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Concrete work. Residential Construction Unit 2 Site Work and Concrete Mr. Todzia. What is this?. What is Concrete?. Mixture of: Aggregate (Stone) Sand Portland Cement Water + + + =. Proportions. Aggregate Sand Portland Cement
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Concrete work Residential Construction Unit 2 Site Work and Concrete Mr. Todzia
What is Concrete? • Mixture of: • Aggregate (Stone) • Sand • Portland Cement • Water + + + =
Proportions • Aggregate • Sand • Portland Cement • Water 1 cement : 2 sand : 3 gravel : and 1 water Mix dry ingredients and then water is slowly added to the mix
Types of Concrete Work • Concrete work can be split into 3 categories: • Walls • Flat work • Stamped
Concrete Reinforcement How is concrete reinforced? Using corrugated steel rods called REBAR
How is Rebar sized? • In 1/8th of inches • For example you can have #5 rebar which means it is 5/8 of an inch in diameter. • #4 rebar= 4/8 = ½ inch diameter • #3 rebar = 3/8 inch diameter • #2 rebar = 2/8 = ¼ inch • Sizes are available from #2 rebar to #12 rebar
Footings • Purpose- to spread and distribute the load of the building above. • Preparation- soil must be compacted and a layer of stone put down and also compacted • Size- is determined by a designer who takes into account the soil types, bearing capacity and the load of the building. • A general rule of thumb is how ever thick your wall is, double that number and that is how wide your footing needs to be. So an 8” wall needs a 16” wide footing
Footings Continued • Formwork- usually for residential work, footing are formed using conventional lumber such as 2x10’s. • They are staked to the ground using metal stakes and strapped across the top with wood or metal strapping
Footings continued • Reinforcement- footings like walls, are reinforced with rebar that is laid in place and connected with twist ties. • A Keyway is put into the top of the footing to help tie into the foundation wall which will be poured directly on top of the footing. It helps minimize lateral/horizontal movement of the foundation wall on the footing.
Concrete walls Concrete walls are made by setting up some type of Formwork in the desired shape and size of the foundation wall you are building, installing reinforcement (rebar) and then pouring the concrete in the formwork.
Types of Forms • Dura-form (premade, lock together) • Plywood forms • No matter what type of form, there are always ties that connect the two sides of the forms that maintain a constant wall thickness. The ties also act as great supports for the horizontal rebar to laid on and tied to.
How rebar is installed • Rebar is then laid on top of the ties and wired in place. • Rebar is fastened by twisting wire ties around adjoining pieces
Tools used for rebar tying • Twisting tool • Automatic tiers
The Pour • There needs to be a number of guys at the pour ready to work. Some need to direct the pouring concrete with shovels, others need to poke the wet concrete with a piece of rebar to make sure there is no air and all voids are filled in. • Need to remember that there are no second chances when dealing with concrete. You only have so long before it is rock!
Finishing • Concrete walls need to be floated and then troweled to a finish.
Flat work • Types of flatwork • Footings • Slabs (floors) • Walkways
Footings • Footings are often considered part of the foundation walls, but they are actually a type of flat work. Their preparation and forming is similar to slabs.
Slabs • Preparation- Soil must be compacted, a few inches of stone laid down and compacted again. • After compaction, form work must be put up. • Most slabs are between 4 and 6 inches thick. • That means forms are probably built from 2x4’s or 2x6’s staked to the ground.
Moisture barrier • Often a moisture barrier is put down under the slab. • The most common material used is 6 mil polyethylene plastic sheeting. • Thin (1/2 in or 1 inch) rigid foam insulation is also used.
Slab Preparation • Reinforcement- Slabs also use steel reinforcement, but a different type. • WWM stands for welded wire mesh. • It is cut and put under slab floors. • Ends and sides are are fastened together with the twisted metal ties. • The grid is then propped up so when concrete is poured the WWM is in the middle of the slab
Finishing slabs • Usually slabs are a finished surface that gets used for various things so they need to look good. • The first step to finishing is floating the concrete. This is done with a bull float.
Second Step to finishing • Slab then needs to be troweled to its final finish. • This can be done by hand with a small hand trowel, or can be done with a power trowel.
Stamped Concrete • Stamped concrete has aesthetic purposes. It makes the outermost part of the concrete pour appear to be made out of some type of masonry product. • They are made to look like bluestone walkways, brick patios, stone walls, etc. • They are a very simple concept. • Slabs- after concrete is poured the stamping forms are laid on top and weight is applied and they are allowed to partially dry. When the form is removed, the desired pattern remains.
Stamped Concrete Walls • Walls are a little different in the fact that the stamped patterns have to be applied to the inside of the form before the pour. • After the walls are poured, forms are removed and the pattern is left on the inside.
Finishing/coloring stamped concrete • Because the concrete is made to look like another material, it must be colored so it doesn’t still look like concrete. • There are 3 types of coloring: Integral coloring is added to the truck load of concrete at the plant. Accent coloring is a powder that is spread on the top of the partial cured concrete. • Acid staining- this coloring is usually applied after the concrete has cured and is applied with a brush.
Finishing/coloring stamped concrete continued • When slabs or floors are colored, they usually spread the coloring powder on the wet concrete after they float it but before they lay the stamps on top.
Precast Concrete • What is precast concrete? • It is concrete items that were formed and cast or poured at the plant and then brought to the job to be used. • Examples include: • Stairs • Basement stair wells • Bridge girders • Septic tanks • Mafia blocks • Piping
Example pictures of precast items • Stairs
