ACI Concrete Strength Testing Procedures Questions and Answers

Question 1

According to ASTM C39, what is the specified loading rate for applying a compressive force to a standard 6x12 inch concrete cylinder?

Accepted Answer

35 ± 7 psi/s

Answer

ASTM C39/C39M specifies that the load shall be applied continuously and without shock at a constant rate within the range of 20 to 50 psi/s (0.14 to 0.34 MPa/s). A loading rate of 35 ± 7 psi/s (0.25 ± 0.05 MPa/s) falls within this required range and is the standard rate to be maintained during the latter half of the loading phase.

Question 2

A technician is preparing to perform a flexural strength test (Modulus of Rupture) on a concrete beam specimen in accordance with ASTM C78. Which of the following loading configurations is specified by this standard?

Accepted Answer

Third-point loading

Answer

ASTM C78/C78M, "Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading)," explicitly requires the use of a third-point loading setup. This method applies the load at two points, each one-third of the span length from a support, which creates a region of maximum bending moment in the middle third of the beam.

Question 3

When making standard-cured test specimens in the field per ASTM C31, what is the primary purpose of this type of curing?

Accepted Answer

To check the adequacy of mixture proportions for strength and for acceptance testing.

Answer

ASTM C31/C31M outlines that standard-cured specimens are used for acceptance testing, checking the adequacy of mixture proportions for strength, and for quality control. Field-cured specimens, in contrast, are used to determine form removal times or the adequacy of in-place curing.

Question 4

A 4x8 inch concrete cylinder is being cast for strength testing. According to ASTM C31, how many layers should the concrete be placed in, and how many times should each layer be rodded?

Accepted Answer

2 layers, 25 times each

Answer

ASTM C31 specifies that for cylinder molds with a diameter of 4 inches [100 mm], the concrete shall be placed in two approximately equal layers. Each layer must be rodded 25 times uniformly over the cross-section.

Question 5

During the initial curing period for standard-cured concrete test cylinders on a job site, which of the following conditions is required by ASTM C31?

Accepted Answer

Specimens must be stored in an environment with a temperature between 60°F and 80°F and prevented from moisture loss.

Answer

ASTM C31/C31M requires that during the initial curing period (up to 48 hours), standard-cured specimens must be stored in a temperature range of 60°F to 80°F (16°C to 27°C). Furthermore, measures must be taken to prevent moisture loss, such as using tight-fitting plastic lids or storing them in a curing box.

ACI (American Concrete Institute Certification) Practice Test

ACI (American Concrete Institute Certification) Practice Test

ACI Concrete Strength Testing Procedures Questions and Answers