. What should the technician do?

19. Why does the technician stand on the foot pieces of the cone during filling and rodding, without moving the feet until the cone is lifted?

20. Which sequence is correct immediately after the top surface has been struck off?

21. After the mold is removed, the slump is the vertical distance from the top of the mold to which point on the specimen?

22. A slump test shows a decided shear-off on one side. The retest on another portion of the sample also shears off. What does this most likely indicate?

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