ACI Concrete Strength & Testing Methods 2

Question 1

According to ASTM C39, how many days after casting is the standard compressive strength test for concrete cylinders performed?

Accepted Answer

28 days

Answer

ASTM C39 specifies 28 days as the standard age for compressive strength testing of concrete cylinders.

Question 2

What is the standard size of a concrete cylinder used for compressive strength testing per ASTM C39?

Accepted Answer

6 in × 12 in

Answer

ASTM C39 specifies a 6-inch diameter by 12-inch height cylinder as the standard specimen for compressive strength testing.

Question 3

The Schmidt hammer (rebound hammer) test is used to estimate which concrete property?

Accepted Answer

Surface hardness related to compressive strength

Answer

The Schmidt hammer measures surface rebound to estimate surface hardness, which correlates with compressive strength.

Question 4

When capping concrete cylinders for testing, what material is typically used to create a flat bearing surface?

Accepted Answer

Sulfur mortar or neoprene pad

Answer

Sulfur mortar caps or neoprene pads are used to provide uniform, plane bearing surfaces on concrete test cylinders.

Question 5

A concrete mix has a specified 28-day compressive strength (f'c) of 4,000 psi. What is the minimum acceptable average strength (f'cr) the mix design must target?

Accepted Answer

Greater than 4,000 psi with a safety margin

Answer

ACI 318 requires the mix design target strength (f'cr) to exceed f'c by a margin based on standard deviation to ensure adequate strength.

(ACI) American Concrete Institute Concrete Finisher Practice Test

(ACI) American Concrete Institute Concrete Finisher Practice Test

ACI Concrete Strength & Testing Methods 2