ACI Concrete Laboratory Testing Technician — Level 2

Per ASTM C192/C192M, what is the number of rod strokes required per layer when consolidating a standard 150 x 300 mm (6 x 12 in.) concrete cylinder by rodding?

• A15 strokes per layer
• B20 strokes per layer
• C25 strokes per layer
• D50 strokes per layer

According to ASTM C192/C192M, how is the method of consolidation (rodding vs vibration) selected when not specified by the project?

• AAlways rod cylinders and vibrate beams
• BBy slump — rod if slump ≥ 25 mm (1 in.), vibrate if slump < 25 mm (1 in.)
• CBy aggregate size — vibrate if NMSA > 25 mm
• DBy cylinder size only

ASTM C192/C192M requires initial curing of molded specimens for the first 24 hours at what temperature range?

• A10 to 16 °C (50 to 60 °F)
• B16 to 27 °C (60 to 80 °F)
• C20 to 30 °C (68 to 86 °F)
• D23.0 ± 2.0 °C (73.5 ± 3.5 °F)

Per ASTM C192/C192M, what temperature is required for the moist room or water tank used for final curing of strength-test specimens?

• A18.0 ± 2.0 °C (64.4 ± 3.6 °F)
• B21.0 ± 2.0 °C (70 ± 3.6 °F)
• C23.0 ± 2.0 °C (73.5 ± 3.5 °F)
• D27.0 ± 2.0 °C (80.6 ± 3.6 °F)

Per ASTM C192/C192M, after a 0.028 m³ (1 ft³) drum batch is mixed, what is the minimum allowed mixing time after all ingredients are in the mixer?

• A1 minute mixing, 2 minutes rest, 1 minute remix
• B3 minutes mixing, 3 minutes rest, 2 minutes remix
• C5 minutes mixing then immediate discharge
• D10 minutes mixing then 5 minutes rest

When using internal vibration to consolidate a 150 mm (6 in.) diameter cylinder per ASTM C192, how many insertions per layer are required, and how many layers should the cylinder be filled in?

• A2 insertions per layer, 2 layers
• B1 insertion per layer, 2 layers
• C3 insertions per layer, 1 layer
• D4 insertions per layer, 3 layers

Per ASTM C192/C192M, what is the maximum permissible elapsed time between completing mixing of a batch and starting molding of strength specimens?

• A15 minutes
• B30 minutes
• C45 minutes
• D60 minutes

ASTM C192 requires the tamping rod for a standard 150 mm cylinder to have what diameter and tip configuration?

• A10 mm (3/8 in.) diameter, flat tip
• B16 mm (5/8 in.) diameter, hemispherical tip
• C16 mm (5/8 in.) diameter, flat tip
• D20 mm (3/4 in.) diameter, hemispherical tip

Per ASTM C192, beams for flexural strength testing 150 x 150 x 530 mm (6 x 6 x 21 in.) consolidated by rodding require how many strokes per layer and how many layers?

• A25 strokes per layer in 2 layers
• B50 strokes per layer in 2 layers (one stroke per 14 cm² of top surface)
• C60 strokes per layer in 1 layer
• D100 strokes per layer in 2 layers

After molding cylinders per ASTM C192, what is the standard tolerance window for demolding the specimens?

• A8 ± 2 hours
• B16 ± 4 hours
• C24 ± 8 hours
• D48 ± 8 hours

Which ASTM C192 requirement governs the temperature of materials brought into the laboratory before mixing trial batches?

• AAll materials must be at 21 to 25 °C (70 to 77 °F) when introduced to the mixer
• BAggregates may be at any temperature so long as cement is at 21-25 °C
• COnly water needs temperature control
• DMaterials must be heated to 38 °C (100 °F) before mixing

ASTM C192/C192M requires the mixer to be charged in what order for typical normal-weight concrete batches?

• AAll ingredients dumped simultaneously and mixed
• BCoarse aggregate, fine aggregate, cement; start mixer; add water with admixtures; mix 3 m…
• CWater, cement, then aggregates after 1 minute
• DCement and water first as a paste, then aggregates

Per ASTM C192, when consolidating by rodding, what should the technician do if voids remain along the side of a cylinder mold after the last layer is rodded?

• AAdd more concrete and rod again
• BTap the outside of the mold lightly 10 to 15 times with a mallet to close voids
• CInsert a vibrator
• DDisregard — voids are unavoidable

Per ASTM C192, for cylinder consolidation by rodding the second layer of a 150 mm cylinder, the rod should penetrate the underlying first layer by approximately how much?

• AJust touch the top of the lower layer
• BPenetrate about 25 mm (1 in.) into the layer below
• CPenetrate halfway into the layer below
• DPenetrate to the bottom of the mold

Per ASTM C192, what is the maximum acceptable difference in cylinder diameter measured at the top and bottom of a single-use plastic mold for it to remain acceptable?

• A±1% of the nominal diameter
• B±2% of the nominal diameter
• C±5% of the nominal diameter
• DAny deviation is acceptable as long as the cylinder is round

ASTM C192 requires that fresh-concrete sampling for laboratory test batches conform to which standard?

• AASTM C172
• BASTM C31
• CASTM C143
• DASTM C231

Per ASTM C192, what is the proper action if slump exceeds the target by more than 25 mm (1 in.) on a laboratory trial batch?

• AAdd cement to compensate
• BReject the batch and re-mix with adjusted water content
• CMold the specimens anyway and note the slump
• DMix the batch for 5 more minutes

Per ASTM C192, on a 150 mm cylinder vibrated externally on a vibrating table, how should the duration of vibration be judged?

• AVibrate exactly 30 seconds regardless of mixture
• BVibrate until the surface becomes relatively smooth and large air bubbles cease to break…
• CVibrate until the cylinder is half full
• DVibrate exactly 90 seconds

Per ASTM C192, what is the minimum batch volume relative to the mixer capacity for laboratory trial batches?

• AAt least 10% of mixer capacity
• BApproximately 50% of mixer capacity, not exceeding the rated capacity
• CAlways exactly the rated mixer capacity
• DAt least 90% of mixer capacity

ASTM C192 cites which standard for the moist room or curing tank used in final curing?

• AASTM C31
• BASTM C470
• CASTM C511
• DASTM C617

Per ASTM C192, the strike-off of the top of a cylinder must produce a surface that is flat to what tolerance prior to capping or grinding?

• AWithin 1 mm of plane and 3 mm below the rim
• BPlane and even with the top of the mold (within 3 mm)
• CCrowned 5 mm above the rim
• DRecessed 10 mm below the rim

Per ASTM C192, what action is required before specimens are moved out of the laboratory after the final curing period?

• ADry the specimens at 60 °C for 24 hours
• BKeep specimens moist using wet burlap or in saturated lime water during transport to the…
• CApply a sealing compound
• DCap immediately with sulfur

Per ASTM C157/C157M, what are the standard prism dimensions and gage length used for length-change measurements on concrete with NMSA up to 25 mm (1 in.)?

• A50 x 50 x 250 mm, gage length 200 mm
• B75 x 75 x 285 mm, gage length 250 mm
• C100 x 100 x 285 mm, gage length 250 mm
• D150 x 150 x 530 mm, gage length 500 mm

Per ASTM C157, at what age after molding are specimens demolded and the initial comparator reading taken?

• A6 ± 0.5 hours
• B23.5 ± 0.5 hours, with reading at 24 ± 0.5 hours after a 30-minute lime-water bath
• C48 hours
• D7 days

Per ASTM C157, after the initial comparator reading, where are concrete specimens stored prior to drying when length change in water is NOT measured?

• AAir at 50% RH starting immediately
• BSaturated lime water at 23.0 ± 2.0 °C until age 28 days (or as specified)
• COven at 50 °C
• DDry storage at 23 °C

Per ASTM C157, what are the required environmental conditions in the drying room used to expose specimens to air drying?

• A23.0 ± 2.0 °C and 50 ± 4% RH
• B23.0 ± 2.0 °C and 30 ± 4% RH
• C20 °C and 65% RH
• D27 °C and 50% RH

Per ASTM C157, comparator readings during air drying are required at which ages after the start of drying?

• A1, 3, 7 days only
• B4, 7, 14, 28 days and 8, 16, 32, 64 weeks
• CEvery day for the first month
• D7 days and 90 days only

Per ASTM C157, what is the formula for length change (ΔLx) of a hardened concrete specimen at any age relative to the initial reading?

• AΔLx = (CRx − CRi) / G × 100
• BΔLx = (CRx − CRi) × L
• CΔLx = CRx / CRi
• DΔLx = (Lx − Li) / Li × 100

Per ASTM C157, what is the minimum number of specimens that must be molded from one batch for a single test result?

• A1
• B2
• C3
• D5

Per ASTM C157, what is the function of the reference bar used during comparator readings?

• ACalibrate the length comparator and account for instrument drift between readings
• BHold the specimens in place
• CProvide moisture for the specimen
• DMeasure ambient room temperature

Per ASTM C157, gage studs cast into shrinkage prisms must be made of what material?

• AAluminum
• BBrass or stainless steel (non-corrosive)
• CCarbon steel
• DPlastic

Per ASTM C157, when project specifications require comparing different concrete mixtures for shrinkage, what is the minimum air-drying period typically required before comparing results?

• A7 days drying
• B14 days drying
• C28 days drying
• D1 year drying

Per ASTM C157, after the lime-saturated water bath, what surface condition should the specimen be in when placed in the comparator for reading?

• ACompletely dry surface
• BWiped damp (saturated surface dry) — surface water blotted off but pores saturated
• CCoated with a release agent
• DEncased in plastic film

Per ASTM C157, the length comparator must be capable of reading to what minimum precision?

• A0.1 mm
• B0.025 mm (0.001 in.)
• C0.0025 mm (0.0001 in.)
• D1 mm

Per ASTM C157, what is the orientation of the gage studs in a 100 x 100 x 285 mm concrete prism?

• AStuds on opposite long ends, coaxial with the longitudinal axis of the specimen
• BStuds on opposite long sides, perpendicular to the long axis
• CStuds on the top and bottom faces
• DStuds on all four corners

Per ASTM C157, results are typically reported in what units?

• AInches
• BMicrostrain (millionths) or percent length change
• CPounds per square inch
• DMegapascals

Per ASTM C157, if the second comparator reading (called the 7-day reading) deviates from the initial reading by an excessive amount during lime-water storage, the specimens may indicate what?

• ACompressive failure
• BSignificant initial expansion or swelling, which should be reported
• CLoss of mass
• DImproper cap thickness

Per ASTM C157, what is the maximum allowable elapsed time between removing a specimen from lime water and completing its comparator reading?

• A1 minute
• BLess than 15 seconds for stud seating, then read as soon as the instrument stabilizes (ty…
• C30 minutes
• D1 hour

Per ASTM C157, what is the minimum gage length for the standard 100 x 100 x 285 mm concrete prism specimen?

• A100 mm (4 in.)
• B200 mm (8 in.)
• C250 mm (10 in.)
• D285 mm (11.25 in.)

Per ASTM C157, the curing tank for the lime-water storage stage must maintain what temperature?

• A23.0 ± 2.0 °C (73.4 ± 3.6 °F)
• B20 ± 1 °C
• C27 ± 2 °C
• DRoom temperature, ±5 °C

Per ASTM C42/C42M, what is the preferred length-to-diameter (L/D) ratio of a drilled core specimen when tested in compression?

• AL/D between 1.0 and 1.2
• BL/D between 1.9 and 2.1
• CL/D between 2.5 and 3.0
• DL/D = 1.5 exactly

Per ASTM C42, what is the strength correction factor for a core with L/D = 1.50?

• A1.00
• B0.98
• C0.96
• D0.87

Per ASTM C42, what is the strength correction factor for a core with L/D = 1.00?

• A1.00
• B0.96
• C0.93
• D0.87

Per ASTM C42, what is the minimum diameter of a drilled core relative to the nominal maximum size of aggregate (NMSA)?

• AAt least equal to the NMSA
• BAt least 2 times the NMSA, preferably 3 times
• CAlways 100 mm regardless of NMSA
• DAlways 4 times the NMSA

Per ASTM C42, when must a core's measured compressive strength be corrected for L/D?

• AWhenever L/D < 2.0
• BWhenever L/D ≤ 1.75
• COnly when L/D = 1.00
• DNever — the correction has been removed

Per ASTM C42, after drilling, how must cores be moisture-conditioned before compression testing?

• ASoaked in water at least 40 hours before testing
• BWiped surface-dry and stored in sealed plastic bags for at least 5 days at 16-27 °C befor…
• CDried in an oven at 60 °C for 24 hours
• DTested immediately with no conditioning

Per ASTM C42, what is the maximum allowable departure from perpendicularity of a core end relative to the axis prior to compression testing?

• A0.5°
• B1°
• C2°
• D5°