Concrete

Question 1

Admixture

Answer 1

A substance other than cement, water and aggregates included in a concret mixture for the purpose of altering one or more properties of the concrete.

Question 2

Aggregate

Answer 2

Inert particles, such as sand, gravel, crushed stone or expanded minerals in concrete or plaster mixtures.

Particales occupy about 70% tp 75% of total volume of concrete.

Question 3

Air-Entraining Agents

Answer 3

Agents that form tiny, disperes bubbles in concrete.

• Increase workability & durability
• Improves resistance to freezing and thawing cycles
• Reduce segregation

Question 4

Chair

Answer 4

Metal wire devices places on concrete formwork to hold the rebars above the bottom of the form at the proper distance.

Question 5

Concrete

Answer 5

A material combination of cement, fine and course aggregates and water mixed in the proper portions and allowed to cure.

Question 6

Concrete Architectural Finishes

Answer 6

Finishes where concrete will be exposed and appearance is a consideration

• Form Liner
• Scrubbed
• Acid Wash
• Water Jet

Question 7

Concrete Rubbed Finishes

Answer 7

• Smooth
• Grout Cleaned

Question 8

Concrete Slab Finishes

Answer 8

• Float finish (sandpaper like textures)
• Light steel trowel finish
• Hard steel troweled finish (very smooth surface)
• Broom finish
• Superflat floor finish (level)

Question 9

Concrete Tooled & Sandblasted Finishes

Answer 9

Tooled finishes produces by mechanically modifying concrete surface:

• Brushed Hammering
• Grinding
• Applied
• Sandblasted Finsihes

Question 10

Construction Joint

Answer 10

A joint that occures wherever there are two sucessive pours of concrete.

Beacause a construction joint creates a plane of weakness, it should be located at points of minimal shear.

Question 11

Control Joint

Answer 11

An intentinoal, linear discontinuity in a structure or component, designed to form a plane of weakness where cracking can occur in response to various forces so as to minimize or elimiate cracking elsewhere.

Question 12

Design Strength

Answer 12

The compressive strength of concrete after it has cured and hardened for 28 days.

Question 13

Expansion Joints

Answer 13

A surface divider joint that provides space for the surface to expand.

Question 14

Fly Ash

Answer 14

A waste material obtained from coal-fired power plants.

Used in concret to:

• increase strength
• decrease permeability
• reduce temparature rise
• increase sulfate resistance
• improve workability
• decrease total amount of cement needed

Question 15

Flying Forms

Answer 15

Large fabricated sections of framework that are removed, once the concrete has cured, to be reused in forming an identical section above.

Question 16

Form Ties

Answer 16

Metal wires or rods used to hold opposite sides of the form together and also to prevent their collapse.

Question 17

Formwork

Answer 17

A system of boards, ties and bracing required to construct the mold in which wet concrete is placed.

Economy: One of the biggest expenses for C.I.P. concrete. To reduce cost the forms should be reusable as much as possible.

Question 18

Hydration

Answer 18

The chenical hardening of concrete

A process of combining chemicall with water to form molecules or crystals that include hydroxide radicals or water or crystallization.

Question 19

Isolation Joints

Answer 19

Allows two adjecent sections to move independenlt of one another, but are not as complex as expansion joints.

Often to separate columns from slabs and slabs from foundation.

Question 20

Laitance

Answer 20

A chalky surface deposit of low-strength concrete.

Caused by too much water in the concrete mixture resulting in water bleeding to the top.

Must be removed to bond with additional layer of concrete.

Question 21

Plasticizers

Answer 21

Reduce the amount of water need in concrete while maintinging the necessary consistency for correct placement compaction.

Benefits:

• Makes it possible to mix higher-strength concrete

Question 22

Portland Cement

Answer 22

The binding agent in concrete.

Made from:

• Lime
• silica
• iron oxide
• alumina

Question 23

Reinforcing Bars

(rebar)

Answer 23

Steel to reinforce contrete to increase tensile strength.

Diameters are in 1/8” increments.

Common grades:

• grade 40
• grade 60

Question 24

Segregation

Answer 24

Separation of the constituents of wet concrete caused by excessive handeling or vibration.

Question 25

Slip Forming

Answer 25

A special form where it moves as the concrete cures. This type of forming is used to form continuous surfaces such as tunnels and high-rise building cores.

Question 26

Type I Cement

Answer 26

Standard Cement or Normal Cement

Used for most general construction where the other types are not needed.

Question 27

Type II Cement

Answer 27

Modified cement

Used in places where a modest amount of sulfate resistance is needed and where the heat of hydration needs to be controlled.

• Dams
• Other massive structures

Question 28

Type III Cement

Answer 28

High-early-strength cement

Used where a quick set is needed. Has a higher heat of hydration, suitable for cold-weather concreting.

Question 29

Type IV Cement

Answer 29

Low-heat cement

Used in massive structures to minimize cracking. Very slow setting.

Question 30

Type V Cement

Answer 30

Sulfate-resisting cement

Used for structures that will be exposed to water or soil with a high alkaline content.

Question 31

Concrete Sealers

Answer 31

• Coating sealer types
• Penetrating sealer types

Question 32

Precast Concrete

Answer 32

Concrete cast and cured in a postion other than its final position in the structure