ACI Certification Concrete Mix Design

Question 1

According to ACI 211.1, which factor most directly influences the required water content for a given slump?

Accepted Answer

Maximum size of aggregate

Answer

ACI 211.1 tables show that water demand decreases as maximum aggregate size increases for a given slump, due to reduced total surface area.

Question 2

In the absolute volume method of mix design, the sum of volumes of all ingredients for one cubic yard of concrete must equal:

Accepted Answer

27 cubic feet

Answer

One cubic yard equals 27 cubic feet, so the absolute volumes of all ingredients—cement, water, aggregates, and air—must sum to 27 ft³.

Question 3

What is the approximate specific gravity of Type I portland cement used in absolute volume calculations?

Accepted Answer

3.15

Answer

Portland cement has a specific gravity of approximately 3.15, which is used to calculate its absolute volume in mix design.

Question 4

A lower water-to-cement (w/c) ratio generally produces concrete with:

Accepted Answer

Higher strength and improved durability

Answer

Reducing the w/c ratio decreases capillary porosity in the hardened paste, resulting in stronger and more durable concrete.

Question 5

According to ACI 318, the maximum w/cm ratio for concrete exposed to freezing and thawing in a moist condition is:

Accepted Answer

0.45

Answer

ACI 318 limits the w/cm to 0.45 for concrete subjected to freezing and thawing in moist conditions to control permeability.

ACI (American Concrete Institute Certification) Practice Test