Making and Curing Specimens Flashcards

What is the maximum elapsed time allowed between obtaining the final composite sample increment and beginning to fill the first test cylinder per ASTM C31?

Answer: 5 minutes

ASTM C31 requires that cylinder filling begin within 5 minutes of obtaining the composite sample, consistent with the ASTM C172 requirement that all tests begin within 5 minutes of sampling.

How should concrete test cylinders be protected from vibration during the first 24 hours in the field?

Answer: Cylinders should be placed in an isolated location away from construction traffic, vibrating equipment, and vehicle movement, using padded supports or an insulated curing box

ASTM C31 requires that cylinders be protected from disturbance during initial curing; vibration from construction equipment during the early plastic and hardening stages can create cracks that reduce measured strength.

When making beam specimens for flexural strength testing per ASTM C31, how does the consolidation procedure differ from cylinder fabrication?

Answer: Beams are filled in two or three layers based on depth, and rodded at a rate of one rod stroke per 2 in² (14 cm²) of cross-sectional area per layer rather than a fixed 25 strokes

ASTM C31 requires beams to be filled in two or three layers based on beam depth, with rodding at a rate of one rod stroke per 2 in² of cross-sectional area per layer, rather than the fixed 25 strokes used for cylinders.

Under ASTM C31, what curing conditions are required for laboratory-cured test cylinders after transport from the field?

Answer: Cylinders must be stored in a moist room or water tank maintained at 73°F ± 3°F (23°C ± 2°C) from the time they arrive at the lab until testing

After transport, ASTM C31 requires continuous moist curing at 73°F ± 3°F in a curing room or water tank until testing; interruption or drying of standard curing invalidates the test.

What is an 'accelerated curing' method for concrete cylinders, and when would it typically be used on a construction project?

Answer: Curing at elevated temperature (e.g., boiling water or warm water at 35°C per ASTM C684) to estimate 28-day strength within 24–48 hours, used when early strength information is needed for critical decisions

Accelerated curing per ASTM C684 uses elevated temperature to speed hydration; 24-hour or 28-hour accelerated break results provide early indication of mix quality for form stripping decisions or identifying suspect batches.

What is the minimum number of test cylinders that ACI 318 recommends making per strength test (using 4×8-inch cylinders) for acceptance testing purposes?

Answer: At least four, to provide three for testing (one 7-day and two 28-day) plus one spare

ACI 318 requires a strength test to be the average of at least three 4×8-inch cylinders; most QC plans make four per test to provide a 7-day break, two 28-day breaks (the acceptance average), and one spare held for retesting if needed.