SOC Concrete Flashcards
- What are the raw materials in Portland cement?
Limestone Cement rock Oyster shells Marl (lime rich mud-lake sediment) Clay Silica Sand Iron Ore
- What is the “clinkers”?
The raw material finely ground and carefully proportioned before heated to temperatures from 2000 to 3000 degrees (F) to form hard pellets called “Clinkers”
- What is air entrainment?
The international creation of tiny air bubbles in concrete
- What is the composition of concrete?
Mix of aggregates and entrained air held together by hardened paste made of cement and water
- What is the most commonly used cement by the military?
Portland cement
- What is hydration?
Hydration is the chemical reaction. It occurs when Portland cement is mixed with water.
- What causes concrete to harden and what is the desired temperature?
Hydration and 73 degrees
- What are the three major components?
Water
Aggregates
Portland Cement
- What are two types of aggregate
1) Coarse aggregate (Rock)
2) Fine aggregate (sand)
- What is aggregate?
It used as an inner filling material, made of sand and gravel. 60 to 80 percent of total concrete volume.
- What is primary purpose of aggregates?
To gain economy
- What are the most common contaminating materials of aggregate?
Dirt, clay and salt
- What are the five types of Portland cement?
Type I (Normal Portland) Type ll (Modified) Type III (High early) Type IV (Low heat) Type V (Sulfate Resistant)
- What is the normal cure time and some uses of type 1 portland cement?
28 days
It used for Pavement, Sidewalks, Bridges, Reservoirs, Building and etc
- What is the normal cure time and some uses of type 2 portland cement?
45 days
Large super structures, large piers, heavy retaining walls
- What is the normal cure time and some uses of type 3 portland cement?
High early -7 days
Used in cold weather and high heat
- What is the normal cure time and some uses of type 4 portland cement?
Low heat -90 days
Large massive structures
- What is the normal cure time and some uses of type 5 portland cement?
Sulfate Resistant – 60 days
Used where the soil, or water, in contact with the concrete has a high sulfate content
- What types of Portland cement are air entrained?
Types1, 2 and 3
- What does calcium chloride do to Portland cement?
It accelerates both hardening and strength gain by 2% the weight of cement
• 2 hours vs 6 hours
- How does Portland cement ship?
Bags
94lb, contain one cu ft of loose measurement
Barrels
376lb = 4 bags
Rail cars
- What is warehouse pack?
Sacked cement in storage packed too tightly
- What are the types of concrete?
Reinforced
Prestressed
Precast
Lightweight
- What is reinforced concrete?
Steel rods imbedded into the concrete is defined as reinforced concrete (strong in compression, but weak in tensile strength)
- What is prestressed concrete?
Reinforced steel or welded wire mesh that is stretched out with tension before the concrete is poured.
- What is precast concrete?
Concrete cast into something other than its final position
- What is benefits of lightweight concrete?
a) In dead-loads making savings in foundations and reinforcement
b) Improved thermal properties
c) Improved fire resistance
- What is benefits of plastic state?
a) Readily moldable
b) Changes shape slowly if forms are removed
c) Uniform
d) Workable nonsegregated
• It can be cast or molded into nearly any size or shape
- What are some advantage of concrete?
a) High compressive strength
b) Can be cast, molded or shaped
c) Little maintenance and economical
d) Durable
e) Strength can be pre-determined
- What are some disadvantage of concrete?
a) Low tensile strength
b) Expands and contracts
c) Shrinks when dry
d) Heavy
- What is expands and contracts?
it is chemical reaction that occurs by moisture and temperature changes
- What is width of expansion joint should never be?
Expansion joints should never be less than ¼ inch wide.
- What is the difference between construction joints and expansion joints?
Construction joints are not intended to allow for movement of concrete. Expansion joints and contraction joints could be move around.
- When can you place concrete underwater?
Placed underwater only when unavoidable.
- If concrete must be placed underwater, what should the max velocity of the current be?
10 ft per min
- When hand mixing cement, how much cement can be mixed by one man
One man can mix 1 cu yd per hour
- When hand mixing concrete the sand, gravel and cement should be dry mixed how many times before adding water?
Three times
- What is the formula for project volume (PV)?
PV = Length x Width x depth x number of structures.
• Make sure keep in feet
- What is the formula for Loss Factor (LF)?
• for cu ft
LF = PV x LF(<5400 cu ft =1.1 or > 5400 cu ft = 1.05)
• for cu yrds
LF = PV x LF(< 200 cu yds =1.1 or > 200 cu yds = 1.05)
- What is the formula for loose volume (LV)?
LV = LF X 1.5
- What rule do you use when calculating for materials when laying concrete?
1-2-3 rule
1/6 cement, 2/6 sand, and 3/6 gravel
- What is the formula for convert cu ft to cu yrds?
Cu ft / 27 = cu yrds
- When estimating for concrete work what is the rule called?
3/2 rule
- What is forms?
it hold concrete until sets, produces the desired shapes and sometimes surface finishes. Can represent up to 1/3 of concrete structure’s total cost.
- What is essential when set up forms?
Must be tight, rigid, and strong
- What materials can be used make forms?
Wood (most common and economical)
Metal
Earth
Fiber
- What are the elements of wooden forms (Concrete wall)?
Sheathing Stud Wales Strong backs Braces Shoe plates Spreaders Tie wires
- What are the elements of wooden forms (Concrete column)?
Sheathing
Batten
Yokes
Bracing
- The rate of filling should not be exceed?
4 feet per hour vertically, to avoid excessive pressure on the forms
- What is screeding?
Process of stiking off the excess concrete in order to bring the surface to the right elevation
- What are techniques of finishing operation?
a) Floating If smooth surface is required b) Troweling If smoother surface is required c) Brooming d) If non-skid surface is required
- What determines the strength of concrete?
Ratio of cement to water
- What are the rules of thumb for the maximum size aggregates should be in concrete?
The maximum size should not exceed 1/5 the minimum diameter of a wall or similar structure Not to exceed 1/3 the slab thickness Not to exceed 3⁄4 of the clear space between reinforcing bars
- Where are isolation joints used?
where a pavement joins sidewalks and building, and intersects other pavements or bridge.
- What do expansion joints do?
Permit volume change movement of a concrete structure or member.
- How much concrete can one person mix per hour?
1 cubic yard
- how deep does the land under a slab need to be moistened?
6 inches
- Slabs which will support load bearing walls must be what?
Reinforced with rebar
- What is different between construction joint and Control joint?
1) Construction joints y allows builder to continue construction process.
2) Control joint is used at finishing state of construction.
- What is sequence of concrete hand mixing?
a) Mix dry materials three times (sand, cement, and grave)
b) Add water to achieve desire concrete strength
- Ingredient Equation
PV = L x W x H x ( number of structure) • Keep measurement in feet Loss factor LF= PV ( <5400 cu ft, add 10% (1.1) LF= PV ( >5400 cu ft, add 5% (1.05) Loose Volume LV= LF X 1.5 • LV round up to whole number CEMENT 1/6 X LV = bag of cement SAND 2/6 X LV = CU ft Gravel 3/6 x LV = CUft Water 8 gal per bag of cement 8 x # of bag cement
If you ordering from truck,
LF = PV x (loss factor)(1.05)
Always going to be CU yard
- Special curing techniques
1) Hot weather keep temperature below 90 F degree Loosen forms ASAP Add accelerators Remove forms (7 days)
2) Cold weather
40 degrees F or lower
Keep concrete above 70 degrees F
Add accelerators
