Chapter 13: Concrete Construction

Question 1

What is the purpose of embedding steel in concrete?

Answer 1

Increases tensile strength and resilience

Question 2

Artificial cement whose durability as a building stone made it extremely popular. Reinforced steel bars are embedded to resist tensile forces.

Answer 2

Portland cement

Question 3

Rocklike material produced by mixing coarse and fine aggregates, Portland cement, and water, and allowing the mixture to harden.

Answer 3

Concrete

Question 4

Gravel/crushed stone

Answer 4

Coarse aggregate

Question 5

Sand

Answer 5

Fine aggregate

Question 6

Hardening of concrete

Answer 6

Curing

Question 7

When the cement combines chemically with water to form strong crystals that bind the aggregates together.

Answer 7

Hydration

Note: heat of hydration is the considerable heat given off during this process.

Question 8

The concrete shrinkage that occurs as excess water evaporates from the concrete during hydration.

Answer 8

Drying shrinkage

Question 9

A stage of Portland cement when crushed and blended constituents are put through a long, rotating kiln.

Answer 9

Clinker

Question 10

What are the steps in the manufacture of Portland cement?

Answer 10

Materials are extracted from the earth and transported.

1. The stone is crushed to 5 inches, then 3/4 inches, and stored.
2. Raw materials are ground to powder and blended (dry process), or are ground and mixed with water to form slurry, and then blended (wet process).
3. Burning changes the raw mixture chemically into the cement clinker.
4. Clinker with gypsum added is ground into Portland cement and shipped.

Question 11

Contain ingredients that cause microscopic air bubbles to form in the concrete during mixing.

Answer 11

Air-entraining cements

Question 12

Produced by controlling the quantities of certain minerals that contribute to the cement’s color; used for architectural applications for lighter and more uniform concrete, and to enhance the appearance.

Answer 12

White Portland cement

Question 13

Added to concrete as a partial substitute for Portland cement, increases concrete strength and durability, improves workability or wet concrete, and reduces drying shrinkage.

Answer 13

Supplementary cementitious materials

Question 14

Added ingredients that alter or improve concrete properties: coloring, air-entraining, water-reducing, cure accelerating, corrosion inhibiting, and freeze protecting.

Answer 14

Admixtures

Question 15

Normal strength of concrete is up to about _____ psi, and higher strengths may be up to _____ psi.

Answer 15

6,000; 20,000

Question 16

For the water-cement ratio, lowering water to cement increases concrete _____, decreases _____, and increases _____.

Answer 16

Strength; workability; cost

Question 17

Prepared at batch plants and delivered to the site on trucks. Ingredients are mixed in the rotating drum in the truck, while smaller batches are prepared on site.

Answer 17

Mixing concrete

Question 18

Rough measure of the workability of wet concrete

Answer 18

Slump test

High slump: too much water, low slump: difficult to place; maximum slump is usually 3-5 inches.

Question 19

What is true about concrete strength?

Answer 19

It has no useful tensile strength, but can resist stretching forces.

Question 20

Bars or wires, usually steel, that are laid into concrete along lines of tension to provide resistance to these forces. The most common reinforcing material. Deformed with surface ridges so as to bond with concrete.

Answer 20

Rebar (reinforcing bars)

Question 21

Bar size numbers generally correspond to diameter in _____ of an inch.

Answer 21

8ths

Question 22

Prefabricated welded grids of reinforcing bars or wires, common for concrete slab reinforcing.
Ex: 6x12-W12xW5 represents W12 longitudinal wires spaced at 6 inches and W5 transverse wires spaced at 12 inches.

Answer 22

Welded wire reinforcing (WWR)

Question 23

How do you reinforce a simple concrete beam?

Answer 23

The greatest tension forces occur at the bottom middle of the beams. Steel reinforcing bars are bent to follow these lines of tension, and the bunching of the bars at midspan would serve to resist the higher stresses at that point.

Question 24

How do you reinforce a column?

Answer 24

Vertical/column bars (large-diameter) are placed vertically in the column to share the compressive loads with the concrete, resist tensile stresses, and impart ductility to the column. Ties and spirals wrap around the vertical bars.

Question 25

Used with precast concrete members; high-strength steel strands are stretched tightly between abutments in a precasting plant before the concrete is cast.

Answer 25

Pretensioning

Question 26

High-strength steel strands (tendons) are covered with a steel or plastic tube to prevent them from bonding to the concrete and are not tensioned until the concrete is poured and has achieved adequate strength. Done almost exclusively in place on the building site.

Answer 26

Posttensioning

Question 27

Concrete will gradually and permanently shorten over a period of months or years when placed under sustained stress from its own weight or other permanent building components.

Answer 27

Creep