Ag System Technology II Concrete Ag System Technology II

Objectives Objective A: Explain the composition and characteristics of concrete Objective B: Place concrete

What is concrete? Concrete is a mixture of 4 items: Course aggregate (gravel) Fine aggregate (sand) Portland cement Water Cement and water harden and fuse the aggregates together into a stone-like substance

Advantages of concrete Fire, storm, insect and rodent proof Decay resistant Wear resistant Waterproof Strong (compression) Attractive Easy to make on the job Molded to any shape Sanitary, easy to clean

Disadvantages of concrete Low tensile strength (pulling) Low ductility (ability to deform, bend) Low strength to weight ratio Susceptible to cracking Still an excellent building material

Where can I use concrete in Ag? Pens Floors Roadways Building foundations/walls Storage areas (feed silos, manure bunkers) Landscaping - walks, borders, etc.

Ingredients in concrete No soil in sand or gravel Clean water with no debris. Mixed in a 1-2-3 ratio 1 part cement 2 parts fine aggregate (usually sand) 3 parts course aggregate (usually gravel) Different ratios for different jobs/types of aggregate

Ingredients in concrete Water Add water slowly and mix thoroughly If mix is crumbly - too little water If mix is soupy – too much water Too much water weakens the finished concrete

How much concrete will I need? Sold by the cubic yard or “yard” Cubic Yards = (T x W x L) / 27 T is thickness in feet (4” is .33, 6” is .5) W is width in feet L is length in feet 27 is the number of cubic feet in a cubic yard Calculate a little extra – easier to deal with extra than not have enough to finish a pour

Example I want to pour a 10’ by 12’ 6 inch pad, how many yards do I need? .5’ x 10’ x 12’ = 60 cubic feet 60/27 = 2.22 cubic yards Try it! How many yards if: 4’ x 8’ 4 inch pad .39 yard 20’ x 50’ 6 inch pad 18.5 yards

Concrete Forms Forms hold concrete in the desired shape and location until it hardens Commonly wood or metal Stake forms so they aren’t moved out of place Wood or metal stakes nailed with double headed nails Coat forms with oil to prevent sticking

Concrete Forms Top of form will determine the top of the cement slab Use a level on the form to create the desired slope of the slab Base inside the form should be gravel or roadbase compacted firmly. Soil will settle and crack the concrete. Can be removed after concrete hardens

Reinforcing Steel Steel rods or wire added to increase tensile strength of concrete Called reinforced concrete Place in a grid pattern Wire or weld together where they cross for strongest reinforcement Should be in middle of slab vertically and not too close to edges or top surface

Concrete Tools Wheelbarrow Mixing or moving concrete

Concrete Tools Shovel

Concrete Tools Drag or Rake

Concrete Tools Bull Float

Concrete Tools Magnesium Float Wood Float

Concrete Tools Edger

Concrete Tools Jointer

Concrete Tools Screed Board Generally 2x4 Can be anything straight and strong

Concrete Tools Broom

Concrete Tools Finishing Trowel

Placing Concrete Wet down formed area so water doesn’t leave concrete too soon Have everything ready – concrete begins to harden soon after mixing Start on one side of the forms and work continuously to the other side Very heavy, use chutes and wheelbarrows to place then reposition with shovels, rakes and drags

Striking Off (Screeding) Rest straight board (screed board) on top of forms Two people slide board back and forth across top of forms in a sawing motion Levels concrete to the top of forms Third person on unleveled side can drag concrete to low areas Tap form boards with hammer or use a spade between board and concrete to push course aggregate away from form

Floating Float is used to push course aggregate down Brings fine aggregate and cement to surface for smooth finish Bull float Magnesium, aluminum or wood hand float Done immediately after striking off

Edging Edger used to round top corner Pushes course aggregate away from form Keeps edge from chipping or breaking off

Jointing Creating grooves or lines in the concrete Gives nice appearance Directs cracking along grooves rather than across the pad

Finishing Creates final surface Allow concrete to set up a little then finish Float finish is acceptable for some areas like livestock feed areas, has a rough finish Broom finish gives some traction, pull a course broom over the surface

Finishing Metal trowel rubbed over the surface makes a very smooth finish Dip in water to aid process Excessive troweling makes surface weak, may break off and crumble Fine broom may be dragged across the surface to make it less slick

Curing Proper drying and hardening of concrete Dries too quickly, doesn’t reach full strength The slower the moisture leaves the stronger the concrete Protect from drying wind, heat or freezing Water can be sprayed on concrete to slow drying after it is setup At least 7 day wait before driving over