1. Ag System Technology II
Concrete
Ag System Technology II

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

3. 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

4. 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

5. 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

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

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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. Concrete Tools
Wheelbarrow
Mixing or moving
concrete

15. Concrete Tools
Shovel

16. Concrete Tools
Drag or Rake

17. Concrete Tools
Bull Float

18. Concrete Tools
Magnesium Float
Wood Float

19. Concrete Tools
Edger

20. Concrete Tools
Jointer

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

22. Concrete Tools
Broom

23. Concrete Tools
Finishing Trowel

24. 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

25. 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

26. 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

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

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

29. 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

30. 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

31. 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