ARE BDCS 15- FOBC Concrete

Blast furnace slag

A byproduct of iron that can improve concrete workability, increase strength, reduce permeability, reduce temperature rise, and improve sulfate resistance

Silica fume, also known as microsilica

A powder that is approximately 100 times finer than Portland cement. Silica fume is used to produce extremely high-strength concrete that also has a very low permeability.

He three-quarter inch or 1 1/2 inch maximum aggregate diameter is common for most slab and structural work

Aggregate diameters up to 6 inches are used in dams and other massive structures

Air entrained concrete is commonly used for paving's and exposed architectural concrete in cold climates.

Air entrained concrete can achieve the same structural strength as normal concrete.

Water reducing admixtures

Allow a reduction in the amount of mixing water while retaining the same workability, which results in a higher strength concrete

Galvanize reinforcing bars in the epoxy coated reinforcing bars

Are often used in marine structures, highway structures, and parking garages to resist corrosion from dicing salts or those in seawater.

Steel is protected from corrosion by the alkaline chemistry of the concrete

Concrete bonds strongly to steal, providing a convenient means of adapting brittle concrete to structural elements that must resist tension, sheer, and bending as well as compression.

Because concrete cures by hydration, it is essential that it be kept moist until its required strength is achieved

Concrete is commonly designed to be used at the strength it reaches after 28 days of curing

During the curing process

Concrete shrinks slightly

Concrete has no useful tensile strength

Concrete was limited in its structural use into the concept of steel reinforcing was developed

Coloring agents

Dies in pigments used to alter in control the color of concrete for building components whose appearance is important.

Fibrous admixtures are short fibers, usually of glass, steel, or poly propylene

Fibrous admixtures are added to a concrete mix to act as micro reinforcing. Fibrous admixtures reduce plastic shrinkage cracking that sometimes occurs during curing of slabs.

Course aggregate is normally gravel or crushed stone

Fine aggregate is sand

Fly ash, a fine powder that is a waste product from coal fired power plants

Fly ash increases concrete strengths, decreases permeability, increases sulfate resistance, reduces temperature rise, reduces mixing water, and improves pump ability and workability of concrete.

In general, the maximum aggregate size should not be greater than three fourths of the clear space between bars or one third the depth of the slab.

For very thin slabs, and toppings, a 3/8 inch maximum aggregates diameter is often specified

All formwork services in contact with concrete must be coated with a form release compound.

Form release compound is in oil, wax, or plastic that prevents adhesion of the concrete to the form

Glassfiber reinforced concrete, GFRC

Glassfiber reinforced concrete is used for cladding panels

Grade 60 is the most readily available reinforcing bar strength

Higher reinforcing strength bars are useful where there is a restricted amount of space available for bars and a concrete member

The weight of the water in the mix of concrete should not be more than 60% of the weight of the cement

Higher water cement ratio then this are often favored by concrete workers because they produce a fluid mixture that is easy to place in the forms, but results in deficient strengths in surface qualities.

If concrete and steelhead different coefficients of thermal expansion, a reinforced concrete structure would tear itself apart during cycles of temperature variation

If concrete and steel were chemically incompatible, the Steel would corrode or the concrete would be degraded. If concreted not it here to steal, a more expensive configuration of reinforcing would be necessary.

If concrete must be dropped a distance of more than three or 4 feet, it should be deposited through drop shoots, that break the fall of the concrete

If concrete must be moved a large horizontal distance, it should be pumped through hoses, or conveyed in buckets or buggies, rather than pushed across or through the form work

Wet concrete is not a liquid but a slurry, and unstable mixture of solids and liquids.

If wet concrete is vibrated excessively, dropped from heights, or move towards onto any distance in formwork, it is likely to segregate.

In very hot weather, dehydration reaction is greatly accelerated

In hot weather, concrete may begin curing before it can be placed and finished

At Low temperatures, the curing reaction in concrete proceeds at a much reduced rate

In subfreezing temperatures, the curing reaction stops completely until the temperature of the concrete rises above the freezing mark.

Air in training admixtures

Increased workability of wet concrete, reduce freeze thaw damage, and create very lightweight nonstructural concretes with thermal insulating properties.

The tendency to cure before being placed in hot weather can be controlled by using cool ingredients in by replacing some of the mixing water with an equal quantity of crushed ice

Making sure that the ice has melted fully in the concrete has been thoroughly mix before placing. Another method of cooling concrete is to bubble liquid nitrogen through the mixture at the batch plant

Hi Range water reducing admixtures, also known as superplasticizer's

Organic compounds that transform a stiff concrete mix into a free-flowing liquid. They are used either to facilitate placement of concrete under difficult circumstances, or to reduce the water content of a concrete mix to increase its strength.

The basic theory of concrete reinforcing

Put the steel where the tension is in a structural member and let the concrete resist the compression.

Pozollans

React with the calcium hydroxide in wet concrete to form cementing compounds. Use for reducing internal temperatures of curing concrete, reducing the reactivity of concrete with aggregates containing sulfates, or improving the workability of concrete.

Reinforcing bars for concrete construction are hotrolled much the same as structural shapes

Reinforcing bars are rounded cross-section, with surface ribs for better bonding to concrete

Accelerating admixtures cause the concrete to cure more rapidly

Retarding admixtures slow concrete curing to allow more time for working with the wet concrete

The opposite of precasting is site casting, or cast in place concrete

Site casting, concrete is poured into forms that are directed in place on the job site.

Steel is used to resist some of the compression in concrete columns and in beams his height must be reduced for architectural reasons

Steel is also used to resist cracking that might otherwise be caused by curing shrinkage, and by thermal expansion and contraction in slabs and walls

Lightweight aggregates are used instead of sand and crushed stone for various special types of concrete

Structural lightweight aggregates are made from minerals such as shale. She'll is crushed to the desired particle sizes, heated. Concrete made from this aggregate has a density of about 80% of normal concrete, but retains most of the strength of normal concrete.

Nonstructural lightweight concretes are made as insulating rooftop things in densities from one fourth up to one sixth that of normal concrete

The aggregates in these concretes are really expanded Mika, vermiculite, or expanded volcanic glass, perlite. The density concrete is further reduced by admixtures that entrain large amounts of air during mixture

If concrete is allowed to dry at any point during its 28 day curing.

The strength of the cured concrete will be reduced, and its surface qualities will be adversely affected

Aggregates make up roughly 3/4 of the volume of concrete

The structural strength of a concrete is heavily dependent on the quality of its aggregates

Concrete elements casted formwork are largely protected from dehydration by the formwork

The top surfaces must be kept moist by repeatedly spraying or flooding with water, by covering with moisture resistant sheets of paper or film, or by spraying on a curing compound that seals the surface against loss of moisture

Precasting concrete is cast into permanent, reusable forms at and industrial plants, and transported as fully cured structural units to the job site

The units are hoisted into place and connected much as if they were structural steel shapes.

Air in training cements Contain small amounts of additives that's cause microscopic air bubbles to form any concrete during mixing

These bubbles give improved workability during placement of the concrete, and greatly increase the resistance of the cured concrete to damage caused by repeated cycles of freezing and thawing.

Type III cement, Hight early strength cement

Type 3A, high early strength cement, air entraining

Type one cement is used for most purposes in construction. Types two and five are used where the concrete will be in contact with water with a high sulfate concentration.

Type III is employed in situations where a reduced curing. Is desired, such as with cold-weather, in the precasting of concrete structural elements, or when the construction schedule must be accelerated.

Type four cement, low heat of hydration cement

Type five cement, high resistance to sulfate attack.

Type four cement

Type for cement is used in massive structures, such as dams, where the heat emitted by the curing concrete may accumulate and raise the temperature of the concrete to damaging levels.

Type one cement, normal cement

Type one-A cement, normal, air in training cement

Type two cement, moderate resistance to sulfate attack

Type two-A cement, moderate resistance to sulfate attack, air entraining

If freshly poured concrete is covered or insulated, it's heat of hydration is often sufficient to maintain an adequate temperature in the concrete

Under more severe winter conditions, the ingredients of the concrete may have to be heated before mixing, and a temporary enclosure in a temporary source of heat may have to be provided

Low water cement ratios will make concrete that is dense and strong

Unless air in training or workability admixtures are included in the mix to substitute for the lost water, the concrete will not flow easily into the forms and will leave large voids.

Corrosion inhibitors

Used to reduce corrosion of reinforcing steel and structures that are exposed to Road dicing salts or other corrosion causing chemicals.

Workability agents

Workability agents make the wet concrete easier to place in forms and finish by improving its plasticity. Workability agents include Pozzolans and air in training admixtures, along with certain fly ashes and organic compounds.