Building Materials - Concrete Part 3

110問 • 1年前

問題一覧

Concrete is completely mixed in a truck

transit-mixed concrete

Process of providing gentle motion in mixed concrete, just sufficient to prevent segregation of materials and loss of plasticity

Agitation

Has a large rotating drum on the rear of its chassis to used to mix concrete ingredients and to ensure it doesn't set whilst in transit

agitator truck

What is the maximum recommended time of transporting concrete from mixer to the forms

30 minutes

How many hours until after mixing is the initial set of the concrete

1 to 3 hours

Why is retempering of concrete generally prohibited

It changes the water-cement ratio

Also known as retempering of concrete that has been allowed to stand more than one half hour is not to be permitted

regaging

Concrete can be transported by several methods. which of the following is not mentioned as method of transporting concrete NOT

cranes

Shrinkage of concrete due to hardening and contraction from temperature changes causes cracks. how can the size of these cracks be minimized

by placing reinforcement to break up large cracks in the smaller ones

When using chutes transport concrete,what is recommended maximum slope

1 vertical to 2 horizontal

What is the process called where concrete is allowed to harden after it placed

curing

For how many days after placing should fresh concrete be protected from excessive vibration, loads, extreme heat or cold, two rapid drying, and contract with impurities to ensure favorable hardening

7 days

Any substance added to cement,mortars,and concrete to the purpose of improving or impact imparting particular properties

admixtures

In machine mixing of concrete,how long should the mixing of each batch continue after all material are in the mixer

not less than 1 minute

Compared to the hand mixing, machine mixing of concrete generally results in

more uniform quality and lower cost for large volumes

Materials used in very small amount to modify spacific property of another material in order to improve its characteristics; used in paints, plaster, mortars, concrete etc

admixtures

The curing period or required time for: balustrades, coping etc for steel and side forms:_________

1 day (24 hrs)

The curing period or required time for: arches spandrel walls:_______ spandrel arches:________ main arches:__________

7 days (168 hours), 14 days (336 hours), 21 days (504 hours)

the curing period or required time for: beams and girders sides:_______ beams and girders bottoms:________

3 days, up to 14 ft. 14 days (336 hours). Add 1 day for every 1 ft. additional span or fraction where of but not more than 28 days (672 hour)

the curing period or required time for: 3 to 7 ft spans:_______ Over 7 ft spans:________

3 ft span, 5 days (120 hours) add 1/2 day (12 hours) for every additional one fit span or refraction, 7 ft span, 7 days (168 hours) add 1 day (24 hours) for every additional one fit span or refraction thereof but not more than 28 days (672 hours)

the curing period or required time for: massive footings:_________ cantilever footings and slab footings:_________

1 day (24 hrs), 5 days (120 hrs)

the curing period or required time for: massive walls, 30 cms. thick or more:_________ thin walls less than 30 cms thick:_________ cantilever walls, buttresses, counterfort diagrams:__________

up to 2 m high. 1 day (24 hrs). add 1 day (24 hrs) for every additional meter or fraction thereof, up to 2 m high. 2 day (24 hrs). 1-1/2 days (34 hrs) for every additional meter or fraction thereof, without loads as same as: up to 2 m high. 2 day (24 hrs). 1-1/2 days (34 hrs) for every additional meter or fraction thereof

How do you mix concrete manually or by hand mixing

1. Sand + Cement (mix) 2. Form a crater + add water 3. Add gravel 4. Mix all inwand

what is the total weight of portland cement is sold in bags

40 kilos

The increase of the compressive strength of concrete is rapid in the early stage and slow down a time passes, approximately what percentage of its minimum compressive strength does concrete reach at 28 days of age

60%

How does the water-cement ratio affect the strength of concrete

strength decrease as the water-cement ratio increase

In less highly reinforced part of structures (like footings, thick walls, pan massive work),course aggregate may range up to

50 mm (2")

For reinforced beams, floor slabs, and thin walls, maximum size of coarse aggregate should not exceed

25 mm (1")

Course aggregate in concrete consists of which materials

crashed stones, travel or other inert materials of similar characteristics

What is a characteristic of desirable aggregates for concrete

being strong, clean, hard and uncoated

What is the name given to the mixture of cement water and find aggregate less than 6 mm

mortar

Which of the following is not a characteristic of a good concrete NOT

easily molded after setting

In reinforced-concrete construction, what type of portland cement is recommended

high-grade type I portland cement (type C-150)

Aggregate in concrete are best described as

Inert minerals fillers used with cement and water

How do you mix concrete using Machine mixer

1. Add Gravel 2. Add Sand 3. Add Cement 4. Add Water

Concrete should never be allowed to drop freely for unexposed work

over 5ft

Concrete should never be allowed to drop freely for exposed work

over 3ft

Reduces the amount of mixing water required for the desirable workability. Lowering water-cement ratio generally results in increased strength

Water reducing agent

Prevents the evaporation of water form concrete and allow it to be retained for hydration

Surface sealing agent

Water Reducing Agent

Superplasticizer

Other term of Water Reducing Agent

Superplasticizer

Used for reducing the surface tension of the mixing water in a concrete mix thereby facilitating the wetting and penetrating action of water

Surfare-active agent

Causes cement particles to separate by importing like electrostatic charges. It prevents bleeding o water to the surface of concrete

Dispersal agent

Other term of Surface-Active Agent

Surfactant

Are added to improve workability, used as per manufacturer’s directions. Hydrated lime is usually in the proportion of 10 to 15% of the cement by volume.

Inert, finely divided powders such as powdered glass , silica sand, stone dust, hydrated lime

An admixture that disperses entrained air in a concrete or mortar mix to increase workability, improved resistance to crackling indiced by free-thaw cycles ch the scaling caused by de-icing chemicals

Air Entraining Agents

Causes a slight expansion in plastic concrete or mortar and thus reduces or eliminates voids caused by settlement

Gas Forning Agent

Hastens the setting and strength development of a concrete, mortar or plaster mix. Principal ingredients are caluium chloride

Accelerators

Slow the setting of concrete, mortar or plaster mix in order to allow more time for placing and working the mix

Retarders/Decelarators

Improves denseness of concrete surface which are subjected to rolling live loads and impact

Concrete hardener

Improves bond between two concrete surfaces

Bonding agent

Prevents cement paste from bonding to the surface and inhibits the setting of cement paste

Set inhibiting agent

An abrasive materials used as topping to prevent slippery surfaces

Non-skid surface agent

Sometimes used in structures where it is desirable to avoid high temprature or in structures exposed to seawater or water containing sulfate

Pozzolanic admixture

Renders concrete more impermeable

Concrete waterproof

Manufactured from stearic acid or its compounds, mainly calcium stearate, and include asphalt emulsions

Waterproofing (perameability - reducing) compounds

For surface coloring. They are dusted on, usually in two coats, after all surface water has disappeared. The surface is then finished with a steel trowel .

Dry-cast, broadcast or dust-on

For body coloring. Integral color pigments are incorporated in the mortar topping. They are mixed dry with the cement and aggregate before water is added. Amount of color pigment required is not more than 10% of the cement by weight, generally 3 to 6 lbs. per bag of cement .

Integral colors

Employed to test existing concrete structure by drawing out a core cylinder

concrete core test

Most widely used test fan concrete compressive strength

compresive test

A cylinder concrete, cast form a representative batch and cured in a laboratory or in the field under controlled conditions

test cylinder

A compression test a cylinder cut from a hardened concrete structure, usually means of a core drill

core test

What is the minimum age (days) required ultimate compressive strenght

28 days

What is the minimum required ultimate compressive strength for Class AA: Cylinder: _________ psi Cube: _________ psi

2400, 2800

What is the minimum required ultimate compressive strength for Class A: Cylinder: _________ psi Cube: _________ psi

2000, 2400

What is the minimum required ultimate compressive strength for Class B: Cylinder: _________ psi Cube: _________ psi

1600, 2000

What is the minimum required ultimate compressive strength for Class D: Cylinder: _________ psi Cube: _________ psi

1000, 1200

What is the minimum required ultimate compressive strength for Class C: Cylinder: _________ psi Cube: _________ psi

1300, 1600

Due to hardening and contraction from temperature changes, causes cracks the size o which depends on the extent of the mass

Shinkage of concrete & temperature changes

The contracting of a hardened concrete mixture due to the loss of capillary water

drying shrinkage

Contracting of a concrete prior to its final set caused by hydration of the cement paste

plastic shrinkage

In an important phenomenon in a young concrete. At low water/cement ratio, less than about 0.42, all the water is rapidly drawn into the hydration process and the more creates very fine capillaries

autogenous shrinkage

Occurs when the concrete is exposed to air containing carbon dioxide. When the handened concrete is exposed to this type of air, the weight increase, and the concrete undergoes irreversible

carbonation shrinkage

Powdering at the surface of concrete slab

dusting

caused by vapor migrating through the stab bringing soluble salts to the surface of the concrete

efflorescence

Are hollow spaces and cavities left in concrete mass on surfaces or inside the concrete mass could not reach where concrete

honeycomb

What is the thickness of lumber commonly used for columns, beams, and girder bottoms in concrete forms

What is the thickness of lumber commonly used for floor panels in concrete forms

Which of the following lumber sizes is commonly used for struts, posts, shores, and uprights

2"x4"

What are the typical thicknesses of cleats used in concrete forms

1" or 2"

Used where a smooth surface is required. It should be waterproof, Grade A and at least 12mm (1/2") thick

plywood forms

Uses pans for concrete joist construction, steel decking a corrugated steel for concrete slabs and slab-and-joist construction

steel form

What is the main use of steel bars in construction

To reinforce concrete

What are steel bars commonly called

Billet-steel bars and rail-steel bars

What are common sizes of steel bars

1/4 inch to 1-1/4 inches

What are typical lengths of steel bars

20 or 30 feet

What are the two common types of steel bars

Billet-steel bars and rail-steel bars

What are the two types of steel bars based on surface texture

Plain and deformed

How are billet-steel bars made

By rolling billets from ingots

What are the grades of billet-steel bars

Structural, Intermediate, Hard

How many grades do rail-steel bars have

How are rail-steel bars made

By rolling standard T-rails

What material is wire fabric made of

Cold-drawn steel wireCold-drawn steel wire

What does the first pair of numbers in wire fabric specifications refer to

Spacing of the wires

What sizes are available for welded wire fabric rolls

5 ft or 6 ft wide

The inside of forms which have been used once and are to be used again shall be coated an approved soap or other approved material, or thoroughly wetted before concreting. Should only be partially seasoned

lumber forms

Polystyrene forms are now available for concrete work.

plastic forms

built up of either single or stranded longitudinal wires with cross wires or bond wires running diagonally across the fabric

Triangle-mesh wire fabric

Manufactured from solids steel sheets. The forms into which sheet can be shaped include diamond, crimp, herringbone,and z-rib the name only a few

expanded mesh

100

Are furnished either in flat or segmental sheets, press into a series of solid ribs, between which the metal is stamped, perforated or deformed into an open mesh work. Are furnish painted or galvanized, in open-hearth mild steel or in special copper bearing or alloy steals

lath

Building laws Part 1

Mari Alberca · 100問 · 1年前

Building laws Part 1