1. Concrete Construction

2. 3 major costs of concrete
Formwork costs including labor, equipment, and materials
Cost of reinforcing steel and placement
Concrete materials, equipment, and labor for placing, curing, and finishing
F11-1

3. Cast in Place Traditional method
Allows concrete to be formed to site conditions
Used on most construction sites for structural members
Concrete placed in forms to cure
Forms removed after enough strength in concrete to support self and additional construction loads

4. Cast in Place Walls and wall footings
Need to avoid voids and separation of materials due to large fall
Special care for areas under windows , pipe chases and other formwork installed inside wall forms
Can pump concrete from bottom of form to get rid of voids

5. Cast in Place Floors and roofs
One way slab – only supported in one direction F 11-3
Slab and beam
Slab, beam & girder
Outside beam is called spandrel beam
Columns poured before slabs – shrinkage
If poured same time could stress floors and beams due to shrinkage

6. Cast in Place Floors and roofs
One way slab – only supported in one direction F 11-3
Slab and beam
Slab, beam & girder
Outside beam is called spandrel beam
Two directional slabs (waffles) provide support in two perpendicular directions
supported by columns

7. Cast in Place 2 way Flat slabs Basically joists in both directions
Supported directly by columns
Uses column capitals to distribute load over larger area
More reinforcement needed to carry loads to columns
F 11-6

8. Precast concrete Cast into desired shape at plant and moved to site
Controlled environment -> better finish and quality
All prestressed and pretensioned members are precast
F 11-7, 11-8

9. Precast concrete Types Joists and purlins F 11-7 Roof and floor panels
Flat 1-4” thick, 15 – 32” wide, 4-10’ long
hollow core 4 – 12” thick, 4-8’ wide, 15 – 50’ long
tee, double tee 4-12’ wide span 12 – 100 feet
channel slabs 2 – 5 ‘ wide, ‘ long
F11-8

10. Precast concrete Types Walls
Usually curtain wall construction panels fit between structural components to form wall
But used in tilt up construction
Panels cast horizontally on existing slab and tilted upright
F 11-9

11. Prestressed Concrete Initial compression load applied to concrete
Places entire beam in compression
Makes beam stronger since more force is required to induce a tension component
Reduces deflection
F11-10

12. Prestressed Concrete 2 ways to do
Pretension – place prestressing material in tension in the form while concrete is poured
Once concrete hardened remove tension
Bond between steel and concrete keeps steel in place
Post tensioning – steel is placed inside a plastic tube during concrete pouring
Upon placement steel is tensioned and the steel is mechanically anchored to the concrete at each end
Load is removed and steel cut flush

13. Architectural Concrete
Appearance effects
Shape, size, texture, and color
F & 11-13

14. Concrete Construction Practices
Transporting and Hauling
Need to avoid segregation of materials in concrete
Wheelbarrows, buggies, chutes, pumps, conveyors, buckets, trucks
Placing and consolidating
Need to make sure form surfaces and bracing is right before placing concrete

15. Placing Forms must be coated in oil to allow removal
If placing concrete on ground – must moisten ground
If pouring on top of cured concrete must place bonding agent between pours
Shotcrete (gunite) – concrete placed pneumatically
Consolidation – removing air voids
vibration

16. Finishing & Curing
Finishing – bring surface of concrete to its final position and surface texture
Screeding – striking off excess concrete
Floating – smoothes and compacts concrete imbeds aggregates
Troweling – compacts surface F 11-16
Brooming – surface texture

17. Curing To get good concrete must cure properly
Moisture and temperature are key
Moisture – wet straw or burlap, curing compounds
Vacuum dewatering – mat placed on concrete
Vacuum applied to mat – takes out excess water
Lower W/C ratio -> denser mix

18. Hot weather Concreting
Curing accelerates when concrete temp above 50 – 60 F
How to lower temp
Use cold water in mix
Cool aggregates before mixing
Use Type IV (low heat cement)
Add a retarder
Decrease max time to discharge to 1 hour

19. Cold weather Concreting
Concrete should not freeze for 1st 24 hours
Min temp for placement is 50F
Use type III (hi early strength)
Use accelerator
Heat water and aggregates before mixing
Use vented heaters to keep concrete warm