CCIL - Canadian Council of Independent Laboratories Concrete Field Testing Procedures Questions and Answers — Questions and Answers
Question 1: According to CSA A23.2-5C, when performing a slump test, how should the slump cone be lifted from the concrete sample?
- Quickly and with a twisting motion to break the bond
- Vertically, in a smooth and continuous motion taking approximately 5 seconds (Correct answer)
- Slowly at first, then quickly after the first few centimeters
- By tilting it to one side to allow air to enter before lifting
Correct answer: Vertically, in a smooth and continuous motion taking approximately 5 seconds
CSA A23.2-5C specifies that the slump cone must be lifted vertically without any lateral or torsional motion. The entire lifting process should take approximately 5 seconds to ensure the concrete subsides due to its own weight and not due to the motion of the cone removal.
Question 2: A field technician is preparing to measure the air content of a fresh concrete sample using the pressure method (CSA A23.2-4C). The concrete has a specified slump of 30 mm. How should the concrete be consolidated in the measuring bowl?
- By rodding each of the three layers 25 times
- By tapping the sides of the bowl 50 times for each layer
- By using an internal vibrator (Correct answer)
- By rodding the first layer and vibrating the top two layers
Correct answer: By using an internal vibrator
CSA A23.2-4C and A23.2-3C note that for low slump concrete (≤ 40 mm), consolidation should be achieved through vibration rather than rodding to ensure proper compaction and removal of large entrapped air voids.
Question 3: As per CSA A23.2-1C, a representative sample of concrete for testing must be obtained from which portion of the ready-mix truck's discharge?
- From the first 10% of the discharged load
- From the last 10% of the discharged load
- From a combination of the first, middle, and last portions of the load
- Between the 10% and 90% points of discharge (Correct answer)
Correct answer: Between the 10% and 90% points of discharge
CSA A23.2-1C requires that a grab sample for testing be taken after the first 10% of the load has been discharged and before the last 10% is discharged. This ensures the sample is representative of the entire batch and avoids the less uniform concrete often found at the very beginning or end of the discharge.
Question 4: A technician is casting 100 mm x 200 mm cylinders for compressive strength testing from a concrete mix with a slump of 80 mm. Which of the following correctly describes the rodding procedure according to CSA A23.2-3C?
- Fill the mold in 2 equal layers, rodding each layer 25 times with a 16 mm rod.
- Fill the mold in 3 equal layers, rodding each layer 25 times with a 16 mm rod.
- Fill the mold in 3 equal layers, rodding each layer 20 times with a 10 mm rod. (Correct answer)
- Fill the mold in 2 equal layers, rodding each layer 20 times with a 10 mm rod.
Correct answer: Fill the mold in 3 equal layers, rodding each layer 20 times with a 10 mm rod.
For 100 mm diameter cylinders, CSA A23.2-3C specifies filling the molds in 3 equal layers. Since the slump is greater than 40 mm, rodding is the correct consolidation method. For this cylinder size, a 10 mm diameter rod is used, and each layer is rodded 20 times.
Question 5: When measuring the temperature of freshly mixed concrete according to CSA A23.2-17C, what is the minimum time the temperature measuring device must be left in the concrete?
- 30 seconds or until the reading is constant
- A minimum of 2 minutes or until the reading stabilizes (Correct answer)
- Exactly 5 minutes after obtaining the sample
- 1 minute for every 100 mm of concrete depth
Correct answer: A minimum of 2 minutes or until the reading stabilizes
CSA A23.2-17C requires the temperature measuring device to be immersed in the fresh concrete for at least 2 minutes or until the temperature reading stabilizes to ensure an accurate measurement is taken. The entire test must be completed within 5 minutes of obtaining the sample.
Question 6: During the performance of an air content test using the pressure method (Type B meter), after clamping the cover on the bowl and injecting water to expel the air, what is the next critical step before releasing the main air valve?
- Strike the sides of the bowl sharply with a mallet
- Invert the meter and shake it vigorously for 30 seconds
- Open the main air valve immediately to get a quick reading
- Pump air to the initial pressure line, stabilize it, and then close the petcocks (Correct answer)
Correct answer: Pump air to the initial pressure line, stabilize it, and then close the petcocks
Following the procedure in CSA A23.2-4C, after filling with water and expelling trapped air, the operator must pressurize the air chamber. Air is pumped to a pressure slightly above the predetermined starting pressure, and then the needle is precisely adjusted back to the initial pressure line using the bleed valve. Both petcocks are then closed before the main valve is opened to release the pressurized air into the bowl.
CCIL - Canadian Council of Independent Laboratories Concrete Field Testing Procedures Questions and Answers
According to CSA A23.2-5C, when performing a slump test, how should the slump cone be lifted from the concrete sample?