concrete and forming
when can footings be cast into excavated forms?
when directly on undisturbed ground
three requirements for footings
correctly positioned
accurate dimension
easy to remove (strip)
accurate dimension
easy to remove (strip)
maximum step for a footing
24"
how are inside forms positioned
cleats as spacers
staked in place
height set by levelling
staked in place
height set by levelling
wrap around method of building square column footings
pre-build square boxes centred over the position of the column
type of footing used under a concrete wall
wall footings
continuous strip footings
continuous strip footings
securely weighted or staked footing form
tapered pier
keeps from floating when concrete is poured
keeps from floating when concrete is poured
use of wrap around pad form
faster
more accurate
can be pre-built
more accurate
can be pre-built
dowels tied with re-bar wire to reinforcing steel
to keep bars from moving
concrete form dowel
to connect two separate cast in place concrete sections
made from deformed or smooth steel bars
made from deformed or smooth steel bars
L-shaped anchor bolts
insert into concrete after placement
tap sides with hammer to consolidate fresh concrete around the bolt
tap sides with hammer to consolidate fresh concrete around the bolt
bolt templates
made of 19mm lumber or plywood
form used with dowels
keyway
importance of outside corner of concrete forms
corners define shape of building
strap ties secured to walers
first set of ties set on top of first board
two more boards installed
next set of ties
16" O.C.
two more boards installed
next set of ties
16" O.C.
forces of concrete to wall form tie
form sheathing supports fresh concrete>studs>walers>ties
maximum spacing of studs in double waler
maximum 4'/hour=16"o.c.
3'/hour=24"o.c.
(rate of placement)
3'/hour=24"o.c.
(rate of placement)
rough door and window bucks
wooden key installed to keep door or window from moving after frame is installed
why are bucks made larger than door and window frames
allows the frame to be shimmied until P-L-S
why do bucks not run the full length (top, bottom, sides)
to make later removal easier
to create a pocket for a beam
use blockouts
to set a bulkhead in a steel form
hold in place using 38mm x 89mm blocks between steel forms
to make bulkheads easier to strip
hold in place using a second frame or cleats
to indicate height of finished concrete wall w/o level strips
draw a chalk line inside form and drive nails at regular intervals
finding centreline perimeter
perimeter - (4 x wall thickness)
single vs double waler
double waler uses long end ties
4 walers/ row of ties
takes longer to form and strip
costs more to use
4 walers/ row of ties
takes longer to form and strip
costs more to use
contact area
surface area of form in contact with concrete
what is concrete made of?
portland cement, aggregate and water
what is the average time required for concrete to gain 90% of its full strength?
1 month
what is the hardening of concrete called?
hydration
when is water safe to use in concrete?
if it is safe to drink
what is the amount of water in relation to the amount of portland cement called?
water-cement ratio
what do aggregates serve as?
fillers in concrete
which aggregate size produces the strongest concrete?
19mm (3/4")
what is an advantage of air-entraned portand cement?
it resists freezing and thawing better
what is the typical strength range for concrete?
15 to 32 MPa
how is the strength of concrete often compromised on the jobsite?
water is added
how many cubic feet are in one yard of concrete?
27 cubic feet
how many cubic feet are there in one cubic metre?
31.1 cubic feet
concrete has a high strength of what type?
compressive strength
what is concrete called when steel bars are used to increase concrete's tensile strength?
reinforced concrete
what is the diameter of #5 rebar?
5/8" (15.5mm)
what is the correct term for putting concrete into forms?
placing
what is the name of the test done on the jobsite to test the consistency of concrete?
slump test
when concrete is placed in forms, what is the thickness of the layers?
12 to 18" (300 to 450mm) thick
what is the process called which eliminates honeycomb?
consolidation
what does rapid loss of moisture in concrete cause?
causes concrete to crack
when temps. are 70 degrees F. (21 degrees C.) or above, how long should concrete cure?
at least three days
in areas where frost occurs, where must the footings be placed?
below the frost line
what is done to prevent a lock between the footing and foundation?
a keyway is formed
what type of footing is constructed on sloped ground?
stepped
when a concrete slab is placed directly on the ground, what is it commonly called?
slab on grade
when concrete is thickened under a load bearing wall, what is it called?
haunched
what is a combined slab and foundation called?
monolithic slab
which insulation is suited for underground use?
extruded polystyrene
what are doubled 2 x 4 (38 x 89) pieces with a space between them for form support called?
walers
where do snap ties break off?
at the outside face of the form panels
which forming system uses steel waler bars?
strip-ease
what are walers which extend past corners, lap each other, and are nailed together known as?
yoking
what are vertical thickened portions of a concrete wall that give the wall more lateral strength called?
pilasters
what is the name of vertical framing members placed at right angles to walers?
strongbacks
what are the forms called that are used for providing large openings in a concrete wall?
bucks
what are the recesses in the top of a masonry wall to receive the ends of girders called?
pockets
what is necessary to prevent window and door blockouts from deflecting under the load imposed by plastic concrete?
internal bracing and blocking
which type of column form is not reused?
heavy duty cardboard form
what must be done to the bottom edge of concrete stair form riser boards?
they must be bevelled to allow for finishing
what do the letters ICF stand for
insulated concrete forms
what are three main objectives in building concrete formwork?
quality, safety and economy
cost of formwork materials may be as much as ____% of the final cost of the structure.
35-60%
what is meant by the term "formwork"?
the sheathing plus all supporting members, hardware, and bracing
what is used to keep a form plumb and solid?
a brace
what is the name of the piece that supports key material?
bulkhead
what is placed in the corners of column forms to give a finished appearance to the column?
chamfer strips
the guide that supports the strike off bar is called a___
screed
besides placing them directly into drilled holes, how else may dowels be placed?
they may be threaded into insterts
what term describes a form used to finish the side of a cast in place slab?
edge forms
in formwork, what can be included at construction joints to make the connection btwn side by side concrete placements more solid?
a key and keyway
a piece of lumber used to hold parallel forms a specific distance apart is called a
spreader
what term describes a cast in place structure that has all its concrete components placed at the same time?
monolithic
which concrete formwork component has a flexible bulb in the middle to resist shearing forces?
waterstop
who is responsible for preparing a plan for all formwork that could possibly cause injury to a person?
the employer
what is the name for the structural supports and bracing required for supporting temporary loads during construction?
falsework
what must a formwork designer sign before each concrete placement?
a formwork inspection certificate
whose signature must be on all plans and specifications?
the designers
describe what should be done if any settlement or distortion of the formwork occurs
if the forms appear to be bending, moving, or settling during concrete placement, operation must be stopped immediately. repairs supervised by formwork designer must be done in such a way that no worker is in danger
lumber for concrete formwork should be
partially seasoned
what species and grade of lumber would be a good choice for forms that will be highly stressed?
No. 1 douglas fir
what is the distinctive feature of high density form plywood?
an opaque resin finish
how can textured plywood save money for the contractor?
through reduced sack rubbing costs
how many times may properly cared for plywood forms be used?
200
what is commonly done to concrete forms prior to each use?
they should be oiled
which kind of tie has an economical internal thread?
a coil tie
why are disconnecting ties used?
they can be extended to make wider forms
what is used to secure the ends of button ties?
wedges
which of the following has a channel to hold a 38mm x 89mm waler?
Jahn "A" bracket
what formwork system can be used for loose forming?
strip ease ties
what transfers the load from sheathing to ties?
walers
on very large forms the bracing is likely to be attached to
strongbacks
for light or low framing, wood braces are attached to
stakes
reinforcement for intersecting walls or beams may be attached to ___ in poured walls or beams
inserts
which of the following is used to divert water away from a wall to a roof?
reglet
what requires extra strengthening of the forms?
use of a retardant admixture
what effect does rapid placement of concrete have on the forms?
it may cause the forms to fail
what effect might vibration have on improperly braced forms?
it may cause the forms to float (be pushed out of position by the concrete)
an exposed concrete form should be heated and/or insulated if the atmospheric temp. is below
4 degrees C.
how are very wide forms tied together?
with threaded pole or rebar
what is done to safeguard tall forms against failure?
ties and walers are placed closer together
what are control joints used for?
to direct cracks in straight lines
what should you remember when installing a keyway?
to bevel the key and place the wide side to the bulkhead
what is sometimes used to hide a horizontal construction joint?
a rustication strip
what are waterstops made from?
rubber and neoprene
what is used for a control joint?
plastic control strip
what is the best material for a give and take strip?
compressible material
how can a control joint be created without a plastic control joint or without tooling it into the uncured concrete?
by saw cutting
what is the main reason that the steel used in reinforcing is so compatible with concrete?
they expand and contract at similar rates
the compressive strength of concrete is about ___ times its tensile strength
10
what is the size of 10 M rebar?
11.3mm diameter
what name describes a 60 bar?
hard rebar
what type of construction uses welded wire mesh for reinforcing concrete?
light
welded wire mesh is available in sheets 6100mm long or rolls 61000 mm long. how wide is it?
2288mm long
in the description 11254 x 254 x p13/p1311, what does p13 mean?
the area of cross section is 13mm square
what does yield mean, as applied to reinforcing steel?
the point at which it begins to stretch
why must you be careful about applying oil to wooden reglet blackouts?
caulking may not stick to oily surfaces
why is one type of job constructed reglet made in two parts?
b/c it is easier to strip the formwork correctly without damaging the reglet
which kinds of reglet require no caulking?
cast in place
what is the most economical procedure if large amounts of reglet must be installed?
use one of the manufactured types
under what conditions can footings be cast in excavated forms?
if the concrete is monolithic
what are the two most important factors for footings?
strength and positioning
what kind of footing is placed on sloping ground
stepped footings
once the outside footing forms are in place, how are the inside forms positioned?
using a spreader
which type of footing is similar to a series of boxes piled on each other?
a stepped footing
what type of footing is used to transfer the weight of a column to more than one pad?
a strap footing
which type of footing form must be securely weighted or staked down to keep it from floating when the concrete is poured into it?
tapered footing form
why is a wrap type of residential pad form economical?
the lumber can be reused and doesn't need to be cut to length
why are dowels tied with rebar to the reinforcing steel in each section?
to reduce movement and increase the strength of the bond
what is a concrete formwork dowel?
any bar that penetrates two sections of concrete
how are L-shaped anchor bolts secured to sill plates when great accuracy is not needed?
by inserting the bolts in the concrete before it sets up
of what material are most bolt templates made from?
19mm plywood
what kind of form is often used with dowels?
keyway forms
why is the construction of an outside corner of a concrete form so important?
this part of the form is potentially weak
how are strap ties secured when used with shiplap or 19mm board forms?
they are nailed
cross ties must be placed in an easy strip pilaster if it is more than ____ deep
250mm
when erecting form panels you must set and plumb the corner panels after installing the ties (true or false)
false
how many wedges must be used to hold each piece of waler in place?
two
what is the maximum spacing allowed between double wood walers?
19mm
pilaster form
corbel form
what is the most common type of door frame in concrete walls?
metal frame
wooden door frames are usually cast in place with ____ attached
keys
what is added if door frames are not snug to both sides of the forms?
furring strips