Ballast Concrete Flashcards
What concrete buildings are LeCorbusier famous for?
Marseilles, Ronchamp, Palace of Justice in Chandigarh
What concrete buildings are Frank Lloyd Wright famous for?
Falling Water, Johnson Wax Company and Guggenheim Museum. Also concrete blocks
What is the most common formwork material? What thickness? How is it treated?
Plywood is most common at 3/4” thick coated with oil, water resistant glue or plastic to prevent water penetration
What are prefab steel forms used for?
Strength and reusability for one way joist systems, waffle slabs, round columns and other special shapes
How are joints emphasized in concrete formwork?
Rustication strips, continuous pieces of neoprene, wood or others
What is slip forming and what is it used for? How fast does it move?
A formwork that moves with the confrete until it cures to stand on its own. It is used for tunnes and high rise building cores. It moves continuously at 6” to 12” per hour
Why are flying forms useful?
They are fabricated sections and can be removed and reused for repetitive units like hotels and apartments
How does an architect keep formwork economical?
Making it REUSABLE with uniform and constant thicknesses and dimensions
What is the tolerance for columns, piers and walls?
+/- 1/4” in any 10’ length
What is the tolerance for horizontal elements; ceilings, beam soffits, and slab soffits?
+/- 1/4” in any 10’ length
What is the tolerance for total height structure for interior columns?
1”
What is the tolerance for corner columns for buildings up to 100 ft tall?
1/2”
What is the max variation for the total length of a building?
+/- 1”
What is the tolerance for elevation control points for slabs on grade?
1/2” in any 10’ bay and +/- 3/4” for total length of structure
What is the tolerance for elevated formed slabs?
+/- 3/4”
What is the tolerance for finished concrete floors?
1/8” in 10’
What are ways to minimize moisture in concrete?
Specify low water-cement ratio, schedule construction so slabs have time to cure and dry before sealing floor finishes.
What is the maximum recommended water-cement ratio?
0.45 to 0.5
How long should concrete slabs be allowed to cure and dry before resilient flooring is installed?
6 weeks
Where is it appropriate to place the vapor barrier?
Placed directly below the concrete slab and on top of any sand cushion layer or subbase
What is a vapor retarder vs vapor barrier?
Vapor barrier prevents water vapor from passing through it. Vapor retarder only slows the rate of water vapor transmission
What permeance should a vapor barrier have?
0.04 perm and at least 10 mils thick.
What are the two most common grades of rebar?
Grade 40 and 60
What are the classifications of rebar?
axle, rail and billet (billet most commonly used)
What is the minimum concrete cover for rebar of interior slab?
3/4”
What is the minimum concrete cover for rebar of interior wall?
3/4”
What is the minimum concrete cover for rebar of interior beam
1.5”
What is the minimum concrete cover for rebar of interior column?
1.5”
What is the minimum concrete cover for rebar of exterior footings?
3”
What does 6x6-W1.4x1.4 mean?
Welded wire fabric, 6x6” grid with size of 1.4 hundredths of a square (0.014 in2) W is smooth wire and D is deformed wire
What is concrete made of?
cement, fine and coarse aggregate and water
What is portland cement made of?
lime, silica, iron oxied and alumina
How is cement supplied?
94 lbm bags containing one cubic foot
What is modified cement used for?
In places where a modest amount of sulfate resistance is needed and where heat of hydration needs to be controlled such as dams or massive structures
What are applications for Type III cement?
High early strength cement is used where a quick set is needed. It has a higher heat of hydration so it is suitable for cold-weather concreting
What are the applications for Type IV cement?
Low heat cement is used in massive structures to minimize cracking and is very slow setting
What are the applications for Type V cement?
Sulfate resisting cement is used for structures that will be exposed to water or soil with a high alkaline content
How much water is required for complete hydration? Workable mix?
Water required is 25% of weight. Extra 10-15% required for workable mix. must be potable
What is the minimum water-cement ratio?
0.35 to 0.40 or 4-4.5 gal per 94 lbm sack of cement
How does laitance develop and why is it bad?
It develops when too much water is added. The chalky surface deposit indicates low-strength concrete and must be removed if another pour is to be on top.
Fine aggregates must pass through a no_____ seive,
4
How much percentage do aggregates occupy of the total volume of concrete?
70-75%
What is the weight of standard concrete?
150 lbm/ft3 lightweight concrete is 50-100
What size should the aggregates be?
Not larger than 3/4 the small distance between rebar or larger than 1/5 of smallest dimension of forms or more than 1/3 depth of slab.
What does 1:2:4 mean?
1 part cement: 2 parts sand: 4 parts gravel
How is the strength of concrete specified?
By the compressive strength of concrete after it has cured and hardened for 28 days
What is a typical design strength?
2000 or 4000 psi
What do air entraining agents do to concrete?
increase workability and durability of concrete. improves resistance to freezing and thawing cycles. help reduce segregation of components
What do accelerators do to concrete?
speed up the hydration of cement so that the concrete achieves strength faster
What do plasticizers do to concrete?
reduce the amount of water needed while maintaing the necessary consistency for correct placement and compaction. Makes concrete stronger
What do retarders do to concrete?
slow down steting time to help reduce the heat of hydration
What do waterproofing agents do to concrete?
decrease the permeability
What does fly ash do to concrete?
increase strength and sulfate resustance, decrease permeability, reduce temperature and amount of cement, improve workability
What is so great about autoclaved aerated concrete(AAC)?
it has 1/5 the density of concrete. it is made of blocks. it uses less material and less waste. it has good sound and thermal mass. it is not stronger than concrete, it can’t be load bearing
Why is self-solidating concrete so special?
it can be placed without vibration = less labor. it saves time
Why is carbon fiber concrete so great?
it is used for precast panels, it is non-corrosive so less cover is required. can be fast because prefab
What are poured gypsum decks used for? What is its minimum depth?
roofs for fire resistance. it is poured over reinforcing material like wire fabric. depth is 2.5”
How high is the slump test truncated cone?
12 in. The slump is based off the 12” dimension. Usual dimensions is 2-6”
What does the cylinder test measure? When is it tested?
it measures compressive strength. it is measured in a lab at 7 and 28 days.
What does a core cylinder test measure?
it measures compressive strength by drilling a cylinder from the concrete
What does a kelly ball test measure?
The amount of penetration the ball makes in the concrete compared to 1/2 the slump test
What does the impact hammer test measure?
it measures the rebound of a spring on finished concrete to measure strength.
What does the K-Slump Test measure?
it measures consistency by seeing how much it floats in wet concrete
What does calcium chloride test measure?
it measures moisture content in concrete. sees how much is absorbed in the concrete
What does a hygrometer test measure?
determines the moisture emission by measuring the relative humidity of atmosphere by the floor. relative humidity must be 75% or less
What does a polyethylene sheet test measure?
if water is absorbed in concrete
What does a mat test measure?
if 24”x24” mat bonds with concrete. the level of moisture is low if mat bonds
What does an electrical impedance test measure?
measures conductance and capacitance to determine the moisture content in concrete.
Why is it bad to have concrete with high alkalinity?
alkalinity cannot exist without moisture. high alkalinity can damage tile installation so adhesive doesn’t stick. it also can create ALKALI-SILICA REACTION (ASR) which creates a gel material that puts pressure on concrete pores=blisters the finish.
What is the tool that is used to place concrete under water?
tremie
How do you prevent segregation in concrete?
Don’t drop from long distances. 5 feet max. Don’t use excessive lateral movement. Use vibrators to compact after poured
When do you use a control joint?
to create a weak section so normal temperature and stress cracking occurs on joints where you want it. while still wet
When do you use a construction joint?
whenever there are 2 successive pours at places of minimum shear. use waterstops
When do you use an expansion joint?
between 2 adjacent building sections so they can move independently of one another
When do you use isolation joints?
two successive pours with premolded joints like to separate columns from slabs, slabs from foundations and walls
What do concrete sealers do?
proprietary products applied to concrete to protect against weather and water penetration, provide resistance to chemicals, to prevent dusting of surface or to harden surface.
What is the difference between coating and penetrating type sealers?
dry types has a film made of acrylics, urethanes and epoxies. penetrating types seep into pores made of silicones, silanes and siloxanes. (don’t wear off)
What are 7 types of precast concrete shapes?
rectangular beam, inverted tee beam, L shaped beam, single tee, double tee, hollow core slab and precast column
How thick are cored slabs? When are they used?
they are 6” to 12” thick, 4’ wide. Used when there are heavier loads. Can span 36 feet
What does a bond breaker do?
it prevents wall panels from sticking to casting surface. can be liquid or sheet of plastic.
What is used to minimize corner chipping of concrete?
chamfer strips
What is the primary purpose of the voids in cored slab?
to make more efficient load carrying member
At what temperature do workers need to take steps to protect concrete when cold weather is predicted?
40 degrees F
