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MASSACHUSETTS SEMINAR SERIES 2010 ENGINEERS WITHOUT BORDERS – NORTHEASTERN UNIVERSITY CHAPTER TIM MCGRATH, PH.D., P.E. Turning Cement into Concrete.

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Presentation on theme: "MASSACHUSETTS SEMINAR SERIES 2010 ENGINEERS WITHOUT BORDERS – NORTHEASTERN UNIVERSITY CHAPTER TIM MCGRATH, PH.D., P.E. Turning Cement into Concrete."— Presentation transcript:

1 MASSACHUSETTS SEMINAR SERIES 2010 ENGINEERS WITHOUT BORDERS – NORTHEASTERN UNIVERSITY CHAPTER TIM MCGRATH, PH.D., P.E. Turning Cement into Concrete

2 Outline Speaker and Audience What is Concrete? Components Reinforced Concrete Mixing and Placing Field Mixing

3 Who am I? Senior Principal at Simpson Gumpertz & Heger, Waltham Degrees in Civil (NEU), Structures (MIT) and Geotechnical (UMass, Amherst) Primary work area is buried structures (pipes, culverts, and the soil around them) Mentor for EWB-NEU Uganda team since July ‘09

4 Who are you? Undergrads? Professionals? Engineers (Civil, mechanical, etc)? Architects? Others?

5 What is Concrete? Cement, sand, aggregate, water, additives Strong in compression Weak in tension Readily formed into many shapes

6 Cement

7 Concrete

8 Concrete Truck

9 Cement Truck

10 Concrete Basic Ingredients (by volume)

11 The History of Cement  Ancient Egyptians used calcinated gypsum  Greeks and Romans used lime mortars  Early “Portland Cement” patented in 1824  True hydraulic portland cement manufactured in 1845

12 Cement - Process  Fired at 2,550°F in rotary kiln  Cooled and ground into an extremely fine powder with addition of gypsum

13 Cement – Finished Product  Extremely fine powder (500,000,000,000 particles per pound)  Huge surface area ( ft 2 /lb)  Bulk density of approximately 94 lb/ft 3  “Frozen” solution of many materials

14 Cement – Chemical Components  C 3 S – Tricalcium silicate – 3CaOSiO 2  C 2 S – Dicalcium silicate – 2CaOSiO 2  C 3 A– Tricalcium aluminate – 3CaOAl 2 O 3  C 4 AF – Tetracalcium aluminoferrite – 4CaOAl 2 O 3 Fe 2 O 3  Gypsum – CaSO 4 2H 2 O

15 5 Types of Cement  I – Standard  II – Moderate Sulfate Resistance, Moderate Heat of Hydration  III – High Early Strength  IV – Low Heat of Hydration  V – High Sulfate Resistance

16 Cement – Effect on Heat From Design and Control of Concrete Mixtures, PCA

17 Cement – Effect on Strength From Design and Control of Concrete Mixtures, PCA

18 Batch Design fine and coarse aggregate cement content water/cement ratio flow characteristics

19 Concrete Additives Air (freeze-thaw protection) Water reducers (strength, flow) Retarders (delay set) Fly ash (cost, flow, strength) ….

20 WATER Required for chemical hydration reaction Required for workability

21 Water – Effect of Poor Quality  Setting time  Strength  Efflorescence  Durability Staining Corrosion

22 Water – Permitted Sources  Potable is generally OK  Non-Potable can be OK if:  pH is 6-8  Not saline or brackish  No humic acid or algae

23 Water – Controlling Limits  Chloride: < 500 ppm is “harmless”  Alkali: < 600 ppm  Turbidity: < 2000 ppm clay, fines  Sulfates: < 1000 ppm “harmless”, 3000 limit  Organics: no odor, no color

24 AGGREGATE

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26 Aggregate –General Requirements  Clean  Hard  Strong  Durable

27 Aggregate – Size Effect  Larger stone provides  Less shrinkage  Lower water demand  Less expense  More difficult to place and consolidate

28 Aggregate – Shape Effect  Rounded  Lower bond  Lower strength  Lower water demand  Angular  Higher strength  Better Bond  Elongated  Higher water demand  Reduced workability

29 Aggregate – Gradation Curve From Design and Control of Concrete Mixtures, PCA

30 Reinforced Concrete

31 Reinforcement in Concrete Provides tensile strength for flexure Increases total compression strength for columns As transverse steel, increases shear capacity Controls cracking due to shrinkage and temperature

32 Concrete Design Strength f ’ c = strength used in calculations Typically taken as 28 day strength Often used as the basis for estimating:  modulus of elasticity  tensile strength  shear strength

33 Concrete vs Steel ParameterSteelConcrete Compression strength60,0005,000 Tensile strength60, Modulus of elasticity29,000,0004,500,000 All values in psi

34 Concrete Stress Strain Curves at Various Ages Concrete Strength and Stiffness

35 Reinforced Concrete Typical Reinforced Concrete Beam Span d

36 Mixing – Transit Mixed Used for longer haul times. Mixing efficiency, duration, and consistency depend on equipment and operator.

37 Transit-Mixing revolutions at mixing speed. All subsequent at agitating speed. Overmixing can cause slump loss, irregular setting, slump loss, overheating

38 Placement Wheelbarrow Buggy Conveyor Bucket Pump …

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42 Pumping

43 Finishing Spreading Consolidating Strikeoff Floating Troweling

44 Consolidating

45 Strikeoff

46 Floating

47 Troweling

48 Field Mixing

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58 It’s Concrete!

59 Have a Good Time!


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