ACI Concrete Strength Testing Technician

Under ASTM C39/C39M, what is the specified loading rate for testing hardened concrete cylinders during the second half of the anticipated loading phase?

• A35 ± 7 psi/s (0.25 ± 0.05 MPa/s)
• B15 ± 5 psi/s (0.10 ± 0.03 MPa/s)
• C60 ± 10 psi/s (0.40 ± 0.07 MPa/s)
• D100 ± 20 psi/s (0.70 ± 0.14 MPa/s)

A 6 in. × 12 in. concrete cylinder tested per ASTM C39 fails at a maximum load of 113,100 lbf. What is the compressive strength, rounded to the nearest 10 psi?

• A4,000 psi
• B3,140 psi
• C5,020 psi
• D4,500 psi

In ASTM C39/C39M, a fracture pattern described as 'reasonably well-formed cones on both ends, less than 1 in. of cracking through caps' corresponds to which fracture type?

• AType 1
• BType 2
• CType 3
• DType 4

Per ASTM C39/C39M, if a tested cylinder has a length-to-diameter (L/D) ratio of 1.75, which correction factor must be applied to the calculated compressive strength?

• A0.98
• B0.96
• C0.93
• D0.87

ASTM C39 requires that the diameter of a cylindrical specimen be determined to the nearest _____ by averaging two diameters measured at right angles to each other at about mid-height of the specimen.

• A0.01 in. (0.25 mm)
• B0.1 in. (2.5 mm)
• C0.001 in. (0.025 mm)
• D1/16 in. (1.6 mm)

Under ASTM C39/C39M, diameter measurement may be reduced to one specimen per ten (or three per day, whichever is greater) instead of measuring every cylinder ONLY when:

• AAll cylinders come from a single lot of molds that consistently produce specimens with av…
• BCylinders are tested above 6,000 psi
• CSulfur caps are used
• DThe specimens are larger than 4 in. in diameter

According to ASTM C39/C39M, the ends of a specimen that are not plane within _____ shall be sawed, ground, or capped prior to testing.

• A0.002 in. (0.050 mm)
• B0.005 in. (0.13 mm)
• C0.010 in. (0.25 mm)
• D0.020 in. (0.50 mm)

Per ASTM C39/C39M, the perpendicularity of the ends of a concrete cylinder to its axis shall not depart by more than what tolerance?

• A0.5° (approximately 1/8 in. in 12 in.)
• B1.0° (approximately 1/4 in. in 12 in.)
• C2.0° (approximately 1/2 in. in 12 in.)
• D0.1° (approximately 1/32 in. in 12 in.)

A 4 in. × 8 in. cylinder fractures at 56,550 lbf. Calculate the compressive strength to the nearest 10 psi.

• A4,500 psi
• B1,770 psi
• C9,000 psi
• D5,650 psi

Which of the following is NOT permitted to be reported as the age of a specimen in ASTM C39/C39M?

• AAge based only on when the specimen was removed from the mold
• BAge from the time water was added to the mix
• CAge from the time cement was added to the mix
• DAge counted in days with fractional part for remolded specimens

A Type 2 fracture per ASTM C39/C39M is characterized by which of the following?

• AWell-formed cone on one end, vertical cracks running through caps, no well-defined cone o…
• BReasonably well-formed cones on both ends, less than 1 in. of cracking through caps
• CColumnar vertical cracking through both ends, no well-formed cones
• DDiagonal fracture with no cracking through the ends

A Type 5 fracture per ASTM C39/C39M is best described as:

• ASide fractures at top or bottom (occur commonly with unbonded caps)
• BA well-formed cone on both ends
• CA columnar vertical break through both ends
• DA clean 45° diagonal shear failure

Type 6 fractures per ASTM C39 — similar to Type 5 but with point fractures at the ends — most often indicate:

• AProblems with the capping system or eccentric loading
• BA high-strength concrete performing normally
• CSuccessful third-point loading
• DA correctly calibrated compression machine

Per ASTM C39/C39M, the tolerance on permissible time for tests of the most common standard-cured specimens tested at 28 days is:

• A± 20 hours (about ± 0.83 day)
• B± 2 hours
• C± 48 hours
• D± 8 hours

ASTM C39/C39M requires that when the specimen length before capping is less than ____ times the diameter, the length shall be measured and recorded.

• A1.8
• B1.5
• C2.0
• D2.2

ASTM C39/C39M requires that the loaded bearing faces of the testing machine platens, or spherically seated bearing block, must be plane within ____.

• A0.001 in. (0.025 mm)
• B0.002 in. (0.050 mm)
• C0.005 in. (0.13 mm)
• D0.010 in. (0.25 mm)

A 6 in. × 12 in. cylinder cast for a 5,000 psi mix breaks at a load of 92,400 lbf. What is the reported compressive strength?

• A3,270 psi
• B3,000 psi
• C4,000 psi
• D5,000 psi

ASTM C39/C39M requires the specimen to be tested in the moist condition. How long after removal from moist storage may a specimen typically remain before testing?

• AKept moist using a wet burlap/blanket, until tested; surface drying between removal and t…
• BAllowed to air-dry for at least 4 hours to normalize moisture
• COven-dried to constant mass before testing
• DSoaked in water for 24 hours before testing