Chapter 13

What is the Tension and Compression of Concrete?

0 psi, 2,000 to 22,000+ psi

What is the Tension and Compression of Brick?

0 psi, 250 psi

#8 bar diameter

1 in.

#4 bar diameter

1/2 in.

What is the Tension and Compression of Steel?

22,000 psi

Concrete strength is normally specified at

28 days

Specified maximum slump is usually in the range of

3 to 5 inches

W12 wires spaces at __in. crossed by W5 Wires spaced at __ in.

6, 12

What percent of total concrete volume do coarse and fine aggregates make up

60-80%

What is the Tension and Compression of Wood?

700 psi, 1,100 psi

Affects workability of wet concrete

Aggregate Grading

Strength of concrete is heavily dependent on the quality of the ______

Aggregates

Ingredients added generating bubbles during concrete mixture that create small, distributed voids in the finished concrete

Air-Entraining Cement

This type of cement has a greater resistance to freeze-thaw damage, Improved workability when wet, but reduces concrete strength

Air-Entraining Cement

Solutions for curing concrete in cold weather

Blankets (cover), Temporary Heat

In a simply supported beam, the greatest tension forces occur at the ______ of the beam

Bottom middle

Provide the structural mass of concrete and constitute the majority of the concrete volume

Coarse and Fine Aggregates

Causes hydration to proceeds much slower and risk if freezing

Cold Weather

Temporary structure to hold freshly poured concrete in the desired shape

Concrete Framework

Welded Wire Reinforcing is especially common for _____ reinforcing

Concrete slab

Eliminates voids and air pockets within the concrete pour

Consolidation

Unit of mixture for concrete

Cubic Yard

What is used when the reinforcing may be exposed to salts or sea water

Epoxy Coated Rebar

T or F concrete has a high tensile strength ?

False, no useful tensile strength

Short fibers of glass, steel, or polypropylene are added to the concrete mix

Fibrous Reinforcing

What are the ingredients in concrete?

Fine Aggregate (sand) Coarse Aggregate (gravel) Portland Cement (Calcium Silicates) Water

Oils, waxes or plastic coatings

Form releasing compounds

Distribution of aggregate particle sizes

Grading

In conventional concrete construction, formwork can account for how much of the total concrete construction costs

Half or more

Concrete with too ___ slump may have to much water added

High

Type III

High Early Strength

Type IIIA

High Early Strength, Air Entraining

Type V

High Resistance to sulfate attack

Greater then 6000 psi to roughly 20,000 psi

High-Strength Concrete

What is used to reduce rebar congestion

Higher strength bars

Causes issues such as Premature Drying, and Accelerated Curing

Hot Weather

Concrete is placed into a conical cylinder; the cylinder is removed, and the loss in height of the concrete mass is measured.

How a slump test is performed

The chemical bonding of water and cement

Hydration

Expanded shale,clay,slate,slag Cinders and other volcanic rocks Vermiculate Perlite

Lightweight Aggregates

Used to make lighter-weight concrete

Lightweight Aggregates

Concrete with too ___ slump may be difficult to place

Low

Type IV

Low hear of hydration

A _____ percentage of void space between particles results in a ________ concrete that requires less cement

Lower, Stronger

Greater concentrations of fibers, that also resist longer-term cracking due to drying and thermal stresses

Macrofiber Reinforcing

Relatively low amounts of fibers, to aid concrete in resisting plastic shrinkage

Microfiber Reinforcing

Type IIA

Moderate Resistance to sulfate attack, Air Entraining

Type II Cement

Moderate resistance to sulfate attack

Roughly 60% or less of the weight of ordinary concrete, insulating roof toppings, fill material, density approx. 20-25% of regular concrete

Nonstructural Lightweight Concrete

Up to 6000 psi compressive strength

Normal Strength Concrete

Type IA Cement

Normal, Air entraining

Type I Cement

Normal, General Purpose

Cracking that occurs during early curing

Plastic Shrinkage

This binds the aggregate in concrete

Portland Cement (Calcium Silicates)

Steel strands are tensioned after concrete has been cast and reached adequate strength

Post-tensioning

Applying an initial compressive strength to a concrete member, so as to improve its structural efficiency

Prestressing

High-strength steel strands are stretched tightly and then restrained by the concrete, putting the concrete into initial compression

Prestressing

Its advantages include Increase the load carrying capacity Increase span length Reduce member size

Prestressing

Steel strands are tensioned before concrete is cast

Pretensioning

Hot-rolled steel, deformed with surface ridges so as to better bond with concrete

Rebar

Most common concrete reinforcing material

Rebar

When reinforcing becomes crowded and concrete placement

Rebar Congestion

Who prepares shop drawings that are reviewed by the structural engineer

Reinforcing Fabricator

What is the advantage to WWR

Saves Labor

Excessive vibration, dropping from excessive heights, and moving concrete horizontally have what effect on the concrete

Segregation

Seperation of large aggregate from the finer portions of the mix, must be avoided

Segregation

Provides a rough measure of the workability of concrete while wet

Slump test

What are laid into concrete along lines of tension to provide resistance to pulling forces?

Steel Bars or Wires

Also increases the durability of the concrete surface

Steel Fiber Reinforcing

Structural properties when hardened

Strength, stiffness, durability

Where are concrete reinforcing requirements shown

Structural Drawings

Roughly 80% or less of the weight of ordinary concrete, reduced stricture weight saves cost, lower thermal conductivity increases resistance to building fires, Density approx. 80% of regular concrete

Structural Lightweight Concrete

Ability to resist pulling forces

Tensile Strength

Prevent the vertical bars from buckling outward

Ties

Wrap around the vertical bars

Ties or Spirals

T or F Prestressed members are typically more slender and lighter than comparable conventional reinforced members

True

This type of cement is used for cold weather construction, concrete precast on plants, and accelerated construction schedules

Type III

This type of cement is used for massive structures, such as dams, where heat generated during hydration must be limited to avoid excessive temperatures

Type IV

These types of cement is used for concrete in contact with soils or water with high sulfate concentrations

Types II and Type V

Add to the strength of the column in compression, and resist tensile forces that are introduced from wind of seismic forces, or from connections to beams

Vertical Bars

Is necessary for the chemical hydration of the cement and the hardening of the concrete

Water

_____ is an essential ingredient in concrete, that combines chemically with the cement as the concrete hardens

Water

WWF

Welded Wire Fabric

WWR

Welded Wire Reinforcing

Prefab welded grids of reinforcing bars or wires

Welded Wire Reinforcing or Welded Wire Fabric

Ease of placing, consolidating, & finishing wet concrete

Workability

Solutions for curing concrete in hot weather

ice subsisted for water, early or late placement times

Slump tests are performed on batches of concrete as

they arrive on the site