Class Update

1. Class Update • Exam 2 Schedule – Need evening hours (6-8PM). • April 13, 14, or 15. • Extra Credit Field Trip – Bluegrass Army Depot – April 2nd Afternoon

2. CE 403 Extra Credit Opportunity • Groups who volunteer to present on April 22nd will receive 4 points added to Exam 1.

3. CE403 Construction Methodology Concrete Construction

5. Concrete’s Origins • 690 B.C. – The Assyrians used a mixture of one part lime, two parts sand, and four parts limestone aggregate to create a crude concrete for the Bavian Canal • 1824 – Joseph Aspdin files a patent in England on “Portland Cement” • 1825 – Erie Canal, used the first modern concrete to be manufactured in the USA

6. Concrete Materials & Properties • Components: • Water • Cement • Aggregate • Additives

7. Water • Primary reason is to provide the moisture for hydration of the portland cement. • Hydration is the chemical reaction between the cement and the water that produces hardened concrete. • The heat produced is called the heat of hydration – exothermic. • The desired characteristics are related to the water-to-cement ratio • (ranges from 0.30 to 0.70 by weight).

8. Portland Cement

9. Aggregates • 60 to 80% of the mixture. • Free of Fines • Angularity increases strength

10. Additives • Air-Entraining agents increase resistance to freezing and thawing and scaling. • Good for pavements. • Plasticizers - increase the slump and workability of a concrete mix • Retarder slow the rate of hardening of concrete. Used sometimes to offset high temperatures. • Accelerators decrease the setting time and increase the high early strength of concrete. • Calcium Chloride is most common, and corrosive to steel. • Pozzolans, i.e. fly ash, • Replace some cement in mix • increases the workability

11. Distribution of Concrete Construction Costs • Formwork • Labor & Equipment 39% • Material 10% • Concrete • Labor & Equipment 24% • Material 8% • Reinforcing Steel • Labor & Equipment 7% • Material 12%

12. Cast-In-Place Concrete Walls & Wall Footings

13. One-way Slabs • Advantages Low cost formwork Fast • Disadvantages Low shear capacity Low Stiffness (notable deflection)

14. Two-way Slab • Advantages Carries heavy loads Attractive exposed ceilings Fast • Disadvantages Formwork with panels is expensive

15. Pre-Cast Concrete • Subsets: pre-stressed, tilt-up, lift slab • Applications: lots!! • Advantages: quality control, all-weather construction, fast-track concurrency (no form-work req’d – concrete already cured) • Disadvantages: fab plant overhead (more cost), transport cost, lifting equipment (larger cranes), and require economic quantities (need to exploit repetition)

16. Precast Beam Shapes

18. Pre-Cast Concrete • 3 types of joints (concrete to concrete) • Exposed, lapped rebar • Dowels, sleeves, & grout • Topping Slab

19. Prestressed Concrete • Concrete in compression state before load is applied • 2 types: • Pretensioned • Tension cables tensioned in the concrete form before concrete is placed • After concrete hardens, tensioning devices are removed • Done in fab shop – can be difficult to transport • Post tensioned • Tension cables tensioned after the concrete member has been erected • Done in field – QC can be challenging

20. Prestressed Concrete Beam

21. Prestressed Concrete • Concrete in compression state before load is applied • 2 types: • Pretensioned • Tension cables tensioned in the concrete form before concrete is placed • After concrete hardens, tensioning devices are removed • Done in fab shop – can be difficult to transport • Post tensioned • Tension cables tensioned after the concrete member has been erected • Done in field – QC can be challenging

22. Tilt-Up Construction • Vertical wall elements are cast horizontally and then tilted into place • Advantage: save formwork expense • Lifting stresses may control geometry of design.

24. Tilt Wall Construction • Ideal for projects where time and budget are critical • Appropriate for large, horizontal projects with three stories or less

25. Tilt Wall Construction • Engineering Intensive • Tilt-up structures require less maintenance (mason blocks are likely to crack and leak water) • Safer to build – more work at grade

26. Lift Slab Construction • Floor slabs cast one on atop another • Slabs raised with column-mounted jacks.

27. Lift Slab Construction • Advantages: minimize form costs & speed up construction • 1987 failure L’Ambiance Plaza (Connecticut) • 28 fatalities • Cause: column to slab connection

28. Lift Slab Construction

29. Steel Fiber Reinforced Concrete • Fiber Content: 0.5 to 0.2% by weight • Added paste (needs more cement and sand) needed to coat fibers • Advantages: resistance to impact, cracking, thermal shock, and fatigue • Applications: cavitations exposures (foot of dam, tunnel lining) • Problems: loose fibers

30. Transporting & Handling • Equipment commonly used: • Wheelbarrows, • small amounts; max distance ~ 200’ • Buckets • good for low slump • Buggies, • Manual or powered • Powered can carry up to 14 cf & traverse up to 1000’ • Chutes, Swivel over large area • Conveyors, • Horz. or Vert.; optimum slump 2.5” to 3” • Pumps, • can move material up to 5000’ horizontally and 1000’ vertically

31. Placing & Consolidating • The movement of plastic concrete into its final position is called ”PLACING”. ”NOT POURING” • Avoid Segregation when handling. • Height of free fall should be limited to 5ft. • Forms should be clean & tight, and the interior of forms should be oiled or coated with a parting agent for later form stripping. • When placed directly on the subgrade, the subgrade should be moistened, or provided with a moisture barrier.

33. Typical Wall Form

34. Gang Forms • AKA prefabricated forms

35. Maturity Method

36. Maturity Method Calibrate Mixture

37. Maturity Method

38. Reinforcing Steel, “ReBar” Also welded wire fabric and spirals