ACI Certification Concrete Strength Testing Procedures 2

Question 1

According to ASTM C39, what is the required rate of load application during compressive strength testing of a concrete cylinder?

Accepted Answer

20 to 50 psi/s (0.14 to 0.34 MPa/s)

Answer

100 to 150 psi/s (0.69 to 1.03 MPa/s)

Answer

5 to 10 psi/s (0.03 to 0.07 MPa/s)

Answer

150 to 250 psi/s (1.03 to 1.72 MPa/s)

Question 2

What is the maximum permissible departure from perpendicularity of the end surface of a concrete test cylinder when measured with a square?

Accepted Answer

0.5°

Answer

1.0°

Answer

2.0°

Answer

3.0°

Question 3

What is a Type B fracture pattern in a compressive strength test per ASTM C39, and is it considered acceptable?

Accepted Answer

A well-formed cone with slight cracking through one base; it is an acceptable fracture pattern

Answer

Columnar vertical cracking through both ends; it is not acceptable

Answer

Diagonal fracture with no cracking through either end; it is acceptable

Answer

Side fracture at mid-height without any cone formation; it is not acceptable

Question 4

If a compressive strength test result falls below f'c by more than 500 psi, what condition must be checked first according to ACI 318?

Accepted Answer

Whether the strength test is the average of at least two cylinders (or three for 4×8-inch cylinders) from the same sample

Answer

Whether the concrete truck was overloaded at delivery

Answer

Whether the aggregate used was from a pre-approved quarry

Answer

Whether the batch plant was certified within the past year

Question 5

Why must concrete test cylinders be stored in a standardized moist curing environment (73 ± 3°F / 23 ± 2°C) after the initial 24-hour field period?

Accepted Answer

To simulate ideal hydration conditions and produce strength results that reflect the concrete's potential strength, not the field curing quality

Answer

To accelerate the hydration reaction and obtain results faster

Answer

To prevent carbonation of the surface mortar

Answer

To allow cylinder molds to be reused immediately after stripping

Question 6

What is the maximum permitted length-to-diameter ratio (L/D) for a concrete test cylinder per ASTM C39?

Accepted Answer

Between 1.8D and 2.2D (where D is diameter), with 2.0D being the standard

Answer

Exactly 3.0D for all cylinder sizes

Answer

Between 1.5D and 1.8D

Answer

Between 2.5D and 3.0D