Glencoe: Section 60 Flashcards
What steps are involved in finishing concrete
Screeding, bullfloating, edging, jointing, floating, and troweling.
Screeding:
First step in finishing
concrete is struck off using a screed which rides on the edges of side forms or pipes. Two poeple move the screed in a sawing motion. Leaves surface level with coarse finish
Bullfloating:
After screeding, bullfloating makes the surface even more even with. A bullfloat is a wide, flat metal or wood pad that is pushed back and forth over the concrete to make the surface even. Long handle.
Darby:
Similiar tool to bullfloat but with a shorter handle.
When is bullfloating done?
shortly after screeding while concrete is still wet enough to allow a slight paste of mortar to be brought to the surface. There must be no water visible on surface. Otherwise excess amounts of fines and moisture will come to the surface
When is Edging and Jointing done:
When the sheen has left the surface, the concrete has started to stiffen.
Edging and Jointing
edging produces a rounded edge on slab to prevent chipping. The edger is run back and forth covering corse aggregate particls.
Immediately following edging, jointing is done. Jointing tool is used to cut control joints 3/4” deep into slab perpendicular to slab endge.
Why is jointing done?
shrinkage causes concrete to crack, joints controls where these cracks occur.
To ensure straight joints
guide the jointer with straight 1/8 or 1x10 called a guideboard.
Hand floating:
In some cases, additional floating step is done. Wood or metal trowels called floats further even the surface and compacts the surface mortal.
If the concrete is air-entrained, floating must be done with an
aluminum or magnesium float because wood sticks to the concrete.
If floating is the last step on finishing concrete, it may
be done a second time after the concrete has hardened slightly
Troweling:
For a dense smooth finish a steel trowel is used. For large areas a power trowel is used.
When can troweling be done
cannot be started until the concrete has hardened enough to prevent fine material and water from working to the surface. Concrete troweled too early will not be durable, too late will be difficult to finish.
For a fine textured troweled surface
trowling is immediately followed by a second where trowel is held flat with circular motions
For a hard steel-troweled finish
second troweling is delayed until oncrete is hard enough to make ringing sound under trowel. Trowel is tilted slightly and heavy pressure is applied to compact surface.
Frenso
another type of concrete finishign tool. Allows concrete finishers to trowel without having to use knee boards.
Kneeboard:
distributes the weight of a finisher over surface of concrete.
Why wont the concrete finished with a fresno be as dense as one finished with hand trowel
the finisher can not put as much pressure on a fresno
Special finishes
Colors, patterns, or texture.
When are special finishes done
after concrete has been placed but before cured
Broom finish
to make the concrete more slip resistant a stiff bristled brush is dragged over the surface in parallel strokes. After bleed water is gone.
Rubbed finish
shortly after concrete is hardened and forms removed, the surface is rubbed with abrasives to create a uniform surface that is very smooth.
Salt finish
broadcasting rock salt onto fresh concrete. Roller presses salt into surface. Salt is then washed away to leave shallow angular indentations.
After finishing flatwork, concrete should
be kept moist for at least 2 days to ensure hydration continues.
If the finished floor is exposed concrete, how long should the concrete be kept moist
at least 5 days.
What kinds of materials can cover the concrete during the curing process
burlap, canvas, or waterproof. if burlap is used, it should be kept wet by sprinkling it with water.
When can wall plates be laid out and construction continues on a flatwork
when the concrete has cured enough to withstand foot traffic
Placing concrete in unusually hot weather can
reduce its strength because workers add more water to the mix.
In hot weather, water and aggregates of concrete mix should be
kept as cool as possible before being mixed with the cement.
In hot weather, forms, rebar and subgrade
should be sprinkled with water to keep it wet.
If concrete is subjected to below freezing shortly after being placed
it can loose up to 50% of its strength.
Try to insulate it
What types of concrete can be used to counteract cold weather.
high-early strength, air-entrained, and low slump concrete.
You can kill a tree by too much
gradework
No more than X inches of backfill around tree.
12
Solid wood is used for many types of construction for several reasons:
1 strong, some woods are strong as steel
2 Easily fastened with snails, bolts, screws, glue
3 Wood buildings easily altered or repaired
4 Low heat conductivity reduces heat loss
5 accepts coatings such as paint and stains
6 resists acid, saltwater and corrosives
7 renewable
Most wood in united states is harvested from
north america
Benefits of taking good care of forest resources
Continued ability to harvest lumber
protection of important water resources
soil conservation
production of oxygen and absorption of carbon dioxide
preservation of wildlife and plant habitats and endangered species
maintenance of scenic areas
Forest ecosystems are
fragile and may take thousands of years to mature
Anatomy of a tree
Tips of roots, buds, leaves, thin layer of cells just inside bark called cambium.
